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Effects of caffeine on time trial performance insedentary menGeorge Laurence a , Karen Wallman a & Kym Guelfi aa The University of Western Australia, 35 Stirling Highway, Crawley, 6014, Perth, AustraliaVersion of record first published: 30 May 2012.

To cite this article: George Laurence , Karen Wallman & Kym Guelfi (2012): Effects of caffeine on time trial performance insedentary men, Journal of Sports Sciences, 30:12, 1235-1240

To link to this article: http://dx.doi.org/10.1080/02640414.2012.693620

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Effects of caffeine on time trial performance in sedentary men

GEORGE LAURENCE, KAREN WALLMAN, & KYM GUELFI

The University of Western Australia, 35 Stirling Highway, Crawley, Perth, 6014 Australia

(Accepted 10 May 2012)

AbstractIt is not known if ergogenic effects of caffeine ingestion in athletic groups occur in the sedentary. To investigate this, we useda counterbalanced, double-blind, crossover design to examine the effects of caffeine ingestion (6 mg � kg71 body-mass) onexercise performance, substrate utilisation and perceived exertion during 30 minutes of self-paced stationary cycling insedentary men. Participants performed two trials, one week apart, after ingestion of either caffeine or placebo one hourbefore exercise. Participants were instructed to cycle as quickly as they could during each trial. External work (J � kg71) aftercaffeine ingestion was greater than after placebo (P¼ 0.001, effect size [ES]¼ 0.3). Further, heart rate, oxygen uptake andenergy expenditure during exercise were greater after caffeine ingestion (P¼ 0.031, ES¼ 0.4; P¼ 0.009, ES¼ 0.3 andP¼ 0.018, ES¼ 0.3; respectively), whereas ratings of perceived exertion and respiratory exchange ratio values did not differbetween trials (P¼ 0.877, ES¼ 0.1; P¼ 0.760, ES¼ 0.1; respectively). The ability to do more exercise after caffeineingestion, without an accompanying increase in effort sensation, could motivate sedentary men to participate in exercisemore often and so reduce adverse effects of inactivity on health.

Keywords: ergogenic aid, performance, energy expenditure, weight management

Introduction

Caffeine is the most widely consumed psychoactive

substance in the world (Sokmen et al., 2008), with

daily consumptions reported to be between 70–76 mg

per person worldwide (Gilbert, 1981), with more

than 400 mg consumed daily in Sweden and Finland

(Debry, 1994). Caffeine is an easily accessible central

nervous system stimulant that has minimal negative

side-effects and high social acceptability (Fredholm,

Battig, Holmen, Nehlig, & Zvartau, 1999). These

factors, combined with the removal of caffeine from

the World Anti-Doping Agency’s list of banned

substances on 1 January, 2004, have made caffeine

popular among athletes competing in a range of

sports. As a result, numerous studies have investi-

gated caffeine’s effect on sporting performance and

have found it can prolong time to exhaustion at 70–

85% of maximal oxygen uptake (Graham, Hibbert, &

Sathasivam, 1998; Van Soeren & Graham, 1998),

lower ratings of perceived exertion during sub-

maximal exercise (Doherty & Smith, 2005) and

decrease time to complete set distances (Bridge &

Jones, 2006).

Although there is still controversy about exact

mechanisms responsible for the ergogenic effects of

caffeine, the most widely accepted is adenosine

receptor antagonism, which has been proposed to

result in a variety of effects, such as increased

neurotransmission and decreased perceptions of pain

and fatigue (Sinclair & Geiger, 2000).

While the effects of caffeine have been well studied

in an athletic population, there have been only two

published studies known to the authors to date that

have assessed the effects of caffeine consumption on

exercise performance in the sedentary (Engels &

Haymes, 1992; Wallman, Goh, & Guelfi, 2010).

Engels and Haymes (1992) investigated effects of

caffeine ingestion (5 mg � kg71 body mass) on

energy metabolism during treadmill walking at 30%

and 50% of maximal oxygen uptake in eight

sedentary men. These researchers reported higher

minute ventilation and an increase in blood free fatty

acids both before and after exercise. However the

ability of caffeine to improve exercise performance

was not assessed. To address this, a recent study by

Wallman et al. (2010) investigated effects of caffeine

ingestion (6 mg � kg71) on 15 minutes of stationary

cycling performed at 65% of maximal heart rate (220

minus age), as well as 10 minutes of self-paced

stationary cycling in 10 sedentary women. For the

self-paced cycling, there were no differences in total

Correspondence: Karen Wallman, The University of Western Australia, 35 Stirling Highway, Crawley, Perth, 6014 Australia.

E-mail: kwallman@cyllene.uwa.edu.au

Journal of Sports Sciences, August 2012; 30(12): 1235–1240

ISSN 0264-0414 print/ISSN 1466-447X online � 2012 Taylor & Francis

http://dx.doi.org/10.1080/02640414.2012.693620

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external work performed, or energy expenditure after

the ingestion of caffeine or placebo. However, a

potential limitation to this study was that 10 minutes

of self-paced exercise might not have been long

enough to provoke differences between the placebo

and caffeine trials.

Studies that assess effects of caffeine on exercise

performance in the sedentary are important because

caffeine ingestion might be of benefit by lowering the

perception of effort and pain during exercise, so

increasing external work performed and energy

expended during an exercise session. Of relevance,

a reduction in discomfort and effort associated with

exercise could lead to increased motivation in

establishing a regular pattern of exercise. This is

important, as low physical activity has been linked to

many adverse health effects, such as obesity and type

2 diabetes (Mokdad et al., 2003).

Consequently, the aim of this study was to

examine the effects of caffeine ingestion on exercise

performance, as well as several physiological mea-

sures, during 30 minutes of self-paced stationary

cycling in sedentary men. Based on the results found

in athletic groups, it was hypothesised that compared

with placebo, caffeine ingestion would result in more

exercise being performed during the 30-minute time

period and consequently an increase in oxygen

consumption and energy expenditure. It was also

hypothesised that accompanying ratings of perceived

exertion and respiratory exchange ratio would be

either lower or unchanged after caffeine ingestion.

Methods

Twelve sedentary (5 60 minutes of moderate

intensity exercise per week), non-smoking men who

were non-regular caffeine users (5 120 mg per day)

were recruited to this study (age 25.5+ 2.2 years,

stature 178.7+ 7.1 cm, body-mass 76.2+ 12.2 kg).

All participants were initially screened using a

medical screening questionnaire to ensure that they

were healthy and able to exercise. Additionally,

participants completed a questionnaire on their

normal daily caffeine consumption. Participants were

informed of all testing procedures to be undertaken

and written informed consent was acquired from

each volunteer. Research progressed in conformity

with the Statement on Human Experimentation by

the National Health and Medical Research Council

of Australia, after approval by The University of

Western Australia Research Ethics committee.

Participants were required to attend the exercise

physiology laboratory at the University of Western

Australia on three occasions: once for a practice

session and twice for the two experimental trials. All

three sessions involved 30 minutes of stationary

cycling at a self-selected intensity. A practice session

using the testing protocol was performed to ensure

that each participant understood how to pace

themselves during the subsequent experimental

trials. Participants were shown how to use all

equipment, while all testing procedures were ex-

plained in detail. During this visit, stature was

determined using a stadiometer (Seca, model 222,

Hamburg, Germany) to the nearest 0.1 cm, while

body-mass was determined (to the nearest 0.1 kg)

using Sauter scales (model ED3300, Ebingen, West

Germany).

One week after the practice session, participants

took part in the two experimental trials that were

conducted at the same time of day, approximately

one week apart, after the administration of either

caffeine or placebo in a double-blind, counter-

balanced, crossover design. Before each testing

session, participants were required to abstain both

from caffeine and exercise for 48 hours and fast for

12 hours before the commencement of exercise, with

only water and the given capsules (caffeine or

placebo) to be consumed in this time period. A list

of foods and beverages containing caffeine was

provided to each participant to ensure that they were

aware of the foods that they should avoid. Partici-

pants were also required to keep a food diary

documenting their diet 24 hours before the first

testing session and were asked to replicate this diet

before their second trial.

One hour before each trial, participants ingested

either 6 mg � kg71 body-mass of caffeine (No-Doz

Awakeners, Key Pharmaceuticals, NSW, Australia)

or the equivalent amount of placebo (Sugarine,

Boots Healthcare, NSW, Australia) contained in

opaque gelatine capsules. Both the participants and

the researcher were blinded to the allocation of either

caffeine or placebo. Of relevance, a 6-mg � kg71 dose

of caffeine has been well documented as having

ergogenic effects on endurance performance in

athletic groups (Doherty & Smith, 2004), and has

been used in a previous study that assessed time-trial

performance in a sedentary group without adverse

side-effects (Wallman et al., 2010). The exercise

component of all sessions began with an active

warm-up consisting of five minutes of stationary

cycling performed at low-to-moderate intensity

chosen by the participant. All exercise tests were

performed on a calibrated, front-access cycle erg-

ometer (Model EX-10, Repco, Australia). This

ergometer was interfaced with an IBM-compatible

computer system to allow for the collection of data

for the calculation of external work generated during

each flywheel revolution (Cyclemax, The University

of Western Australia, Perth, Australia). This erg-

ometer required participants to pedal against an air

resistance caused by rectangular vanes attached

perpendicular to the axis of rotation of the flywheel.

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The power output of the air-braked cycle ergometer

is proportional to the cube of the flywheel velocity.

An optical sensor monitored the velocity of the

flywheel at a sampling rate of 80 pulses per pedal

revolution.

After the warm-up, participants were required to

cycle at a self-selected intensity for 30 minutes.

Before the commencement of exercise, participants

were specifically told that ‘their aim was to cycle as

hard as they could for 30 minutes.’ As all participants

had previously performed a practice session where

they were required to cycle at a self-selected intensity

for 30 minutes, they were well aware of the demands

of the task. As participants had been asked to cycle as

quickly as they could during these trials, pedalling

rates differed according to the participants’ abilities.

During the 30-minute trials, encouragement was

given regularly to ensure that motivation and effort

were maintained by the participant and that the time

remaining to complete the exercise was always

known.

During the cycling exercise, participants were

required to breathe through a mouthpiece connected

to a computerised gas analysis system, comprising a

Morgan Ventilation Monitor (Morgan, Reinham,

Kent, UK), an oxygen analyser (Ametek SOV S-

3A11, Applied Electrochemistry, Ametek, Pitts-

burgh, PA) and a carbon dioxide analyser (Ametek

COV CD-3A, Applied Electrochemistry, Ametek,

Pittsburgh, PA), for the determination of oxygen

uptake and respiratory exchange ratio values. Repro-

ducibility of oxygen uptake during sub-maximal

exercise had been previously performed on this

system and resulted in a typical error of 0.075

(L � min71) and a coefficient of variation of 3.1%.

The oxygen and carbon dioxide sensors were

calibrated before and immediately after each test

using reference gases that had been gravimetrically

determined on a previous occasion. The Morgan

ventilometer was calibrated immediately before and

after each test according to the manufacturer’s

instructions. If the post-test calibration demonstrated

that ventilatory drift had occurred, then a correction

factor (based on the magnitude of the drift) was

applied to test data. Additionally, gas analyser drift

was assessed on the completion of each test. This

process consisted of the oxygen and carbon dioxide

sensors sampling the reference gases continuously for

a period of two to three minutes immediately after the

completion of the exercise test. The last minute of

data recorded during this process was averaged and

assessed for analyser drift. If analyser drift occurred

then a correction factor was determined based on the

reference gas values and applied to the exercise data

collected during the testing process.

Total external work completed during the 30

minutes of cycling was recorded using a customised

computer program interfaced with the cycle erg-

ometer (Cyclemax, School of Sports Science, Ex-

ercise and Health, UWA). In addition, heart rate

(Polar Electro Oy, Kempele, Finland) and ratings of

perceived exertion (Borg, 1982) were recorded every

5 minutes during exercise. Participants did not

receive any verbal or visual feedback about their

exercise performance. After the 30 minutes of

cycling, participants performed a slow self-paced

warm down for 5 minutes on the cycle ergometer

before leaving the laboratory.

Data analysis

Total external work (J � kg71), mean oxygen uptake,

total energy expenditure, final heart rate, rating of

perceived exertion and respiratory exertion ratio

values were compared between trials using one-way

repeated-measures analysis of variances (ANOVAs).

In addition, the 5-minute split data for each of these

variables were compared with fully within-groups

factorial ANOVAs. Statistical significance was ac-

cepted where P� 0.05. Where significant F values

were obtained, post-hoc paired samples t-tests were

then used to locate specific differences. Cohen’s d

effect sizes (ES) and thresholds (5 0.5, small; 0.5–

0.79, moderate;� 0.8, large: Cohen, 1988) were also

used to identify the magnitude of difference between

trial scores.

Results

All results are presented as mean + s. While there

was no interaction (P¼ 0.101), caffeine resulted in a

greater amount of external work being performed

during the 30 minutes of self-paced cycling than the

placebo trial (P¼ 0.001, ES¼ 0.3; Table I), with

external work performed during each 5-minute

interval being greater after caffeine ingestion.

Final rating-of-perceived-exertion scores for the

30-minute trial did not differ between the caffeine

and placebo trials (17+ 2.2 vs 17+ 2.4, P¼ 0.877,

ES¼ 0.1; Figure 1). Furthermore, there was no

interaction (P¼ 0.532) when the 5-minute interval

results were analysed. Conversely, caffeine ingestion

resulted in higher mean heart rate values over the

entire 30-minute cycling period than placebo

(168+ 19 bpm vs 161+ 17 bpm, P¼ 0.031,

ES¼ 0.4; Figure 2), however there was no interac-

tion (P¼ 0.697) when the five-minute split data was

analysed.

Mean oxygen uptake values (ml � kg71 � min71

and L � min71) during 30 minutes of self-paced

cycling were higher after caffeine ingestion than the

placebo trial (P¼ 0.009, ES¼ 0.3 and P¼ 0.019,

ES¼ 0.3, respectively; Table II). Similarly, mean

energy expenditure was higher than the placebo trial

Caffeine and exercise in sedentary males 1237

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(P¼ 0.018, ES¼ 0.3; Table II). There were no

interactions for oxygen uptake (L � min71 and

ml � kg71 � min71) and energy expenditure

(P¼ 0.369, P¼ 0.413, P¼ 0.263, respectively), how-

ever values for all these measures were higher after

caffeine ingestion for every 5-minute interval as-

sessed. In contrast, mean respiratory exchange ratio

values were similar between trials (P¼ 0.760,

ES¼ 0.1; Table II), with there being no interaction

(P¼ 0.472) when individual 5-minute values were

compared between trials.

Of importance, the only reported side-effect of

caffeine ingestion related to one participant feeling

marginally agitated. This sensation might have been

because this participant typically did not drink tea,

coffee or other caffeinated drinks.

Discussion

This study assessed the effects of caffeine ingestion

on various measures of exercise performance in 12

sedentary men during 30 minutes of stationary

cycling in which participants were instructed to

complete as much external work as they could in

the time allowed. Caffeine ingestion increased total

external work, mean oxygen uptake, total energy

expenditure and final heart rate values during self-

paced exercise. There was no increase in ratings of

perceived exertion and respiratory exchange ratios

associated with caffeine ingestion, despite the sig-

nificant increase in external work performed. This

study is the first to assess the effects of caffeine on

measures of exercise performance during 30 minutes

of self-paced exercise in sedentary men.

The performance improvements found in this

study are similar to those in previous studies using

well-trained athletes, which reported significantly

more external work completed in set times after

caffeine ingestion (Bridge & Jones, 2006; Collomp,

Ahmaidi, Chatard, Audran, & Prefaut, 1992; Ivy,

Costill, Fink, & Lower, 1979; Schneiker, Bishop,

Dawson, & Hackett, 2006). However, these findings

differ from those of the only previous study to

investigate the effect of caffeine on external work

performed in a sedentary population. Wallman et al.

(2010) reported no significant difference in total

external work performed in 10 sedentary women

during 10 minutes of stationary cycling, in which

participants were instructed to cycle as quickly as

they could. It was concluded that the exercise

Table I. Effect of caffeine on the total amount of external work performed during 30 minutes of self-paced stationary cycling. (N¼ 12).

Mean+ s Mean change

%+ 95%

Time Placebo Caffeine p P confidence limits

External Work Done (J � kg71) 5 min 514+113 578+ 132 12.4+ 8.2

10 min 550+119 601+ 147 9.3+ 5.6

15 min 569+117 594+ 156 4.2+ 6.0

20 min 572+128 598+ 153 4.5+ 4.5

25 min 591+133 604+ 115 2.2+ 5.5

30 min 668+188 670+ 146 0.4+ 6.6

Total 3465+718 3646+ 799 0.001 0.101 5.2+ 2.5

p indicates statistical difference between total values for each trial

P indicates interaction result

Figure 1. Effect of caffeine on ratings of perceived exertion (RPE)

at 5-minute intervals during 30 minutes of self-paced stationary

cycling. Values are meanþ s (N¼ 12).

Figure 2. Effect of caffeine on heart rate at 5-minute intervals

during 30 minutes of stationary cycling. Values are meanþ s

(N¼ 12).

1238 G. Laurence et al.

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duration might have been too short to provoke an

effect. Therefore, it is possible that the use of a 30-

minute protocol in the present study explains the

differences in outcome between the two studies.

Additionally, women might respond differently to

caffeine than men because of hormonal differences.

Further, the inclusion of 15 minutes of steady state

cycling (65% of maximum heart rate) in the study by

Wallman et al. (2010) may have confounded the

effects of caffeine on self-paced cycling performance

undertaken immediately after this exercise.

The current study also found that oxygen uptake

and energy expenditure increased after caffeine

ingestion during self-paced cycling, with a similar

increase for heart rate. These results most likely

reflect the corresponding significant improvement in

exercise performance (greater external work), con-

sidering that these variables are often used as

measures of intensity.

Despite the significant increases in total external

work, oxygen uptake and energy expenditure re-

ported in this study, rating of perceived exertion and

respiratory exchange ratio values were similar be-

tween trials. Caffeine has been reported to lower

perceived ratings of exertion and pain during

exercise (Doherty & Smith, 2005; Wiles, Coleman,

Tegerdine, & Swaine, 2006). In support of this, a

meta-analysis by Doherty and Smith (2004) con-

cluded that compared with placebo, caffeine inges-

tion resulted in a 6% reduction in rating of perceived

exertion values during sub-maximal exercise. Given

that exercise performance significantly increased in

the current study, without an accompanying change

in rating of perceived exertion values, caffeine has a

similar effect in sedentary men to that described by

Doherty and Smith (2004) in an athletic group. The

most likely mechanism responsible for this effect is

adenosine receptor antagonism that reduces the

effects of adenosine, resulting in reduced perceptions

of pain and fatigue and increased arousal and motor

function (Sinclair & Geiger, 2000).

The respiratory exchange ratio is known to rise in

response to increased exercise intensity as carbohy-

drate becomes favoured as a fuel source (McArdle,

Katch, & Katch, 1991). Notably, respiratory ex-

change ratios in the present study remained un-

changed during the caffeine trial despite increases in

exercise intensity, suggesting a preference for lipid

Table II. Effect of caffeine on oxygen uptake ( _V O2), energy expenditure and respiratory exchange ratio (RER) during 30 minutes of self-

paced cycling. N¼12.

Mean+ sMean change %+ 95%

Time Placebo Caffeine p P confidence limits

_VO2 (ml � kg � min71) 5 min 21.6+3.3 23.6+4.4 12.4+ 10.8

10 min 25.5+4.6 27.8+5.4 9.3+ 5.1

15 min 27.2+4.8 28.7+6.0 4.2+ 6.0

20 min 27.8+4.8 29.3+5.8 4.5+ 3.8

25 min 28.7+5.5 30.0+5.1 2.2+ 3.7

30 min 31.1+7.4 31.6+6.4 0.4+ 6.5

Mean 27.0+4.8 28.5+5.2 0.009 0.413 5.6+ 3.9_VO2 (L � min71) 5 min 1.64+0.47 1.81+0.33 10.06+ 9.24

10 min 1.94+0.50 2.12+0.41 9.47+ 6.16

15 min 2.07+0.49 2.18+0.44 5.52+ 6.11

20 min 2.12+0.48 2.23+0.45 5.23+ 4.48

25 min 2.18+0.45 2.28+0.50 4.19+ 6.02

30 min 2.35+0.50 2.39+0.58 1.48+ 6.45

Mean 2.05+0.46 2.17+0.43 0.019 0.369 5.67+ 4.51

Energy Expenditure

(kJ � min71)

5 min 34+07 37+10 10.2+ 9.8

10 min 41+09 45+11 9.9+ 6.5

15 min 43+09 46+11 5.4+ 6.4

20 min 44+09 46+10 5.1+ 4.9

25 min 46+10 47+09 3.9+ 5.7

30 min 49+12 50+11 1.3+ 6.3

Mean 43+09 45+10 0.018 0.263 5.6+ 4.5

RER 5 min 0.94+0.07 0.93+0.04 71.0+ 4.3

10 min 0.97+0.06 0.98+0.05 1.1+ 3.8

15 min 0.96+0.04 0.96+0.05 70.7+ 3.9

20 min 0.94+0.06 0.95+0.04 0.2+ 5.7

25 min 0.96+0.03 0.95+0.04 71.4+ 2.6

30 min 0.97+0.06 0.96+0.06 71.2+ 3.5

Mean 0.96+0.04 0.95+0.04 0.760 0.472 70.5+ 3.4

p indicates statistical difference between mean values for each trial

P indicates interaction result

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metabolism. While Engels and Haymes (1992) did

not find any difference in respiratory exchange ratio

values during steady-state walking in sedentary men

after a 5-mg � kg71 dose of caffeine compared with

placebo, they did report greater free fatty acid and

glycerol concentrations in the blood associated with

the caffeine trial. Further studies are needed to

explore the impact of caffeine on substrate utilisation

during exercise in the sedentary as increased free

fatty acid metabolism during self-paced exercise

might have positive implications for weight main-

tenance in this population.

Conclusion

This study demonstrated that a moderate dose of

caffeine improved cycling performance in sedentary

men. Additionally, caffeine increased oxygen uptake

and energy expenditure, without increasing ratings of

perceived exertion. This is an important finding

because despite performing more external work,

participants felt the exercise to be no more difficult

than that performed during the placebo trial. This

could motivate previously sedentary individuals to

become more active, which in turn has positive

effects on aerobic fitness and overall health. Future

studies could assess the effect of caffeine ingestion

over the course of an extended training programme

on physical fitness (maximal oxygen uptake), body

composition, motivation and exercise compliance in

a previously sedentary group. While the ingestion of

a 6-mg � kg71 daily dose of caffeine over an extended

period might be of concern to some individuals, it is

important to note that this dose has been associated

with minimal side-effects in athletes, as well as in a

sedentary group (Wallman et al., 2010). Further-

more, an extensive review by Fredholm et al. (1999)

of effects of caffeine ingestion on health concluded

that caffeine is not detrimental. Nonetheless, caffeine

ingestion can be addictive with a variety of symptoms

when withdrawal is attempted (Fredholm et al.,

1999). Consequently, prescription of its use during

exercise should be as a motivating tool during the

initial stages of exercise only, particularly as the

ergogenic effects of caffeine are partially diminished

in habitual users (Jacobson & Kulling, 1989).

Conflict of interests

None.

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