EFFECT OF PRECOOLING AND ACCLIMATION ON REPEAT … · 2" " Peer-Reviewed Conference Proceedings...

EFFECT OF PRECOOLING AND ACCLIMATION ON

REPEAT-SPRINT PERFORMANCE IN HEAT IN MALES

This thesis is presented for the degree of

Doctor of Philosophy at the University of Western Australia

Carly Brade

Bachelor of Science (Honours)

Faculty of Life and Physical Science

School of Sport Science, Exercise and Health

2013

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Publications Arising from this Thesis

Brade, C., Dawson, B., & Wallman, K. (2012). Effects of different precooling

techniques on repeat-sprint ability in team-sport athletes. European Journal of Sport

Science, (accepted for publication December 2011; DOI: 10.1080/17461391.2011.

651491). This paper appears in Chapter Three.

Brade, C., Dawson, B., & Wallman, K. (2012). Effect of precooling and acclimation on

repeat-sprint performance in heat. Journal of Sports Sciences, (accepted for publication

November 2012; Volume 31, Number 7, Pages 779-786, 2013. This paper appears in

Chapter Four.

Brade, C., Dawson, B., & Wallman, K. (2012). Effect of precooling on repeat-sprint

performance in seasonally acclimatised males during an outdoor simulated team-sport

protocol in warm conditions. Journal of Sports Science and Medicine, (accepted for

publication July 2013; Volume 12, Issue 3, Pages 565-570, 2013. This paper appears in

Chapter Five.

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Peer-Reviewed Conference Proceedings


techniques on repeat-sprint ability in team-sport athletes. 16th Annual Congress of the

European College of Sport Science, Liverpool, United Kingdom, 6th – 9th July 2011

(Poster Presentation).

Brade, C., Dawson, B., & Wallman, K. (2012). Effect of precooling and acclimation on

repeat-sprint performance in heat. 17th Annual Congress of the European College of

Sport Science, Bruges, Belgium, 3rd – 7th July 2012 (Poster Presentation).

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Overview

Precooling is an acute method of cooling the body prior to exercise. It is used

principally in an attempt to lower core temperature, thus increasing the time taken to

reach a critical thermal maximum during exercise, at which a given intensity can no

longer be maintained. To date, most research has focused on the effects of precooling

on endurance exercise, with results consistently showing performance benefits.

Currently, only limited research is available on the effects of precooling on repeat-sprint

exercise, which is surprising as these demands form a major component of team-sport

performance.

Notably, many precooling methods used in previous research are not practical to an

actual field situation, i.e., cold water immersion and the use of climate chambers.

Consequently, the main objective of this thesis was to investigate practical methods of

precooling that involved internal and external techniques alone or in combination (i.e.,

ice slushy ingestion and/or cooling jacket) on repeat-sprint performance in heat, in both

a laboratory situation, as well as an outdoor setting. This thesis also explored the use of

precooling in conjunction with heat acclimation/acclimatisation, as this area has not

been previously well researched.

Study one, the first of three experimental studies, evaluated the effects of different

precooling procedures on prolonged repeat-sprint cycling exercise (2 x 30-min halves

comprising 30 x 4 s maximal sprints interspersed with sub-maximal intensity exercise)

in heat (~35°C and 60% relative humidity). This study aimed to determine whether

internal (ice slushy) or external (cooling jacket) precooling methods would provide any

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benefit to repeat-sprint exercise performance and whether any improvement would be

greater using these methods simultaneously. The most effective precooling method

would then be used in both subsequent studies. Study two aimed to investigate the

effect of partial heat acclimation (5 sessions of cycling at 80% maximum power output

for 3-min with 1-min passive rest, for 32 to 48 min) on repeat-sprint performance (as in

study one) in heat and to determine whether any further benefits would occur with the

addition of precooling performed both prior to and during exercise. Study three

assessed the effects of precooling used prior to and during an outdoor simulated running

team-sport game (4 x 20-min quarters with 2 x 5-min quarter and 1 x 10-min half-time

break) on seasonally heat acclimatised individuals.

Results from study one indicated better repeat-sprint performance (total mean power

and work: 972 ± 130 W and 233.6 ± 31.4 kJ) following the use of the combined method

(ice slushy and cooling jacket) compared with ice slushy (882 ± 144 W and 211.8 ±

34.5 kJ) or jacket (968 ± 91 W and 232.4 ± 21.8 kJ) alone. In addition, core

temperature was lower, as shown by moderate effect sizes (d = 0.67) following the

combined method (36.8 ± 0.3°C) compared with singular methods (jacket; 37.0 ± 0.3°C

and CONT; 37.0 ± 0.3°C) following precooling and half-time cooling (combined; 38.2

± 0.3°C vs ice slushy; 38.4 ± 0.4°C). These findings suggest that the simultaneous use

of internal (ice slushy) and external (cooling jacket) precooling methods results in better

prolonged repeat-sprint performance, compared with singular techniques. In study two,

repeat-sprint cycling performance following a short-term, high-intensity partial heat

acclimation protocol was improved, however there were no further performance

enhancements with the addition of precooling. This was demonstrated by inferential

statistics showing better performance in Post Acc compared with both Pre Acc and Post

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Acc + PC. Additionally, core temperature was lower in both post acclimation trials

compared with the Pre Acc. In study three no beneficial effects (smallest worthwhile

change) were recorded between conditions for total circuit times, 20 m sprint times for

each quarter and overall, or for the best and first sprint of each quarter. Moderate

(d=0.67; 90% CL=-1.27-0.23%) effect sizes indicated lower core temperatures in PC at

the end of the precooling period and the first quarter. It was concluded that repeat-

sprint running performance of naturally heat acclimatised participants was not enhanced

following precooling performed prior to and during exercise performance in warm

conditions.

These studies suggest that if athletes are not heat acclimated or seasonally acclimatised,

then a combined precooling method of cooling jacket and ice slushy will result in better

prolonged repeat-sprint performance than either cooling method used alone.

Furthermore, if athletes are partially acclimated or seasonally acclimatised, precooling

is not necessary in order to enhance subsequent repeat-sprint performance in heat.

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Table of Contents

Publications Arising from this Thesis 1

Peer-Reviewed Conference Proceedings 2

Overview 3

Table of Contents 6

Acknowledgements 7

Statement of Originality 8

List of Tables 9

List of Figures 10

List of Abbreviations 11

CHAPTER ONE

Introduction

12

CHAPTER TWO

Literature Review

19

CHAPTER THREE

Study One: Effects of different precooling techniques on repeat-sprint

ability in team-sport athletes.

55

CHAPTER FOUR

Study Two: Effect of precooling and acclimation on repeat-sprint

performance in heat.

81

CHAPTER FIVE

Study Three: Effect of precooling on repeat-sprint performance in

seasonally acclimatised males during an outdoor simulated team-sport

protocol in warm conditions.

106

CHAPTER SIX

Discussion

129

CHAPTER SEVEN

Appendices

142

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Acknowledgements

Most sincere thanks and appreciation go to all of whom were involved and contributed

to the completion of this thesis. In particular:

Winthrop Professor Brian Dawson, for your motivation, wisdom and knowledge,

which has been truly inspiring. The opportunity to work with you has been an honour

and one that has provided invaluable lessons.

Associate Professor Karen Wallman, for providing the original inspiration to attempt

a PhD, as early as second year, the encouragement, guidance and countless hours spent

on this project. Your assistance is very much appreciated and I will forever be thankful.

Sport Science, Exercise and Health and Postgraduate Students, for making this

experience a wonderful journey, I have enjoyed being involved with such a great

working community.

Research Participants, for your cooperation and commitment, these studies would not

have been possible without your generous donation of time and effort under hard

conditions.

Friends, for your support and patience throughout and your acknowledgement of the

demands of completing a PhD.

Family, Mum and Dad for your encouragement and love always and allowing me to

pursue my ambitions owing to your hard work and determination. Dustin, for your

100% participation record, support, reassurance and highlighting that “worrying is like a

rocking chair, it gives you something to do, but it doesn’t get you anywhere.”

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Statement of Originality

This thesis describes original research conducted by the author at the School of Sport

Science, Exercise and Health at the University of Western Australia from March 2009

to March 2013.

The author, under the guidance and assistance of Winthrop Professor Brian Dawson and

Associate Professor Karen Wallman is responsible for the research concept and design.

Participant recruitment, data collection, and data analysis were carried out by the

candidate, as well as the implementation of the experiments.

The candidate drafted the thesis, and the papers which have been accepted and/or are

currently being considered for publication, with assistance in writing and submission

processes by both Winthrop Professor Brian Dawson and Associate Professor Karen

Wallman. Feedback on the thesis was provided by Winthrop Professor Brian Dawson

and Associate Professor Karen Wallman.

Signature:

Carly Brade (Candidate)

Signature:

Winthrop Professor Brian Dawson (Supervisor)

Signature:

Associate Professor Karen Wallman (Supervisor) "

"

"

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List of Tables

Chapter Three

Table 1. Mean ± SD (n = 12) performance data for each half for the

control (CONT), ice jacket (J), ice slushy and the combination of cooling

techniques (J + ice slushy).

67

Table 2. Mean ± SD (n = 12) core (TC) and mean skin (mean TSk)

temperature at the start and finish of each phase (precooling, 1st half, half-

time and 2nd half) for the control (CONT), ice jacket (J), ice slushy and the

combination of cooling techniques (J + ice slushy).

68

Chapter Four

Table 1. Mean ± s (n = 10) performance data for each half for the pre

acclimation (Pre Acc), post acclimation precooling (Pre Acc +PC) and post

acclimation (Post Acc) trials.

94

Table 2. Mean ± s (n = 10) Core (TC) and mean skin (mean TSk)

temperature at the start and finish of each phase (precooling, 1st half, half-

time and 2nd half) for the pre acclimation (Pre Acc), post acclimation

precooling (Post Acc +PC) and post acclimation (Post Acc) trials.

95

Chapter Five

Table 1. Mean (± SD) 20 m sprint and circuit times overall and for each

quarter, plus first and best sprint times of each quarter for the precooling

(PC) and control (CONT) trials.

117

Table 2. Mean (± SD) core (TC; n = 10) and mean skin (mean TSk; n = 9)

temperature over the baseline period and at the end of each quarter for the

precooling (PC) and control (CONT) trials.

118

Table 3. Mean (± SD) heart rate (HR), thermal sensation (TS) and rating of

perceived exertion (RPE) at the end of each quarter for the precooling (PC)

and control (CONT) trials.

118

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List of Figures

Chapter Four

Figure 1. Study design 88

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List of Abbreviations

bpm beats per minute N number

BM body mass PC precooling

cm centimetre PC25 phase change 25

CONT control O2peak peak oxygen consumption

TC core temperature RPE rating of perceived exertion

°C degrees Celsius RH relative humidity

g grams S second

g·kg-1 grams per kilogram TS thermal sensation

HR heart rate O2max maximal oxygen consumption

h hour W watts

IS ice slushy W·kg-1 watts per kilogram

J jacket Y year

kg kilograms Δ change

kJ kilojoules

kJ·kg-1 kilojoules per kilogram

km kilometre

Mean TSk mean skin temperature

m metre

m2 metre squared

m·s-1 metres per second

min minute

ml millilitres

mm millimetre

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CHAPTER ONE Introduction

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Introduction

Background

Prolonged endurance and repeat-sprint exercise are often impaired when performed in

hot and humid environmental conditions, which may (at least in part) be manifested by

the attainment of a critically high core temperature (Gonzalez-Alonso et al., 1999;

MacDougall, Redden, Layton & Dempsey, 1974; Nielsen et al., 1993).

Notwithstanding the effects of environmental and metabolic heat on endurance exercise,

repeat-sprint tasks have been associated with greater thermal loads compared with

endurance exercise at a matched intensity (Kraning & Gonzalez, 1991; Nevill, Garrett,

Maxwell, Parsons & Norwitz, 1995).

Methods used to counteract the detrimental effect of heat on exercise performance

include acute methods of precooling and the more chronic technique of heat

acclimation/acclimatisation. Precooling has been commonly shown to enhance

endurance exercise performance, however results for repeat-sprint exercise have been

less conclusive (Marino, 2002; Quod, Martin & Laursen, 2006). For example, some

researchers have reported no benefit of precooling on repeat-sprint performance (Drust,

Cable & Reilly, 2000; Duffield, Dawson, Bishop, Fitzsimons & Lawrence, 2003),

whilst others have reported improvements (Castle et al., 2006; Minett, Duffield, Marino

& Portus, 2012). Further, both endurance (Nielsen et al., 1993; Nielsen, Strange,

Christensen, Warberg & Saltin, 1997) and repeat-sprint exercise (Castle, Mackenzie,

Maxwell, Webborn & Watt, 2011; Sunderland, Morris & Nevill, 2008) performed in

heat have been reported to be improved when preceded by both full and partial heat

acclimation/acclimatisation.

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In spite of this research, practical and convenient methods of cooling which may be

transferable to the field, and used both prior to and during exercise performance are yet

to be widely identified and trialled. In addition, the combination of both precooling and

acclimation together to enhance performance in heat has received little research

attention.

Statement of the problem

The main aim of this thesis was to determine the effect of precooling and heat

acclimation on prolonged repeat-sprint performance in heat. In particular, a specific

objective was to compare different practical precooling methods in order to determine

whether the simultaneous use of a combination of external (cooling jacket) and internal

(ice slushy) cooling methods would provide any advantage compared with the

application of only a singular method. In addition, the effect of precooling and

acclimation/acclimatisation on repeat-sprint performance in heat in both a controlled

laboratory and an outdoor field setting was investigated. This thesis begins with an

extensive review of the literature focusing primarily on the effect of precooling on

exercise performance, followed by individual chapters (chapters three to five) that each

represent a different experimental study.

Specific Aims of the Studies

Study One: Effects of different precooling techniques on repeat-sprint ability in team-

sport athletes.

The aim of this study was to compare different precooling techniques (ice slushy,

cooling jacket and the combination of the two) and their effect on prolonged repeat-

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sprint exercise in heat and to determine whether the simultaneous use of a combination

of internal and external cooling methods would provide any advantage compared with

only a singular method. Participants completed four identical trials (control; ice slushy;

cooling jacket; ice slushy plus cooling jacket) involving a 30-min precooling/baseline

period followed by a prolonged repeat-sprint cycling protocol (2 x 30-min halves

consisting of 30 x 4 s maximal sprints interspersed with sub-maximal exercise and

separated by a 10-min half-time cooling/recovery period) in hot and humid conditions

(~35°C and 60% relative humidity).

Study Two: Effect of precooling and acclimation on repeat-sprint performance in heat.

The purpose of this study was to ascertain if partial heat acclimation would improve

prolonged repeat-sprint performance in heat and whether the addition of precooling

would provide any additional advantage. Participants completed three trials; a pre-

acclimation and two post-acclimation trials, one with precooling (ice slushy and cooling

jacket as determined from study one) and one without. These trials were identical to the

repeat-sprint protocol performed in study one. Separating the pre- and post-trials were

five heat acclimation sessions (cycling at 80% maximum power output for 3-min with

1-min passive rest for 32 to 48 min).

Study Three: Effect of precooling on repeat-sprint performance in seasonally

acclimatised males during a simulated team-sport protocol in warm conditions.

This study aimed to determine the effect of a practical cooling method used prior to and

during a simulated team-sport game in warm outdoor conditions. Seasonally

acclimatised participants completed two duplicate trials (precooling and no precooling)

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involving a 30-min precooling/baseline period followed by an 80 min repeat-sprint

exercise protocol (4 x 20-min quarters with 2 x 5-min quarter and 1 x 10-min half-time

break).

Significance of the studies

The findings of these studies will potentially aid coaches and athletes who participate in

team-sports involving repeat-sprint exercise performed in hot and humid environmental

conditions. It will also assist sports scientists in prescribing methods appropriate for

limiting the effects of heat on repeat-sprint exercise performance. Finally, it will

determine practical and convenient methods of precooling prior to and during a team

game.

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References

Castle, P.C., Macdonald, A.L., Philp, A., Webborn, A., Watt, P.W., & Maxwell, N.S.

(2006). Precooling leg muscle improves intermittent sprint exercise performance

in hot, humid conditions. Journal of Applied Physiology, 100, 1377-1384.

Castle, P., Mackenzie, R.W., Maxwell, N., Webborn, A.D.J., & Watt, P.W. (2011). Heat

acclimation improves intermittent sprinting in the heat but additional pre-cooling

offers no further ergogenic effect. Journal of Sports Sciences, 29 (11), 1125-

1134.

Drust, B., Cable, N.T., & Reilly, T. (2000). Investigation of the effects of pre-

cooling on the physiological responses to soccer-specific intermittent exercise.

European Journal of Applied Physiology, 81, 11-17.

Duffield, R., Dawson, B., Bishop, D., Fitzsimons, M., & Lawrence, S. (2003). Effect of

wearing an ice cooling jacket on repeat sprint performance in warm/humid

conditions. British Journal of Sports Medicine, 37, 164-169.

Gonzalez-Alonso, J., Teller, C., Andersen, S.L., Jensen, F.B., Hyldig, T., & Nielsen, B.

(1999). Influence of body temperature on the development of fatigue during

prolonged exercise in the heat. Journal of Applied Physiology, 86 (3), 1032-

1039.

Kraning, K.K., & Gonzalez, R.R. (1991). Physiological consequences of intermittent

exercise during compensable and uncompensable heat stress. Journal of Applied

Physiology, 71 (6), 2138-2145.

MacDougall, J.D., Reddan, W.G., Layton, C.R., & Dempsey, J.A. (1974). Effects of

metabolic hyperthermia on performance during heavy prolonged exercise.

Journal of Applied Physiology, 36 (5), 538-544.

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Marino, F.E. (2002). Methods, advantages, and limitations of body cooling for exercise

performance. British Journal of Sports Medicine, 36, 89-94.

Minett, G.M., Duffield, R., Marino, F.E., & Portus, M. (2012). Duration-dependent

response of mixed-method pre-cooling for intermittent-sprint exercise in the

heat. European Journal of Applied Physiology, 112, 3655-3666.

Nevill, M.E., Garrett, A., Maxwell, N., Parsons, K.C., & Norwitz, A. (1995). Thermal

strain of intermittent and continuous exercise at 10 and 35°C in man. Journal of

Physiology, 483P, 124-125.

Nielsen, B., Hales, J.R.S., Strange, S., Christensen, N., Warberg, J., & Saltin, B.

(1993). Human circulatory and thermoregulatory adaptations with heat

acclimation and exercise in a hot, dry environment. Journal of Physiology, 460,

467-485.

Nielsen, B., Strange, S., Christensen, N., Warberg, J., & Saltin, B. (1997). Acute and

adaptive responses in humans to exercise in a warm, humid environment.

Pflügers Archives - European Journal of Physiology, 434, 49-56.

Quod, M.J., Martin, D.T., & Laursen, P.B. (2006). Cooling athletes before competition

in the heat: Comparison of techniques and practical considerations. Sports

Medicine, 36 (8), 671-682.

Sunderland, C., Morris, J.G., & Nevill, M.E. (2008). A heat acclimation protocol for

team sports. British Journal of Sports Medicine, 42, 327-333.

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CHAPTER TWO Literature Review

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Introduction

Strenuous exercise, particularly in hot and humid conditions, imposes considerable

thermoregulatory strain on the body’s physiological processes, and negatively affects

performance. Numerous studies support the notion that a critical core temperature

exists and is the primary reason for causing premature (voluntary) termination of

exercise and a reduction in peak or mean power output. Heat

acclimatisation/acclimation and precooling are two methods that have successfully been

used to limit the effect of heat strain on performance. This literature review will firstly

examine the effect of heat on the physiological processes that occur during exercise,

touching briefly also on the psychological effects. Next, the practices of heat

acclimation and precooling prior to performance in heat will be reviewed, with

particular emphasis on precooling and its physiological rationale, the common methods

used and lastly its effects on different modes of exercise (endurance, short sprint and

prolonged repeated sprint) performance.

Effect of Heat on Exercise Performance

Thermoregulation Overview

Internal (core) temperature is one of the many homeostatic mechanisms that the body

needs to maintain within a small range. Having a core body temperature between 36.5

to 38.5°C permits the normal functioning of many integrated physiological processes

(Moran & Mendal, 2002). Core temperature is influenced by two major sources: firstly,

endogenous heat production from within the organism (metabolism and muscle action)

and secondly, environmental factors, including temperature, humidity, wind, sun

exposure and clothing (Sandor, 1997).

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At rest, in order to achieve a constant internal temperature of approximately 37.0°C, the

body must maintain a fine balance between heat production and dissipation (Sandor,

1997). The thermoregulatory system coordinates this process by reacting appropriately

to any environmental stress acting on the body and by dissipating any internal heat not

required for the generation of mechanical power (Gonzalez-Alonso, Crandall &

Johnson, 2008). Through the processes of conduction (transfer of heat down a thermal

gradient from the body to an object), convection (the transfer of heat through a moving

liquid or gas), radiation (transferring heat by infrared heat rays) and evaporation (loss of

heat by sweating or insensible water loss), the body attempts to lose excessive heat

(Wendt, van Loon & van Marken Lichtenbelt, 2007).

Physiological Effects of Heat on Performance

For some of the mechanisms of heat loss (namely convection and radiation) to

effectively function in maintaining homeostasis, a thermal gradient between the skin

and surrounding environment must exist in which the environment is cooler than the

skin. However, if the ambient air temperature exceeds 35-36°C, thereby being warmer

than the skin, this temperature gradient is reversed, resulting in the body gaining heat

via convection and radiation (Nielsen, 1996; Wendt et al., 2007). This particular

situation causes the evaporation of sweat to become the main avenue of heat loss

(Hasegawa, Takatori, Komura & Yamasaki, 2005; Wendt et al., 2007). Importantly, it

is the process of sweat evaporating (changing state from liquid to gas) that causes this

mechanism to be effective, not just the act of physically sweating (Wendt et al., 2007).

Therefore, environmental factors such as insufficient air movement and excessive

ambient water vapour pressure (humidity in excess of 60%; Nielsen, 1996) provide

barriers that impair the sweat evaporative process (Kraning & Gonzalez, 1991; Wendt et

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al., 2007). As a result, hot and humid environments limit cooling, causing the body to

store excessive heat, which subsequently increases core temperature (Marino, 2002).

The human body is extremely efficient in most aspects of its function, including

thermoregulation. As approximately 75% of the energy produced by the oxidation of

skeletal muscle substrate is liberated as heat (Marsh & Sleivert, 1999) and must be

dissipated from the body, the ability to lose heat via evaporation is vital. The

importance of the human eccrine sweat glands to produce sweat for evaporation is

underscored by the fact that “metabolic heat production has the potential to increase 15

to 20 times above that of normal basal levels during exercise (Casa, 1999), causing

corresponding increases in core temperature. An increase in endogenous heat

production as a result of exercise, coupled with uncompensable environmental

conditions, places two primary circulatory demands on the body during exercise. These

are blood flow to the working skeletal muscles, to aid in nutrient transportation and

waste removal, and blood flow to the periphery, to facilitate heat loss to the surrounding

environment (Gonzalez-Alonso et al., 2008; Quod, Martin & Laursen, 2006). During

intense exercise in the heat (with accompanying dehydration), blood flow to the

periphery (skin) is diminished as the body attempts to maintain cardiac output in

response to a steadily reducing plasma volume (Gonzalez-Alonso et al., 2008).

Consequently, core temperature increases, which has the potential to severely affect an

individual’s health and well-being (Coyle, 1999).

Prolonged exercise in heat can result in the attainment of a critically high core

temperature, which is commonly in the range of 39.4 – 40.0ºC (Gonzalez-Alonso et al.,

1999; MacDougall, Reddan, Layton & Dempsey, 1974; Nielsen et al., 1993). Attaining

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a critically high core temperature has been proposed by many researchers as an

important factor in the premature (voluntary) termination of exercise (Gonzalez-Alonso

et al., 1999; MacDougall et al., 1974; Nielsen et al., 1993; Nielsen, Strange,

Christensen, Warberg & Saltin, 1997). Notably, Gonzalez-Alonso et al. (1999)

demonstrated that despite manipulating initial core temperatures (~35.9, 37.4 and

38.2°C) or the rate of heat storage (0.10 vs. 0.05°C·min-1), exhaustion from cycling in

the heat (40°C and 19% relative humidity; RH) consistently coincided with a core

temperature of ~40°C. Further, Nielsen et al. (1993) noted that, regardless of

undergoing 9-12 days of acclimation in dry heat (40°C, 10% RH), continuous exercise

performed at 60% of maximal oxygen consumption ( O2max) in hot environmental

conditions was terminated when core temperature reached ~39.7°C. Here, it should be

acknowledged that these studies are laboratory-based protocols, which may not truly

reflect field scenarios.

While there is strong support for this notion of a “critical core temperature” it has

recently been challenged. Ely et al. (2009) concluded that despite rectal temperatures

reaching 40°C, running velocity during an 8 km (average time 27-30 min) time trial,

performed in both cool and warm (wet bulb globe temperature ~13°C and 26-28°C,

respectively) environmental conditions, was unchanged and pace variations were not

affected by the rate of heat storage. These authors made note that literature supporting

the relationship between a critical core temperature and fatigue also reported increased

skin (~37°C; narrow core to skin gradients) and muscle temperatures (~41°C), as well

as elevated cardiovascular strain (represented by high heart rates), yet disregarded that it

was the combination of these thermoregulatory stressors that impaired exercise

performance, rather than just core temperature alone. Given that mean skin

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temperatures were ~30°C and 34°C during the cool and warm environments

respectively, Ely et al. (2009) stated that when skin temperatures were low, the

detrimental impact of a 40°C core temperature was absent. Further research is needed

to confirm this relationship. Although there is much literature to support the existence

of a critical core temperature being an important factor for the limitation of exercise

performance, it should be acknowledged that there is evidence that athletes are able to

continue exercise despite having high core temperatures (Arngrimsson et al., 2004;

Duffield et al., 2013; Morris et al., 2005; Ross et al., 2011).

Associated with the concept of a critical core temperature negatively affecting exercise

performance, studies that have compared endurance exercise performed in warm-hot

and thermoneutral environments have reported that performance is significantly

influenced by ambient conditions and impaired in warm-hot conditions (Galloway &

Maughan, 1997; MacDougall et al., 1974). For example, MacDougall et al. (1974)

reported that time to exhaustion whilst running on a treadmill was significantly reduced

in hyperthermic conditions (48 min) when compared with normothermic (75 min) and

hypothermic (91 min) conditions. Another study by Galloway and Maughan (1997)

compared times to exhaustion whilst cycling at 70% O2max in ambient temperatures of

4°C, 11°C, 21°C and 31°C. Results showed that exercise duration was significantly less

in 31°C (52 min), with the longest duration being reported in 11°C (94 min).

Notwithstanding the effects on endurance exercise, hot and humid conditions have also

been reported to have a detrimental effect on prolonged, repeat-sprint exercise (Drust,

Rasmussen, Mohr, Nielsen & Nybo, 2005; Morris, Nevill, Lakomy, Nicholas &

Williams, 1998; Morris, Nevill & Williams, 2000; Morris, Nevill, Boobis, Macdonald

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& Williams, 2005). These studies showed that the distance covered during a prolonged

high-intensity intermittent running protocol was significantly less when performed in

hot (30-33°C) compared with thermoneutral (16-20°C) environmental conditions (8842

vs 11280 m, Morris et al., 1998; 7876 vs 10995 m, Morris et al., 2000; 11216 vs 21644

m, Morris et al., 2005). Similarly, mean power output achieved during a repeat-sprint

protocol performed in the heat (40°C; 558 W) was significantly lower than that

achieved in normal conditions (20°C; 618 W; Drust et al., 2005).

It has been further suggested that intermittent exercise is often associated with greater

thermal loads, compared with endurance exercise of a matched intensity (Kraning &

Gonzalez, 1991; Nevill, Garrett, Maxwell, Parsons & Norwitz, 1995). Specifically,

Kraning and Gonzalez (1991) calculated that the rise in core temperature during repeat-

sprint exercise (2.16°C·h-1) in uncompensable environmental conditions (30°C and

vapour pressure of 6.3 Torr) was 33% greater compared with continuous exercise

(1.62°C·h-1) performed in the same conditions at the same average intensity. In

addition, exercise times were significantly shorter for intermittent exercise (65 min)

compared with continuous, when performed in uncompensable conditions (79 min;

Kraning & Gonzalez, 1991). Shorter exercise times when cycling to exhaustion at

100% O2max were also apparent following a 30-min intermittent exercise protocol (82

s) compared with 30-min of continuous exercise (289 s) performed at the same average

intensity in 35°C heat (Nevill et al., 1995). It was concluded that intermittent exercise

resulted in a higher thermal strain compared with continuous exercise, as was

demonstrated by the attainment of higher average heart rate and rectal temperatures. A

higher degree of thermal strain in prolonged intermittent exercise may be due to the

extra metabolic heat generated by working at a higher absolute intensity during the

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repeated sprints, compared with the steady state (lower intensity) nature of continuous

exercise.

Associated with the effect of increasing core temperature on exercise performance is the

additional impact of a warm-up performed prior to exercise. While there are numerous

temperature related benefits associated with warm-up on subsequent exercise

performance (see review by Bishop, 2003), warm-up may also further reduce heat

storage capacity in the body, resulting in a critical core temperature being achieved

sooner (Nadel & Horwarth, 1977). This process is accentuated when exercise is

performed in hot and humid conditions. Consequently, any extra heat storage in the

body, especially as a result of warm-up can be detrimental to subsequent exercise

performance. This effect was demonstrated by significantly reduced endurance exercise

times, whilst running on a treadmill (70% O2max) in moderate environmental

conditions (~22°C and 37% RH), following active (48 min) and passive warm-up (40

min), compared with no warm-up (62 min; Gregson, Drust, Batterham & Cable, 2002).

It was concluded by these researchers that the significantly higher rectal (38°C vs 37°C)

and body temperatures (37.4 °C vs 36.3°C) resulting from the warm-up conditions

subsequently compromised heat storage capacity and hence exercise performance

(Gregson et al., 2002).

Psychological Effects of Heat on Performance

In addition to increases in core temperature, as sweating continues during exercise

(particularly in the heat), an athlete may lose a considerable amount of body fluid. If

not replaced by voluntary fluid ingestion, dehydration and reduced blood flow to the

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periphery can result. Dehydration levels, equal to and greater than a 2% body-mass

(BM) deficit, have been reported to significantly reduce mental efficiency. Sharma,

Sridharan, Pichan and Panwar, (1986), produced levels of dehydration corresponding to

a 1, 2 or 3% BM deficit, whilst in hot, dry (45°C dry bulb and 30% RH) or hot, humid

(39°C dry bulb and 60% RH) conditions. Following 90-min of seated rest in

thermoneutral conditions, psychological tests (substitution, concentration and

coordination) were then completed. At levels of 2 and 3% dehydration, performance

scores in the coordination and concentration tests were significantly lower compared

with euhydration and 1% BM loss. These results were also evident following 40-min of

exercise (cycling at 40 W) performed in hot, dry and hot, humid conditions, whilst

participants were in the 1, 2 or 3% dehydrated state (Sharma et al., 1986).

Despite this, there is evidence to suggest that sweat loss during exercise has no

conclusive effect on final core temperature or performance during a triathlon done in

warm environmental conditions (Sharwood, Collins, Goedecke, Wilson & Noakes,

2002). These divergent findings are perhaps due to the latter study being done in the

field, where environmental conditions are variable, whereas the previously mentioned

study was done in controlled laboratory conditions. Furthermore, this could also be due

to individual variability, whereby some individuals are able to perform efficiently

despite high levels of dehydration and core temperatures. However, these results still

provide evidence that exercise in the heat is detrimental to not only physiological

performance but also to psychological function (when compared to exercise in

temperate conditions). With particular reference to team-sports, where the added

element of decision making is of vital importance, these detrimental effects of heat on

mental processes may potentially influence the outcome of a game.

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Heat Acclimation

Many sports are held in climates that are hot and humid. For example, in Australia,

several sports are played during summer, such as the Australian Open (tennis) and

summer cricket series, where average temperatures and RH can reach ~30°C and 60%

RH. Further, major sporting events such as the Commonwealth games have been held

in extreme environments, such as the 2008 games held in Dehli, India, where average

ambient conditions were ~31°C and RH ranged between 31-78% and upcoming events

such as the 2014 FIFA World Cup in Brazil where temperatures around 27°C and

exceeding 32°C are expected. Due to the detrimental effects of heat on exercise

performance, various procedures have been trialled in an effort to counteract these

negative effects. To date, the most reputable and well-studied technique designed to

minimise the effects of heat on exercise performance is heat acclimatisation/acclimation

(Marino, 2002), which is widely practiced by athletes in order to prepare for exercise in

hot and humid environments. Heat acclimatisation or acclimation is the process by

which adaptive physiological changes occur within the body that improves an

individual’s ability to tolerate heat (McArdle, Katch & Katch, 2001). The process of

acclimatisation occurs when physiological adaptations to heat occur in a natural (hot)

field environment, while acclimation relates to physiological changes which occur in

response to repeated exposure to an artificially hot environment, such as a climate

chamber.

Heat acclimatisation/acclimation involves the regular exposure to a hot and/or humid

environment, with a period of 7-14 days being the time required for full adaptation to

occur (Wendt et al., 2007). Physiological adaptations which are advantageous to the

athlete include a lower threshold for the commencement of sweating, increased total

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sweat output and sensitivity, enhanced cutaneous blood flow, expansion of plasma

volume, better distribution of cardiac output and lower heart rate, core and skin

temperature for a typical exercise bout (Armstrong & Maresh, 1991; McArdle at al.,

2001; Nielsen et al., 1997). The stimulus required for heat acclimatisation/acclimation

to occur is the repeated maintenance of an elevated core temperature and the onset of

sweating (Armstrong & Maresh, 1991; Nielsen et al., 1997; Wendt et al., 2007). The

benefits of heat acclimatisation/acclimation may diminish over several days if exposure

to heat is not continued (Pandolf, Burse & Goldman, 1977).

It has been well established that regular exposure to heat enhances endurance exercise

performance by means of improving thermal tolerance. Nielsen et al. (1993) concluded

that after exercising for 9-12 days until exhaustion at 60% O2max in hot, dry ambient

conditions (40°C and 10% RH), full acclimation had occurred, as suggested by lower

rates of rise in core temperature and heart rate, and increased sweating. Furthermore, an

increased time (48 to 80 min) to volitional fatigue was evident after this form of

exposure (Nielsen et al., 1993). A later study by Nielsen et al. (1997) reported that

cycling time to exhaustion was increased (45 to 52 min) after acclimation to the heat

following 8-13 consecutive days of exercising for 45-min at 45% O2max in hot, humid

(35°C and 87% RH) conditions.

Generally, acclimation protocols have been investigated with the intent of improving

endurance performance in the heat, with these protocols involving low-intensity (45-

60% O2max) exercise performed daily for a prolonged duration (45-80-min).

However, this form of exercise is very different to that performed by team-sport

athletes, where exercise involves many repeated short sprint efforts. Recently, an

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acclimation protocol designed for team-sports, which differs from conventional

acclimation protocols by using fewer and shorter sessions of high variable intensity

exercise was tested on highly trained athletes (Sunderland, Morris, & Nevill, 2008).

Here, participants performed only four acclimation sessions (over 10 days) involving

high-intensity intermittent running for 30-45 min in 30°C and 27% RH. Following this

partial acclimation process, total running distance covered (before volitional fatigue)

during the Loughborough Intermittent Shuttle Test was 33% greater compared with

control, with this improvement attributed to increases in thermal comfort during

exercise and lower core temperature values at the start of exercise (Sunderland et al.,

2008). Petersen et al. (2010) also noted that similar (partial) acclimation resulted in

decreases in heart rate and sweat electrolyte concentrations following four high-

intensity acclimation sessions performed in 30°C and 65% RH. Potentially, short-term

(i.e. partial), high-intensity, intermittent acclimation protocols may be more appropriate

for team-sport athletes who require improved heat tolerance and who do not have the

time nor the financial resources to fully acclimate via several (daily) exercise-heat

exposures. In summary, both full and partial acclimation protocols are effective in

aiding both endurance and repeat-sprint performance respectively, when performed in

hot and/or humid conditions.

Precooling

Premise

In addition to heat acclimation, an acute (pre-exercise) method of preparing for exercise

in heat is precooling. The rationale behind precooling is to delay the rise in core

temperature to increase the time taken to reach a critical thermal maximum, at which a

particular exercise intensity cannot be maintained (Arngrimsson, Petitt, Stueck,

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Jorgensen & Cureton, 2004; Marino, 2002; Olschewski & Bruck, 1988; Quod et al.,

2006; Schmidt & Bruck, 1981; Siegel et al., 2010; Wendt et al., 2007). The exact

mechanisms by which precooling enhances exercise performance are not fully

understood (see reviews; Marino, 2002; Quod et al., 2006), however several have been

suggested.

One of the most widely accepted mechanism proposed to explain the beneficial effects

of precooling on subsequent exercise performance relates to an increased heat storage

capacity that occurs as a result of cooling both the core and skin (Arngrimsson et al.,

2004; Booth, Marino & Ward, 1997; Duffield & Marino, 2007; Hasegawa, Takatori,

Komura & Yamasaki, 2006; Kay, Taaffe & Marino, 1999; Lee & Haymes, 1995;

Marino, 2002; Quod et al., 2006; Quod et al., 2008). In particular, the act of lowering

both core and skin temperatures prior to activity brings about a negative heat content,

therefore allowing a greater amount of heat to be stored during exercise (Arngrimsson et

al., 2004), delaying the onset of heat dissipating mechanisms and reducing thermal

strain (Drust, Cable & Reilly, 2000; Kay et al., 1999; Lee & Haymes, 1995).

Further, it has been proposed that enhanced exercise performance following precooling

may be the result of an increase in central blood volume (Hessemer, Langusch, Bruck,

Bodeker & Breidenbach, 1984; Marino, 2002; Marsh & Sleivert, 1999; Sleivert, Cotter,

Roberts & Febbraio, 2001). Specifically, precooling may initiate peripheral

vasoconstriction, therefore directing more blood to the working muscles to aid in waste

removal and delivery of oxygen and nutrients, thus aiding in the maintenance of a high

exercise intensity (Marsh & Sleivert, 1999; Sleivert et al., 2001).

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In addition, there is growing support that better performance following precooling may

be related to the evoking of different pacing strategies, compared with a no cooling

control trial (Arngrimsson et al., 2004; Duffield, Green, Castle & Maxwell, et al., 2010;

Skein, Duffield, Cannon, Marino, 2012; Quod et al., 2006). It seems that the lower

perceptual and thermoregulatory strain resulting from precooling allows athletes to

select and maintain higher intensities during exercise and hence delay the self-selected

reduction in intensity that is typically seen during exercise performed in heat (Duffield

et al., 2010; Skein et al., 2012; Quod et al., 2006). Specifically, maximal voluntary

contraction has been shown to be maintained following precooling and exercise

performed in heat, despite a greater work capacity, which suggests the preservation of

muscle recruitment and neuromuscular function (Minett, Duffield, Marino & Portus,

2011; Minett, Duffield, Marino & Portus, 2012). Interestingly, increases in work have

been more evident during the latter stages of exercise when the physiological

advantages of precooling (i.e. lower core and skin temperature and heat rate) have

diminished (Arngrimsson et al., 2004; Duffield et al., 2010; Duffield, Coutts, McCall &

Burgess, 2013; Skein et al., 2012). According to Arngrimsson et al. (2004), athletes

regulate their pace according to cues received concerning thermal and cardiovascular

strain and feelings of fatigue.

Methods of Precooling

Numerous methods of precooling exist, including cold air exposure, water immersion,

cooling jackets, ice packs and more recently, the ingestion of an ice slushy and the

combination of several cooling techniques. Although all of these methods have been

associated with exercise performance benefits, some present logistical problems with

regards to their application within a field setting. For example, issues such as ease of

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application, transport, access to materials and facilities required, cost, pre-competition

schedule and athlete comfort need to be considered (Quod et al., 2006), in addition to

the cooling efficiency of the particular method used.

Early precooling studies used cold air exposure as a precooling method, with this

procedure involving exposure to ambient (climate chamber) temperatures of 0-10°C, for

a total time of 30-80 min (Hessemer et al., 1984; Lee & Haymes, 1995; Olschewski &

Bruck, 1988; Schmidt & Bruck, 1981). Often, a rewarming period was incorporated for

the purpose of reducing thermal discomfort and shivering, with this further adding to

the time required to complete cooling. Core temperature reductions that occurred over

the precooling period using this method ranged between 0.2-1.0°C. This wide

temperature range may be at least partly attributed to the differing core temperature

measurement sites used (oesophageal, tympanic, rectal), as well as the use of different

precooling protocols (duration and temperature of cooling). Of relevance, cold air

exposure represents a whole body cooling procedure similar to that of cold water

immersion, which is perhaps the most commonly used precooling method.

The rationale for using water immersion as a means of cooling is due to the high

thermal conductivity of water (Mitchell, Schiller, Miller & Dugas, 2001). Therefore,

warmer temperatures (14-25°C) and shorter exposure times (20-60 min), compared with

those used for cold air exposure have resulted in similar reductions (0.3-0.7°C) in core

temperature (Booth et al., 1997; Castle et al., 2006; Duffield & Marino, 2007; Duffield

et al., 2010; Hasegawa et al., 2006; Kay et al., 1999; Marsh & Sleivert, 1999; Quod et

al., 2008). Similarly, Drust et al. (2000) reported a decrease in rectal temperature of

0.6°C following a 60-min cold shower (24°C). In addition to cooling a large surface

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area, water immersion results in uniform skin temperatures that closely match the water

temperature that the skin is exposed to (Marino & Booth, 1998; Marino, 2002). Of

importance, both cold air exposure and water immersion are impractical for use during

typical team-sport competitions due to the equipment needed and time required for

adequate precooling to occur (Kay et al., 1999; Quod et al., 2006). Moreover, these two

methods are often associated with the stimulation of thermoregulatory control

mechanisms, such as peripheral vasoconstriction and shivering, both of which act to

increase or maintain core temperature.

Another method of cooling, which represents a more practical and convenient way of

reducing core and skin temperature on the sporting field, is the wearing of cooling

jackets. These exist in a variety of types, including gel and ice jackets, with ice jackets

containing either ice or frozen goods such as bottled water. One major advantage of the

ice jacket compared with cold air exposure and water immersion is the ability for it to

be worn during active warm-up, as well as during quarter and half-time breaks during a

team-sport game. Studies that have used a cooling jacket during warm-up (described

later in this review) have reported that although core temperature increased over the

warm-up period as cooling was applied, it was still lower at the beginning of exercise

(0.2°C, Arngrimsson et al., 2004; 0.5°C, Uckert & Joch, 2007) when compared with a

control condition. Other studies that have assessed the effect of a cooling jacket on

subsequent exercise performance (without cooling during a warm-up procedure) have

reported reductions in core temperature in the range of 0.3–0.5°C (Duffield, Dawson,

Bishop, Fitzsimons & Lawrence, 2003; Castle et al., 2006; Cheung & Robinson, 2004).

There are however, logistical problems with the use of conventional cooling jackets, in

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that melting of the ice eventually occurs and the replenishment of ice or the reactivation

of gel is the only means of continued cooling.

With regard to cooling during breaks in play (such as half-time), the purpose is to blunt

the rise in core and skin temperature to potentially enable better second half

performance and to limit the effect of an increasing core temperature on exercise

performance. Price, Boyd and Goosey-Tolfrey (2009) examined the physiological

benefit of precooling combined with half-time cooling, compared with no cooling and

precooling alone, across 90 min of intermittent running in the heat. They concluded

that the use of a gel cooling jacket during the 20-min precooling and 15-min half-time

cooling period (where both core and skin temperature were significantly reduced

compared with the other conditions) was more effective than just precooling alone in

offsetting heat storage. However, no performance measures were assessed in their

study. Duffield et al. (2003) also found a tendency (large ES) for a lower third and

fourth quarter starting mean skin temperature associated with wearing a cooling jacket,

as well as significantly lower chest skin temperatures after quarter and half-time

cooling. While core temperature values may not be greatly reduced, the use of cooling

jackets during exercise breaks in hot/humid conditions is likely to produce significant

decreases in mean skin temperature, which may assist subsequent exercise performance

(Duffield et al., 2003; Price et al., 2009).

Recently, it was suggested that any exercise performance benefits seen as a result of

prior cold water ingestion may be greater if ice was used instead. Ihsan, Landers,

Brearley and Peeling (2010) reported a decrease in core temperature of 1.1°C after

ingesting 6.8 g/kg-1 BM of ice, while Siegel et al. (2010) found a 0.6°C decrease in core

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temperature after the ingestion of 7.5 g/kg-1 BM of ice slurry, with the ice in both trials

being ingested at a constant rate over a 30-min period prior to subsequent exercise

performance. Performance details relating to both these studies are discussed in the

latter part of this literature review. In addition to the cooling efficiency of ice ingestion,

limited equipment is required, plus ice/water is a valuable source of pre-exercise

hydration. When ingested, ice undergoes a phase change, creating a heat sink into

which a large amount of the body’s heat can be transferred, rather than being stored

(Ihsan et al., 2010; Siegel et al., 2010).

More recently, mixed-method cooling techniques have been evaluated. To date, varying

decreases in core temperature have been reported after cooling for similar durations (20-

30 min) in warm conditions using methods such as ice bath and vest, ~0.2°C (Duffield

& Marino, 2007); head, neck, hand, cooling jacket and ice packs on thighs, ~0.2°C

(Minett et al., 2011; Minett et al., 2012); iced towels on torso and legs plus ice slushy,

~0.2°C or water immersion and cooling jacket, ~0.6°C (Ross et al., 2011) and an ice

bath followed by 40-min of wearing a cooling jacket, ~0.7°C (Quod et al., 2008). One

common feature between all of the above mentioned studies was that these combined

methods of precooling all resulted in better exercise performance (refer to next section)

compared with methods which involved only one cooling technique.

With regards to the best method of precooling prior to exercise performance, the

practicality and convenience of administration within a field environment needs

consideration. Methods such as cooling jackets, ice slushies and iced towels require

little equipment or preparation. Furthermore, Minett and colleagues (2011) found that

there appeared to be a dose-response relationship between the volume of cooling

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(surface area coverage) and subsequent performance enhancements, concluding that

better exercise performance was found after a whole body cooling approach (head, neck

and hand cooling plus jacket and ice packs on thighs vs head vs head and hand). In

addition, the same researchers found that there was also a relationship between the

duration of cooling and performance results, concluding that 20-min of cooling, using

the same mixed-method procedure as described above, resulted in better repeat-sprint

performance compared with no cooling and 10-min of cooling (Minett et al., 2012).

Effect of Precooling on Exercise Performance

Endurance Performance

Due to the potential benefits of cooling prior to exercise, much research has assessed its

effectiveness on exercise performance. To date, the majority of studies have assessed

endurance exercise performed in both moderate (18-24°C; Hessemer et al., 1984; Lee &

Haymes, 1995; Olschewski & Bruck, 1988; Schmidt & Bruck, 1981) and hot and humid

(30-34°C; Arngrimsson et al., 2004; Booth et al., 1997; Duffield et al., 2010; Hasegawa

et al., 2005; Hasegawa et al., 2006; Kay et al., 1999; Quod et al., 2008; Siegel et al.,

2010; Uckert & Joch, 2007) environmental conditions, finding exercise performance to

be significantly improved following a precooling procedure.

For example, studies by Hasegawa and colleagues (2005 and 2006) showed that a

combination of cooling methods (cooling jacket and water ingestion, J + W; cold water

immersion and water ingestion, C + W, respectively) significantly increased time to

exhaustion (2005; J + W = 471.7 s vs Cont = 151.5 s; 2006; C + W= 481 s vs Cont =

152 s) whilst cycling at 80% VO2max. Lee et al. (1995) and Olschewski et al. (1988)

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both used cold air exposure in order to decrease core temperature (0.37°C and 0.2°C,

respectively), with this resulting in significantly longer endurance times (running, 17%

and cycling, 12.5%, respectively) compared with a no cooling condition. Furthermore,

longer running times (50.2 vs 40.7 min) were reported after ingestion of an ice slushy

compared with an equivalent volume of tap water (Siegel et al., 2010).

In addition, exercise completed within a fixed period of time at a self-selected pace has

been shown to improve following precooling. For example, Hessemer et al. (1984)

reported a 6.8% increase in mean one hour cycling work rate when exercise was

preceded by cold air exposure. Further, Booth et al. (1997) found that the distance

covered in a 30-min running period was increased by 4% following 60-min of cold

water immersion (24°C), while Kay et al. (1999), using the same method, reported a

greater cycling distance covered (0.9 km), when compared with a control condition. In

addition, Duffield et al. (2010) observed that mean power (198 vs 178 W) and distance

(19.3 vs 18.0 km) covered during a 40-min cycling time trial were significantly higher

compared with a no cooling condition following a 20-min precooling condition

consisting of immersion of the legs (only) in cold (14°C) water.

With ice ingestion of 6.8 g/kg-1 BM, Ishan et al., (2010) found that endurance exercise

performed over a fixed distance was 6.5% faster during a 40 km cycling time trial

(compared with a control condition). In addition, Quod et al. (2008) compared the

effects of wearing an ice jacket for 40-min in the heat (34°C and 41% RH) to a

combined precooling procedure consisting of 30-min of water immersion (24°C)

immediately followed by 40-min of cooling with an ice jacket. These researchers

reported faster cycling times (1055 s vs. 1081 s) during a variable time trial which was

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preceded by a fixed 20-min time trial, following the combined cooling procedure.

Unfortunately, comparisons between studies are difficult due to the different cooling

and exercise protocols employed and the use of different core temperature measurement

sites. However there is sufficient evidence to suggest that endurance exercise

performance is usually improved following precooling.

Sprint Performance

During single, short, high-intensity sprint bouts of exercise the role of thermoregulation

is minor, consequently little research has focused on precooling prior to this type of

exercise. Marsh and Sleivert (1999) did however assess the effect of precooling on an

acute sustained sprint bout of exercise, reporting greater power output (3.3%; 603 vs

581 W) during a 70 s cycling test performed in warm, humid conditions (29°C and 80%

RH) that followed cold water (12-14°C) immersion (of the torso only) for 30-min. They

concluded that better performance was most likely the result of cold water immersion

causing peripheral vasoconstriction of the upper body, which resulted in an increased

central blood volume. Although blood flow to the working muscles was not measured,

it was suggested that more blood was made available to the active musculature, thereby

aiding in enhanced oxygen delivery and metabolic waste removal, allowing for the

maintenance of a higher exercise intensity throughout the sprint (Marsh & Sleivert,

1999).

Conversely, Sleivert et al. (2001) reported that precooling the torso and thighs (ice vest

whilst in 3°C cold air and 4°C cold water perfused cuffs on the thigh) for 45-min

resulted in significantly reduced peak and mean power output during a 45 s cycle sprint

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test in warm conditions, compared with torso cooling whilst participants legs were

being warmed (~38°C water perfused cuffs) and a control (no cooling) condition. This

performance difference was even more pronounced in the absence of a warm-up. These

contrasting results emphasise the importance of not cooling the active musculature prior

to exercise, as it is commonly accepted that this impairs exercise performance (Sleivert

et al., 2001). Specifically, impaired exercise performance in their study following both

pre-performance procedures was concluded to be the result of poor muscular contractile

function resulting from reduced muscle temperature. Furthermore, these researchers

found no difference in sprint performance between control and torso only cooling and

concluded that their results differed from those of Marsh and Sleivert (1999) due to the

longer (10-min) warm-up protocol used by them, as this would have increased muscle

temperature to a more optimal level, although this variable was not measured. Despite a

shorter precooling duration (30-min, Marsh & Sleivert, 1999 vs 45-min Sleivert et al.,

2001), starting core temperature was slightly lower (~36.6°C vs 36.8-37.0°C) in their

earlier study, with this factor also potentially contributing to the different results.

Intermittent (repeat) Sprint Performance

With regards to precooling prior to repeat-sprint exercise, results have been equivocal,

probably due to the varied exercise protocols and cooling methods used. No

physiological or performance benefits (distance covered; 9.5 km vs 9.4 km) were

apparent during a 90 min soccer specific exercise test completed in cool conditions

(20°C) after a 60-min cool (24°C) shower, which decreased core temperature by 0.6°C,

compared with no cooling (Drust et al., 2000). Similarly, Cheung et al. (2004) reported

no benefit during 30-min of intermittent sprint cycling performed in moderate ambient

conditions following precooling (which continued until core temperature decreased by

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0.5°C) achieved by wearing a cooling jacket compared with a no cooling condition.

Another study by Duffield et al. (2003) reported that five of seven participants produced

more work and higher power outputs over a 60 min intermittent sprint protocol in hot

and humid conditions (30°C and 60% RH) after cooling (using an ice vest), but overall

these results were not significantly different to the control condition. However, only

brief (5-min precooling and at 1st and 3rd quarter breaks and 10-min at half-time)

cooling periods were used here, resulting in only a small decrease in core temperature

(0.1°C) over these periods, suggesting that these time periods were possibly too short to

result in any exercise benefit, especially in warm and humid conditions.

In contrast, precooling that involved the use of ice packs placed on the thighs for 20-

min (resulting in a decrease in rectal temperature of 0.2°C) enhanced peak power output

by 4% during a 40 min intermittent sprint cycling protocol performed in hot and humid

conditions (33.7°C and 51.6% RH; Castle et al., 2006). These results differed to those

of Sleivert et al. (2001), who reported that cooling the active musculature resulted in

impaired cycling performance in a single sustained (45-s) sprint effort. Importantly, the

different nature of the repeat-sprint task, which extended over 40 min (rather than a

single 45-s sprint) may have allowed any initial sub-optimal muscle temperature to be

corrected. It was also apparent that pre-exercise starting core temperature in the study

by Castle et al. (2006) was higher (~37.3°C) than that in the study by Sleivert et al.

(2001; ~36.8°C), which was perhaps facilitated by a shorter precooling period (20-min

vs 45-min). In addition, total work done during the repeated sprints in the study by

Castle et al. (2006) was significantly higher after both the cooling vest and ice packs

compared with a control condition.

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Duffield and Marino (2007) investigated the effect of whole body mixed-method

precooling on an exercise protocol that consisted of 2 x 30-min halves of repeat-sprint

exercise interspersed with sub-maximal activity in warm environmental conditions

(32°C and 30% RH). This was the first study to measure both sprint and sub-maximal

exercise performance together after precooling. Results showed that sub-maximal

running bouts improved after precooling, but not sprint performance. Improvement in

sub-maximal exercise tasks was proposed to be due to lower core and skin temperature,

heart rate and thermal sensation associated with the cooling period. In later, follow up

studies using similar environmental conditions and performance measures, whole body

cooling (mixed-method) was found to aid sprint performance and improve sub-maximal

performance (greater total and “hard” running distances), compared with a no cooling

control, during an 85 min repeat-sprint exercise protocol in warm conditions (~33°C-

34% RH; Minett et al., 2011; Minett et al., 2012).

These results are similar to the current literature examining the effect of precooling on

repeat-sprint training and competition performed in heat (29-32°C and 44-78% RH) in a

field setting (Duffield, Steinbacher & Fairchild, 2009; Duffield et al., 2013). Duffield et

al. (2009) found that total distance and distance covered at moderate intensity during a

30-min repeat-sprint conditioning session was significantly greater following mixed-

method precooling (cooling vest, cold towels on neck, ice on upper, anterior leg).

Although the more recent results of Duffield et al. (2013) were less conclusive, they did

demonstrate similar trends, with total distance and that covered at moderate intensity

during a typical repeat-sprint training session (2 x 10-min running intervals and 6 x 3-

min small sided games) being greater, as indicated by moderate-large effect sizes,

following 20-min of precooling (ice vest, head and neck iced towels, 350 ml ice slushy).

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In addition, under similar conditions and following similar precooling procedures,

during a 90 min soccer match, moderate effect sizes were found, reflecting a greater

overall distance and that covered at moderate and low-intensity during the second half

after precooling. The somewhat equivocal findings from this study may be the result of

difficulties with replicating (in the field) laboratory protocols which are often associated

with significant and more conclusive findings (Duffield et al., 2013). Of importance,

few studies have examined the effect of precooling on team-sport performance in field

conditions using a protocol that replicates a team game with regards to total duration

and quarter and half-time breaks in play.

Precooling and Heat Acclimation

Of interest is whether precooling could further improve exercise-heat performance if an

athlete had previously acclimated to heat. Castle et al. (2011) reported that a traditional

(low-intensity endurance exercise) 10 day acclimation period resulted in a 2% increase

in peak power output during a 40 min intermittent sprint protocol performed in heat.

However, when participants were precooled (ice packs on thighs) prior to exercise, no

further performance benefits were observed. As precooling is proposed to only be of

benefit to exercise performance when heat strain is high (Duffield and Marino, 2007),

Castle et al. (2011) suggested that the acclimation process resulted in physiological

adaptations to heat that reduced heat strain in participants, thus rendering precooling

ineffective.

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Future Directions

From a performance perspective, it is well established that endurance exercise

performance (running and cycling) is enhanced following precooling. More research

needs to examine precooling and its effects on repeat-sprint performance to add to the

current literature in order to provide (potentially) consistent and conclusive results.

Additionally, the use of mixed-method cooling techniques, which have been shown to

aid performance more than singular methods, and which may easily be translated to a

field environment should be examined. In particular, the effects of a combination of

external (cooling jacket) and internal (ice slushy) cooling methods simultaneously has

not been trialled previously. Further, while traditional full acclimation using low-

intensity endurance exercise has been shown to decrease heat strain associated with

exercise performance and render precooling ineffective, perhaps partial acclimation, as

achieved by using high-intensity interval efforts, may still allow precooling to be

effective. Furthermore, the majority of studies have examined the effect of precooling

on prolonged repeat-sprint performance in controlled laboratory settings, with only

limited research assessing the effect of precooling in a field environment in warm

conditions, which is more ecologically valid for making practical recommendations to

coaches and athletes.

Conclusion

It is well recognised that both endurance and prolonged repeat-sprint exercise

performance is impaired when performed in hot and humid conditions. Heat

acclimatisation/acclimation and precooling are both effective ways of reducing these

detrimental effects and can be achieved through a variety of acclimation protocols and

45""

cooling methods. Thus far, it seems precooling is more effective on sub-maximal

exercise during intermittent type tasks and when heat strain is high.

46""

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" "

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CHAPTER THREE Study One

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Effects of different precooling techniques on repeat-

sprint ability in team-sport athletes

This paper has been published by the

European Journal of Sports Science

DOI: 10.1080/17461391.2011.651491

Presented here in the journal submission format

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Abstract

This study aimed to compare the simultaneous use of internal and external precooling

methods with singular methods and their effect on repeated sprint cycling in hot/humid

conditions. Twelve male team-sport players completed four experimental conditions,

initially involving a 30-min precooling period consisting of either a cooling jacket (J);

ingestion of an ice slushy (ice slushy); combination of cooling jacket and ice ingestion

(J + ice slushy); or control (CONT). This was followed by 70 min of repeat-sprint

cycling (in ~35°C, 60% relative humidity [RH]), consisting of 2 x 30-min halves,

separated by a 10-min half-time period where the same cooling method was again used.

Each half comprised 30 x 4 s maximal sprints on 60 s, interspersed with sub-maximal

exercise at varying intensities. Total mean power and work performed were

significantly higher (p = 0.02) in J + ice slushy (233.6 ± 31.4 W) compared with ice

slushy (211.8 ± 34.5 kJ), while moderate effect sizes (ES; d = 0.67) suggested lower

core temperatures (TC) in J + ice slushy (36.8 ± 0.3°C) compared with J (37.0 ± 0.3°C)

and CONT (37.0 ± 0.3°C) following precooling. A moderate ES (d = 0.57) also

indicated lower TC in J + ice slushy (38.2 ± 0.3) compared with ice slushy (38.4 ±

0.4°C) after half-time cooling. Change (Δ) in mean skin temperature over half-time

cooling was significantly greater (p = 0.036) for J (1.0 ± 0.4°C) compared with ice

slushy (0.5 ± 0.5°C), and ES (d = 0.5-1.10) also suggested a greater Δ for J compared

with the other conditions. Sweat loss was significantly greater (p < 0.05) in ice slushy

and J + ice slushy compared with J and CONT. In conclusion, a combination of

(external and internal) body cooling techniques may enhance repeated sprint

performance in the heat compared to individual cooling methods.

Keywords: Cooling jacket, ice ingestion, core temperature, peak power, work

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Introduction

Precooling is the process of cooling the body prior to exercise in an attempt to delay the

rise in core temperature (TC), and to lower the thermal load, therefore increasing the

time taken to reach a critical thermal maximum (Arngrimsson, Petitt, Stueck, Jorgensen,

& Cureton, 2004; Marino, 2002; Quod, Martin, & Laursen, 2006), which is often

associated with the premature termination of exercise (Gonzalez et al., 1999;

MacDougall, Reddan, Layton, & Dempsey, 1974; Nielsen et al., 1993). Most studies

assessing the effects of precooling on exercise report both endurance (Booth, Marino, &

Ward, 1997; Lee & Haymes, 1995; Quod et al., 2008; Siegel et al., 2010), and single,

short, sprint (Marsh & Sleivert, 1999) exercise benefits.

For repeated sprint exercise, results are equivocal, possibly due to the varied exercise

protocols and cooling methods used. Precooling (ice packs) enhanced peak power

output by 4% during 40 min of intermittent sprint cycling performed in hot/humid

conditions (Castle et al., 2006). Conversely, performance during 70 min of intermittent

sprint exercise in hot conditions was only enhanced by precooling (jacket and cold

water immersion) during sub-maximal running bouts interspersed between sprints

(Duffield & Marino, 2007). Similarly, whole body cooling (mixed-method) was able to

maintain sprint performance and improve sub-maximal running during 85 min of

repeat-sprint exercise in warm conditions (Minett, Duffield, Marino, & Portus, 2011).

Furthermore, no precooling (by cold shower) performance benefits were apparent

during 105 min of soccer-specific exercise completed in cool conditions (Drust, Cable,

& Reilly, 2000) or after using a cooling jacket before 80 min of repeat-sprint cycling

performed in warm/humid conditions (Duffield, Dawson, Bishop, Fitzsimons, &

Lawrence, 2003).

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While some precooling methods have shown improved exercise performance, it is vital

for team-sports that precooling methods be practical and easily applied within a field

environment. The use of cooling jackets represents one such method, with performance

benefits being associated with their use (Arngrimsson et al., 2004; Duffield & Marino,

2007; Uckert & Joch, 2007). Of interest, a cooling jacket containing phase change

material with a melting point of 17°C has recently been trialled (Brade, Dawson,

Wallman, & Polglaze, 2010). While similar cooling rates have been reported between

this and a conventional gel jacket (Brade et al., 2010), a jacket containing phase change

material (PC17) may be more practical to use as ice is not required and there is no

activation period necessary. Phase change material which has a melting point of 25°C

(PC25) has now been developed, which may be more effective for cooling, particularly

in hot/humid conditions.

Recently, ice ingestion, as an alternative precooling method has been trialled (Ihsan,

Landers, Brearley, & Peeling, 2010; Siegel et al., 2010). Ishan et al. (2010) reported a

6.5% faster 40-km cycling time trial performance in warm conditions following ice

ingestion of 6.8 g/kg-1 body mass (BM), whilst Siegel et al. (2010) found 19% longer

running times to exhaustion in warm conditions after precooling by 7.5 g/kg-1 BM ice

slurry ingestion. The rationale for using ice ingestion as an internal precooling method

is that a larger amount of heat energy is required to change its state from a solid to a

liquid; therefore, more internal heat is used when compared to ingesting liquid alone

(Siegel et al., 2010).

Using multiple precooling methods simultaneously may result in better subsequent

exercise performance. To date, little research has focused on this rationale. Minett et

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al. (2011) attempted to determine the optimal volume of cooling necessary to enhance

repeat-sprint exercise by comparing simultaneous head and hand cooling, a mixed-

method whole body cooling technique (head and neck, hand, cooling jacket and ice

packs on thighs) and head cooling separately. Another study by Ross et al. (2011)

assessed the effects of a combination of precooling methods (that can cool the body

both externally and internally) used simultaneously. These investigators reported

improved mean power (3.0%) and endurance (46.4 km) time trial performance (1.3%)

after precooling for 30-min using ice slushy (14 g/kg-1 BM) ingestion and ice towels

(covering torso and legs).

Our study aimed to compare different precooling methods and their effect on long-term

repeated sprint performance to determine whether a simultaneous combination of

external (jacket) and internal (ice ingestion) cooling methods would provide any

advantage compared with a singular method. An advantage of both ice ingestion and a

cooling jacket containing PC25 is that phase change will occur, creating a heat sink into

which some of the body’s heat can be transferred, rather than stored (Ishan et al., 2010;

Siegel et al., 2010). It was therefore hypothesised that the combination of cooling

methods would enhance exercise performance more than singular applications.

Methods

Participants

Twelve male team-sport players (mean ± SD: age 21.8 ± 2.3 y, height 183.6 ± 5.3 cm,

BM 77.5 ± 10.0 kg, sum of seven skin-folds 55.6 ± 8.1 mm and body surface area 1.98

± 0.15 m2) were recruited as participants. All provided informed consent and ethical

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approval was granted by the Human Research Ethics Committee of the University of

Western Australia. Testing was conducted during the winter months; thus, participants

had been absent from prolonged heat exposure for at least two months and were not

fully heat acclimatised.

Overview

Four experimental trials followed a familiarisation session, each separated by ~7 days,

with participants assigned to each trial in a Latin squares design. All trials were

performed at the same time of day (± 1 h). Experimental trials consisted of 30-min of

precooling followed by 70 min (to replicate the duration of a typical team-sport game)

of repeat-sprint cycling consisting of 2 x 30-min halves, separated by a 10-min half-

time (cooling) recovery period. The trials included a control condition (no cooling;

CONT), wearing a cooling jacket containing phase change material (PC25; J), ice

slushy (7 g·kg-1 BM; ice slushy) ingestion and the combination of J and ice slushy (J +

ice slushy). Participants replicated food and fluid intake for 24 h prior to each session,

and abstained from alcohol and vigorous activity for 24 h and caffeine for 3 h prior to

testing.

Familiarisation Session

Anthropometric measures including height (cm), BM (kg), sum of seven skin-folds

(Harpenden callipers; mm; triceps, subscapular, chest, midaxillary, abdominal,

suprailiac and thigh) and body surface area (m2: Dubois nomogram; McArdle, Katch, &

Katch, 2001) were recorded. Participants then performed 10-15 min of the repeat-sprint

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cycling protocol in the climate chamber in order to be familiarised, in part, to the

demands of the exercise protocol.

Cooling Intervention

Trials began with 30-min of precooling completed under normal laboratory conditions

(23.5 ± 0.7°C; 44.1 ± 8.6% RH) whilst seated. During the J condition, participants wore

a cooling jacket containing PC25 (PCP Australia, West Perth, WA). When frozen, it

appears as a white, crystalline solid substance that has a melting point of 25°C and an

ability to transfer 3.5 Watts (W) of heat per square cm from the body (manufacturers

details). The jacket, designed by the Australian Institute of Sport (Canberra, Australia),

is a vest with four anterior and posterior pockets. Sealed packets (140 mm x 140 mm,

120 g) of frozen PC25 were fitted into these pockets for precooling. Participants in the

ice slushy condition ingested 7 g·kg-1 BM (Ishan et al., 2010) of plain ice (0.6°C) over

30-min for precooling. Ice cubes were shaved in an ice shaver (Avalanche, Sunbeam,

Australia) for easy digestion. To ensure consistency across trials, the ice slushy was

consumed at a constant rate of 2.3 g·kg-1 BM every 10 min, and participants wore a J

without the phase change material inserted. In the J + ice slushy condition, participants

performed both precooling procedures simultaneously. For the CONT condition,

participants sat quietly in the laboratory for 30-min. During the half-time recovery

period, participants again adopted their precooling condition for approximately 8-min.

The amount of ice ingested in the ice slushy and J + ice slushy conditions during half-

time was 2.1 g·kg-1 BM. The jacket containing PC25 was retrieved from the refrigerator

where it was stored during the first half. To control for fluid intake between conditions,

during CONT and J conditions, participants consumed identical amounts of tap water

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(~23°C) to ice consumed during the ice slushy and J + ice slushy conditions in both the

precooling and half-time periods.

Exercise Protocol

Following precooling, participants entered the climate chamber (~35.2 ± 0.3°C and

~57.8 ± 1.2% RH) and completed a 5-min cycling warm-up at varying intensities (25–

100 W) for 30 s periods and also performed 2 x 4 s maximal sprints at 3.5 and 4.5 min.

The 70 min repeated sprint protocol, consisting of 2 x 30-min halves separated by a 10-

min break, was then commenced. Each half comprised 30 x 4 s maximal sprints

interspersed by 56 s of light exercise performed at intensities of 25, 50, 75 and 100 W.

In addition to these sprints, six extra maximal sprints were performed at 2.5, 7.5, 12.5,

17.5, 22.5 and 27.5 min to replicate the unpredictable nature of team-sport. The repeat-

sprint cycling protocol was similar to that used by Duffield et al. (2003). Participants

ingested 100 ml of tap water (~23°C) at the 15th min of both halves, while 100 ml of a

commercial sports drink (Powerade: 8% carbohydrate content) was consumed during

half-time. Cycling exercise was performed on calibrated, front access cycle ergometers

(Model EX-10, Repco, Australia).

Measures

Nude BM was measured prior to precooling and then after exercise (towel dried) using a

digital platform scale (model ED3300; Sauter Multi-Range, Ebingen, West Germany ±

10 g) for the purpose of calculating sweat loss (pre - post nude mass + fluid ingested).

Heart rate (HR) values (Polar F1TM HR monitor, Kempele, Finland) were made every 5

min. An ingestible radiotelemetry capsule (VitalSense, Mini Mitter, USA) swallowed 8

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h prior to testing by participants was used to measure TC. Skin temperature (TSk) was

measured by dermal patches (VitalSense, Mini Mitter, USA) placed on the sternal

notch, mid-forearm and medial calf. Temperature measurements were made every 5

min throughout the entire trial. Mean TSk [= (0.5 x sternum temperature) + (0.14 x

forearm temperature) + (0.36 x calf temperature)] was calculated by the method of

Burton (1934). Ratings of perceived exertion (RPE; Borg, 1970; 6-20 scale) and

thermal sensation (TS; 0 = unbearably cold to 8 = unbearably hot) were measured at the

15th and 30th min of the first and second halves of exercise. Performance variables

measured for each sprint included peak power (W), peak power per kilogram BM, mean

power, work (kJ) and work per kilogram BM, measured via a customised computer

program (Cyclemax version 6.3, School of Sport Science, Exercise and Health, UWA).

Performance variables were not measured during the extra sprints.

Statistical Analysis

A two-way, repeated measures (condition x time) ANOVA was used to test for

significant differences in TC, mean TSk, HR, RPE, TS and performance variables. One-

way, repeated measures ANOVA were used to determine significance between

conditions for sweat loss and changes (Δ) in mean TSk. Where appropriate, post hoc

comparisons using Bonferroni adjustments and paired sample t-tests were used. Data

were analysed using SPSS (Version 17.0 for Windows; SPSS Inc, Chicago, IL) with

significance set at p < 0.05. Cohen’s d effect sizes (ES) calculated meaningful

differences in the data (Cohen, 1988). Only moderate (0.5 – 0.79) and large ( ≥ 0.8) ES

are reported. All values are expressed as mean ± SD.

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Results

Total (first and second half combined) mean power and total work performed were

significantly higher (p < 0.05) in J + ice slushy compared with ice slushy (Table 1), but

no significant differences were observed between or within conditions for either half.

However, moderate to large ES suggested better performance in J and J + ice slushy

compared with ice slushy for all performance variables at every stage, except for peak

power and peak power per kilogram BM. For these variables, moderate ES were

evident during the first half, suggesting better performance in J compared with ice

slushy (Table 1).

Core temperature, on average, decreased by 0.2-0.4°C during precooling in all

conditions. Following precooling, moderate ES suggest lower TC in J + ice slushy (36.8

± 0.3°C) compared with both J (37.0 ± 0.3°C; d = 0.67) and CONT (37.0 ± 0.3°C; d =

0.67; Table 2). Effect sizes also suggested the Δ (as can be determined from Table 2) in

TC over the precooling period was greater during ice slushy (-0.4 ± 0.4°C) compared

with J (-0.2 ± 0.2°C; d = 0.63). During precooling mean TSk stayed relatively stable in

all conditions, with no significant differences (p > 0.05) recorded between any

conditions.

Core temperature increased by 1.5–1.7°C over the first half of exercise, while mean TSk

increased by 1.4-2.0°C across all conditions. Moderate ES (d = 0.50–0.75) suggested a

lower starting TC (post-warm-up) in J + ice slushy compared with all other conditions

(Table 2). Moderate to large ES (d = 0.50–0.88) also suggested lower starting mean TSk

66""

values in J and J + ice slushy (post-warm-up) compared with CONT and ice slushy

(Table 2).

Over half-time TC decreased by 0.1-0.2°C in all conditions. At completion, a moderate

ES (d = 0.57) suggested a lower TC in J + ice slushy (38.2 ± 0.3°C) compared with ice

slushy (38.4 ± 0.4°C). Across all conditions, mean TSk decreased by 0.5-1.0°C over

half-time. The Δ in mean TSk was significantly greater during J (-1.0 ± 0.4°C)

compared with ice slushy (-0.5 ± 0.5°C; p < 0.05). Moderate ES (0.50–0.60) calculated

at completion indicated a tendency for lower absolute mean TSk in J (35.9 ± 0.5°C)

compared with ice slushy (36.2 ± 0.5°C) and CONT (36.2 ± 0.6°C; Table 2).

Over the second half, mean TC increased by 0.6°C, whilst mean TSk increased by 0.6-

0.8°C in all conditions. Moderate ES at the start (d = 0.57) and finish (d = 0.57) of the

second half suggested a lower TC in J + ice slushy compared with ice slushy. Mean TSk

at the beginning of the second half was slightly lower in J compared with CONT and ice

slushy (d = 0.50 and d = 0.60, respectively).

After warm-up mean HR was 105 ± 5 bpm across all conditions, with this value

increasing to 170 ± 2 bpm by the end of the first half of exercise. During the second

half of exercise, mean HR increased from 126 ± 3 bpm to 179 ± 1 bpm. While HR,

RPE and TS increased over the course of the exercise protocol, there were no significant

differences between conditions for any of these variables at any time point (p > 0.05).

Sweat loss was significantly greater (p < 0.05) in ice slushy (1.6 ± 0.3 kg) and J + ice

slushy (1.6 ± 0.2 kg) compared with CONT (1.4 ± 0.3 kg) and J (1.3 ± 0.3 kg).

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Table 1. Mean ± SD (n = 12) performance data for each half for the control (CONT), ice jacket (J), ice slushy and the combination of cooling

techniques (J + ice slushy).

Peak Power Output (Watts)

Peak Power (W·kg-1) Mean Power (Watts) Work (kJ)

Work (J·kg-1) Total Mean Power (Watts)

Total Work (kJ)

1st Half 2nd Half 1st Half 2nd Half 1st Half 2nd Half 1st Half 2nd Half 1st Half 2nd Half CONT 1302 ± 179 1287 ± 204 16.91 ± 1.99 16.75 ± 2.28 921 ± 180 927 ± 205 110.5 ± 21.7 111.3 ± 24.5 1425 ± 186 1435 ± 223 924 ± 188 221.8 ± 45.2 J 1354 ± 116a 1340 ± 124 17.60 ± 2.12a 17.38 ± 2.08 966 ± 87a 970 ± 104a 116.0 ± 10.5a 116.4 ± 12.5a 1499± 179a 1506 ± 172a 968 ± 91a 232.4 ± 21.8a

ice slushy 1262 ± 170 1275 ± 158 16.47 ± 1.71 16.67 ± 1.83 867 ± 147 897 ± 145 104.1 ± 17.6 107.7 ± 17.4 1354 ± 166 1401 ± 160 882 ±144 211.8 ± 34.5

J + ice slushy 1337 ± 165 1338 ± 134 17.35 ± 2.41 17.36 ± 1.97 968 ± 144a 976 ± 122a 116.5 ± 17.5a 117.1 ± 14.6a 1492 ± 187a 1513 ± 138a 972 ± 130a,b 233.6 ± 31.4a,b

a = Moderate to large effect size with ice slushy ( > 0.50). b = Significantly different (p < 0.05) from ice slushy. #

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Table 2. Mean ± SD (n = 12) core (TC) and mean skin (mean TSk) temperature at the start and finish of each phase (precooling, 1st half, half-

time and 2nd half) for the control (CONT), ice jacket (J), ice slushy and the combination of cooling techniques (J + ice slushy).

Precooling Period (30 min) 1st Half of Exercise Half-Time Cooling (10 min) 2nd Half of Exercise Start Finish Start Finish Start Finish Start Finish

TC CONT 37.3 ± 0.3 37.0 ± 0.3 37.0 ± 0.4 38.5 ± 0.3 38.5 ± 0.3 38.3 ± 0.4 38.3 ± 0.4 38.9 ± 0.3 J 37.2 ± 0.2 37.0 ± 0.3 36.9 ± 0.3 38.5 ± 0.4 38.5 ± 0.4 38.3 ± 0.6 38.3 ± 0.6 38.9 ± 0.5 ice slushy 37.3 ± 0.3 36.9 ± 0.4 36.9 ± 0.4 38.5 ± 0.4 38.5 ± 0.4 38.4 ± 0.4 38.4 ± 0.4 39.0 ± 0.4 J + ice slushy 37.1 ± 0.2 36.8 ± 0.3b,c 36.7 ± 0.4a,b,c 38.4 ± 0.3 38.4 ± 0.3 38.2 ± 0.3a 38.2 ± 0.3a 38.8 ± 0.3a

Mean TSk CONT 31.0 ± 0.6 31.1 ± 0.5 35.2 ± 0.4 36.9 ± 0.5 36.9 ± 0.5 36.2 ± 0.6 36.2 ± 0.6 36.8 ± 0.6 J 31.7 ± 0.7 32.2 ± 0.5 34.9 ± 0.5a,c 36.9 ± 0.4 36.9 ± 0.4 35.9 ± 0.5a,c 35.9 ± 0.5a,c 36.7 ± 0.5 ice slushy 32.6 ± 0.7 32.7 ± 0.5 35.3 ± 0.4 36.7 ± 0.4 36.7 ± 0.4 36.2 ± 0.5 36.2 ± 0.5 36.9 ± 0.6 J + ice slushy 31.4 ± 0.8 31.8 ± 0.6 35.0 ± 0.4a,c 36.8 ± 0.5 36.8 ± 0.5 36.1 ± 0.5 36.1 ± 0.5 36.7 ± 0.6

a = Moderate to large effect size with ice slushy ( > 0.50). b = Moderate to large effect size with J ( > 0.50). c = Moderate to large effect size with CONT ( > 0.50).

69##

Discussion

This study compared different precooling methods, both individually and in

combination, on repeat-sprint performance in hot/humid conditions. The main finding

was a significantly improved overall exercise performance (total work and mean power)

during J + ice slushy compared with ice slushy, which surprisingly resulted in the

lowest performance. Furthermore, there was a tendency for lower TC throughout

exercise in J + ice slushy (as demonstrated by moderate ES), compared with ice slushy.

This study was the first to assess the effect of using a combination of cooling jacket and

ice slushy simultaneously on repeat-sprint performance in hot/humid conditions, both

before and during exercise.

Exercise Performance

Previous research comparing the effect of ice and either tap (26.8°C) or cold (4°C)

water ingestion on exercise performance have reported significantly improved

endurance performance with an ice slushy (Ihsan et al., 2010; Siegel et al., 2010).

Interestingly, our results showed no significant differences in repeat-sprint performance

between ice slushy and CONT, where participants in the CONT ingested tap water

(~23°C) during cooling periods. These divergent findings may be due to the varied

exercise protocols used (endurance cycling; graded treadmill running to exhaustion;

repeat-sprint cycling) as this seems to be the primary difference between studies.

Furthermore, the above mentioned study protocols were both self-paced endurance

exercise, as opposed to the current study where pacing during set intensities and

maximal sprints is more difficult.

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The improved overall exercise performance demonstrated in J + ice slushy may be

primarily due to the lower TC associated with this condition throughout the entire

exercise protocol, which occurred as a result of the combined cooling effects of J and

ice slushy. Although the mechanisms by which precooling may aid performance are not

fully known, the lower TC and mean TSk values associated with J + ice slushy and J may

have enabled more blood to be directed to working muscles to aid in waste removal and

delivery of oxygen and nutrients, both of which would aid performance (Marsh &

Sleivert, 1999; Sleivert, Cotter, Roberts, & Febbraio, 2001). Furthermore, as an

elevated TC has been reported to impair central nervous system motor drive by reducing

force output, neuromuscular recruitment and voluntary activation (Kay et al., 2001;

Morrison, Sleivert, & Cheung, 2004), a blunted increase in TC as seen in the J + ice

slushy condition compared with the other conditions may have resulted in improved

sprint performance. Interestingly, no differences between conditions were recorded for

HR (consistent with Duffield et al., 2003; Ihsan et al., 2010; Ross et al., 2011; Siegel et

al., 2010), RPE or TS, therefore in J + ice slushy, exercise performance was somewhat

enhanced, compared with the IS condition, despite similar values being recorded for

physiological and perceived effort, as well as thermal comfort.

Exercise performance in J was also very similar to that of J + ice slushy, suggesting that

J may have contributed more than ice slushy to any exercise performance benefits.

However, few studies have found performance benefits in repeat-sprint exercise in

warm-hot conditions after using a cooling jacket. Castle et al. (2006) did find that the

total work performed during repeated short sprints over 40 min was significantly higher

after using a cooling vest compared with control. In contrast, Duffield et al. (2003)

reported no differences in work and power output over 80 min of intermittent sprints in

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hot/humid conditions after using an ice vest, although insufficient precooling time (5-

min) and low statistical power (n = 7) may have influenced these results. In addition,

Duffield and Marino (2007) only found improved sub-maximal running performance

(not sprint performance) due to lower TC, TSk, HR and TS after cooling using an ice

bath followed by a cooling vest. Only one study has used a cooling jacket in

combination with other precooling methods (ice towel to head and neck, hands in iced

water, ice packs on quadriceps) simultaneously and found sprint performance was

maintained and sub-maximal performance significantly better (Minett et al., 2011).

Based on our results, using an ice slushy alone as a means of precooling prior to

intermittent exercise in the heat is not recommended, but in combination with a J, may

be beneficial. Why the ice slushy condition in isolation was no different to CONT and

was associated with lesser repeat-sprint performance than J and J + ice slushy remains

unclear. A possible explanation for the comparable results between the ice slushy and

CONT conditions is that despite being encouraged to sprint maximally, participants

may have adopted a pacing strategy, whereby they reduced their sprint efforts, during

the prolonged repeat-sprint protocol in order to be able to finish it. A similar

explanation was provided by Bishop and Maxwell (2009) and Bishop and Claudius

(2004), to explain comparable, prolonged intermittent sprint performance (36 and 72

min, respectively) between a trial that was preceded by a warm-up and one that was not.

Temperature Responses

The decrease in TC resulting from pre-exercise ingestion of an ice slushy (0.4°C)

recorded here was less than that found in previous research (1.1°C, Ihsan et al., 2010;

0.6°C, Siegel et al., 2010). Minor differences in ice slushy properties between studies

are unlikely to explain these results: Ihsan et al. (2010) had participants ingest 6.8 g·kg-1

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of an ice slushy (1.4°C) over 30-min, Siegel et al. (2010) used a 7.5 g·kg-1 ice slurry (-

1°C) ingested over 30-min and we used a 7g·kg-1 ice slushy (0.6°C), again ingested over

30-min. Of relevance is that participants in ice slushy in the current study wore the J

(without the frozen PC25 packs), during the cooling periods. This may have had an

insulating effect, by impairing heat flow along a temperature gradient from body core to

skin, perhaps accounting for the relatively small (0.4°C) decrease found in TC with pre-

exercise cooling in ice slushy.

Decreases in TC over precooling (0.2°C) in J are consistent with other research using

cooling vests in similar experimental conditions (Castle et al., 2006; Price, Boyd, &

Goosey-Tolfrey, 2009). Mean TSk remained relatively stable here over precooling, with

no differences between conditions recorded. With TSk being heavily influenced by the

surrounding air temperature, these results are likely to reflect the change in TSk caused

by entering the laboratory (~23°C) and removing some clothing layers, as outside air

temperature was lower than in the laboratory. Both Castle et al. (2006) and Duffield

and Marino (2007) observed relatively stable TSk over their precooling periods in the ice

vest conditions, although cooling took place in hot/humid conditions and over shorter

periods of time (20-min and 15-min, respectively). However, in contrast, Price et al.

(2009) found a 1.3°C decrease in TSk over 20-min of precooling using a gel jacket in an

18°C air conditioned room.

Increases in TC during exercise in the current study (first half ~1.6°C and second half

~0.6°C) are similar to the overall increases reported by Castle et al. (2006) and Duffield

and Marino (2007). However, these values are higher than those of Duffield et al.

(2003), whose protocol consisted of 4 x 15-min quarters with cooling applied during the

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5-min quarter and 10-min half-time breaks. Therefore, their participants had the

opportunity for more frequent cooling than in our study, while the ambient temperature

was 5°C lower than here. Similar results for TC between CONT and other experimental

conditions in the current study may be due to the minimal attire (shorts, socks and shoes

only) worn by participants in CONT during the cooling periods, which would have

exposed a large body surface area to the cool, air conditioned laboratory (23°C),

compared to the wearing of the J in all other conditions.

Half-time cooling performed in the current study resulted in a tendency for lower

second half starting TC and mean TSk in J + ice slushy and J compared with ice slushy,

respectively (see Table 2). Price et al. (2009) examined the physiological benefit of

precooling combined with half-time cooling compared with no cooling and precooling

alone across 90 min of intermittent running in heat. They concluded that using a gel

cooling jacket during the 20-min precooling and 15-min half-time cooling period

(where TC and TSk were significantly reduced compared to other conditions) was more

effective than precooling alone in offsetting heat storage. However, no performance

measures were included in their study. Duffield et al. (2003) also found a tendency

(large ES) for a lower third and fourth quarter starting mean TSk in the cooling jacket

condition, as well as significantly lower chest temperatures after quarter and half-time

cooling. Similar results occurred in the current study, although half-time cooling only

lasted for ~8 min. While TC values may not be reduced greatly, using cooling jackets

during exercise breaks in hot/humid conditions can produce significant decreases in

mean TSk, which may assist subsequent exercise performance (Duffield et al., 2003;

Price et al., 2009).

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Our rationale for using two field appropriate precooling methods simultaneously was to

provide an additive (internal and external) cooling effect on both TC and TSk. Ross et al.

(2011) compared the simultaneous use of an ice slushy and iced towels with no cooling

and cold water immersion (10°C), during an endurance cycling time trial. Similar to

our study, they found improved performance associated with the combined cooling

techniques. Other studies have also assessed single compared to two methods of

cooling, used consecutively rather than simultaneously (Duffield & Marino, 2007: ice

vest vs ice vest and ice bath; Quod et al., 2008: ice jacket vs water immersion and ice

jacket) and reported greater performance benefits when using both cooling methods.

In contrast to previous findings, sweat loss here was significantly greater in J + ice

slushy and ice slushy, compared with J and CONT. The reason for this is unclear, as

generally sweat loss is either lower in precooling conditions compared with control

(Arngrimsson et al., 2004; Duffield et al., 2003; Duffield & Marino, 2007; Hasegawa et

al., 2005), or unchanged (Castle et al., 2006; Price et al., 2009; Siegel et al., 2010).

Having lower sweat losses has been suggested to be one of the potential physiological

advantages of precooling, as any performance effects due to increasing dehydration may

be minimised (Hasegawa et al., 2005).

Limitations

As with most precooling studies, it is difficult to blind participants to the aims of the

study due to the need for participants to wear a chilled jacket and to ingest an ice slushy

in certain trials. Furthermore, while participant numbers in this study (n=12) were

similar to other studies that have assessed precooling methods (Castle et al., 2006;

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Duffield & Marino, 2007; Minett et al., 2011), a larger cohort may have provided more

conclusive results.

Conclusion

Our results suggest that using an ice slushy alone for precooling prior to long-term

repeat-sprint exercise in heat is not beneficial, but when used in combination with a J

may lower TC and improve long-term repeated sprint performance. These methods

provide another practical and easily applied strategy for precooling in field

environments, extending the recent work of Ross et al., (2011). The ingestion of an ice

slushy in combination with using a J not only aids in cooling the body, resulting in

greater heat storage capacity, but also provides a valuable source of pre-exercise

hydration (Siegel et al., 2010). Practically combining external (jacket) and internal (ice

slushy) cooling methods should provide a greater cooling effect than when either

method is used individually.

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CHAPTER FOUR Study Two

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Effect of precooling and acclimation on repeat-sprint

performance in heat


Journal of Sports Sciences

Volume 31, Number 7, Pages 779-786, 2013


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Abstract

This study determined whether precooling would have an additive effect on repeat-

sprint cycling performance in heat following partial acclimation. Ten males completed

three trials: Pre Acclimation (Pre Acc) and two Post Acclimation trials, one with

precooling (ice jacket and slushy; Post Acc +PC) and another without (Post Acc).

Trials consisted of a 30-min baseline period followed by a 70 min repeat-sprint protocol

in ~35°C and 60% relative humidity. Separating pre and post trials were five heat

acclimation sessions. Although no significant differences were found for performance

variables, inferential statistical analysis resulted in moderate effect sizes, which

suggested more work (J·kg-1) was performed in Post Acc compared with Pre Acc.

Further, ‘possible’ and ‘very likely’ benefits were found for every performance variable

for Post Acc compared with Pre Acc, while ‘possible’ benefits were found for Post Acc,

compared with Post Acc +PC, for peak power output (W and W·kg-1). Moderate to

strong effect sizes suggested lower core temperatures in both post acclimation trials

compared with Pre Acc. Sweat loss was significantly higher (P < 0.05; 23.1%) in Post

Acc +PC compared with other trials. In conclusion, no additional performance

enhancement was seen when partially acclimated individuals precooled prior to repeat-

sprint performance in heat.

Keywords: core temperature, peak power, work, sweat loss

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Introduction

Hot and humid environmental conditions have consistently resulted in detrimental

effects on prolonged, repeat-sprint exercise. Both Morris, Nevill, Lakomy, Nicholas,

and Williams (1998) and Morris, Nevill, and Williams (2000) reported reduced total

distance completed during prolonged, intermittent high-intensity exercise performed in

hot (30°C) compared to thermoneutral (16-20°C) conditions. Similarly, mean power

output during repeated sprints in heat (40°C) was lower compared with normal (20°C)

conditions (Drust, Rasmussen, Mohr, Nielsen, & Nybo, 2005).

Impaired exercise performance in heat has consistently been attributed to increases in

heat load that result in critically high core temperatures (TC; Gonzalez-Alonso et al.,

1999; MacDougall, Reddan, Layton, & Dempsey, 1974; Nielsen et al., 1993).

Elevations in TC have been reported to affect metabolic (Febbraio, Snow, Stathis,

Hargreaves, & Carey, 1994), central nervous system (Drust et al., 2005), cardiovascular

(Gonzalez-Alonso, Mora-Rodriguez, Below, & Coyle, 1995), and physiological

(Brooks, Hittelman, Faulkner, & Beyer, 1971) responses to exercise.

The most reputable and well-studied technique used to counteract the negative effects of

heat on exercise performance is heat acclimatisation/acclimation (Marino, 2002).

Improved exercise performance (time to exhaustion) after heat acclimation has been

reported by Nielsen et al. (1993) and Nielsen, Strange, Christensen, Warberg and Saltin

(1997) after 8-13 days of exercise training sessions in the heat, in conjunction with the

classical indicators of acclimation; lower heart rate (HR) and TC and increased

sweating.

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These types of acclimation protocols have commonly involved low-intensity (50-60%

maximal oxygen uptake; O2max) exercise performed daily for a prolonged duration

(greater than 45 min). However, this form of exercise is very different to that

performed by team-sport athletes. Recently, an acclimation protocol designed for team-

sports, which differs from conventional acclimation protocols by using fewer and

shorter sessions of high-intensity exercise, was tested (Sunderland, Morris, & Nevill,

2008). Here, participants performed only four acclimation sessions (over 10 days)

involving high-intensity intermittent running for 30-45 min in 30°C. Following this

partial acclimation process, total running distance covered (before volitional fatigue)

during the Loughborough Intermittent Shuttle Test was 33% greater compared with

control, with this improvement attributed to increases in thermal comfort during

exercise and lower TC values at the start of exercise (Sunderland et al., 2008). Petersen

et al. (2010) also noted that similar (partial) acclimation resulted in decreases in HR and

sweat electrolyte concentrations following four high-intensity acclimation sessions

performed in 30°C. Potentially, short-term (i.e., partial), high-intensity, intermittent

acclimation protocols may be more appropriate for team-sport athletes who require

improved heat tolerance and who do not have the time nor the financial resources to

fully acclimate.

In addition to heat acclimation, an acute (pre-exercise) method of preparing for exercise

in heat is precooling, which can enhance prolonged repeated sprint performance by

lowering pre-exercise TC and allowing greater heat storage capacity (Brade, Dawson, &

Wallman, 2012, Chapter 3; Castle et al., 2006; Duffield & Marino, 2007; Minett,

Duffield, Marino, & Portus, 2011). These studies used a mixture of precooling methods

for 20-30-min prior to exercise; ice vest and cold bath immersion (Duffield & Marino,

86##

2007), plus a mixed-method whole-body cooling technique (ice towels on head and

neck, hands immersed in cold water, cooling jacket and ice packs on thighs; Minett et

al., 2011), just ice packs on thighs (Castle et al., 2006) and cooling jacket and slushy

(Brade et al., 2012, Chapter 3). Specifically, Brade et al. (2012, Chapter 3)

demonstrated that the combination of a cooling jacket and ice slushy resulted in

improved prolonged (70 min) repeat-sprint performance in the heat, compared with ice

slushy, cooling jacket and a control condition alone.

Of interest is whether precooling could further improve exercise-heat performance if an

athlete had previously acclimated. To date, only Castle, Mackenzie, Maxwell,

Webborn, and Watt (2011) have reported that a traditional (low-intensity endurance

exercise) 10 day acclimation period resulted in a 2% increase in peak power output

during a 40 min intermittent sprint protocol performed in heat. However, when

participants were precooled (ice packs on thighs) prior to exercise, no further

performance benefits were observed. They proposed that precooling was only

beneficial when heat and exercise strain were high, with this benefit being negated by

the effects of full heat acclimation (which reduced heat strain). They also speculated

that precooling may improve exercise performance when individuals were only partially

heat acclimated, as heat strain during exercise would still be high. These findings

require further confirmation before any effect of precooling on heat acclimated exercise

performance can be concluded. In addition, the effect of precooling on repeat-sprint

performance following a short-term, high-intensity (rather than sub-maximal aerobic

exercise) acclimation protocol has yet to be investigated. Therefore, the aim of this

study was to determine if partial heat acclimation would improve prolonged repeat-

sprint performance in heat and if further benefits would occur if precooling was then

practised, both prior to and during exercise. We hypothesised that partial heat

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acclimation would enhance repeat-sprint performance in heat but the addition of

precooling may reduce the heat strain sufficiently to render precooling ineffective, even

though participants will only be partially heat acclimated.

Methods

Participants

Ten moderately trained males (mean ± s: age 22 ± 3 years, height 179.6 ± 6.3 cm, body-

mass 76.2 ± 8.1 kg, O2peak 55.3 ± 5.4 ml·kg-1·min-1, sum of seven skin-folds 54.4 ±

9.6 mm and body surface area 1.9 ± 0.12 m2), who were all currently involved in team-

sports and trained at least twice a week, were recruited as participants. All provided

informed consent and ethical approval was granted by the Human Research Ethics

Committee of the University of Western Australia.

Overview

Participants completed two familiarisation sessions (5-7 days apart) at least five days

prior to performing the first (pre acclimation; Pre Acc) of three experimental trials,

consisting of a 30-min baseline period (rest) followed by a 70 min repeat-sprint cycling

protocol performed in heat (Figure 1). This protocol comprised 2 x 30-min exercise

periods separated by a 10-min half-time break (rest for Pre Acc). Participants then

completed five acclimation sessions spread over 10 days (one day between; based upon

Sunderland et al., 2008), and then completed, in random order, two post acclimation

trials, which consisted of either cooling performed during the baseline period and at the

half-time break (Post Acc +PC), or without cooling (Post Acc; Figure 1). These trials

(one day between) were completed within four days of the last acclimation session, with

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all trials performed at the same time of the day ± 2 h. Participants replicated food and

fluid intake for 24 h prior to each session, and abstained from alcohol and vigorous

activity for 24 h and caffeine for 3 h prior to testing.

Figure 1. Study Design

Familiarisation Sessions

In the first familiarisation session, anthropometric measures including height (cm),

body-mass (BM; kg), sum of seven skinfolds (Harpenden callipers; mm; triceps, biceps,

subscapular, abdominal, suprailiac, thigh and calf) and body surface area (m2: Dubois

nomogram; McArdle, Katch, & Katch, 2001) were recorded. In addition, participants

completed a O2peak test on a calibrated, front access cycle ergometer (Model EX-10,

Repco, Australia) to ensure that individuals exercised at similar relative intensities

during the acclimation sessions. A metabolic cart, incorporating Applied

Electrochemistry oxygen (SOV S-3A11) and carbon dioxide (COV CD-3A) analysers

(Pittsburgh, PA, USA) and a ventilometer (Universal ventilation meter, VacuMed,

Ventura, California, USA) was used. The gas analysers and ventilometer were

connected to a PC that measured and displayed variables ( O2, and E) every 15 s

Familiarisation Sessions

Anthropometric Measures and

O2peak Test

Experimental + Acclimation Familiarisation

Experimental Session

Pre Acc Repeat-sprint Protocol

+ Tap Water

#

5 sessions over 10 days

Cycling 80% O2peak for 3-min with 1-min break

for 32 to 48 min

Acclimation Sessions

Post Acc +PC Repeat-sprint Protocol

+ Precooling (J + IS)

Experimental Sessions

Post Acc Repeat-sprint Protocol

+ Tap Water

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throughout the test. The O2peak test began with a starting intensity of 100 W, which

increased every 3 min by 50 W until volitional exhaustion. During the second

familiarisation session, participants completed one half (30-min) of the repeat-sprint test

and four blocks (16 min) of the acclimation exercise in the climate chamber for

familiarisation to these protocols.

Baseline and Repeat-sprint Exercise Protocol

Trials began with a 30-min baseline period completed under normal laboratory

conditions (23.5 ± 0.7°C; 44.1 ± 8.6% relative humidity; RH) whilst seated. During the

Post Acc +PC trial, participants precooled during this time by ingesting 7 g·kg-1 BM

(Ishan, Landers, Brearley, & Peeling, 2010) of plain ice (0.6°C) and by wearing a

cooling jacket containing PC25 (PCP Australia, West Perth, WA) simultaneously. To

ensure consistency across trials, the ice slushy was consumed at a rate of 2.3 g·kg-1 BM

every 10 min. When frozen, PC25 appears as a white, crystalline solid substance that

has a melting point of 25°C and the ability to transfer 3.5 Watts (W) of heat per square

cm from the body (manufacturer’s details). The jacket, designed by the Australian

Institute of Sport (Canberra, Australia), is a vest with four anterior and posterior

pockets. Sealed packets (140 mm x 140 mm, 120 g) of frozen PC25 were fitted into

these pockets. During the half-time recovery period, participants in the Post Acc +PC

used these precooling methods again for ~8-min. The amount of ice ingested was 2.3

g·kg-1 BM. The jacket was retrieved from the refrigerator where it was stored during

the first half. To control for fluid intake between trials, participants in the Pre Acc and

Post Acc trials consumed identical amounts of tap water (~23°C) to ice ingested during

the Post Acc +PC trials in both the precooling and half-time periods.

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Following baseline, participants entered the climate chamber (~35.2 ± 0.3°C and ~57.8

± 1.2% RH) and completed a 5-min cycling warm-up at varying intensities (25–100 W)

for 30 s periods and performed 2 x 4 s maximal sprints at 3.5 and 4.5 min. The repeat-

sprint protocol was then commenced. Each half comprised 30 x 4 s maximal sprints,

interspersed by 56 s of light exercise performed at intensities of 25, 50, 75 and 100 W.

In addition, to replicate the unpredictable nature of team-sports, six extra maximal

sprints were performed in each half at 2.5, 7.5, 12.5, 17.5, 22.5 and 27.5 min (Duffield,

Dawson, Bishop, Fitzsimons, & Lawrence, 2003). Participants ingested 100 ml of tap

water (~23°C) at the 15th min of both halves, while 100 ml of a commercial sports drink

(8% carbohydrate content) was consumed during half-time. Cycling exercise was

performed on the same ergometer used during the O2peak test.

Nude BM was measured prior to baseline and then after exercise (towel dried) using a


10 g) for the purpose of calculating sweat loss (pre - post nude BM + fluid ingested).

During the repeat-sprint protocol, HR (Polar F1TM HR monitor, Kempele, Finland) was

recorded every 5 min. An ingestible radiotelemetry capsule (VitalSense, Mini Mitter,

USA) swallowed 8 h prior to testing was used to measure TC. Skin temperature (TSk)

was measured by dermal patches (VitalSense, Mini Mitter, USA) placed on the sternal

notch, mid-forearm, mid-quadriceps and medial calf. Temperature measurements were

made every 5 min for TC and 10 min for TSk throughout the entire trial. Mean TSk [=

(0.3 x sternum temperature) + (0.3 x forearm temperature) + (0.2 x quadriceps

temperature) + (0.2 x calf temperature)] was calculated (Ramanathan, 1964). Ratings of

perceived exertion (RPE; Borg, 1970; 6-20 scale) and thermal sensation (TS; 0 =

unbearably cold to 8 = unbearably hot) were measured at the 15th and 30th min of both

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halves of exercise. Performance variables measured for each sprint included peak

power (W), peak power per kilogram BM (W·kg-1), mean power (W), work (kJ) and

work per kilogram BM (J·kg-1). These variables were measured using a customised

computer program (Cyclemax version 6.3, School of Sport Science, Exercise and

Health, UWA). Performance variables were not measured during the extra sprints.

Acclimation

The five acclimation sessions (35°C and 60% RH), involved repeated cycling for 3-min

at 80% maximum power output (group mean ± s: 244 ± 40 W), as determined from the

O2peak test, with 1-min of passive rest between. During the first session, this protocol

was repeated eight times (32 min), with an additional bout added to each session until a

total of 12 repeats were performed (48 min). Participants drank ad libitum in these

sessions, with total water ingested recorded for the purpose of calculating sweat loss.

Core temperature was assessed during the first and last acclimation session using

ingestible capsules (as described earlier), whilst tympanic temperature (Braun,

Thermoscan 3000, Australia) was measured during the other sessions (for participants

safety). Heart rate, RPE and TS were recorded during each minute of passive rest.

Statistical Analysis

A two-way, repeated measures (trials x time) analysis of variance (ANOVA) tested for

significant differences in TC, mean TSk, HR, RPE, TS and performance variables (first

and second half). One-way, repeated measures ANOVAs were used to determine

significance between trials for sweat loss, sweat sensitivity and overall mean power and

work. Where appropriate, post hoc comparisons using Least Significant Difference

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adjustments were calculated. Data were analysed using SPSS (Version 17.0 for

Windows; SPSS Inc, Chicago, IL) with significance set at P < 0.05. Cohen’s d effect

sizes (ES) were calculated (< 0.5, small; 0.5-0.79, moderate; ≥ 0.8, large) to identify the

magnitude of difference between trial scores (Cohen, 1988). Smallest worthwhile

effects were also calculated for all performance variables. Where the chance of benefit

or harm were both calculated to be > 5%, the true effect was deemed unclear

(Batterham & Hopkins, 2005). Otherwise, chances of benefit or harm were assessed as

follows: < 1%, almost certainly not; 1-5%, very unlikely; 5-25%, unlikely; 25-75%,

possible; 75-95%, likely; 95-99%, very likely; > 99%, almost certain. All values are

expressed as mean ± s.

Results

The first and last acclimation sessions resulted in changes (Δ) in TC of 1.01 ± 0.42°C

and 1.45 ± 0.49°C, respectively. Sweat loss was 0.76 ± 0.34 kg over the first trial and

1.08 ± 0.46 kg over the last. Mean HR (174 ± 15 vs 176 ± 13 beats·min-1), RPE (16 ± 3

vs 16 ± 2) and TS (6 ± 1 vs 6 ± 1) were similar between the first and last trials,

respectively.

While performance results were higher for both post acclimation trials (highest for Post

Acc) versus Pre Acc for every variable assessed, these differences were not significant

(P > 0.05; Table 1). However, higher performance scores following Post Acc,

compared with Pre Acc, were supported by moderate ES (d =0.56-0.73) for work (J·kg-

1; first and second half), as well as ‘possible’ to ‘very likely’ benefits for every

performance variable assessed. Further, ‘possible’ benefits were found for mean power

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(W; first half) and work (kJ; first half) for Post Acc +PC compared with Pre Acc.

Finally, ‘possible’ benefits were found for peak power output (W; second half), peak

power (W·kg-1; first and second half) and work (J·kg-1; second half) for Post Acc

compared with Post Acc +PC.

Mean TC decreased by 0.5°C in Post Acc +PC over the precooling period, but stayed

relatively stable in both other trials. Following precooling, moderate ES suggested

lower TC in Post Acc +PC compared with Pre Acc (d=0.67). The Δ (as can be

determined from Table 2) in TC over the precooling period was significantly greater

during Post Acc +PC (-0.5 ± 0.2°C) compared with Post Acc (-0.2 ± 0.1°C; P ≤ 0.05).

No significant differences (P > 0.05) were recorded for mean TSk between any trials

over the precooling period.

Core temperature increased by 1.2–1.5°C over the first half of exercise, while mean TSk

increased by 1.8-2.1°C across all trials. Moderate ES (d=0.57) suggested a lower

starting TC (post warm-up) in Post Acc +PC compared with Pre Acc, whilst at the end

of the first half, Post Acc TC was lower compared with Post Acc +PC (d=0.67) and Pre

Acc (d=0.85; Table 2). Moderate to strong ES (d=0.66–0.95) also suggested lower

starting mean TSk values in Post Acc +PC (post warm-up) compared with both other

trials (Table 2). In addition, both post acclimation trials had lower mean TSk values at

the end of the first half compared with Pre Acc, as suggested by moderate ES (d=0.60-

0.66).

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Table 1. Mean ± s (n = 10) performance data for each half for the pre acclimation (Pre Acc), post acclimation precooling (Pre Acc +PC) and

post acclimation (Post Acc) trials.

1 = moderate effect size with Pre Acc (d = 0.50-0.79). # = Where the chance of benefit or harm were both calculated to be > 5%, the true effect was deemed unclear. Otherwise, chances of benefit or harm were assessed as follows: < 1%, almost certainly not; 1-5%, very unlikely; 5-25%, unlikely; 25-75%, possible; 75-95%, likely; 95-99%, very likely; > 99%, almost certain.

Mean ± s Cohen’s d Effect Size / Mean change (%) ± 90 % confidence limits / Percentage chance that effect is beneficial (trivial/harmful)#

Pre Acc Post Acc +PC Post Acc Post Acc +PC vs. Pre Acc Post Acc vs. Pre Acc Post Acc vs. Post Acc +PC

Peak Power Output (W) 1st Half 1318 ± 151 1328 ± 168 1357 ± 174 0.06 / 0.8 ± 0.5 / 27 (61/12) 0.24 / 3.0 ± 0.6 / 61 (37/2) 0.17 / 2.2 ± 0.4 / 42 (57/1) 2nd Half 1298 ± 137 1308 ± 185 1348 ± 172 0.06 / 0.8 ± 0.4 / 27 (63/10) 0.32 / 3.8 ± 0.6 / 88 (12/0) 0.22 / 3.1 ± 0.5 / 54 (45/1)

Peak Power (W·kg-1) 1st Half 17.45 ± 1.58 17.61 ± 1.45 17.97 ± 1.80 0.11 / 0.9 ± 0.6 / 35 (51/14) 0.31 / 3.0 ± 0.8 / 68 (28/4) 0.22 / 2.0 ± 0.7 / 58 (37/5) 2nd Half 17.18 ± 1.18 17.33 ± 1.54 17.84 ± 1.63 0.11 / 0.9 ± 0.7 / 41 (45/14) 0.46 / 3.8 ± 0.9 / 95 (5/0) 0.32 / 2.9 ± 0.8 / 70 (27/3)

Mean Power (W) 1st Half 967.8 ± 142.2 998.1 ± 148.5 1012.1 ± 125.2 0.21 / 3.1 ± 0.6 / 53 (43/4) 0.33 / 4.6 ± 0.6 / 73 (26/1) 0.10 / 1.4 ± 0.3 / 20 (78/2) 2nd Half 971.4 ± 130.2 989.4 ± 162.7 1012.1 ± 119.5 0.12 / 1.9 ± 0.5 / 38 (56/6) 0.33 / 4.2 ± 0.6 / 77 (23/0) 0.16 / 2.3 ± 0.4 / 32 (67/1) Overall 969.6 ± 134.1 993.7 ± 155.0 1012.1 ± 120.7 0.17 / 2.5 ± 0.6 / 46 (49/5) 0.33 / 4.4 ± 0.6 / 78 (22/0) 0.13 / 1.9 ± 0.3 / 25 (74/1)

Work (kJ) 1st Half 116.1 ± 17.1 119.8 ± 17.8 121.5 ± 15.0 0.21 / 3.2 ± 0.6 / 53 (43/4) 0.34 / 4.7 ± 0.6 / 74 (25/1) 0.10 / 1.4 ± 0.3 / 20 (78/2) 2nd Half 116.6 ± 15.6 118.7 ± 19.5 121.4 ± 14.3 0.12 / 1.8 ± 0.5 / 38 (56/6) 0.32 / 4.1 ± 0.6 / 76 (24/0) 0.16 / 2.3 ± 0.4 / 32 (67/1) Overall 232.7 ± 32.2 238.5 ± 37.2 242.9 ± 29.0 0.17 / 2.5 ± 0.6 / 47 (48/5) 0.33 / 4.4 ± 0.6 / 78 (22/0) 0.13 / 1.8 ± 0.3 / 25 (74/1)

Work (J·kg-1) 1st Half 1533 ± 153 1585 ± 129 1606 ± 1021 0.37 / 3.4 ± 0.9 / 67 (27/6) 0.56 / 4.8 ± 1.0 / 84 (14/2) 0.18 / 1.3 ± 0.6 / 44 (47/9) 2nd Half 1538 ± 109 1568 ± 130 1605 ± 711 0.25 / 2.0 ± 0.9 / 58 (31/11) 0.73 / 4.4 ± 1.1 / 90 (9/1) 0.35 / 2.4 ± 0.7 / 63 (33/4)

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Table 2. Mean ± s (n = 10) Core (TC) and mean skin (mean TSk) temperature (°C) at the start and finish of each phase (precooling, first half,

half-time and second half) for the pre acclimation (Pre Acc), post acclimation precooling (Post Acc +PC) and post acclimation (Post Acc) trials.

Precooling Period (30 min) 1st Half of Exercise Half-Time (10 min) 2nd Half of Exercise Start Finish Start Finish Start Finish Start Finish

TC Pre Acc 37.3 ± 0.3 37.0 ± 0.3 37.0 ± 0.4 38.4 ± 0.4 38.4 ± 0.4 38.3 ± 0.4 38.3 ± 0.4 38.8 ± 0.4 Post Acc +PC 37.3 ± 0.4 36.8 ± 0.3a 36.8 ± 0.3a 38.3 ± 0.3 38.3 ± 0.3 38.0 ± 0.3a 38.0 ± 0.3a 38.6 ± 0.3a

Post Acc 37.1 ± 0.2a,b 36.9 ± 0.2 36.9 ± 0.3 38.1 ± 0.3a,b 38.1 ± 0.3a,b 38.0 ± 0.3a 38.0 ± 0.3a 38.5 ± 0.3a

Mean TSk Pre Acc 32.0 ± 1.2 32.9 ± 0.9 34.9 ± 0.8 36.7 ± 0.5 36.7 ± 0.5 36.1 ± 0.5 36.1 ± 0.5 36.6 ± 0.5 Post Acc +PC 31.8 ± 0.4 32.0 ± 0.5a 34.3 ± 0.4a 36.4 ± 0.4a 36.4 ± 0.4a 35.7 ± 0.6a 35.7 ± 0.6a 36.5 ± 0.4 Post Acc 31.7 ± 0.8 32.3 ± 1.0a 34.6 ± 0.5b 36.4 ± 0.5a 36.4 ± 0.5a 35.9 ± 0.5 35.9 ± 0.5 36.4 ± 0.5

a = moderate to large effect size with Pre Acc (d > 0.50). b = moderate to large effect size with Post Acc +PC (d > 0.50).

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Over half-time TC decreased by 0.1-0.3°C in all trials. After half-time, a strong ES

(d=0.85) suggested a lower TC in Post Acc +PC and Post Acc compared with Pre Acc

(see Table 2). Across all trials, mean TSk decreased by 0.5-0.7°C over half-time. A

moderate ES (d=0.72) calculated after half-time indicated a lower absolute mean TSk in

Post Acc +PC compared with Pre Acc (Table 2).

Over the second half, mean TC increased by 0.5-0.6°C, whilst mean TSk increased by

0.5-0.8°C in all trials. Moderate ES at the end (d=0.57-0.85) of the second half

suggested a lower TC in both Post Acc and Post Acc +PC compared with Pre Acc.

Mean TSk for Post Acc +PC was lower (d=0.72) at the start of the second half compared

with Pre Acc, while all final values were similar.

After warm-up, mean HR was 105 ± 16 beats·min-1, with this value increasing to 160 ±

13 beats·min-1 (across all trials) by the end of the first half of exercise. At the end of the

second half of exercise, mean HR in Pre Acc was significantly higher (P ≤ 0.05) than in

Post Acc +PC and Post Acc (171 ± 10 vs 165 ± 16 and 158 ± 17). While RPE and TS

increased over the course of the exercise protocol, there were no significant differences

between trials at any time point (P > 0.05). At the end of exercise, RPE for Pre Acc,

Post Acc +PC and Post Acc was 16 ± 1, 15 ± 2 and 15 ± 2 respectively, and for TS 6 ±

0, 6 ± 1 and 6 ± 1. Sweat loss was significantly greater (P ≤ 0.05) in Post Acc +PC (1.8

± 0.6 kg) compared with Pre Acc (1.4 ± 0.5 kg) and Post Acc (1.4 ± 0.5 kg). In

addition, sweat sensitivity (ml of sweat per 1°C rise in TC) was significantly higher (P ≤

0.05) in both Post Acc +PC (1033 ± 421) and Post Acc (968 ± 252) compared with Pre

Acc (805 ± 261). Finally, there were no significant order effects (first and second half)

for work (kJ; P=0.30, P=0.18), work (kJ·kg-1; P=0.30, P=0.15), mean power (W;

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P=0.31, P=0.17), peak power (W; P=0.75, P=0.73), and peak power (W·kg-1; P=0.71,

P=0.70).

Discussion

This study aimed to determine whether partial heat acclimation would improve

prolonged repeat-sprint performance and if further benefit would occur if precooling

was practised prior to and during exercise performance. To the authors’ knowledge,

this is the first study to assess the combined effects of precooling and partial

acclimation on repeat-sprint performance. The main finding was that a short-term,

high-intensity exercise acclimation protocol resulted in improved exercise performance

(work and power output) compared with non-acclimation, as determined by qualitative

analyses and moderate to large ES. Further, precooling provided no additional benefit

to exercise performance in the heat after partial acclimation. Evidence that partial

acclimation occurred in our participants is provided by lower exercise HR, TC and TSk

values, as well as greater sweat loss and sweat sensitivity following the partial

acclimation protocol.

Our study supports the work of Sunderland et al. (2008), who also found a benefit of

partial heat acclimation on subsequent exercise in team-sport athletes, although this

related to exercise capacity rather than performance. Of note, the acclimation sessions

used by Sunderland et al. (2008) were similar to those used in the current study in

relation to the number of exercise sessions performed and the duration and intensity of

exercise undertaken (i.e. 4 x 35-45 min sessions of repeat-sprints compared to 5 x 32-48

min sessions of repeat-sprints, respectively). Further, Castle et al. (2011) reported that

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full heat acclimation resulted in an increased peak power output during intermittent

sprint cycling (compared with a non-acclimation trial) in the heat (~33°C and 50% RH).

They speculated that improved exercise performance after heat acclimation might have

been due to reduced reliance on muscle glycogen, as a result of lower epinephrine

concentrations and reduced muscle temperatures, which resulted in a higher power

output over time (King, Costill, Fink, Hargreaves, & Fielding, 1985). While these

variables were not measured in the current study (or in the study by Castle et al., 2011),

it is possible that some glycogen sparing effects might have occurred in our participants,

which may have impacted upon their repeated sprint performance. Further studies are

needed to confirm or refute the role of these variables on exercise performance in heat

acclimated individuals.

Heat acclimation has been reported to delay the attainment of a critical Tc, which has

consistently been linked to numerous effects that impair exercise performance (see

introduction). A critical TC has been reported to be between 39.4–40.0ºC for prolonged

intermittent exercise (Drust et al., 2005; Morris et al., 1998). While TC did not reach

this critical level during exercise performance in any trial, TC was lower during both

post acclimation trials, compared with the pre-acclimation trial (supported by numerous

moderate to large ES), suggesting that at least partial adaptation to heat had occurred.

Our study provides further support to the findings of Sunderland et al. (2008), in that

partial acclimation (as well as full acclimation), can improve high-intensity intermittent

exercise performance in the heat.

Lack of benefit associated with precooling on exercise performance in heat after

acclimation was surprising, considering the number of studies that have reported

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improved exercise performance following this procedure. For example, Brade et al.

(2012, Chapter 3) found a benefit of precooling, using the same method employed in the

current study, on similar intermittent sprint cycle exercise performance (significantly

higher overall work and mean power). Similarly, Castle et al. (2006) found a 4%

increase in peak power during 40 min of intermittent sprint exercise following 20-min

of precooling the thighs. Whilst Duffield and Marino (2007) and Minett et al. (2011)

found no significant improvements in sprint performance, they did find significant

increases in the distance run during sub-maximal bouts of exercise following

precooling.

Similarly, Castle et al. (2011) reported a lack of benefit of precooling (cold packs placed

around the thighs for 20-min) on intermittent sprint cycle performance in heat

acclimated participants. They suggested the similar performance results between a

precooling (post acclimation) and a control trial were related to the effects of a full

acclimation protocol performed, which resulted in maximal physiological adaptation to

heat reducing the heat strain associated with exercise. According to Duffield and

Marino (2007), precooling is only of benefit when heat strain is high. In our study,

reduced heat strain was supported by lower TC and mean TSk values recorded after both

acclimation trials during the entire exercise protocol (compared with the pre-acclimation

trial), with many time points assessed supported by moderate to large ES. These results

suggest that partial acclimation, similar to full acclimation, may reduce heat strain to a

point where precooling confers no further significant or meaningful advantage.

Another factor that may have reduced the role of precooling in improving exercise

performance in the heat may be related to the BM of acclimated participants.

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According to Marino, Lambert, and Noakes (2004), heavier athletes produce heat at a

faster rate than lighter athletes to achieve the same work due to a higher level of

metabolically active, heat-producing muscle. Based on this premise, Castle et al. (2011)

suggested that precooling might be better suited to heavier athletes. This observation

was based on their earlier study (Castle et al., 2006) that found a benefit of precooling

(thigh cooling) on peak power output during intermittent sprint cycle performance in the

heat (34°C and 52% RH), where these athletes were 10–20 kg heavier (yet similar skin

folds) compared with athletes in their later study, where no benefit of precooling was

found. However, participants in their later study were heat acclimated (those in the

earlier study were not), leaving the influence of precooling and BM on exercise-heat

strain in acclimated participants unclear. As participants in the current study had a

similar average BM (76.2 ± 8.1 kg) to participants in the later study by Castle et al.

(2011; 73.9 ± 4.9 kg), it is possible that this factor might have resulted in reduced heat

strain and a consequent lack of effect of precooling. Further investigation is needed to

clarify the role and effect of precooling and BM on heat strain in acclimated individuals.

It should also be acknowledged that participants may have paced themselves during the

prolonged exercise tests (Bishop & Claudius, 2004; Bishop & Maxwell, 2009) and this

may not have allowed the benefits associated with acclimation and precooling to be

fully realised.

Sweat loss in the current study was significantly greater (P ≤ 0.05) following

acclimation and precooling compared with Pre Acc and Post Acc. This finding is

consistent with our earlier work, where higher sweat loss was seen in a combined jacket

and ice slushy (precooling) condition compared with a control (Brade et al., 2012,

Chapter 3). The reason for this is still unclear as generally exercise sweat losses are

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lower after precooling (Duffield et al., 2003; Duffield & Marino, 2007). It is possible

that higher sweat rates are seen when ingesting an ice slushy as cooler fluid moves

through the body at a faster rate than fluid of a higher temperature (McArdle et al.,

2001). Finally, the sweat sensitivity results here are consistent with those usually seen

post acclimation as sweating efficiency commonly increases as part of the heat

adaptation process (Cohen & Gisolfi, 1982; Nielsen et al., 1993).

Finally a limitation of this study is the omission of a non-acclimatised trial. This was

excluded because of the long logistical considerations of having to wait some months

for the winter season, which in turn may have further limited the study via participant

changes in training status and a likely increase in participant drop-out. Using an

independent groups study design also provides its own limitations in trying to recruit

well matched participants in terms of physical characteristics (i.e. body mass/surface

area, important for precooling/thermoregulatory studies), aerobic and anaerobic fitness

capacities and training history and status.

Conclusion

Partial heat acclimation improved prolonged repeat-sprint performance in the heat:

however, precooling provided no additional benefit. This would suggest that heat

acclimation alone is a more powerful method for improving exercise performance in the

heat than acute (pre-exercise) precooling. Of practical importance, our results suggest

that if team-sport athletes are partially acclimated, then precooling is not necessary in

order to enhance subsequent repeat-sprint performance in heat.

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Febbraio, M., Snow, R., Stathis, C., Hargreaves, M., & Carey, M. (1994). Effect of heat

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MacDougall, J., Reddan, W., Layton, C., & Dempsey, J. (1974). Effects of metabolic

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CHAPTER FIVE Study Three

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Effect of precooling on repeat-sprint performance in

seasonally acclimatised males during an outdoor

simulated team-sport protocol in warm conditions


Journal of Sports Science and Medicine

Volume 12, Issue 3, Pages 565-570, 2013


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Abstract

Whether precooling would provide any additional benefit to exercise performance in

warm climates of heat acclimatised individuals is unclear. The purpose of this study

was to determine the effect of precooling on repeat-sprint performance during a

simulated team-sport circuit performed outdoors in warm, dry field conditions in

seasonally acclimatised males (n=10). Participants performed two trials, one with

precooling (PC; ice slushy and cooling jacket) and another without (CONT). Trials

began with a 30-min baseline/cooling period followed by an 80 min repeat-sprint

protocol, comprising 4 x 20-min quarters, with 2 x 5-min quarter breaks and a 10-min

half-time recovery/cooling period. No beneficial effects (smallest worthwhile change)

were recorded between conditions for total circuit times, 20 m sprint times in each

quarter and overall, or for the best and first sprint of each quarter. Moderate (d=0.67;

90% CL=-1.27-0.23%) effect sizes (ES) indicated lower core temperatures in PC at the

end of the precooling period and quarter 1. No moderate or large ES were found

between trials for mean skin temperature, heart rate, thermal sensation, or rating of

perceived exertion. However, moderate ES suggested a greater sweat loss in PC

compared with CONT. In conclusion, repeat-sprint performance was not improved in

seasonally acclimatised players by using a combination of internal and external cooling

methods prior to and during exercise performed in the field in warm, dry conditions. Of

practical importance, precooling appears unnecessary for repeat-sprint performance if

athletes are seasonally acclimatised or artificially acclimated to heat, as it provides no

additional benefit.

Keywords: Cooling jacket, ice slushy, core temperature, 20 m sprint.

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Introduction

Strenuous exercise (both intermittent and continuous) in heat can result in the

attainment of a critically high core temperature (TC), which is commonly in the range of

39.4 – 40.0ºC (Gonzalez-Alonso et al., 1999; MacDougall et al., 1974; Nielsen et al.,

1993). Reaching a “critically high TC” has been proposed by many researchers as an

important factor in the premature (voluntary) termination of exercise and can often

occur regardless of external conditions (Galloway and Maughan, 1997; Gonzalez-

Alonso et al., 1999; MacDougall et al., 1974; Nielsen et al., 1993). Numerous studies

comparing exercise performance in warm-hot (30-40°C) and thermoneutral (16-23°C)

environments have reported impaired exercise performance (reduced time to exhaustion

and total distance completed and mean power output) in warm-hot conditions in both

endurance (Galloway and Maughan, 1997; MacDougall et al., 1974) and prolonged

repeat-sprint exercise (Drust et al., 2005; Morris et al., 1998; Morris et al., 2000; Morris

et al., 2005) tasks. Further, intermittent exercise is often associated with greater thermal

loads, compared with endurance exercise of a matched intensity (Kraning and Gonzalez,

1991; Nevill et al., 1995).

An acute method proposed to improve exercise performance in heat is precooling. The

rationale behind precooling is to delay the rise in TC to a critical level, where exercise

intensity may then not be able to be maintained (Marino, 2002; Quod et al., 2006;

Wendt et al., 1997). Precooling may aid exercise performance by increasing heat

storage capacity and delaying the activation of heat dissipating mechanisms (Booth et

al., 1997; Kay et al., 1998; Marino, 2002; Quod et al., 2006), as well as by inducing

perceptual alterations that can cause a change in pacing strategies so to better cope with

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the metabolic, thermoregulatory and neuromuscular loads (Duffield and Marino, 2007;

Minett et al., 2011).

To date, results from laboratory based studies examining the effect of precooling on

repeat-sprint cycling performance in heat have been equivocal. Castle et al. (2006)

reported a 4% improved peak power output in heat (~34°C and 52% relative humidity;

RH) after precooling (ice packs on upper legs) compared with no precooling, whereas

Duffield et al. (2003) found no significant benefit of using an ice jacket prior to and

during exercise in 30°C and 60% RH. Other studies have examined the effects of

combined precooling methods compared with singular methods, including ice vest vs

ice bath and vest (32°C and 30% RH; Duffield and Marino, 2007); head vs head and

hand vs a mixed-method including head, neck, hand, cooling jacket and ice packs on

thighs (33°C and 34% RH; Minett et al., 2011); ice slushy and cooling jacket alone vs

ice slushy and cooling jacket combined (35°C and 58% RH; Brade et al., 2012a,

Chapter 3). Notably, Brade et al. (2012a, Chapter 3) reported improved repeated sprint

performance, while Duffield and Marino (2007) and Minett et al. (2011) only reported

improved sub-maximal exercise performance in heat following combined precooling

techniques.

Another well-established technique used to counteract the negative effects of heat on

exercise performance is heat acclimatisation/acclimation (Marino, 2002). To date,

numerous studies have reported improved exercise performance in heat when

participants were heat acclimated (Nielsen et al., 1993; Nielsen et al., 1997; Sunderland

et al., 2008). Two recent studies reported that heat acclimation alone resulted in

improved repeat-sprint cycle performance in heat when compared with various

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precooling methods (ice packs on thighs: Castle et al., 2011; ice slushy and cooling

jacket combined; Brade et al., 2012b, Chapter 4). As precooling is proposed to only be

of benefit to exercise performance when heat strain is high (Duffield and Marino, 2007),

both Castle et al. (2011) and Brade et al. (2012b, Chapter 4) suggested that the

acclimation process resulted in physiological adaptations to heat that reduced heat strain

in participants, thus rendering precooling ineffective.

Importantly, both studies by Castle et al. (2011) and Brade et al. (2012b, Chapter 4)

were performed in controlled laboratory conditions using a repeat-sprint cycle (weight

assisted) protocol. Possibly, if exercise consisted of repeated running sprints performed

in the field during summer (with direct solar radiation), higher levels of heat strain

might be produced, raising the potential for precooling to have a beneficial effect on

exercise performance, despite heat acclimatisation or acclimation being in place. To

date, no studies have assessed the effects of combined internal and external precooling

methods, on sport specific repeat-sprint efforts performed by heat acclimated or

acclimatised athletes. Therefore, the purpose of this study was to assess the effect of

precooling (ice slushy and ice jacket combined) on repeat-sprint running performance in

seasonally acclimatised team-sport athletes in a field setting in warm outdoor

conditions.

Methods

Participants

Ten physically active males (mean ± SD: age 22 ± 3 y, height 178.5 ± 3.5 cm, body

mass 73.3 ± 5.1 kg, sum of seven skin-folds 53.6 ± 12.6 mm and body surface area 1.9

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± 0.1 m2) were recruited as participants. All provided informed consent and ethical

approval was granted by the Human Research Ethics Committee of the University of

Western Australia. Testing was conducted during the latter summer months (where

monthly average maximum temperatures were; 30.5°C, December; 33.5°C, January;

31.1°C, February; 31.4°C, March) so that participants were naturally heat acclimatised

prior to participation in the study.

Overview

Following a familiarisation session (completed 5-7 days prior), participants completed

two experimental trials (randomised, crossover design) performed at least 5 days apart

and at the same time of day (± 2 h). The experimental sessions included a control (no

cooling) trial (CONT) and a precooling (PC) trial that involved the simultaneous use of

an ice slushy and cooling jacket. Both trials included a 30-min baseline/precooling

period followed by 4 x 20-min quarters of repeat-sprint exercise separated by 2 x 5-min

quarter breaks and a 10-min half-time recovery/cooling period. Participants replicated

food and fluid intake for 24 h prior to each session, and abstained from alcohol and

vigorous activity for 24 h and caffeine for 3 h prior to testing.

Procedures

Familiarisation Session

Anthropometric measures including height (cm), body-mass (BM; kg), sum of seven

skin-folds (Harpenden callipers; mm; triceps, biceps, subscapular, abdominal,

suprailiac, thigh and calf), body surface area (m2; Dubois nomogram; McArdle et al.,

2001) were recorded. In addition, participants then performed one half of the exercise

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protocol in similar environmental conditions to the testing sessions to ensure

familiarisation to the testing regime.

Cooling Intervention

Trials began with a 30-min baseline period completed under normal laboratory

conditions (21.9 ± 0.9°C; 55.3 ± 6.6% RH) whilst seated. During the PC trial,

participants precooled during this time by simultaneously ingesting 7 g·kg-1 BM (Ishan

et al., 2010) of plain ice (0.6°C) and by wearing a cooling jacket containing PC25 (PCP

Australia, West Perth, WA, Australia). To ensure consistency across trials, the ice

slushy was consumed at a rate of 2.3 g·kg-1 BM every 10 min. When frozen, PC25

appears as a white, crystalline solid substance that has a melting point of 25°C and the

ability to transfer 3.5 Watts (W) of heat per square cm from the body (manufacturer’s

details). The jacket, (Australian Institute of Sport, Canberra, ACT, Australia), is a vest

with four anterior and posterior pockets into which sealed packets (140 mm x 140 mm,

120 g) of frozen PC25 were fitted. During the half-time recovery period, these

precooling methods were used again in the PC trial for ~8-min. The amount of ice

ingested was 2.3 g·kg-1 BM and the jacket was retrieved from the refrigerator where it

was stored during the first half of the exercise protocol. To control for fluid intake

between trials, participants in the CONT trial consumed identical amounts of tap water

(~23°C) to ice consumed during the PC trial in both the baseline and half-time periods.

Exercise Protocol

Following precooling, participants went to the outdoor exercise laboratory, where mean

± SD environmental conditions on test days were; dry bulb 26.5 ± 4.2°C; black bulb

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38.0 ± 8.9°C; wet bulb temperature 21.0 ± 3.1°C (38 ± 11% RH) and wind speed 0.9 ±

0.6 m·s-1. The wet bulb globe temperature index was ~25°C. To account for the

(uncontrolled) outdoor environmental conditions and circadian variability, on every test

day both PC and CONT trials were held at the same time of the day. Participants

completed a 10-min warm-up which replicated that typically undertaken prior to a team-

sport game and included light jogging, run throughs and stretching. The 80 min

exercise circuit used (Bishop et al., 2001; Duvnjak-Zaknich et al., 2011) was designed

to replicate the typical intermittent exercise demands and movement patterns observed

in team-sports. Each 20-min quarter consisted of 20 x 1 lap repetitions, with a lap

beginning each minute. Each lap involved three maximal sprints (2 x 10 m, 1 x 20 m), a

12 m agility (change of direction) section, one 30 m striding effort, two periods of

jogging and three periods of walking. The total distance per lap repetition was ~122 m,

equating to a total distance of 9760 m over the 80 min period (80 laps). The time taken

to complete each lap was ~ 44-45 s. The first and third 20-min quarters were separated

by a 5-min break, with a 10-min recovery/cooling period at half-time. Every 10 min of

each quarter, 100 ml of water was ingested, as well as 50 ml each of water and a

commercial sports drink (Powerade: 8% carbohydrate) during the 1st and 3rd quarter

breaks, with 100 ml of the sports drink taken during half-time.

Measures

Nude BM was measured prior to baseline and then after exercise (towel dried) using a


10 g) for the purpose of calculating sweat loss (pre - post nude BM + fluid ingested).

Heart rate (HR) values (Polar F1TM HR monitor, Kempele, Finland) were recorded at 0,

10 and 20 min of every quarter. Core temperature was also measured at these time

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points by an ingestible radiotelemetry capsule (VitalSense, Mini Mitter, OR, USA)

swallowed 8 h prior to testing. Skin temperature (TSk) was measured at the beginning

and end of every quarter by dermal patches (VitalSense, Mini Mitter, OR, USA) placed

on the sternal notch, mid-forearm, mid-quadriceps and medial calf. Mean TSk [= (0.3 x

sternum temperature) + (0.3 x forearm temperature) + (0.2 x quadriceps temperature) +

(0.2 x calf temperature)] was calculated using the method described by Ramanathan

(1964). Heart rate, TC and TSk were also taken at the beginning and end of the baseline

period. Ratings of perceived exertion (RPE; Borg, 1970; 6-20 scale) and thermal

sensation (TS; 0 = unbearably cold to 8 = unbearably hot) were measured at the

beginning and end of every quarter of exercise. Sprint times (20 m: 0.001 s) were

recorded by electronic timing gates (Fitness Technology Inc., Skye, SA, Australia) for

sprints 5, 10 and 20 of each quarter, whilst circuit times were recorded for every lap

using a digital stopwatch (Hart Sport, Virginia BC, QLD, Australia; 0.01 s). Previous

work from our laboratory has established the CV for mean (quarter) sprint time as 3.7%

(90% CL, 2.7-6.0%) and for best sprint time as 2% (90% CL, 1.4-3.1%) within this

circuit (Singh et al., 2010).

Statistical Analyses

Given the likely small changes in 20 m sprint and lap times, the data were analysed

using Cohen’s d effect sizes (ES;< 0.5, small; 0.5 - 0.79, moderate; ≥ 0.8, large) to

identify the magnitude of difference between sprint and trial scores (Cohen, 1988).

Smallest worthwhile changes were also calculated for sprint times (Batterham and

Hopkins, 2005), with the smallest worthwhile change value over a 20 m sprint being

calculated using a Cohen’s unit of 0.2. Where the chances of benefit or harm were both

calculated to be > 5%, the true effect was deemed unclear (Batterham and Hopkins,

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2005). Otherwise, chances of benefit or harm were assessed as follows: < 1%, almost

certainly not; 1-5%, very unlikely; 5-25%, unlikely; 25-75%, possible; 75-95%, likely;

95-99%, very likely; > 99%, almost certain. All values are expressed as mean ± SD.

Results

No significant order effects (one-way ANOVA and t-tests) were found for mean sprint

times in quarter 1 (p=.954), 2 (p=.299), 3 (p=.276) and 4 (p=.412) or overall (p=.418).

There were no moderate to large effect sizes or beneficial smallest worthwhile changes

found between PC and CONT trials for total circuit times, mean sprint times for any

quarter, or the best and first sprint of each quarter (Table 1).

By the end of the precooling period, TC was lowered by ~0.4°C. Moderate ES (d=0.67;

90% CL=-1.27-0.23%) suggested a lower TC in PC compared with CONT at the end of

the precooling period (min 30; Table 2). Over the duration of the exercise protocol, TC

increased by ~1.7°C in both trials, with a moderate ES (d=0.67; 90% CL=-1.27-0.23%)

suggesting a lower TC in PC, compared with CONT, at the end of quarter 1 (Table 2).

Mean skin temperature between trials was not different with precooling before exercise

and remained relatively stable (~33-34°C) over the exercise protocol (Table 2).

No moderate or large ES were found for HR, RPE or TS measured at the end of each

quarter between trials (Table 3). However a moderate ES (d=0.67; 90% CL=-0.07-

1.45%) suggested a greater amount of sweat loss in PC (2.16 ± 0.23 kg) compared with

CONT (1.96 ± 0.30 kg).

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Table 1. Mean (± SD) 20 m sprint and circuit times overall and for each quarter, plus

first and best sprint times of each quarter for the precooling (PC) and control (CONT)

trials.

Trial

Cohen’s d Effect Size / Mean change (%) ± 90 % confidence limits / Percentage chance that effect is

beneficial (trivial/harmful)# PC CONT PC vs. CONT

Overall Sprint Time (s) 3.821 (0.440) 3.772 (0.404) 0.12 / 1.3 ± 0.48 / 7 (58/35)

Quarter Sprint Time (s)

1 3.744 (0.335) 3.744 (0.306) 0.00 / 0.0 ± 0.50 / 24 (52/24) 2 3.849 (0.455) 3.797 (0.418) 0.12 / 1.4 ± 0.53 / 9 (54/37) 3 3.860 (0.523) 3.794 (0.486) 0.14 / 1.7 ± 0.45 / 4 (60/36) 4 3.829 (0.475) 3.753 (0.484) 0.16 / 2.0 ± 0.50 / 4 (55/41)

First Sprint Time (s) 1 3.680 (0.328) 3.753 (0.457) 0.16 / 1.9 ± 0.42 / 45 (40/14) 2 3.794 (0.453) 3.821 (0.390) 0.07 / 0.7 ± 0.32 / 27 (61/12) 3 3.784 (0.469) 3.778 (0.482) 0.01 / 0.2 ± 0.30 / 11 (76/13) 4 3.835 (0.559) 3.772 (0.559) 0.11 / 1.6 ± 0.58 / 12 (51/37)

Best Sprint Time (s) 1 3.597 (0.255) 3.577 (0.300) 0.07 / 0.6 ± 0.35 / 6 (74/20) 2 3.709 (0.398) 3.720 (0.400) 0.03 / 0.3 ± 0.28 / 17 (72/11) 3 3.751 (0.501) 3.742 (0.477) 0.02 / 0.2 ± 0.29 / 9 (79/12) 4 3.698 (0.429) 3.651 (0.432) 0.11 / 1.3 ± 0.39 / 4 (68/28)

Overall Circuit Time (s) 44.53 (4.21) 44.05 (4.13) 0.12 / 1.1 ± 0.40/ 4 (66/30)

Quarter Circuit Time (s) 1 44.67 (3.97) 43.37 (3.25) 0.40 / 2.9 ± 0.68 / 0 (12/88) 2 44.78 (4.24) 44.40 (4.34) 0.09 / 0.8 ± 0.46 / 9 (62/29) 3 44.61 (4.51) 44.29 (5.06) 0.06 / 0.7 ± 0.42 / 10 (65/25) 4 44.07 (4.88) 44.16 (4.57) 0.02 / 0.2 ± 0.23 / 11 (82/7)

#Where the chance of benefit or harm were both calculated to be > 5%, the true effect was deemed unclear. Otherwise, chances of benefit or harm were assessed as follows: < 1%, almost certainly not; 1-5%, very unlikely; 5-25%, unlikely; 25-75%, possible; 75-95%, likely; 95-99%, very likely; > 99%, almost certain.

! !

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Table 2. Mean (± SD) core (TC; n = 10) and mean skin (mean TSk; n = 9) temperature

(°C) over the baseline period and at the end of each quarter for the precooling (PC) and

control (CONT) trials.

* = moderate effect size with PC (d = 0.50-0.79).

Table 3. Mean (± SD) heart rate (HR; bpm), thermal sensation (TS) and rating of

perceived exertion (RPE) at the end of each quarter for the precooling (PC) and control

(CONT) trials.

#

Baseline Period (30 min) Quarter Start Finish 1 2 3 4

TC PC 37.1 (0.3) 36.7 (0.4) 38.2 (0.4) 38.7 (0.6) 38.5 (0.7) 38.6 (0.6)

CONT 37.1 (0.3) 36.9 (0.3)* 38.4 (0.3)* 38.8 (0.4) 38.6 (0.3) 38.6 (0.4) Mean TSk

PC 31.0 (0.8) 31.9 (0.6) 33.7 (1.5) 33.4 (1.6) 33.1 (1.5) 32.9 (1.3) CONT 30.7 (0.9) 31.9 (0.8) 33.7 (2.4) 33.4 (2.8) 32.9 (3.1) 33.0 (3.2)

Quarter 1 2 3 4

HR PC 168 (15) 169 (16) 166 (18) 171 (17)

CONT 166 (20) 167 (16) 168 (14) 171 (12) TS

PC 5 (1) 6 (1) 6 (1) 6 (1) CONT 6 (1) 6 (1) 6 (1) 6 (1)

RPE PC 15 (2) 16 (2) 16 (1) 17 (1)

CONT 15 (2) 16 (2) 16 (1) 17 (1)

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Discussion

The purpose of this study was to determine the effect of using a combination of internal

and external precooling methods (ice slushy and cooling jacket) simultaneously on

repeat-sprint performance, in seasonally acclimatised participants, in warm/dry outdoor

conditions. This is the first study to examine the effect of precooling on repeat-sprint

performance using a prolonged simulated team-sport protocol in a field setting, thereby

providing some ecological validity. The main finding from this study was that despite a

lower TC being measured after the precooling period, repeat-sprint performance was not

improved compared with a no cooling (control) trial. In addition, no differences in

measures of physiological strain (HR, RPE, TS) were apparent between conditions.

Performance results from the current study are comparable to those of previous research

(Duffield and Marino, 2007; Minett et al., 2011), which also found no significant

improvement in repeat-sprint performance following precooling. Specifically, Duffield

and Marino (2007) and Minett et al. (2011) both used similar running protocols,

consisting of 2 x 30-35-min halves of repeat-sprint exercise interspersed with self-

paced, sub-maximal activity performed at varying intensities indoors in a heated room

with 32-34°C air temperatures and 30-33% RH. In addition, no differences were found

for high speed running distance during a competitive 90 min soccer match performed in

warm ambient conditions (29°C and 78% RH; Duffield et al., 2013). According to

Duffield and Marino (2007), the lack of significant improvement in sprint performance

may have been due to heat strain not being high enough for precooling to have any

significant effect. This explanation may also apply to the results of the current study,

where the outdoor air temperature and humidity (with solar radiation), were possibly not

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high enough to produce greater environmental thermal stress and hence higher heat

strain.

In support of the above supposition, studies that have reported significantly improved

sprint performance following precooling (Brade et al., 2012a, Chapter 3; Castle et al.,

2006) were performed in a climate chamber, where ambient conditions were somewhat

higher (~33-35°C and 51-57% RH) than those of the current study. Comparison of

physiological measures showed that mean TSk values were higher in the studies by

Brade et al. (2012a, Chapter 3) and Castle et al. (2006), being ~34-37°C vs 32-33°C in

the present study, while other indicators of thermal strain (such as TC, HR, RPE and

TS), were similar between all of these aforementioned studies and the current one.

Possibly, in environmental conditions where high skin temperatures are manifested,

such that the core-skin temperature gradient is narrowed, then precooling might become

more effective. Furthermore, it should be acknowledged that (in the present study)

enhanced heat dissipation, via the avenues of convection and evaporation, as expected

in an outdoor environment, would also reduce the levels of heat strain compared to the

same exercise performed in a climate chamber (Saunders et al., 2005). It should also be

acknowledged here that precooling has been shown to be effective in normothermic

conditions, although this was for endurance exercise where participants ran to

exhaustion in 24°C (Lee and Haymes, 1995).

Another contributing factor that may have resulted in precooling being ineffective in the

current study may be the seasonal heat acclimatisation of the participants; lessening the

level of heat strain and potentially attenuating any ergogenic effects. Importantly, heat

acclimation/acclimatisation has been reported to be the most reputable and well-studied

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technique used to counteract the negative effects of heat on exercise performance

(Marino, 2002). Recently, both Castle et al. (2011) and Brade et al. (2012b, Chapter 4)

concluded that precooling provided no additional benefit to repeat-sprint performance in

heat when participants are fully or partially heat acclimated.

In the current study, 30-min of precooling reduced TC by ~0.4°C while resting in

thermoneutral lab conditions. This reduction is greater than reported in previous

studies, where a decrease of ~0.2°C after precooling (using an ice bath and vest and

whole body cooling) was found by both Duffield and Marino (2007) and Minett et al.

(2011), respectively. However, precooling in both of these studies was performed in

warm conditions (32-34°C and 30-33% RH), which may have limited the potential

reductions in TC. Notably, the greater decrease in TC seen after precooling in the current

study did not translate into a markedly lower physiological strain during exercise, as

demonstrated by measures of mean TSk, HR, RPE and TS, which were not different

between conditions. In addition, TC was relatively similar between conditions for the

duration of the exercise protocol, other than at the end of quarter 1 when it was ~0.2°C

lower in PC. This may further explain the lack of performance benefits in the current

study, as the precooling here resulted in no marked reduction of physiological strain

measures, which has been evident in other studies that have seen performance

enhancements (Arngrimsson et al., 2004; Booth et al., 1997; Duffield et al., 2010; Kay

et al., 1999).

Sweat loss in the current study was ~0.2 kg higher following PC compared to CONT

(d=0.67). This finding is consistent with our earlier work (Brade et al., 2012a, Chapter

3; Brade et al., 2012b, Chapter 4) where we proposed that a higher sweat loss in PC

122##

may have been due to the ingestion of the ice slushy. Being cold, the ice slushy fluid

may move through the body at a faster rate than the same volume of fluid of a higher

temperature (Costill and Saltin, 1974), and potentially increase fluid supply to the sweat

glands. Commonly, sweat loss is reported to be lower after precooling (Arngrimsson et

al., 2004; Duffield and Marino, 2007; Duffield et al., 2010; Kay et al., 1999; Minett et

al., 2011), but such studies have generally employed only external (rather than internal)

cooling methods, such as vests/jackets, ice baths and iced towels. If used in isolation, or

in combination with external cooling methods, ice slushy ingestion may produce a

higher sweat loss in prolonged, repeated short sprint exercise, but not necessarily confer

any performance advantage.

A limitation to the current study is the absence of a non-acclimatised trial (or group).

This was excluded from the experimental design because of the long logistical

considerations of having to wait some months for the winter season, which in turn may

have further limited the study via participant changes in training status and the likely

increase in participant drop-out. A further limitation to this study relates to the use of a

simulated exercise team-sport circuit, as opposed to an actual team-game, where

movement patterns and energy use may have been different.

Conclusion

In conclusion, it appears that precooling does not enhance repeat-sprint performance in

the field in warm conditions in seasonally acclimatised participants. This result may be

mostly due to the only moderate levels of heat strain produced here by the warm (as

opposed to hot) environmental conditions and/or the fact that participants were

123##

seasonally acclimatised. Consequently, precooling appears unnecessary if athletes are

heat acclimatised/acclimated and environmental conditions are not overly hot or humid.

The results of this study further support the notion that acclimatisation/acclimation is a

more effective method of protecting against heat strain than precooling.

Acknowledgments

The authors wish to acknowledge the funding of this study by The University of

Western Australia and the individuals who participated in this study. The experiments

comply with the current laws of Australia.

124##

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Batterham, A. and Hopkins, W. (2005) Making meaningful inferences about

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Bishop, D., Spencer, M., Duffield, R. and Lawrence, S. (2001) The validity of a

repeated sprint ability test. Journal of Science and Medicine in Sport 4, 19-29.

Booth, J., Marino, F. and Ward, J. (1997) Improved running performance in hot humid

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Journal of Rehabilitation Medicine 3, 92-98.

Brade, C., Dawson, B. and Wallman, K. (2012a) Effects of different precooling

techniques on repeat sprint ability in team sport athletes. European Journal of

Sport Science DOI: 10.1080/17461391.2011.651491.

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10.1080/02640414.2012.750006.

Castle, P., Macdonald, A., Philp, A., Webborn, A., Watt, P. and Maxwell, N. (2006)

Precooling leg muscle improves intermittent sprint exercise performance in hot,

humid conditions. Journal of Applied Physiology 100, 1377-1384.

125##

Castle, P., Mackenzie, R., Maxwell, N., Webborn, A. and Watt, P. (2011) Heat


offers no further ergogenic effect. Journal of Sports Sciences 29, 1125-1134.

Cohen, J. (1988) Statistical power analysis for the behavioural sciences. 2nd edition.

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Drust, B., Rasmussen, P., Mohr, M., Nielsen, B. and Nybo, L. (2005) Elevations in core


Scandinavica 183, 181-190.

Duffield, R., Dawson, B., Bishop, D., Fitzsimons, M. and Lawrence, S. (2003) Effect of


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Duffield, R., Coutts, A., McCall, A. and Burgess, D. (2013) Pre-cooling for football

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Duvnjak-Zaknich, D., Dawson, B., Wallman, K. and Henry, G. (2011) Effect of

caffeine on reactive agility time when fresh and fatigued. Medicine and Science

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Ihsan, M., Landers, G., Brearley, M. and Peeling, P. (2010) Beneficial effects of ice


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Marino, F.E. (2002) Methods, advantages, and limitations of body cooling for exercise

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in Sports and Exercise 43, 1760-1769.

Morris, J., Nevill, M., Lakomy, H., Nicholas, C. and Williams, C. (1998) Effect of a hot

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128##

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Sports Medicine 37, 669-682.

129##

CHAPTER SIX Discussion

130##

Discussion

Thesis summary

Methods such as precooling and heat acclimation/acclimatisation, which can enhance

exercise performance in hot and humid environmental conditions, are important to

athletes and coaches not only from a performance standpoint, but also for the athlete’s

well-being. This thesis comprises three practical studies that add to the current

literature and provide further insight into methods for limiting the detrimental effect of

heat on repeat-sprint exercise performance. The following discussion summarises each

study and their findings and highlights the similarities between studies, as well as

defining practical applications and areas of future research.

Study one (see chapter three) tested the effectiveness of different precooling methods,

including an ice slushy, cooling jacket and the combination of the two on a prolonged

repeat-sprint protocol performed in a controlled hot and humid environment. The main

findings were significantly improved overall sprint performance (total work and mean

power) and lower core temperatures using the combined method compared with ice

slushy. These results suggest that using an ice slushy alone is not beneficial for

prolonged repeat-sprint performance in heat, but in combination with a cooling jacket

can lower core temperature and enhance performance. This study adds to the current

literature which supports the use of mixed-method cooling techniques compared with

singular methods (Minett, Duffield, Marino & Portus, 2012; Ross et al., 2011).

Importantly, using a combination of external and internal cooling methods not only

cools the body but provides a source of pre-exercise hydration and offers a practical and

convenient method which may be easily transferable to a field setting.

131##

As the combined method of cooling (ice slushy and cooling jacket) resulted in the best

performance in study one, the same method was chosen for use in subsequent studies.

Study two (see chapter four) aimed to determine if partial heat acclimation would

improve repeat-sprint exercise and if further benefits would occur with the addition of

precooling performed both prior to and during performance. The results showed that

exercise performance was improved following a short-term, high-intensity heat

acclimation protocol, however precooling provided no additional benefit. These results

are similar to those of Castle et al. (2011), who found improved performance in

participants who were fully heat acclimated, yet no further performance enhancement

from precooling the thighs. It has been suggested that precooling is only of benefit

when heat strain is high (Duffield & Marino, 2007), therefore it seems that partial

acclimation (similar to full acclimation), may reduce heat strain to a point where

precooling confers no further advantage.

The premise behind carrying out the final study (see chapter five) was based on the

limited amount of current literature focusing on the effect of precooling on team-sport

performance in the field. For example, the study by Castle et al. (2011) and study two

of this thesis (see chapter four) were performed in controlled laboratory conditions

using a repeat-sprint cycle (weight assisted) protocol. Therefore, to further examine the

potential impact of precooling on prolonged, repeat-sprint exercise protocols in the

field, a running based simulated team-sport circuit was used outdoors with seasonally

acclimatised athletes.

The purpose of study three (chapter five) was to assess the effect of precooling (again

using the combined method of ice slushy and ice jacket) on repeat-sprint running

132##

performance in seasonally acclimatised team-sport athletes in a field setting in warm

outdoor conditions. The results showed that despite slightly lower core temperatures

being measured in the precooling trial, no performance enhancement was seen. A

potential mitigating factor here may have been the relatively mild degree of heat strain

produced, as a result of the following factors: participants were seasonally heat

acclimatised, environmental conditions were warm rather than hot and relatively low

skin temperatures were produced during exercise, helping to maintain a larger core-skin

temperature gradient than seen in laboratory based studies. The findings of this study

support those of study two (chapter four) in concluding that precooling may be

unnecessary if athletes are heat acclimated/acclimatised and environmental conditions

are moderate rather than severe.

Synthesis of results

In order to easily compare results between the different studies of this thesis, similar

protocols and measurement devices were used as much as possible. Performance tests

for study one and two used the same 2 x 30-min repeat-sprint protocol performed in the

same environmental conditions. As mentioned earlier, the results for study one

determined the method and duration of cooling used for studies two and three. The

repeat-sprint protocols used in this thesis have been widely used for published research

within our School. With regards to the final study (see chapter five) previous work

from our laboratory has established the CV for mean (quarter) sprint time as 3.7% (90%

CL, 2.7-6.0%) and for best sprint time as 2% (90% CL, 1.4-3.1%) within this circuit

(Singh et al., 2010). To aid in reliable comparisons of data across the three studies the

same physiological measurement devices, which are widely used within the literature,

were used for core and skin temperature and heart rate, as well as the same rating scales

133##

for perceived exertion and thermal sensation. Taking all three experimental studies as a

whole, it is evident that few significant results were recorded. In the absence of these,

statistics that referred to the meaningfulness of the results were used, namely effect

sizes and smallest worthwhile effects. Literature investigating the effect of precooling

on repeat-sprint performance has thus far shown few significant results. This thesis

shows that despite no widespread or consistent statistical significance being recorded,

there is nevertheless some meaningful results to suggest that using a combination of

precooling methods has more benefits when compared against singular methods and

that acclimation/acclimatisation is a more beneficial method of enhancing repeat-sprint

performance in heat compared to precooling.

Across all three experimental studies core temperature responses to exercise were

similar. When using the combination of precooling methods (cooling jacket and ice

slushy) the average reduction in core temperature prior to exercise for all studies was

0.3-0.5°C. This decrease is comparable with the ranges reported for other mixed-

method approaches to precooling for similar durations (20-30-min) in warm conditions,

such as ice bath and vest, ~0.2°C (Duffield & Marino, 2007); head, neck, hand, cooling

jacket and ice packs on thighs, ~0.2°C (Minett, Duffield, Marino & Portus, 2011;

Minett et al., 2012); iced towels on torso and legs plus ice slushy, ~0.2°C or water

immersion and cooling jacket, ~0.6°C (Ross et al., 2011) and a 30-min ice bath

followed by wearing a cooling jacket for 40-min, ~0.7°C (Quod et al., 2008). At the

conclusion of the exercise protocols maximum core temperatures were also comparable

between studies (38.8°C; study one; 38.6°C; study two and three). One reason for the

slightly lower final core temperatures recorded in study two and three may be due to

participants being partially heat acclimated and seasonally acclimatised, respectively.

134##

The performance of the exercise task outdoors in study three, which may have

facilitated greater evaporative and convective heat loss may also be a factor in the

slightly lower core temperature responses.

With regards to mean skin temperature, results were similar between the first two

studies, with values during exercise ranging from ~34.6-36.7°C, with these being higher

than those measured in study three (~33°C). The reason for this is most likely the lower

environmental heat stress encountered outdoors in study three, compared with the

warmer and controlled laboratory conditions used in study one and two. Furthermore,

enhanced heat dissipation, via the avenues of convection and evaporation, as expected

in a moderate outdoor environment, would also help explain lower skin temperatures

when compared with similar exercise performed in a climate chamber (Saunders,

Dugas, Tucker, Lambert & Noakes, 2005). The lower skin temperatures would also

allow for a larger core to skin temperature gradient to operate, thereby facilitating heat

loss from the body and assisting in the maintenance of a lower overall core temperature.

The sweat loss results from the repeat-sprint exercise tasks used here were also similar,

and somewhat unexpected. Generally, prior research (Arngrimsson, Petitt, Stueck,

Jorgensen & Cureton, 2004; Duffield & Marino, 2007; Duffield, Green, Castle &

Maxwell, 2010; Kay, Taaffe & Marino, 1999; Minett et al., 2011) shows that sweat loss

following precooling is lower compared with control trials. In contrast, the studies of

this thesis found that sweat loss following precooling was higher (~0.2 kg) in the

mixed-method trials than with other forms of precooling (study one) or control (no

cooling) trials (study one, two and three). Although the exact reason for this response is

unclear it may possibly be due to the ice slushy being cold and moving through the

135##

body at a faster rate (Costill & Saltin, 1974), which could potentially increase fluid

supply to the sweat glands. Furthermore, the aforementioned studies generally

employed external cooling methods (such as water immersion and cooling jackets) thus,

if used in isolation, or in combination with external cooling methods, ice slushy

ingestion may produce a higher sweat loss in prolonged, repeated short-sprint exercise.

Other studies using ice slushies have generally been endurance type exercise. Of these

studies, all found better exercise performance after ice ingestion, however only one

study reported significantly lower body mass (sweat loss) changes (Ross et al., 2011), as

compared with others reporting no significant changes in body mass (Ihsan, Landers,

Brearley & Peeling, 2010; Siegel, Mate, Brearley, Watson, Nosaka & Laursen, 2010).

Finally, sweating is initiated via sympathetic stimulation of the sweat glands in the skin.

As high intensity exercise and ingestion of ice would both act as a stimulus for an

increase in sympathetic nervous system activity, this may lead to greater sweat gland

activity, which may explain the sweat loss results found in each of the experimental

studies here.

Limitations of the thesis

As with most precooling studies, it is difficult to blind participants to the aims of the

study due to the need for participants to wear a cooling (chilled) jacket and to ingest an

ice slushy in certain trials. Therefore, when participants were being cooled by these

methods they may have perceived that performance should be enhanced and therefore

may have subconsciously altered their performance during those trials, compared with

the no cooling trials. Further, while participant numbers for each study (n=10-12) were

similar to other studies that have assessed precooling methods (Duffield & Marino,

2007; Castle et al., 2006; Minett et al., 2011), a larger cohort may have provided more

136##

conclusive results. A limitation of study one was that participants in the ice slushy

condition wore the cooling jacket (without the frozen PC25 packs), during the cooling

periods. This may have had an insulating effect, by impairing heat flow along a

temperature gradient from body core to skin, which perhaps accounts for the relatively

small (0.4°C) decrease found in TC with pre-exercise cooling in ice slushy. Finally,

study three does not include a non-acclimatised trial. This was excluded because of the

logistical considerations of having to wait some months for the winter season, which in

turn may have further limited the study via participant changes in training status and a

likely increase in participant drop-out. Using an independent groups study design also

provides its own limitations: recruiting perfectly matched participants in terms of

physical characteristics such as body mass/surface area, aerobic/anaerobic fitness

capacities and training history and status is often difficult.

Conclusions

• Mixed-method cooling (jacket and ice slushy) resulted in better repeat-sprint

performance in heat compared with jacket and ice slushy alone.

• Partial heat acclimation achieved by a short-term, high-intensity cycling

protocol improved repeat-sprint performance yet additional precooling provided

no further benefit.

• Seasonally acclimatised participants’ repeat-sprint exercise performance was not

enhanced during an outdoor team-sport protocol in warm conditions following

precooling.

137##

Practical Applications

The following practical recommendations are presented for athletes and coaches, based

on the results of this thesis:

• A mixed-method (using two cooling methods simultaneously) approach to

precooling may be more beneficial to repeat-sprint performance compared with

singular methods.

• The simultaneous use of a cooling jacket and ice slushy not only aids with

cooling but also provides a source of hydration, and both are practical and

convenient methods of cooling in the field prior to and during exercise.

• A short-term, high-intensity acclimation protocol (5 sessions within 10 days)

which results in partial heat acclimation is effective in aiding prolonged repeat-

sprint performance in heat.

• If athletes are at least partially heat acclimated, it appears that additional

precooling prior to and/or during exercise is ineffective and unnecessary due to

the level of heat strain already being sufficiently lowered, especially in

conditions where the environmental heat stress is not marked. It would seem

that heat acclimatisation/acclimation is a more powerful method than

precooling for improving exercise performance in heat.

Future Research

Some relevant areas of research which follow on from the findings of this thesis are:

• Further examining the effect of precooling via an ice slushy on sweat loss during

repeat-sprint exercise in hot and humid conditions, to determine why an increase

138##

in sweat loss using this cooling method may manifest (compared with external

cooling methods).

• To repeat study three in hotter conditions, therefore increasing the

environmental heat stress, to assess whether precooling may be beneficial to

repeat-sprint performance.

• The inclusion of a non-heat-acclimatised group in a study design as for study

three, to allow for comparisons in precooling effects during repeat-sprint

exercise performance between heat acclimatised and non-acclimatised

participants.

139##

References

Arngrimsson, S.A., Petitt, D.S., Stueck, M.G., Jorgensen, D.K., & Cureton, K.J.

(2004). Cooling vest worn during active warm-up improves 5-km run

performance in the heat. Journal of Applied Physiology, 96, 1867-1874.







1134.

Costill, D., & Saltin, B. (1974). Factors limiting gastric emptying during rest and

exercise. Journal of Applied Physiology 37, 679-683.

Duffield, R., & Marino, F. (2007). Effects of pre-cooling procedures on intermittent-



Duffield, R., Green, R., Castle, P., & Maxwell, N. (2010). Precooling can prevent the






140##

Kay, D., Taaffe, D.R., & Marino, F.E. (1999). Whole-body pre-cooling and heat

storage during self-paced cycling performance in warm humid conditions.

Journal of Sports Sciences, 17, 937-944.

Minett, G.M., Duffield, R., Marino, F.E., & Portus, M. (2011). Volume-dependent


Science in Sports and Exercise, 43 (9), 1760-1769.




Quod, M.J., Martin, D.T., Laursen, P.B., Gardner, A.S., Halson, S.L., Marino, F.E.,

Tate, M.P., Mainwaring, D.E., Gore, C.J., & Hahn, A.G. (2008). Practical

precooling: Effect on cycling time trial performance in warm conditions.

Journal of Sports Sciences, 26 (14), 1477-1487.

Ross, M.L.R., Garvican, L.A., Jeacocke, N.A., Laursen, P.B., Abbiss, C.R., Martin,

D.T., & Burke, L.M. (2011). Novel precooling strategy enhances time trial

cycling in the heat. Medicine and Science in Sports and Exercise, 43 (1), 123-

133.

Saunders, A., Dugas, J., Tucker, R., Lambert, M., & Noakes, T. (2005). The effects of

different air velocities on heat storage and body temperature in humans cycling

in a hot, humid environment. Acta Physiologica Scandinavica 183, 241-255.

Siegel, R., Mate, J., Brearley, M.B., Watson, G., Nosaka, K., & Laursen, P.B. (2010).


heat. Medicine and Science in Sports and Exercise, 42 (4), 717-725.

141##

Singh, T., Guelfi, K., Landers, G., Dawson, B. And Bishop, D. (2010) Reliability of a

contact and non-contact simulated team game circuit. Journal of Sports Science

and Medicine 9, 638-642.

142##

CHAPTER SEVEN Appendices

143##

Appendix A Ethics Approval Letter

145##

Appendix B Study One – Raw Data

146##


Peak Power / kg (W·kg-1)

1st Half 2nd Half CONT J ice

slushy J + ice slushy CONT J ice

slushy J + ice slushy

1 1097 1253 1108 1029 1081 1166 1079 1143 2 1267 1243 1313 1242 1165 1316 1259 1272 3 1565 1331 1392 1335 1675 1407 1318 1391 4 1234 1246 1260 1360 1189 1214 1244 1286 5 1159 1360 1002 1288 1170 1367 1062 1282 6 1131 1390 1185 1424 1111 1307 1262 1401 7 1525 1517 1597 1561 1564 1490 1592 1566 8 1370 1424 1357 1328 1176 1320 1315 1307 9 1494 1514 1390 1562 1550 1507 1460 1535 10 1343 1401 1304 1313 1334 1369 1275 1281 11 1415 1427 1212 1502 1325 1485 1363 1448 12 1019 1139 1021 1100 1098 1134 1067 1146

Average 1302 1354 1262 1337 1287 1340 1275 1338 SD 179 116 170 165 204 124 158 134




1 16.32 18.68 16.57 15.25 16.08 17.37 16.14 16.93 2 15.68 15.18 16.21 15.31 14.42 16.07 15.55 15.69 3 16.30 13.94 14.62 13.89 17.44 14.74 13.84 14.47 4 18.98 18.93 19.26 20.99 18.29 18.45 19.00 19.80 5 17.59 20.06 15.23 19.36 17.76 20.17 16.15 19.27 6 12.86 15.81 13.66 15.90 12.64 14.88 14.55 15.63 7 17.21 17.00 17.96 17.44 17.65 16.70 17.90 17.49 8 15.44 16.34 15.79 15.26 13.56 15.16 15.31 15.02 9 20.15 20.52 18.88 20.89 20.91 20.42 19.82 20.52 10 18.06 19.41 17.76 17.69 17.92 18.50 17.37 17.22 11 18.90 19.11 16.37 19.82 17.80 19.89 18.40 19.14 12 15.38 16.24 15.36 16.41 16.53 16.19 16.04 17.11

Average 16.91 17.60 16.47 17.35 16.75 17.38 16.67 17.36 SD 1.99 2.12 1.71 2.41 2.28 2.08 1.83 1.97

147##

Mean Power (Watts)

Work (kJ)




1 757 908 758 663 718 866 733 780 2 905 894 861 915 813 979 918 927 3 1266 971 995 1043 1389 1116 983 1145 4 799 858 868 934 772 831 843 869 5 792 975 667 918 826 973 697 933 6 794 1006 857 1052 819 972 948 1062 7 1082 1081 1150 1147 1123 1050 1143 1119 8 1056 987 955 1019 897 902 958 985 9 1077 1052 968 1111 1161 1061 1055 1105 10 949 1089 944 1025 999 1076 974 1019 11 960 961 735 1047 887 1028 848 975 12 615 805 650 741 714 785 668 791

Average 921 966 867 968 927 970 897 976 SD 180 87 147 144 205 104 145 122




1 90.8 109.3 90.9 79.6 86.2 103.9 87.9 93.6 2 108.5 107.3 103.3 110.2 98.8 117.4 110.1 111.3 3 151.9 116.6 119.4 125.2 166.7 133.9 117.9 137.4 4 95.9 103.0 104.1 112.3 92.6 99.7 101.2 104.0 5 95.0 117.0 80.1 110.2 99.2 116.8 83.6 112.4 6 95.3 120.7 102.9 130.3 98.2 116.7 113.8 127.4 7 129.9 130.2 138.0 137.7 134.7 126.0 137.2 134.3 8 126.7 118.5 114.6 122.3 107.6 108.3 115.0 118.2 9 129.3 126.3 116.2 133.4 139.3 127.3 126.6 132.2 10 113.8 130.7 113.3 123.0 119.9 129.1 116.9 122.3 11 115.2 115.3 88.2 125.5 106.5 123.4 101.8 117.0 12 73.8 96.6 78.0 88.9 85.7 94.2 80.2 94.9

Average 110.5 116.0 104.1 116.5 111.3 116.4 107.7 117.1 SD 21.7 10.5 17.6 17.5 24.5 12.5 17.4 14.6

148##

Work / kg (J·kg-1)

Total Mean Power (Watts)




1 1352 1629 1360 1179 1283 1549 1315 1387 2 1342 1310 1276 1359 1222 1434 1360 1372 3 1582 1221 1254 1303 1736 1403 1238 1430 4 1475 1505 1591 1734 1425 1515 1546 1610 5 1442 1726 1217 1655 1505 1723 1271 1689 6 1084 1373 1186 1454 1118 1327 1312 1422 7 1466 1459 1552 1538 1521 1413 1542 1501 8 1428 1360 1334 1406 1241 1243 1339 1359 9 1743 1711 1577 1783 1879 1725 1720 1773 10 1530 1768 1544 1653 1582 1746 1592 1644 11 1538 1543 1190 1507 1423 1651 1374 1547 12 1113 1381 1173 1327 1293 1346 1205 1417

Average 1425 1499 1354 1492 1435 1506 1401 1513 SD 186 179 166 187 223 172 160 138

CONT J ice slushy

J + ice slushy

1 738 887 745 722 2 859 936 889 921 3 1327 1044 989 1094 4 785 845 855 902 5 809 974 682 926 6 807 989 903 1057 7 1102 1066 1147 1133 8 976 945 956 1002 9 1119 1057 1012 1108 10 974 1083 959 1022 11 924 994 791 1011 12 664 795 659 766

Average 924 968 882 972 SD 188 91 144 130

149##

Total Work (kJ)

Sweat Loss (kg)

CONT J ice slushy

J + ice slushy

1 177.0 213.3 178.8 173.2 2 207.2 224.7 213.5 221.5 3 318.6 250.5 237.3 262.7 4 188.5 202.7 205.3 216.4 5 194.2 233.8 163.7 222.6 6 193.6 237.4 216.7 257.7 7 264.6 256.2 275.2 272.0 8 234.4 226.7 229.6 240.5 9 268.6 253.6 242.8 265.6 10 233.7 259.8 230.2 245.3 11 221.6 238.7 189.9 242.5 12 159.5 190.9 158.2 183.9

Average 221.8 232.4 211.8 233.6 SD 45.2 21.8 34.5 31.4

CONT J ice slushy

J + ice slushy

1 1.2 1.2 1.8 1.4 2 1.1 1.1 1.3 1.5 3 1.6 1.4 1.8 1.8 4 1.1 1.0 1.7 1.3 5 1.4 1.2 1.2 1.5 6 1.4 1.9 2.0 2.1 7 1.8 1.6 2.0 1.8 8 1.4 1.5 1.7 1.7 9 1.0 1.0 1.1 1.6 10 1.7 1.7 1.9 1.8 11 1.7 1.7 1.7 1.7 12 1.1 0.9 1.3 1.4

Average 1.4 1.3 1.6 1.6 SD 0.3 0.3 0.3 0.2

150##

TC - Precooling Period (30-min; °C)

TC - First Half of Exercise (°C)

Start Finish CONT J ice



1 37.3 37.2 37.3 36.8 36.7 36.8 36.9 36.6 2 36.9 37.1 36.9 37.0 36.8 36.7 36.8 36.5 3 37.4 37.3 37.4 37.1 36.8 36.8 36.6 37.1 4 37.5 37.6 37.3 37.3 37.7 37.5 37.1 37.3 5 37.9 37.6 37.6 37.4 37.5 37.5 37.4 37.2 6 37.1 37.2 37.3 37.3 37.1 37.0 36.4 36.8 7 37.2 37.1 37.5 37.3 37.4 36.8 36.7 37.0 8 37.5 37.3 37.6 36.7 37.0 37.1 37.5 37.0 9 37.1 37.1 37.2 37.4 36.9 36.9 36.9 36.8 10 37.3 37.1 37.1 36.8 37.1 37.2 37.1 36.4 11 36.9 37.0 37.7 37.2 36.8 37.1 36.7 36.8 12 36.9 37.0 36.6 36.8 36.7 36.8 36.2 36.4

Average 37.3 37.2 37.3 37.1 37.0 37.0 36.9 36.8 SD 0.3 0.2 0.3 0.2 0.3 0.3 0.4 0.3




1 36.8 36.7 36.9 36.1 38.8 38.8 38.9 38.1 2 36.7 36.8 36.7 36.3 38.2 38.3 37.9 38.6 3 36.9 36.8 36.5 37.1 38.6 37.9 38.5 38.1 4 37.5 37.4 37.0 37.3 38.9 38.8 38.1 38.9 5 37.6 37.4 37.3 37.2 38.7 39.0 38.5 38.5 6 37.1 37.0 36.5 36.6 38.4 38.5 38.4 38.1 7 37.4 36.6 36.8 36.9 38.2 37.6 38.5 38.3 8 37.1 37.1 37.6 37.0 38.3 38.5 39.1 38.4 9 36.9 36.8 36.9 36.8 38.8 38.4 39.1 38.6 10 37.2 37.0 37.3 36.4 38.7 38.5 38.9 38.3 11 36.7 37.1 36.7 36.7 38.4 39.0 38.3 38.6 12 36.5 36.5 36.1 36.2 37.9 38.4 38.3 38.2

Average 37.0 36.9 36.9 36.7 38.5 38.5 38.5 38.4 SD 0.4 0.3 0.4 0.4 0.3 0.4 0.4 0.3

151##

TC - Half-Time (10-min; °C)

TC - Second Half of Exercise (°C)




1 38.8 38.8 38.9 38.1 38.5 38.9 39.0 37.7 2 38.2 38.3 37.9 38.6 38.2 37.9 38.1 38.3 3 38.6 37.9 38.5 38.1 38.6 37.3 38.1 37.7 4 38.9 38.8 38.1 38.9 38.8 38.8 38.1 38.5 5 38.7 39.0 38.5 38.5 38.5 39.1 38.5 38.6 6 38.4 38.5 38.4 38.1 38.3 38.7 38.5 38.4 7 38.2 37.6 38.5 38.3 38.3 37.3 38.2 38.1 8 38.3 38.5 39.1 38.4 37.7 38.2 38.9 37.9 9 38.8 38.4 39.1 38.6 38.7 38.2 39.2 38.7 10 38.7 38.5 38.9 38.3 38.5 38.1 38.3 38.1 11 38.4 39.0 38.3 38.6 38.4 39.0 38.3 38.4 12 37.9 38.4 38.3 38.2 37.6 38.4 38.1 38.2

Average 38.5 38.5 38.5 38.4 38.3 38.3 38.4 38.2 SD 0.3 0.4 0.4 0.3 0.4 0.6 0.4 0.3




1 38.5 38.9 39.0 37.7 38.9 39.2 39.2 38.5 2 38.2 37.9 38.1 38.3 38.7 38.8 39.4 39.1 3 38.6 37.3 38.1 37.7 39.3 38.6 38.6 38.5 4 38.8 38.8 38.1 38.5 38.9 39.2 38.3 39.1 5 38.5 39.1 38.5 38.6 38.9 39.1 38.9 38.9 6 38.3 38.7 38.5 38.4 38.6 39.3 39.1 38.8 7 38.3 37.3 38.2 38.1 38.5 37.9 38.9 38.5 8 37.7 38.2 38.9 37.9 38.7 38.5 39.5 38.7 9 38.7 38.2 39.2 38.7 39.6 38.8 39.5 39.4 10 38.5 38.1 38.3 38.1 39.2 38.8 38.8 38.9 11 38.4 39.0 38.3 38.4 38.6 39.6 39.2 38.8 12 37.6 38.4 38.1 38.2 38.5 39.2 38.7 38.8

Average 38.3 38.3 38.4 38.2 38.9 38.9 39.0 38.8 SD 0.4 0.6 0.4 0.3 0.3 0.5 0.4 0.3

152##

Mean TSk - Precooling (30-min; °C)

Mean TSk - First Half of Exercise (°C)




1 30.6 32.1 32.3 31.7 30.8 32.4 32.4 31.8 2 30.8 31.6 32.8 31.7 30.6 32.1 32.5 31.6 3 31.9 32.8 33.0 32.3 32.4 33.0 33.1 32.7 4 30.4 31.0 32.1 31.8 30.5 31.6 32.4 32.2 5 31.2 31.9 33.7 31.6 31.3 32.3 33.5 31.7 6 32.5 31.5 32.5 31.1 31.4 32.7 32.3 31.8 7 30.6 30.7 31.8 30.0 31.1 31.4 32.4 30.8 8 31.0 31.1 32.3 31.0 31.0 31.8 32.5 31.9 9 30.7 30.5 33.0 30.9 31.0 31.5 32.6 31.9 10 31.4 31.4 32.2 31.3 31.1 32.1 32.7 32.0 11 30.5 31.9 31.9 31.6 30.6 32.2 32.7 31.8 12 30.9 32.2 32.3 31.3 31.1 32.0 32.4 31.6

Average 31.0 31.7 32.6 31.4 31.1 32.2 32.7 31.8 SD 0.6 0.7 0.7 0.8 0.5 0.5 0.5 0.6




1 35.8 35.0 35.6 34.6 37.7 36.8 35.9 35.6 2 35.7 35.6 35.1 35.1 37.7 36.9 36.8 36.7 3 35.5 34.6 35.0 35.4 36.7 36.6 36.8 36.9 4 35.3 35.1 34.9 35.4 36.8 37.1 37.2 36.8 5 35.4 35.1 35.1 35.2 36.4 37.5 35.8 37.3 6 35.2 34.5 35.1 34.3 36.5 36.4 36.9 37.1 7 34.7 34.1 35.0 34.8 37.1 36.0 36.5 36.2 8 35.0 35.2 35.5 35.1 36.3 37.0 36.7 36.2 9 34.9 34.7 35.2 35.1 36.9 37.1 37.1 37.1 10 35.4 35.2 36.4 35.1 37.1 36.8 37.1 37.1 11 34.6 35.5 35.2 35.5 37.2 37.2 37.2 37.6 12 34.8 34.4 34.9 34.6 36.8 37.0 36.7 36.9

Average 35.2 34.9 35.3 35.0 36.9 36.9 36.7 36.8 SD 0.4 0.5 0.4 0.4 0.5 0.4 0.4 0.5

153##

Mean TSk - Half-Time (10-min; °C)

Mean TSk - Second Half of Exercise (°C)




1 37.7 36.8 35.9 35.6 37.1 35.5 35.6 35.3 2 37.7 36.9 36.8 36.7 36.9 36.1 36.6 36.0 3 36.7 36.6 36.8 36.9 35.4 35.8 36.6 35.9 4 36.8 37.1 37.2 36.8 36.0 36.6 36.5 35.6 5 36.4 37.5 35.8 37.3 35.9 36.5 36.0 36.7 6 36.5 36.4 36.9 37.1 36.1 36.1 36.4 36.4 7 37.1 36.0 36.5 36.2 36.1 35.2 36.4 35.8 8 36.3 37.0 36.7 36.2 35.6 35.4 35.0 35.5 9 36.9 37.1 37.1 37.1 36.9 36.2 37.1 36.4 10 37.1 36.8 37.1 37.1 36.1 35.5 36.4 36.5 11 37.2 37.2 37.2 37.6 36.7 36.2 36.4 36.7 12 36.8 37.0 36.7 36.9 35.8 36.2 36.0 36.2

Average 36.9 36.9 36.7 36.8 36.2 35.9 36.2 36.1 SD 0.5 0.4 0.4 0.5 0.6 0.5 0.5 0.5




1 37.1 35.5 35.6 35.3 37.4 37.0 35.6 35.8 2 36.9 36.1 36.6 36.0 37.9 37.0 37.0 37.2 3 35.4 35.8 36.6 35.9 36.4 36.5 36.9 36.5 4 36.0 36.6 36.5 35.6 36.7 36.8 37.1 36.1 5 35.9 36.5 36.0 36.7 37.0 37.0 36.2 37.0 6 36.1 36.1 36.4 36.4 36.5 36.4 37.5 36.4 7 36.1 35.2 36.4 35.8 36.1 35.7 36.1 36.0 8 35.6 35.4 35.0 35.5 36.0 36.4 37.4 35.9 9 36.9 36.2 37.1 36.4 37.4 37.4 37.5 37.2 10 36.1 35.5 36.4 36.5 36.5 36.4 36.9 37.4 11 36.7 36.2 36.4 36.7 37.0 36.3 37.0 37.5 12 35.8 36.2 36.0 36.2 36.8 37.0 37.0 37.1

Average 36.2 35.9 36.2 36.1 36.8 36.7 36.9 36.7 SD 0.6 0.5 0.5 0.5 0.6 0.5 0.6 0.6

154##

HR – First Half of Exercise (bpm)

HR – Second Half of Exercise (bpm)




1 102 101 127 113 159 170 162 169 2 102 80 109 120 199 171 202 205 3 84 78 82 91 159 132 156 157 4 103 117 111 134 194 189 188 190 5 135 100 105 126 180 192 166 183 6 102 98 81 92 162 160 162 168 7 90 89 97 77 158 151 158 160 8 109 84 106 110 173 177 175 135 9 110 114 109 100 170 165 182 168 10 74 88 105 135 150 174 178 181 11 115 130 124 113 167 184 186 184 12 102 124 104 124 139 137 152 148

Average 102 100 105 111 168 167 172 171 SD 15 18 14 18 17 19 15 19




1 124 124 132 121 172 177 169 165 2 165 126 128 154 208 204 215 208 3 115 110 94 111 180 161 156 164 4 133 128 129 142 191 188 188 173 5 127 129 107 138 185 212 171 208 6 114 121 121 125 174 170 178 175 7 119 108 128 97 162 155 162 161 8 141 139 130 126 172 180 183 185 9 135 147 150 134 179 170 181 175 10 134 119 119 131 191 183 186 185 11 130 130 134 134 167 189 191 185 12 123 105 100 91 160 155 158 162

Average 130 124 123 125 178 179 178 179 SD 14 12 16 18 14 18 17 16

155##

RPE – First Half of Exercise

RPE – Second Half of Exercise

15th min 30th min CONT J ice



1 16 13 15 14 17 18 16 16 2 15 15 14 14 17 16 15 16 3 17 14 12 16 18 17 15 17 4 13 13 13 13 15 16 16 17 5 15 15 13 14 18 17 15 16 6 14 14 14 15 15 17 16 16 7 12 14 13 15 15 16 15 17 8 15 14 15 13 18 15 17 17 9 12 12 14 11 14 16 17 13 10 14 14 13 10 15 16 15 16 11 15 14 13 14 17 17 16 17 12 13 14 16 16 16 16 17 17

Average 14 14 14 14 16 16 16 16 SD 2 1 1 2 1 1 1 1




1 15 18 16 15 17 19 18 17 2 16 16 16 18 17 17 17 17 3 18 18 17 17 19 19 18 18 4 18 18 17 17 18 18 18 19 5 19 17 16 16 20 18 17 18 6 15 18 16 17 17 18 18 18 7 17 17 16 15 18 18 18 16 8 17 16 16 17 18 18 18 18 9 14 17 17 14 15 17 17 15 10 16 17 16 16 18 18 18 17 11 17 16 16 16 17 18 18 17 12 17 17 18 17 17 19 18 18

Average 17 17 16 16 18 18 18 17 SD 1 1 1 1 1 1 0 1

156##

TS – First Half of Exercise

TS – Second Half of Exercise




1 6 5 6 5 7 7 6 5 2 6 5 5 5 7 6 6 6 3 5 5 5 5 5 5 6 6 4 5 5 5 6 6 6 5 6 5 6 6 6 5 7 6 6 6 6 6 6 5 5 6 6 5 6 7 6 5 5 6 7 6 6 6 8 5 6 6 5 6 7 7 6 9 5 5 6 5 6 6 7 5 10 6 5 4 4 6 5 5 4 11 6 6 5 6 7 7 6 7 12 5 5 6 5 6 6 7 6

Average 6 5 5 5 6 6 6 6 SD 1 0 1 1 1 1 1 1




1 6 7 6 5 7 7 7 7 2 6 5 6 6 7 6 6 6 3 6 6 6 6 7 7 7 7 4 6 6 6 6 7 6 6 7 5 7 6 6 7 8 6 7 6 6 6 7 5 6 6 7 7 6 7 7 7 7 6 7 7 7 7 8 7 7 6 6 7 7 6 7 9 7 7 6 6 7 7 6 6 10 6 5 4 4 7 5 5 5 11 7 7 6 6 7 7 7 7 12 6 6 6 7 7 7 7 7

Average 6 6 6 6 7 7 7 7 SD 1 1 1 1 0 1 1 1

157##

Appendix C Study Two – Raw Data

158##


Peak Power / kg (W·kg-1)

1st Half 2nd Half Pre Acc Post Acc

+PC Post Acc Pre Acc Post Acc +PC Post Acc

1 1201 1160 1164 1158 1085 1151 2 1558 1448 1601 1440 1339 1559 3 1256 1365 1483 1307 1339 1413 4 1303 1272 1283 1260 1266 1296 5 1093 1168 1152 1100 1172 1149 6 1533 1724 1668 1586 1783 1704 7 1355 1393 1313 1295 1338 1290 8 1423 1278 1354 1333 1276 1296 9 1278 1248 1274 1243 1221 1331 10 1181 1223 1276 1256 1262 1287

Average 1318 1328 1357 1298 1308 1348 SD 151 168 174 137 185 172



1 15.83 15.47 15.42 15.27 14.47 15.25 2 19.64 17.98 20.13 18.15 16.63 19.62 3 17.87 19.28 21.20 18.59 18.91 20.20 4 19.73 19.46 19.64 19.08 19.36 19.85 5 15.98 16.90 16.68 16.08 16.96 16.64 6 16.19 18.30 17.84 16.75 18.93 18.22 7 18.29 19.26 17.55 17.48 18.50 17.25 8 18.38 16.54 17.48 17.22 16.52 16.73 9 17.24 16.88 17.13 16.76 16.51 17.89 10 15.39 15.99 16.61 16.37 16.49 16.76

Average 17.45 17.61 17.97 17.18 17.33 17.84 SD 1.58 1.45 1.80 1.18 1.54 1.63

159##

Mean Power (Watts)

Work (kJ)



1 880 866 904 884 831 911 2 1059 959 1050 1042 963 1062 3 879 969 1034 941 936 950 4 924 901 881 845 883 875 5 734 886 906 783 891 953 6 1198 1373 1296 1209 1408 1296 7 987 1057 986 957 982 965 8 1176 1076 1129 1138 1085 1094 9 927 921 958 919 925 1016 10 914 972 976 996 991 999

Average 968 998 1012 971 989 1012 SD 142 149 125 130 163 119



1 105.6 104.0 108.4 106.1 99.7 109.4 2 127.1 115.1 126.0 125.1 115.5 127.5 3 105.5 116.3 124.1 112.9 112.3 114.0 4 110.9 108.5 105.8 101.4 105.9 105.0 5 88.0 106.3 108.7 94.0 107.0 114.4 6 143.8 164.8 155.5 145.1 168.9 155.5 7 118.4 126.9 118.6 114.9 117.9 115.8 8 141.1 129.1 135.5 136.5 130.2 131.3 9 111.2 110.5 115.0 110.3 110.9 121.9 10 109.3 116.6 117.2 119.5 118.9 119.5

Average 116.1 119.8 121.5 116.6 118.7 121.4 SD 17.1 17.8 15.0 15.6 19.5 14.3

160##

Work / Kg (J·Kg-1)

Total Mean Power (Watts)



1 1392 1387 1436 1399 1330 1448 2 1603 1430 1586 1577 1435 1603 3 1501 1643 1774 1606 1586 1630 4 1679 1659 1619 1535 1620 1608 5 1287 1539 1574 1374 1548 1657 6 1518 1749 1662 1532 1794 1662 7 1599 1754 1585 1552 1630 1548 8 1823 1671 1750 1764 1686 1695 9 1500 1494 1545 1487 1499 1638 10 1424 1524 1526 1557 1554 1556

Average 1533 1585 1606 1538 1568 1605 SD 153 129 102 109 130 71

Pre Acc Post Acc +PC Post Acc

1 882 848 907 2 1051 961 1056 3 910 953 992 4 884 892 878 5 758 889 930 6 1204 1390 1296 7 972 1020 976 8 1157 1080 1112 9 923 923 987 10 955 981 988

Average 970 994 1012 SD 134 155 121

161##

Total Work (kJ)

Sweat Loss (kg)


1 211.7 203.6 217.8 2 252.2 230.6 253.5 3 218.4 228.6 238.1 4 212.3 214.4 210.7 5 182.0 213.3 223.1 6 288.9 333.7 311.0 7 233.3 244.7 234.3 8 277.6 259.3 266.8 9 221.5 221.4 236.8 10 228.7 235.5 236.7

Average 232.7 238.5 242.9 SD 32.2 37.2 29.0


1 1.3 1.6 1.4 2 1.4 1.5 1.2 3 1.2 1.6 1.2 4 1.1 1.2 1.0 5 1.1 1.4 1.1 6 2.3 2.6 2.4 7 2.1 3.1 2.0 8 1.7 1.8 1.5 9 1.0 1.4 1.3 10 1.0 1.5 1.1

Average 1.4 1.8 1.4 SD 0.5 0.6 0.5

162##

Sweat Sensitivity (ml·1°C rise in TC)

TC - Precooling Period (30-min; °C)


1 602 899 1019 2 873 1064 1033 3 763 864 763 4 780 875 726 5 801 1019 855 6 1241 971 1027 7 1181 2174 1600 8 870 1054 1007 9 451 740 891 10 485 668 760

Average 805 1033 968 SD 261 421 252

Start Finish Pre Acc Post Acc


1 37.9 37.7 37.4 37.4 37.0 36.9 2 37.3 37.2 37.3 37.1 36.7 37.1 3 37.3 36.6 37.2 37.2 36.5 37.2 4 37.4 37.4 37.3 37.2 37.2 37.1 5 37.1 37.7 37.2 37.0 37.2 37.0 6 37.3 37.3 37.0 37.1 36.5 36.7 7 37.1 37.5 37.2 36.6 37.2 37.0 8 36.8 36.9 36.8 36.6 36.5 36.6 9 37.6 37.5 37.2 36.8 37.1 37.0 10 37.0 37.1 36.7 36.7 36.5 36.7

Average 37.3 37.3 37.1 37.0 36.8 36.9 SD 0.3 0.4 0.2 0.3 0.3 0.2

163##

TC – First Half of Exercise (°C)

TC – Half-Time (10-min; °C)



1 37.6 37.0 37.0 39.3 38.8 37.9 2 37.3 36.5 36.8 38.7 37.8 37.7 3 37.1 36.3 37.2 38.5 38.0 38.3 4 37.2 37.1 37.1 38.6 38.2 38.4 5 37.1 37.0 36.9 38.4 38.5 38.1 6 37.0 36.6 36.5 38.1 38.6 38.6 7 36.6 37.0 37.1 37.8 38.4 38.1 8 36.7 36.4 36.4 38.3 37.7 37.6 9 36.6 37.0 36.9 38.6 38.4 38.3 10 36.5 36.6 36.6 38.1 38.3 37.8

Average 37.0 36.8 36.9 38.4 38.3 38.1 SD 0.4 0.3 0.3 0.4 0.3 0.3



1 39.3 38.8 37.9 39.2 38.0 37.8 2 38.7 37.8 37.7 38.5 37.7 37.7 3 38.5 38.0 38.3 38.2 37.8 38.4 4 38.6 38.2 38.4 38.3 38.3 38.2 5 38.4 38.5 38.1 38.1 37.9 37.9 6 38.1 38.6 38.6 38.3 38.4 38.3 7 37.8 38.4 38.1 37.7 38.2 37.9 8 38.3 37.7 37.6 38.1 37.5 37.6 9 38.6 38.4 38.3 38.7 38.3 37.8 10 38.1 38.3 37.8 38.0 38.0 38.0

Average 38.4 38.3 38.1 38.3 38.0 38.0 SD 0.4 0.3 0.3 0.4 0.3 0.3

164##

TC – Second Half of Exercise (°C)

Mean TSk – Precooling Period (30-min; °C)



1 39.2 38.0 37.8 39.6 38.7 38.3 2 38.5 37.7 37.7 38.8 38.1 38.3 3 38.2 37.8 38.4 38.8 38.3 38.8 4 38.3 38.3 38.2 38.6 38.6 38.5 5 38.1 37.9 37.9 38.4 38.6 38.3 6 38.3 38.4 38.3 38.9 39.2 39.0 7 37.7 38.2 37.9 38.4 38.6 38.3 8 38.1 37.5 37.6 38.5 38.2 38.1 9 38.7 38.3 37.8 39.1 39.0 38.5 10 38.0 38.0 38.0 38.7 38.8 38.5

Average 38.3 38.0 38.0 38.8 38.6 38.5 SD 0.4 0.3 0.3 0.4 0.3 0.3



1 33.4 32.2 31.8 34.1 32.8 33.2 2 33.2 31.3 31.2 33.3 32.5 33.3 3 33.2 32.1 33.2 33.6 32.7 33.6 4 31.0 32.4 32.5 32.5 32.0 33.2 5 30.3 31.4 31.2 32.7 31.7 31.9 6 32.3 31.5 32.1 32.7 32.0 31.8 7 32.0 31.9 31.7 33.3 32.1 32.1 8 32.7 31.7 31.6 32.8 31.4 31.3 9 31.7 31.6 31.1 33.0 31.6 31.4 10 30.0 31.7 30.3 30.5 31.5 30.8

Average 32.0 31.8 31.7 32.9 32.0 32.3 SD 1.2 0.4 0.8 0.9 0.5 1.0

165##

Mean TSk – First Half of Exercise (°C)

Mean TSk – Half-Time (10-min; °C)



1 35.9 34.8 35.2 37.5 36.6 36.4 2 35.3 34.3 34.3 37.4 36.2 36.3 3 35.0 34.3 35.0 36.3 36.8 36.9 4 34.7 34.2 34.6 36.9 36.9 37.3 5 34.6 34.5 34.6 36.2 36.3 36.6 6 34.4 34.2 34.6 36.3 36.3 36.5 7 36.0 34.7 35.3 36.5 36.2 35.9 8 34.8 33.9 34.1 36.8 35.7 35.5 9 35.0 33.7 34.4 36.6 36.9 36.5 10 33.2 33.8 33.7 36.5 36.4 36.4

Average 34.9 34.3 34.6 36.7 36.4 36.4 SD 0.8 0.4 0.5 0.5 0.4 0.5



1 37.5 36.6 36.4 37.0 35.8 36.1 2 37.4 36.2 36.3 36.7 35.8 36.2 3 36.3 36.8 36.9 36.0 36.6 36.5 4 36.9 36.9 37.3 36.2 36.3 36.3 5 36.2 36.3 36.6 35.6 35.0 35.6 6 36.3 36.3 36.5 35.8 35.3 36.0 7 36.5 36.2 35.9 35.6 35.1 35.2 8 36.8 35.7 35.5 35.8 35.2 35.0 9 36.6 36.9 36.5 36.0 36.1 36.0 10 36.5 36.4 36.4 36.4 35.8 35.7

Average 36.7 36.4 36.4 36.1 35.7 35.9 SD 0.5 0.4 0.5 0.5 0.6 0.5

166##

Mean TSk – Second Half of Exercise (°C)

HR – First Half of Exercise (bpm)



1 37.0 35.8 36.1 37.5 36.8 36.3 2 36.7 35.8 36.2 37.2 36.1 36.7 3 36.0 36.6 36.5 36.1 36.9 37.0 4 36.2 36.3 36.3 36.9 36.9 36.8 5 35.6 35.0 35.6 36.1 36.2 36.6 6 35.8 35.3 36.0 36.0 36.3 36.5 7 35.6 35.1 35.2 36.4 36.1 35.3 8 35.8 35.2 35.0 36.4 35.8 35.6 9 36.0 36.1 36.0 36.7 37.0 36.4 10 36.4 35.8 35.7 36.9 36.4 36.4

Average 36.1 35.7 35.9 36.6 36.5 36.4 SD 0.5 0.6 0.5 0.5 0.4 0.5



1 125 94 76 155 159 146 2 102 93 91 164 134 146 3 90 67 119 157 160 162 4 117 111 115 182 173 177 5 91 98 102 167 159 148 6 96 89 89 149 144 143 7 107 113 111 160 167 144 8 133 118 98 185 159 166 9 138 117 130 184 178 175 10 102 112 111 158 158 147

Average 110 101 104 166 159 155 SD 17 16 16 13 13 13

167##

HR – Second Half of Exercise (bpm)

RPE – First Half of Exercise



1 115 101 96 167 165 135 2 103 78 95 164 133 145 3 101 111 109 176 165 154 4 130 110 137 178 184 181 5 105 105 111 170 166 140 6 113 91 105 155 151 151 7 110 107 95 166 175 157 8 134 94 119 185 172 170 9 124 109 114 186 184 186 10 117 116 99 166 150 160

Average 115 102 108 171 165 158 SD 11 11 13 10 16 17

15th min 30th min Pre Acc Post Acc


1 12 13 13 16 16 13 2 13 13 14 15 15 15 3 15 12 15 15 15 17 4 14 14 15 16 16 17 5 13 9 10 15 14 13 6 12 9 9 15 10 10 7 13 13 12 14 15 13 8 12 11 11 15 12 11 9 13 13 12 14 14 14 10 12 13 12 13 15 13

Average 13 12 12 15 14 14 SD 1 2 2 1 2 2

168##

RPE – Second Half of Exercise

TS – First Half of Exercise



1 16 16 14 17 16 15 2 15 15 16 16 15 16 3 14 16 18 17 17 19 4 17 15 17 18 17 18 5 15 11 13 16 15 14 6 15 11 11 16 11 11 7 15 15 13 17 17 14 8 14 12 12 15 13 13 9 15 15 13 16 15 15 10 13 15 14 15 14 15

Average 15 14 14 16 15 15 SD 1 2 2 1 2 2



1 5 5 5 6 5 5 2 6 5 5 6 6 6 3 6 5 6 6 6 7 4 6 6 6 7 6 7 5 5 4 5 6 6 6 6 5 4 4 6 5 5 7 5 5 5 6 6 5 8 5 4 5 6 5 5 9 5 5 5 6 6 6 10 6 5 5 6 6 5

Average 5 5 5 6 6 6 SD 1 1 1 0 0 1

169##

TS – Second Half of Exercise

Acclimation – Sweat Loss (kg)



1 5 5 5 6 5 5 2 5 5 5 6 6 6 3 6 6 7 7 6 7 4 7 6 7 7 7 7 5 6 4 6 6 6 6 6 6 5 5 6 5 5 7 5 5 5 6 6 5 8 6 4 5 6 5 5 9 6 7 6 6 7 7 10 6 6 6 6 6 6

Average 6 5 6 6 6 6 SD 1 1 1 0 1 1

First Session

Last Session

1 0.61 0.71 2 0.60 0.96 3 0.60 0.75 4 0.53 0.75 5 0.65 1.00 6 1.40 1.75 7 1.35 2.05 8 0.85 1.10 9 0.50 0.75 10 0.500 1.00

Average 0.76 1.08 SD 0.34 0.46

170##

Acclimation – TC (°C)

Acclimation – Final HR (bpm)

First Session Last Session 0 min 32nd min 0 min 48th min 1 37.35 37.59 37.68 38.78 2 36.76 37.76 37.10 38.32 3 36.75 38.42 36.83 38.39 4 37.31 38.60 36.64 38.89 5 37.14 37.92 37.16 38.57 6 37.16 37.78 36.51 38.67 7 36.98 38.24 36.78 38.27 8 36.92 38.13 36.88 37.95 9 37.00 38.01 37.56 38.34 10 35.70 37.80 36.20 37.90

Average 37.04 38.05 37.02 38.46 SD 0.22 0.33 0.40 0.29

First Session

Last Session

1 168 167 2 143 154 3 182 176 4 198 195 5 174 192 6 165 160 7 183 182 8 183 179 9 176 185 10 170 168

Average 174 176 SD 15 13

171##

Acclimation – Final RPE

Acclimation – Final TS

First Session

Last Session

1 14 15 2 13 14 3 19 18 4 20 19 5 14 16 6 12 12 7 18 17 8 15 14 9 15 14 10 17 16

Average 16 16 SD 3 2

First Session

Last Session

1 5 5 2 5 6 3 7 7 4 7 7 5 6 6 6 6 6 7 7 7 8 6 5 9 6 7 10 7 6

Average 6 6 SD 1 1

172##

Appendix D Study Three – Raw Data

173##

Quarter Sprint Times (s)

First Sprint Times (s)

PC CONT 1 2 3 4 1 2 3 4 1 3.774 4.081 3.959 3.866 3.513 3.619 3.625 3.493 2 3.310 3.249 3.248 3.241 3.376 3.135 3.166 3.101 3 3.511 3.522 3.321 3.381 4.079 3.605 3.460 3.414 4 3.670 3.650 3.635 3.728 3.867 3.724 3.655 3.548 5 3.866 4.050 4.085 4.064 3.929 4.410 4.445 4.398 6 3.956 4.568 4.583 4.573 3.697 4.009 4.070 3.975 7 4.298 4.362 4.609 4.370 4.063 4.340 4.414 4.385 8 4.189 4.174 4.316 4.259 4.099 4.118 4.346 4.340 9 3.470 3.459 3.503 3.514 3.273 3.315 3.232 3.288 10 3.400 3.375 3.342 3.293 3.543 3.701 3.527 3.583

Average 3.744 3.849 3.860 3.829 3.744 3.797 3.794 3.753 SD 0.335 0.455 0.523 0.475 0.306 0.418 0.486 0.484

PC CONT 1 2 3 4 1 2 3 4 1 3.491 3.740 3.869 3.886 3.513 3.721 3.643 3.452 2 3.340 3.198 3.266 3.258 3.335 3.122 3.152 3.082 3 3.536 3.466 3.345 3.349 4.830 3.677 3.549 3.402 4 3.650 3.627 3.635 3.519 3.920 3.838 3.595 3.471 5 3.841 4.223 4.053 3.912 3.836 4.300 4.505 4.573 6 3.671 4.503 4.385 4.966 3.468 4.044 3.952 4.044 7 3.985 4.312 4.470 4.348 3.794 4.313 4.397 4.262 8 4.423 4.075 4.171 4.289 4.063 4.024 4.273 4.610 9 3.395 3.448 3.244 3.534 3.371 3.288 3.192 3.199 10 3.466 3.351 3.403 3.291 3.400 3.882 3.522 3.628

Average 3.680 3.794 3.784 3.835 3.753 3.821 3.778 3.772 SD 0.328 0.453 0.469 0.559 0.457 0.390 0.482 0.559

174##

Best Sprint Times (s)

Quarter Circuit Times (s)

PC CONT 1 2 3 4 1 2 3 4 1 3.491 3.740 3.869 3.842 3.493 3.526 3.643 3.347 2 3.238 3.167 3.152 3.208 3.106 3.102 3.147 3.082 3 3.456 3.434 3.287 3.311 3.596 3.563 3.354 3.402 4 3.630 3.608 3.609 3.519 3.804 3.650 3.595 3.471 5 3.782 3.933 4.036 3.912 3.836 4.300 4.395 4.131 6 3.671 4.303 4.385 4.032 3.468 3.917 3.952 3.905 7 3.985 4.256 4.470 4.348 3.794 4.264 4.370 4.262 8 3.965 3.971 4.171 4.239 4.063 4.024 4.273 4.182 9 3.395 3.324 3.244 3.294 3.212 3.266 3.190 3.199 10 3.354 3.351 3.282 3.276 3.400 3.587 3.505 3.527

Average 3.597 3.709 3.751 3.698 3.577 3.720 3.742 3.651 SD 0.255 0.398 0.501 0.429 0.300 0.400 0.477 0.432

PC CONT 1 2 3 4 1 2 3 4 1 44.75 46.91 46.14 46.60 44.72 45.45 47.52 46.04 2 49.28 49.41 49.90 49.91 46.43 47.59 49.24 50.50 3 47.13 44.94 44.64 44.60 43.00 43.28 45.38 44.40 4 46.44 42.43 39.64 37.41 44.80 43.24 40.41 39.03 5 46.07 46.34 46.20 47.10 45.53 52.04 51.53 50.57 6 50.43 52.91 53.32 51.72 48.06 49.52 48.66 48.19 7 40.14 39.76 40.29 38.07 39.23 40.51 40.04 39.83 8 43.30 43.06 44.51 44.15 43.85 44.05 44.16 43.89 9 40.34 42.56 41.55 41.44 38.45 38.68 35.74 39.46 10 38.77 39.44 39.94 39.74 39.68 39.60 40.20 39.69

Average 44.67 44.78 44.61 44.07 43.37 44.40 44.29 44.16 SD 3.97 4.24 4.51 4.88 3.25 4.34 5.06 4.57

175##

Overall Sprint Time (s)

Overall Circuit Time (s)

PC CONT 1 3.920 3.563 2 3.262 3.195 3 3.434 3.640 4 3.671 3.699 5 4.016 4.296 6 4.420 3.938 7 4.410 4.300 8 4.235 4.226 9 3.486 3.277 10 3.353 3.588

Average 3.821 3.772 SD 0.440 0.404

PC CONT 1 46.10 45.93 2 49.62 48.44 3 45.33 44.02 4 41.48 41.87 5 46.43 49.92 6 52.10 48.61 7 39.56 39.90 8 43.76 43.99 9 41.47 38.08 10 39.47 39.79

Average 44.53 44.05 SD 4.21 4.13

176##

Sweat Loss (kg)

TC – Precooling Period (30-min; °C)

PC CONT 1 1.90 1.85 2 2.22 2.42 3 1.98 2.28 4 2.30 1.85 5 2.38 2.18 6 2.53 2.06 7 2.05 1.98 8 2.03 1.91 9 2.40 1.65 10 1.85 1.40

Average 2.16 1.96 SD 0.23 0.30

PC CONT Start Finish Start Finish 1 36.8 36.2 36.6 36.61 2 36.9 36.9 36.9 37.02 3 36.7 36.6 37.1 37.05 4 37.0 36.7 36.7 36.51 5 37.4 37.2 37.6 37.52 6 37.7 37.2 37.4 37.32 7 37.5 37.0 37.1 36.91 8 37.1 36.4 37.2 36.55 9 37.2 36.8 36.8 36.68 10 37.1 36.3 37.2 37.03

Average 37.1 36.7 37.1 36.9 SD 0.3 0.4 0.3 0.3

177##

TC – End of each Quarter (°C)

Mean TSk – Precooling Period (°C)

PC CONT 1 2 3 4 1 3 3 4 1 37.9 37.8 37.5 37.6 38.5 38.3 38.1 38.2 2 38.0 37.8 37.8 38.4 38.9 39.0 38.3 38.5 3 38.4 38.9 38.7 38.6 38.1 39.1 38.9 39.1 4 37.8 38.6 38.3 38.5 37.8 38.2 38.1 38.3 5 38.7 38.8 39.0 38.6 38.5 39.0 38.7 38.8 6 38.5 38.9 38.8 38.9 38.8 39.0 38.7 39.0 7 38.8 39.6 39.5 39.7 38.6 39.4 39.1 39.1 8 38.2 38.9 38.7 38.7 38.3 38.5 38.5 38.1 9 38.6 39.3 39.0 39.0 38.5 38.7 38.7 38.8 10 37.7 38.4 37.5 38.1 38.1 38.8 38.5 38.6

Average 38.2 38.7 38.5 38.6 38.4 38.8 38.6 38.6 SD 0.4 0.6 0.7 0.6 0.3 0.4 0.3 0.4

PC CONT Start Finish Start Finish 1 31.1 31.2 31.3 32.7 2 30.1 31.6 31.5 32.9 3 30.4 32.2 30.6 30.9 4 30.1 31.3 29.8 31.6 5 32.2 32.2 32.0 32.9 6 32.0 32.9 31.1 32.0 7 30.7 31.9 29.9 31.2 8 31.8 32.2 30.2 31.1 9 31.0 31.3 29.5 31.8

Average 31.0 31.9 30.7 31.9 SD 0.8 0.6 0.9 0.8

178##

Mean TSk – End of each Quarter (°C)

HR – End of each Quarter (bpm)

PC CONT 1 2 3 4 1 3 3 4 1 32.9 32.9 32.9 32.9 34.9 34.8 35.2 35.4 2 33.7 33.5 33.6 32.9 35.3 35.4 35.9 36.2 3 33.1 33.0 31.6 32.0 34.9 35.8 34.7 34.9 4 34.5 33.8 33.9 33.9 33.3 32.6 31.2 31.8 5 35.5 35.0 34.8 34.7 37.3 37.1 36.4 36.6 6 34.6 34.8 34.2 34.0 34.7 34.5 33.9 33.8 7 31.3 31.3 32.0 32.0 30.3 30.7 30.7 30.5 8 35.3 35.6 34.5 33.2 32.8 31.7 30.2 30.5 9 31.9 31.1 30.2 30.4 30.1 28.4 27.4 27.1

Average 33.7 33.4 33.1 32.9 33.7 33.4 32.9 33.0 SD 1.5 1.6 1.5 1.3 2.4 2.8 3.1 3.2

PC CONT 1 2 3 4 1 3 3 4 1 143 136 137 144 150 147 147 156 2 154 154 150 149 130 169 165 155 3 175 170 175 173 174 177 170 186 4 154 159 164 169 140 148 152 163 5 168 169 156 163 176 151 174 184 6 178 179 181 186 174 175 170 176 7 169 175 183 189 177 179 180 185 8 167 175 167 172 163 160 160 163 9 180 174 155 168 180 171 168 164 10 195 195 195 197 196 195 195 178

Average 168 169 166 171 166 167 168 171 SD 15 16 18 17 20 16 14 12

179##

RPE – End of each Quarter

TS – End of each Quarter

PC CONT 1 2 3 4 1 3 3 4 1 14 15 16 16 15 16 17 17 2 13 15 16 16 14 16 16 16 3 15 16 17 17 16 17 17 18 4 11 13 15 17 14 15 16 17 5 13 14 16 16 15 17 18 17 6 12 15 17 16 11 13 13 15 7 16 19 18 19 17 17 17 18 8 18 19 15 16 17 13 16 15 9 16 16 16 16 15 16 16 16 10 17 18 17 18 15 17 17 17

Average 15 16 16 17 15 16 16 17 SD 2 2 1 1 2 2 1 1

PC CONT 1 2 3 4 1 3 3 4 1 5 5 6 6 5 7 7 7 2 5 6 6 6 5 6 7 7 3 5 6 5 6 5 6 6 7 4 5 5 6 7 5 3 5 6 5 6 6 4 5 7 8 7 7 6 6 7 7 7 6 6 5 6 7 5 5 6 5 6 6 5 5 8 5 5 5 5 5 5 5 5 9 6 6 6 6 6 6 6 6 10 6 6 6 6 5 6 6 6

Average 5 6 6 6 6 6 6 6 SD 1 1 1 1 1 1 1 1

EFFECT OF PRECOOLING AND ACCLIMATION ON REPEAT … · 2" " Peer-Reviewed Conference Proceedings...

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