BMJ Open · For peer review only 2 Abstract Incremental shuttle-walking and treadmill-walking tests...

For peer review only

Pilot investigation of the oxygen demands and metabolic cost of incremental shuttle-walking and treadmill-walking

in patients with cardiovascular disease.

Journal: BMJ Open

Manuscript ID: bmjopen-2014-005216

Article Type: Research

Date Submitted by the Author: 10-Mar-2014

Complete List of Authors: Almodhy, Meshal; Universiity of Essex, Biological Sciences Beneke, Ralph; University of Marburg, Institute of Sports Medicine Cardosos, Fernando; Universiity of Essex, Biological Sciences

Sandercock, Gavin; University of Essex, Biological Sciences Taylor, Matthew; Universiity of Essex, Biological Sciences

<b>Primary Subject Heading</b>:

Cardiovascular medicine

Secondary Subject Heading: Sports and exercise medicine

Keywords: REHABILITATION MEDICINE, Myocardial infarction < CARDIOLOGY, Ischaemic heart disease < CARDIOLOGY

For peer review only - http://bmjopen.bmj.com/site/about/guidelines.xhtml

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Pilot investigation of the oxygen demands and metabolic cost of incremental shuttle-

walking and treadmill-walking in patients with cardiovascular disease.

Sandercock, GRH1

Almodhy, M1., Beneke, R

2., Cardoso, F

1., Taylor, MJ.

1

1Centre for Sports & Exercise Sciences, School of Biological Sciences, University of Essex

Colchester, UK CO4 3SQ

2Institut für Sportwissenschaft und Motologie Medezin, Philipps-Universität Marburg,

Germany.

Oxygen demands of shuttle-walking and treadmill walking

Key words: Cardiovascular disease; metabolism; cardiorespiratory fitness; pilot study

Word Count: 2288

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Abstract

Incremental shuttle-walking and treadmill-walking tests are both used to assess patients with

cardiovascular disease, but it remains unknown whether their energetic costs are comparable..

Patients completed the incremental shuttle walk test (on the ground) and the treadmill-shuttle test

in a randomised order with one week between trials. The 12 stage protocol starts at a walking

speed of 0.5 m.s-1 and increases by 0.17 m

.s-1 each minute. An identical incremental protocol was

programmed into the treadmill. During both tests a portable gas analyser was used to record

expired gas allowing for calculation of metabolic power and energy cost of walking

Average overall energy cost per meter was higher during treadmill-walking (3.22 ± 0.55 J.kg

.m

-1)

than during shuttle-walking (3.00 ± 0.41 J.kg

.m

-1). There were significant post hoc effects at 0.67

m.s-1 and 0.84 m

.s-1, where the energy cost of treadmill-walking was significantly higher than that

of shuttle-walking. This pattern was reversed at higher walking speeds of 1.52 m.s-1 and 1.69 m

.s-

1 where shuttle-walking had a greater energy cost per meter than treadmill-walking

These data demonstrate that the energetic demand of shuttle-walking is fundamentally different

from that of treadmill walking. We suggest that direct comparisons of results from these two

exercise modalities should be made with great caution

Objective

Incremental shuttle-walking and treadmill-walking tests are both used to assess patients with

cardiovascular disease, but it remains unknown whether their energetic costs are comparable..

Design

Patients completed the incremental shuttle walk test (on the ground) and the treadmill-shuttle test

in a randomised order with one week between trials. The 12 stage protocol starts at a walking

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speed of 0.5 m.s-1 and increases by 0.17 m

.s-1 each minute. An identical incremental protocol was

programmed into the treadmill. During both tests a portable gas analyser was used to record

expired gas allowing for calculation of metabolic power and energy cost of walking

Results

Average overall energy cost per meter was higher during treadmill-walking (3.22 ± 0.55 J.kg

.m

-1)

than during shuttle-walking (3.00 ± 0.41 J.kg

.m

-1). There were significant post hoc effects at 0.67

m.s-1 and 0.84 m

.s-1, where the energy cost of treadmill-walking was significantly higher than that

of shuttle-walking. This pattern was reversed at higher walking speeds of 1.52 m.s-1 and 1.69 m

.s-

1 where shuttle-walking had a greater energy cost per meter than treadmill-walking

Conclusion

These data demonstrate that the energetic demand of shuttle-walking is fundamentally different

from that of treadmill walking. We suggest that direct comparisons of results from these two

exercise modalities should be made with great caution.

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INTRODUCTION

Since its conception as an alternative to incremental treadmill testing of chronic obstructive

pulmonary disease (COPD) patients, the incremental shuttle-walking test (ISWT) has gained

popularity as an estimate of functional capacity in numerous clinical populations. The ISWT

appears adequately reliable[1], and is sensitive to changes in functional capacity[2 3]. However,

the ISWT’s validity as an estimate of cardiovascular fitness is only moderate[3] and the use of

the test to estimate oxygen consumption exercise capacity in Metabolic Equivalents (METs) is

questionable[4].

Woolf-May et al.2 found acceptable agreement between the energy cost of treadmill walking and

the ISWT in healthy volunteers using linear regression analyses, but the relationship was not

assessed in cardiac patients. The authors also reported that at walking speeds >1m·s-1, the ISWT

significantly underestimated the actual metabolic demands of shuttle-walking compared with

reference values calculated during treadmill walking in healthy adults. [5] The authors suggested

that cardiac patients may have higher energy demands than predicted, due to poorer walking

economy but made no such comparison of walking economy in cardiac patients between ISWT

and treadmill walking. They also made no calculations of economy during ISWT.

Treadmill and shuttle-walking tests are routinely used to assess cardiovascular disease patients

and we have previously reported discrete values for change in fitness measured using these tests.

[27] Prior to undertaking a proposed multicentre study to identify predictors of change in

cardiorespiratory fitness due to cardiac rehabilitation we performed the present pilot study. Our

aim was to determine whether the metabolic demands and the energy cost of the tests were

comparable in this patient group to the extent that we could combine data from these tests.

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METHODS

Participants (n=8; 7 males; 67±5.2 years: 86.6 ±10.1 kg) were stable cardiac patients attending

community-based rehabilitation. The study was approved by the Faculty ethics board and all

patients gave written, informed consent.

Equipment

The ISWT was performed on a non-slip floor using two cones placed 9 m apart and a portable

CD player. The treadmill test was performed on a motorised treadmill (Quaser, HP Cosmos,

Nussdorf,Germany). During both tests a portable gas analyser (K4b2 Mobile Breath by Breath

Metabolic System, COSMED Pulmonary Function Equipment, Rome, Italy) was used to record

expired gas. This was calibrated using gases of a known concentration and a syringe before each

test.

Protocol

Patients completed the ISWT and the treadmill test in a randomised order with one week

between trials. The ISWT was performed in accordance with national recommendations for

cardiac patients[6]. Briefly, the 12 stage protocol starts at a walking speed of 0.5 m·s-1 (1.12

mph) and increases by 0.17 m·s-1 (0.48 mph) each minute. An identical incremental protocol was

programmed into the treadmill. Patients were accustomed to treadmill walking and following a

brief period of familiarisation this test was also performed by each patient.

Calculation of metabolic power and energy cost of walking

Metabolic power was calculated via indirect calorimetry from and above rest,

caloric equivalent, and body mass by: metabolic power [W.kg

-1] = [ml

.kg

-1.s-1] . respiratory

&VO2 &VCO2

&VO2

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exchange ratio adjusted caloric equivalent [J.ml

-1]. [7 8] To analyse the relationship between

speed and metabolic power of walking the metabolic power was predicted as a quadratic function

of speed: metabolic power = a + b v². [7 9],[10],[11],[12-14]. The energy cost of walking per

metre distance was calculated by: energy cost [J.kg

-1.m

-1] = metabolic power [W

.kg

-1] . speed

-1

[m.s-1]. [7 8 15]

Statistical Analyses

Descriptive results are presented as mean ± SD. A test modality-by-walking speed analysis of

variance (ANOVA) with shuttle vs. treadmill walking as within-subjects factor and walking

speed as the between-subjects factor was performed. Significant interactions and main effects

were further analysed using one-way ANOVA and paired samples t-tests as appropriate. Non-

linear regression models were used to identify significant interrelationships between metabolic

power, energy cost per meter and walking speed, respectively. All analyses were completed

using SPSS v19.0 (SPSS Inc. and IBM Company. Chicago, IL) and statistical significance was

defined as p< 0.05.

RESULTS

Figure 1 shows the metabolic cost at each of seven stages completed by at least 7 patients. There

was a significant main effect for walking speed on oxygen uptake and a significant interaction

between treadmill-walking and shuttle-walking on the ground. Oxygen uptake was higher in

treadmill-walking than shuttle-walking at 0.67 and 0.84 m·s-1 (p < 0.05; n = 8) but the

significantly steeper increases in oxygen demand during shuttle-walking meant the opposite was

true at 1.69 m·s-1 (p < 0.05; n = 7).

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**Insert Fig 1 here**

Figure 2 shows the metabolic power of treadmill-walking and shuttle-walking. There was a main

effect for walking velocity on metabolic power during both treadmill and shuttle walking (p <

0.05). The different effects of walking modality on metabolic power were more pronounced if

power was predicted as a function of walking speed with power-treadmill walking = 2.028 +

1.115 v² and power-shuttle walking on the ground = 1.126 + 1.665 v² where 99 % of the variance

of power were explained by the quadratic curve fits in both modalities (both p < 0.001). The

difference in response to each modality was indicated by a significant interaction between

modality and speed. There were significantly higher metabolic power requirements for treadmill

walking at 0.67 m·s-1 and 0.84 m·s

-1 (p < 0.05; n = 8). Due to the steeper increase observed in

shuttle-walking the metabolic power was significantly higher at 1.52 and 1.69 m⋅s-1 (p < 0.05;

n=7) compared with treadmill-walking.


There were significant main effects for both modality and velocity in relative energy cost (per

metre) of walking again well described as a function of speed by the above approximated

parameters for both walking modalities (energy cost-treadmill walking = 2.028 / v + 1.115 v and

energy cost shuttle-walking on the ground = 1.126 / v + 1.665 v; both p < 0.001). Average

overall energy cost per meter (kg·m-1) was higher during treadmill-walking (3.22 ± 0.55 J·kg·m

-1)

than during shuttle-walking (3.00 ± 0.41 J·kg·m-1). There were significant post hoc effects at 0.67

m·s-1 and 0.84 m·s

-1 (n=8), where the energy cost of treadmill-walking was higher than that of

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shuttle-walking. Again, this pattern was reversed at higher walking speeds of 1.52 m·s-1 and 1.69

m·s-1 (n=7) where shuttle-walking had a greater energy cost per meter than treadmill-walking.


DISCUSSION

This is the first comparative investigation of the metabolic demands and energy cost per meter

walking of incremental treadmill-walking and shuttle-walking in cardiac rehabilitation patients.

The primary finding is that identical walking protocols performed on a treadmill or by shuttle-

walking are not comparable in terms of their oxygen requirements or energy cost. These findings

suggest that cardiorespiratory fitness measured using these different exercise testing modalities

should be compared with caution. Additionally, evaluating exercise capacity of patients with

cardiovascular disease using shuttle-walking by using MET values derived from treadmill-

walking may lead to potentially misleading results and poor clinical decision making.

The ISWT is the most used field test of exercise capacity in UK cardiac rehabilitation

centres[16] and is recommended nationally for this purpose[6]. Test results are used in patient

risk stratification[6], in exercise prescription and to assess the efficacy of exercise training during

outpatient rehabilitation. Current recommendations suggest patients be classed as high risk if

their exercise capacity is <5 METs. Failure to reach this criterion standard may lead to prevent

patients from entering community-based exercise training[17] or being readmitted to hospital-

based programmes.

The present data suggest that the ISWT stage deemed to be equivalent to 5 METs (level 7,

walking speed 1.52 m·s-1), actually has a significantly higher oxygen requirement, electing

greater metabolic power and energy cost per metre than walking at the equivalent speed on a

treadmill. These findings agree with previous data in cardiac patients[4] showing that oxygen

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uptake during shuttle-walking was higher than the value estimated using the American College

of Sports Medicine walking equations. We concur with these data suggesting that oxygen

requirements are higher in shuttle-walking than those estimated from treadmill walking from

level 7 (1.52 m·s-1) onwards.

This level and walking speed is of particular importance as it is the value deemed to indicate a

functional capacity of 5 METs a value used in risk stratification and triaging of patients to

hospital based rehabilitation programmes designed for ‘high risk’ patients or to low risk,

community based exercise. The higher potential ‘real’ energy cost may lead to false-positive

assessment of high risk leading to costly treatment option such as re-enrolment in outpatient

rehabilitation whereas there is good evidence that fitter patients can be successfully ‘fast tracked’

to community rehabilitation saving capacity and money to the health providers [18]. The ISWT

is also used to provide feedback to patients on gains in functional capacity by its application pre-

and post-rehabilitation. The steeper increases in energy requirements beyond 5 METs may make

it difficult to show small improvements in functional capacity reported as estimated MET.

In cardiac patients measured before outpatient rehabilitation, exercise capacity tends to be lower

when estimated from ISWT[19] than when patients are assessed using standard treadmill

protocols [20 21]. The patterns of change in walking energy cost per metre on the treadmill

show the expected pattern. Slow speeds are associated with higher cost per metre which

decreases as optimal (comfortable) walking speed approaches. Continuing to increase walking

speed above this pace requires a greater cost per metre. In contrast to this, the energy cost per

metre in shuttle-walking decreases only very little and only following the first (very slow)

walking pace in the initial stage. The energy cost then increases stage-by-stage throughout the

protocol. The cost is only consistent between treadmill and shuttle-walking between 1.2 - 1.4

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m·s-1 (close to comfortable walking speed) and the increase in energy requirements is much

greater in shuttle walking. When using the ISWT, patients’ cardiorespiratory fitness may need to

be estimated from maximal walking speed below (Stage 2, 0.84 m·s-1) or above (Stage 6, 1.51

m·s-1) the speeds at which treadmill and shuttle-walking agree. The differences in oxygen

consumption at these speeds are simply not comparable, and were large enough to produce

statistically significant differences in the very small numbers (n=8, n=9) used in this pilot

investigation. Given that our multicentre study involves comparisons of hundreds of patients we

plan to report cardiorespiratory fitness values separately according to test modality. The classical

description of the energy cost during locomotion is of a U-shaped relationship[22] – as speed

increases or decreases from the optimal (1.11-1.3 m.s-1 [22-24]) the energy cost of locomotion

increases. For the treadmill protocol our data support this relationship. At slow speeds (0.6-0.8

m.s-1) energy cost was greater than at optimal speeds (1.2-1.4 m

.s-1). As walking speed increased

(1.6-1.8 m.s-1) the energy cost again began to increase. This is comparable to Berryman et al[25]

who reported a similar energy cost pattern for their subjects (healthy elderly aged 68.9 ± 4.6 yrs)

when walking on a treadmill at speeds ranging from 0.67 – 1.56 m.s-1 and the optimal walking

speed was 1.33 m.s-1. A possible hypothesis for this increased energy cost at slower walking

speeds is the increased displacement of the Centre of Mass (CoM) in the mediolateral direction

which progressively reduces as walking speed increases[26]. Conversely the vertical

displacement of the CoM increases with speed, however reducing the vertical CoM displacement

is not a criterion for choosing a comfortable walking speed[26] but it appears that minimising the

mediolateral displacement is more important.

Furthermore our results also suggest that at lower speeds (0.5 – 0.84 m.s-1), the energy cost of

walking on a treadmill is greater than on the ground. This partly agrees with Berryman et al[25]

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who showed that there was greater energy cost of treadmill-walking compared to ground walking

at all the speeds they tested. The explanation for the increased energy cost for treadmill-walking

may be due to a greater need for stabilisation, via muscular contraction, than when walking on

the ground[25]. In addition to advising caution in comparison of test results, we also propose,

that walking tests and clinical cut-offs should be developed on the same testing modality (i.e.

treadmill or ground) as it is proposed to be used in clinic.

The ISWT was originally designed for patients with COPD who typically have much lower

functional capacity than patients referred for cardiac rehabilitation. The relatively higher energy

cost of the (very slow) initial walking speeds may, consequently, lead to undue fatigue. A

modified version of the test starting closer to ‘normal’ walking pace may elicit higher

performance in cardiac rehabilitation patients.

The overall increases in cardiorespiratory fitness in UK patients are low[19 27] compared with

international data[21]. It is of note that this estimate of UK patient gains was based largely on

data from the ISWT and that slightly larger gains reported by the one centre which used treadmill

testing to assess fitness. There appears to be smaller change in exercise capacity reported when

the ISWT is used[2 3 19 28-30] compared with treadmill testing[20]; although it should be noted

that there is a distinct paucity of UK studies using the latter protocol.

Study limitations and conclusions

While we highlight a potential weakness in the ISWT, it is still of clinical utility in measuring

functional capacity and in exercise prescription. Feedback to patients regarding changes in

distance walked during cardiac rehabilitation programs are a valuable motivational tool which is

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easily understood. In conclusion, we do not recommend the direction comparison of estimates of

cardiorespiratory fitness made using shuttle-walking and treadmill walking.

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Figure legends

Figure 1 The oxygen uptake of treadmill-walking (black line) and shuttle-walking (grey line) at

each of the seven stages; * = treadmill-walking different from shuttle walking, p < 0.05.

Figure 2 Metabolic power above rest (PN) of treadmill-walking (black line) and shuttle-walking

(grey line) at each of the seven stages, * = treadmill-walking different from shuttle walking, p <

0.05.

Figure 3 Energy cost above rest (CN) per meter distance of treadmill-walking (black line) and

shuttle-walking (grey line) at each of the seven stages, * = treadmill-walking different from

shuttle-walking, p < 0.05.

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Velocity (m s-1)

0.6 0.8 1.0 1.2 1.4 1.6 1.8

Oxygen Uptake (ml kg-1 min-1)

0

8

12

16

20

24

**

*

Figure 1

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Velocity (m s-1)

0.6 0.8 1.0 1.2 1.4 1.6 1.8

PN (W kg-1)

0

2

3

4

5

6

7

**

*

*

Figure 2

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Velocity (m s-1)

0.6 0.8 1.0 1.2 1.4 1.6 1.8

CN (J kg-1 m

-1)

0.0

2.4

2.7

3.0

3.3

3.6

3.9

4.2

4.5

*

*

*

*

Figure 3

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Journal: BMJ Open

Manuscript ID: bmjopen-2014-005216.R1


Date Submitted by the Author: 20-Jun-2014


Taylor, Matthew; Universiity of Essex, Biological Sciences Sandercock, Gavin; University of Essex, Biological Sciences






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1

Pilot investigation of the oxygen demands and metabolic cost of incremental shuttle-1

walking and treadmill-walking in patients with cardiovascular disease. 2

3


2., Cardoso, F

1., Taylor, MJD.

1 Sandercock, GRH

1 * 4

5

*Corresponding Author 6

1Centre for Sports & Exercise Sciences, School of Biological Sciences, University of Essex 7

Colchester, UK CO4 3SQ 8

2Institut für Sportwissenschaft und Motologie Medezin, Philipps-Universität Marburg, 9

Germany. 10

11

12

13

Oxygen demands of shuttle-walking and treadmill walking 14

Key words: Cardiovascular disease; metabolism; cardiorespiratory fitness; pilot study 15

Word Count: 2498 16

17

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Abstract 1

Objective: To determine if the metabolic cost of the incremental shuttle-walking test protocol is 2

the same as treadmill-walking. 3

Setting: Primary care (Community-based cardiac rehabilitation) 4

Participants: Eight caucasian cardiac rehabilitation patients (7 males) with a mean age 67±5.2 5

years. 6

Primary and secondary outcome measures: Oxygen consumption, metabolic power and 7

energy cost of walking during treadmill- and shuttle-walking performed in a balanced order with 8

one week between trials. 9

Results: Average overall energy cost per meter was higher during treadmill-walking (3.22 ± 10

0.55 J.kg

.m

-1) than during shuttle-walking (3.00 ± 0.41 J

.kg

.m

-1). There were significant post hoc 11

effects at 0.67 m.s

-1 and 0.84 m

.s

-1, where the energy cost of treadmill-walking was significantly 12

higher than that of shuttle-walking. This pattern was reversed at walking speeds of 1.52 m.s

-1 and 13

1.69 m.s

-1 where shuttle-walking had a greater energy cost per meter than treadmill-walking. At 14

all walking speeds, the energy cost of shuttle-walking was higher than predicted. 15

Conclusion: The energetic demands of shuttle-walking were fundamentally different from that 16

of treadmill walking and should not be directly compared. We also warn against estimating 17

cardiorespiratory fitness using predictions of energy cost during shuttle-walking via walking-18

speed equations. 19

20

21

22

23

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ARTICLE SUMMARY – Strengths and limitations of this study. 1

We provide the first direct comparison of the metabolic cost of shuttle-walking and treadmill-2

walking in cardiac patients. 3

Our data suggest metabolic demands of these exercise modalities appear fundamentally different 4

We suggest suggesting current methods to estimate metabolic cost of shuttle-walking are flawed 5

and warn against risk stratification of cardiac patients based on estimates of cardiorespiratory 6

fitness from the incremental shuttle-walking test. 7

The sample size limits generalisability particularly in female patients who are not represented at 8

higher walking speeds – a larger study of metabolic demands of the incremental shuttle-walking 9

test is warranted. 10

11

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INTRODUCTION 1

Since its conception as an alternative to incremental treadmill testing of chronic obstructive 2

pulmonary disease (COPD) patients, the incremental shuttle-walking test (ISWT) has gained 3

popularity as an estimate of functional capacity in numerous clinical populations. The ISWT 4

appears adequately reliable,[1] and is sensitive to changes in functional capacity.[2 3] However, 5

the ISWT’s validity as an estimate of cardiovascular fitness is only moderate[3] and the use of 6

the test to estimate oxygen consumption exercise capacity in Metabolic Equivalents (METs) is 7

questionable.[4] 8

Woolf-May et al. [4] reported acceptable agreement between the energy cost of treadmill 9

walking and the ISWT in healthy volunteers using linear regression analyses, but did not assess 10

this relationship in cardiac patients. The authors reported higher energy demands of shuttle-11

walking in cardiac patients compared with healthy controls. They suggested this may be due to 12

poorer walking economy in the former, they did not report walking economy during ISWT or 13

make comparisons between shuttle- and treadmill-walking economy. 14

Treadmill and shuttle-walking tests are routinely used to assess cardiovascular disease patients 15

and we have previously reported discrete values for change in fitness measured using these 16

tests.[5] Prior to undertaking a proposed multicentre study to identify predictors of change in 17

cardiorespiratory fitness due to cardiac rehabilitation we performed the present pilot study. We 18

examined whether there were differences in the metabolic demands and energy cost of treadmill 19

and shuttle walking in cardiac rehabilitation patients in order to determine whether we could 20

combine data from these tests in our multicentre study. We also compared metabolic demands of 21

the ISWT with predicted values[6] and published estimates [4 7]. 22

23

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METHODS 1

Participants (n=8; 7 males; 67±5.2 years: 86.6 ±10.1 kg) were stable cardiac patients attending 2

community-based rehabilitation. The study was approved by the Faculty ethics board at The 3

University of Essex. All patients gave written, informed consent. 4

Equipment 5

The ISWT was performed on a non-slip floor using two cones placed 9 m apart and a portable 6

CD player. The treadmill test was performed on a motorised treadmill (Quaser, HP Cosmos, 7

Nussdorf, Germany). During both tests a portable gas analyser (K4b2 Mobile Breath by Breath 8

Metabolic System, COSMED Pulmonary Function Equipment, Rome, Italy) was used to record 9

expired gas collected via a face and nose mask (Hans Rudolph, Shawnee, Kansas. US). This was 10

calibrated using gases of a known concentration and a syringe before each test. 11

Protocol 12

Patients completed the ISWT and the treadmill test in a balanced order with one week between 13

trials. The ISWT was performed in accordance with national recommendations for cardiac 14

patients[8]. Briefly, the 12 stage protocol starts at a walking speed of 0.5 m·s-1

(1.12 mph) and 15

increases by 0.17 m·s-1

(0.38 mph) each minute. An identical incremental protocol was 16

programmed into the treadmill. Patients were accustomed to treadmill walking but received a 17

brief period of familiarization in which they were required to walk without holding the treadmill 18

handles before the ISWT protocol was also performed. 19

Calculation of metabolic power and energy cost of walking 20

Metabolic power was calculated via indirect calorimetry from and above rest caloric 21

equivalent, and body mass: metabolic power [W.kg

-1] = [ml

.kg

-1.s

-1]

. respiratory exchange 22

ratio adjusted caloric equivalent [J.ml

-1]. [9 10] To analyse the relationship between speed and 23

&VO2 &VCO2

&VO2

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metabolic power of walking the metabolic power was predicted as a quadratic function of speed: 1

metabolic power = a + b v². [9 11-15]. The energy cost of walking per metre distance was 2

calculated by: energy cost [J.kg

-1.m


.kg

-1]

. speed

-1 [m

.s

-1]. [9 10 16] 3

4

Statistical Analyses 5

Descriptive results are presented as mean ± SD. A test modality-by-walking speed analysis of 6

variance (ANOVA) with shuttle vs. treadmill walking as within-subjects factor and walking 7

speed as the between-subjects factor was performed. Significant interactions and main effects 8

were further analysed using one-way ANOVA and paired samples t-tests as appropriate. Based 9

on the classical descriptions of walking energy cost [17-19], non-linear regression models were 10

chosen to identify significant interrelationships between metabolic power, energy cost per meter 11

and walking speed, respectively. All analyses were completed using SPSS v19.0 (SPSS Inc. and 12

IBM Company. Chicago, IL) and statistical significance was defined as p < 0.05. 13

14

RESULTS 15

Figure 1 shows the metabolic cost at each of seven stages completed by at least 7 patients. There 16

was a significant main effect for walking speed on oxygen uptake and a significant interaction 17

between treadmill-walking and shuttle-walking on the ground. Oxygen uptake was higher in 18

treadmill-walking than shuttle-walking at 0.67 m·s-1

and 0.84 m·s-1

(p < 0.05; n = 8) but the 19

significantly steeper increases in oxygen demand during shuttle-walking meant the opposite was 20

true at 1.69 m·s-1

(p < 0.05; n = 7). 21

**Insert Fig 1 here** 22

23

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Figure 2 shows the metabolic power of treadmill-walking and shuttle-walking. There was a main 1

effect for walking velocity on metabolic power during both treadmill and shuttle walking (p < 2

0.05). The different effects of walking modality on metabolic power were more pronounced if 3

power was predicted as a function of walking speed with power-treadmill walking = 2.028 + 4

1.115 v² and power-shuttle walking on the ground = 1.126 + 1.665 v² where 99 % of the variance 5

of power were explained by the quadratic curve fits in both modalities (both p < 0.001). The 6

difference in response to each modality was indicated by a significant interaction between 7

modality and speed. There were significantly higher metabolic power requirements for treadmill 8

walking at 0.67 m·s-1

and 0.84 m·s-1

(p < 0.05; n = 8). Due to the steeper increase observed in 9

shuttle-walking the metabolic power was significantly higher at 1.52 and 1.69 m⋅s-1

(p < 0.05; 10

n=7) compared with treadmill-walking. 11

12


There were significant main effects for both modality and velocity in relative energy cost (per 14

metre) of walking again well described as a function of speed by the above approximated 15

parameters for both walking modalities (energy cost-treadmill walking = 2.028 / v + 1.115 v and 16

energy cost shuttle-walking on the ground = 1.126 / v + 1.665 v; both p < 0.001). Average 17

overall energy cost per meter (kg·m-1

) was higher during treadmill-walking (3.22 ± 0.55 J·kg·m-

18

1) than during shuttle-walking (3.00 ± 0.41 J·kg·m

-1). There were significant post hoc effects at 19

0.67 m·s-1

and 0.84 m·s-1

(n=8), where the energy cost of treadmill-walking was higher than that 20

of shuttle-walking. Again, this pattern was reversed at higher walking speeds of 1.52 m·s-1

and 21

1.69 m·s-1

where shuttle-walking had a greater energy cost per meter (for the n=7 patients 22

achieving this level) than treadmill-walking. 23

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**Insert 1

2

Figure legends. 3

Figure legends 4

Figure 1 The oxygen uptake of treadmill-walking (black line) and shuttle-walking (grey line) at 5

each of the seven stages; * = treadmill-walking different from shuttle walking, p < 0.05. 6

7

Figure 2 Metabolic power above rest (PN) of treadmill-walking (black line) and shuttle-walking 8

(grey line) at each of the seven stages, * = treadmill-walking different from shuttle walking, p < 9

0.05. 10

11

Figure 3 Energy cost above rest (CN) per meter distance of treadmill-walking (black line) and 12

shuttle-walking (grey line) at each of the seven stages, * = treadmill-walking different from 13

shuttle-walking, p < 0.05. 14

15

Table 1. Predicted values, published data and measures of energy expenditure (METs) during 16

the incremental shuttle-walking test. 17

18

Legend: ISWT – Incremental Shuttle Walking Test, ACSM – American College of Sports 19

Medicine [6]. Published ISWT METs in cardiac patients from Woolf-May & Ferrett [4]. 20

*n=7 subjects only. Predicted METs calculated using formula for walking or jogging** from 21

ACSM [6] 22

3 here** 23

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DISCUSSION 1

This is the first comparative investigation of the metabolic demands and energy cost per meter 2

walking of incremental treadmill-walking and shuttle-walking in cardiac rehabilitation patients. 3

We found differences in the oxygen requirements and energy cost of shuttle and treadmill 4

walking large enough to suggest results from these exercise modalities should not be pooled in 5

any future analyses. 6

Economy and energy-requirements recorded during level 1 are difficult to interpret 7

as they are most affected by oxygen kinetics and because of long standing phases due to slow 8

walking speed and were excluded from our figures. The patterns of change in walking energy 9

cost per metre on the treadmill show the expected pattern. Slow speeds are associated with 10

higher cost per metre which decreases as optimal (comfortable) walking speed approaches. 11

Continuing to increase walking speed above this pace requires a greater cost per metre. In 12

contrast to this, the energy cost per metre in shuttle-walking decreases only very little and only 13

following the first (very slow) walking pace in the initial stage. The energy cost then increases 14

stage-by-stage throughout the protocol. The cost is only consistent between treadmill and shuttle-15

walking between 1.2 - 1.4 m·s-1

(close to comfortable walking speed) and the increase in energy 16

requirements is much greater in shuttle walking. Based on these pilot data, we intend to report 17

cardiorespiratory fitness values separately according to test modality and recommend this 18

practice to others. 19

20

The classical description of the energy cost during locomotion is of a U-shaped relationship[17] 21

– as speed increases or decreases from the optimal (1.11-1.3 m.s

-1 [17-19]) the energy cost of 22

locomotion increases. For the treadmill protocol our data support this relationship. At slow 23

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speeds (0.6-0.8 m.s

-1) energy cost was greater than at optimal speeds (1.2-1.4 m

.s

-1). As walking 1

speed increased (1.6-1.8 m.s

-1) the energy cost again began to increase. This is comparable to 2

Berryman et al[20] who reported a similar energy cost pattern for their subjects (healthy elderly 3

aged 68.9 ± 4.6 yrs) when walking on a treadmill at speeds ranging from 0.67 – 1.56 m.s

-1 and 4

the optimal walking speed was 1.33 m.s

-1. Furthermore our results also suggest that at lower 5

speeds (0.50-0.84 m.s

-1), the energy cost of walking on a treadmill is greater than on the ground. 6

Berryman et al[20] also showed that there was greater energy cost of treadmill-walking 7

compared to ground walking at all the speeds they tested. The explanation for the increased 8

energy cost for treadmill-walking may be due to a greater need for stabilisation, via muscular 9

contraction, than when walking on the ground[20]. 10

Conversely, the oxygen requirement of shuttle-walking are comparatively higher 11

from level 7 (1.52 m·s-1

) onwards than for treadmill walking at the same speed. The 12

requirements are also much higher (18 ml·kg-1

·min-1

) than the value predicted by the ACSM 13

walking speed equations [6] (12.6 ml·kg-1

·min-1

) which are used to estimate cardiorespiratory 14

fitness from ISWT performance[4]. In addition to advising caution in comparison of test results, 15

we also propose, that walking tests and clinical cut-offs should be developed on the same testing 16

modality (i.e. treadmill or ground) as it is proposed to be used in clinic. 17

Cardiac patients’ exercise capacity is commonly expressed as metabolic equivalents 18

(METs) and a comparison of MET values at all ISWT stages, those reported previously[4] and 19

the ACSM-predicted values are shown in table 1. It should be noted that the values predicted 20

using the ACSM walking equations by Woolf-May and Ferret[4] are incorrect. The MET values 21

they reported in cardiac patients are almost double the predicted values using the ACSM 22

equations and much higher than those reported presently. Woolf-May and Ferrett’s [4] MET 23

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values further appear anomalous as they are more than double that age-matched controls and 1

significantly higher than recently-reported values in cardiac patients during the ISWT [7]. These 2

latter values [7] do, however, broadly agree with those reported presently. 3

**Insert Table 1 here** 4

Current recommendations suggest patients be classed as high risk if their exercise capacity is <5 5

METs. Failure to reach this criterion standard may lead to prevent patients from entering 6

community-based rehabilitation [21]. Woolf-May and Ferret’s [4] suggestion that ISWT level 4 7

elicits a 5 MET energy cost in cardiac patients is inconsistent with more-recent data from 8

Meadows et al. [7] and those of the present study; both of which suggest the 5 MET threshold is 9

nearer Level 7 or 8. 10

11

Fitter patients can be successfully ‘fast tracked’ to community rehabilitation saving capacity and 12

money to the health providers [22]. However, where exactly in the ISWT protocol this threshold 13

occurs should be determined in a larger, more representative cohort of cardiac patients. 14

Beyond level 7 (1.52 m·s-1

, 3.8 mph) shuttle-walking incurred an additional extra energy cost 15

compared with treadmill walking which may make it difficult to show small improvements in 16

functional capacity if reported as estimated MET values. The exercise capacity of cardiac 17

patients measured before outpatient rehabilitation tends to be lower when estimated from ISWT 18

[23] than when standard treadmill protocols are used. [24 25] 19

20

Study limitations and conclusions 21

Along with sample size, this study is also limited due to including predominantly male patients 22

and indeed only male’s data at the highest walking speeds. The comparison of treadmill and 23

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shuttle-walking may have been improved by increasing treadmill gradient as is common-1

practice. We omitted to do this for comparability with previous work.[4 6] The accuracy of 2

energy costs calculations would also be improved by including a resting metabolic measure pre-3

exercise instead of an assumed value (4 ml.kg

-1.m

-1). 4

5

In conclusion, the ISWT may have clinical utility as measure of functional capacity to use in 6

exercise prescription and patient monitoring, but we question its use as an estimate of 7

cardiorespiratory fitness in cardiac patients. Importantly, previous estimates of the ISWT’s 8

energy cost appear erroneous and we warn against any clinical decision-making or risk 9

stratification based on the 5 MET threshold estimated from the ISWT. We recommend a more 10

accurate assessment of the ISWT’s metabolic requirements be performed in a larger, more 11

generalisable sample of cardiac patients. 12

13

14

15

16

17

18

19

20

21

Contributorship statement: Sandercock, Beneke and Taylor devised the experimental design. 22

Almodhy & Cardoso collected and analysed the data. Beneke and Taylor performed the 23

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metabolic modeling and advanced statistical analysis. Sandercock and Taylor drafted the 1

manuscript. Beneke, Almodhy and Cardoso revised the manuscript. All authors contributed to 2

the final preparation and drafting of the manuscript. 3

Competing interests None. 4

Funding. None. 5

Data sharing. No additional data available 6

7

8

9

10

11

12

13

14

15

16

17

18

References 19

20 21

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22. Robinson HJ, Samani NJ, Singh SJ. Can low risk cardiac patients be 'fast tracked' to Phase 11

IV community exercise schemes for cardiac rehabilitation? A randomised controlled trial. 12

Int J Cardiol 2011;146(2):159-63 doi: DOI 10.1016/j.ijcard.2009.06.027[published Online 13


23. Almodhy MY, Sandercock GR, Richards L. Changes in cardiorespiratory fitness in patients 15

receiving supervised outpatient cardiac rehabilitation either once or twice a week. Int J 16

Cardiol 2012 doi: 10.1016/j.ijcard.2012.06.071[published Online First: Epub Date]|. 17

24. Sharma A, McLeod AA. Cardiac rehabilitation after coronary artery bypass graft surgery: its 18

effect on ishcaemia, functional capacity and a mulitvariate index of prognosis. Coronary 19

Health Care 2001 5:189-93 20

25. Sandercock G, Hurtado V, Cardoso F. Changes in cardiorespiratory fitness in cardiac 21

rehabilitation patients: A meta-analysis. Int J Cardiol 2011 doi: 22

10.1016/j.ijcard.2011.11.068[published Online First: Epub Date]|. 23

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17

1

2

Table 1. 3 4 5 ISWT

Protocol

Level

Walking

Speed

(m·s-1

)

ACSM

Predicted

METs

Published

ISWT

METs

Recorded METs:

Treadmill Walking.

Mean (Range)

Recorded METs:

Shuttle Walking.

Mean (Range)

1 0.50 1.9 3.0 2.3 (1.6-2.6) 2.0 (1.6-2.2)

2 0.67 2.1 3.7 3.3 (2.8-4.0) 2.7 (2.5-3.1)

3 0.84 2.4 4.4 3.6 (3.1-4.3) 3.1 (2.8-3.3)

4 1.01 2.7 5.1 3.8 (3.2-4.6) 3.6 (3.2-3.8)

5 1.18 3.0 5.9 4.0 (3.6-4.7) 4.0 (3.6-4.6)

6 1.35 3.3 6.6 4.4 (4.3-5.9) 4.4 (4.0-4.9)

7 1.52 3.6 7.3 5.0 (4.6-6.2) 5.3 (4.8-5.6)

8 1.69 3.9 8.0 5.5 (5.0-6.7) 6.1 (5.7-6.6)

9 1.86 4.2 8.7 -- --

10 2.03 4.5/7.9** 9.4 -- --

11 2.20 4.8/8.5** 10.2 -- --

12 2.37 5.1/9.1** 10.9 -- --

6 7

8

9

10

11

12

13

14

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1

2

Figure legends. 3

Figure legends 4



7



0.05. 10

11




15



18




ACSM [6] 22

23

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1

2

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3


2., Cardoso, F

1., Taylor, MJD.

1 Sandercock, GRH

1 * 4

5





Germany. 10

11

12

13



Word Count: 2498 16

17

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2

Abstract 1


the same as treadmill-walking. 3



years. 6





0.55 J.kg

.m


.kg

.m


effects at 0.67 m.s

-1 and 0.84 m

.s

-1, where the energy cost of treadmill-walking was significantly 12

higher than that of shuttle-walking. This pattern was reversed at walking speeds of 1.52 m.s

-1 and 13

1.69 m.s

-1 where shuttle-walking had a greater energy cost per meter than treadmill-walking. At 14

all walking speeds, the energy cost of shuttle-walking was higher than predicted. 15


of treadmill walking and should not be directly compared. We also warn against estimating 17

cardiorespiratory fitness using predictions of energy cost during shuttle-walking via walking-18

speed equations. 19

20

21

22

23

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3






and warn against risk stratification of cardiac patients based on estimates of cardiorespiratory 6

fitness from the incremental shuttle-walking test. 7


higher walking speeds – a larger study of metabolic demands of the incremental shuttle-walking 9

test is warranted. 10

11

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4

INTRODUCTION 1







questionable.[4] 8













combine data from these tests in our multicentre study. We also compared metabolic demands of 21

the ISWT with predicted values[6] and published estimates [4 7]. 22

23

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5

METHODS 1


community-based rehabilitation. The study was approved by the Faculty ethics board at The 3

University of Essex. All patients gave written, informed consent. 4

Equipment 5







Protocol 12




(1.12 mph) and 15







Metabolic power was calculated via indirect calorimetry from and above rest caloric 21

equivalent, and body mass: metabolic power [W.kg

-1] = [ml

.kg

-1.s

-1]

. respiratory exchange 22

ratio adjusted caloric equivalent [J.ml

-1]. [9 10] To analyse the relationship between speed and 23

&VO2 &VCO2

&VO2

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6

metabolic power of walking the metabolic power was predicted as a quadratic function of speed: 1

metabolic power = a + b v². [9 11-15]. The energy cost of walking per metre distance was 2

calculated by: energy cost [J.kg

-1.m


.kg

-1]

. speed

-1 [m

.s

-1]. [9 10 16] 3

4










14

RESULTS 15

Figure 1 shows the metabolic cost at each of seven stages completed by at least 7 patients. There 16




and 0.84 m·s-1

(p < 0.05; n = 8) but the 19

significantly steeper increases in oxygen demand during shuttle-walking meant the opposite was 20

true at 1.69 m·s-1

(p < 0.05; n = 7). 21


23

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7





1.115 v² and power-shuttle walking on the ground = 1.126 + 1.665 v² where 99 % of the variance 5





and 0.84 m·s-1

(p < 0.05; n = 8). Due to the steeper increase observed in 9

shuttle-walking the metabolic power was significantly higher at 1.52 and 1.69 m⋅s-1

(p < 0.05; 10

n=7) compared with treadmill-walking. 11

12








18



0.67 m·s-1

and 0.84 m·s-1

(n=8), where the energy cost of treadmill-walking was higher than that 20

of shuttle-walking. Again, this pattern was reversed at higher walking speeds of 1.52 m·s-1

and 21

1.69 m·s-1

where shuttle-walking had a greater energy cost per meter (for the n=7 patients 22

achieving this level) than treadmill-walking. 23

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8


DISCUSSION 2







as they are most affected by oxygen kinetics and because of long standing phases due to slow 9

walking speed and were excluded from our figures. The patterns of change in walking energy 10

cost per metre on the treadmill show the expected pattern. Slow speeds are associated with 11

higher cost per metre which decreases as optimal (comfortable) walking speed approaches. 12

Continuing to increase walking speed above this pace requires a greater cost per metre. In 13

contrast to this, the energy cost per metre in shuttle-walking decreases only very little and only 14

following the first (very slow) walking pace in the initial stage. The energy cost then increases 15

stage-by-stage throughout the protocol. The cost is only consistent between treadmill and shuttle-16

walking between 1.2 - 1.4 m·s-1

(close to comfortable walking speed) and the increase in energy 17

requirements is much greater in shuttle walking. Based on these pilot data, we intend to report 18

cardiorespiratory fitness values separately according to test modality and recommend this 19

practice to others. 20

21




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9


speeds (0.6-0.8 m.s


.s

-1). As walking 2





-1 and 5



speeds (0.50-0.84 m.s










·min-1



·min-1


fitness from ISWT performance[4]. In addition to advising caution in comparison of test results, 16

we also propose, that walking tests and clinical cut-offs should be developed on the same testing 17

modality (i.e. treadmill or ground) as it is proposed to be used in clinic. 18


(METs) and a comparison of MET values at all ISWT stages, those reported previously[4] and 20

the ACSM-predicted values are shown in table 1. It should be noted that the values predicted 21

using the ACSM walking equations by Woolf-May and Ferret[4] are incorrect. The MET values 22

they reported in cardiac patients are almost double the predicted values using the ACSM 23

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10

equations and much higher than those reported presently. Woolf-May and Ferrett’s [4] MET 1

values further appear anomalous as they are more than double that age-matched controls and 2

significantly higher than recently-reported values in cardiac patients during the ISWT [7]. These 3

latter values [7] do, however, broadly agree with those reported presently. 4





elicits a 5 MET energy cost in cardiac patients is inconsistent with more-recent data from 9

Meadows et al. [7] and those of the present study; both of which suggest the 5 MET threshold is 10

nearer Level 7 or 8. 11

12










21


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11




practice. We omitted to do this for comparability with previous work.[4 6] The accuracy of 4


exercise instead of an assumed value (4 ml.kg

-1.m

-1). 6

7



cardiorespiratory fitness in cardiac patients. Importantly, previous estimates of the ISWT’s 10

energy cost appear erroneous and we warn against any clinical decision-making or risk 11

stratification based on the 5 MET threshold estimated from the ISWT. We recommend a more 12

accurate assessment of the ISWT’s metabolic requirements be performed in a larger, more 13

generalisable sample of cardiac patients. 14

15


Almodhy & Cardoso collected and analysed the data. Beneke and Taylor performed the 17

metabolic modeling and advanced statistical analysis. Sandercock and Taylor drafted the 18

manuscript. Beneke, Almodhy and Cardoso revised the manuscript. All authors contributed to 19

the final preparation and drafting of the manuscript. 20

21

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12


Funding. None. 2

Data sharing. Not applicable – pilot study data. 3

4

References 5

6 7



2010;96(3):222-7 10



e12 13





5. Sandercock GR, Cardoso F, Almodhy M, Pepera G. Cardiorespiratory fitness changes in 18

patients receiving comprehensive outpatient cardiac rehabilitation in the UK: a multicentre 19

study. Heart 2012 doi: 10.1136/heartjnl-2012-303055[published Online First: Epub Date]|. 20



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13











1960;15:1015-21 11



83 14






1974;33(4):293-306 20



1991;62(6):385-9 23

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14


Physiol 1986;61(4):1369-74 2



19. Mian OS, Thom JM, Ardigo LP, Narici MV, Minetti AE. Metabolic cost, mechanical work, 5

and efficiency during walking in young and older men. Acta Physiol (Oxf) 6

2006;186(2):127-39 doi: 10.1111/j.1748-1716.2006.01522.x[published Online First: Epub 7

Date]|. 8

20. Berryman N, Gayda M, Nigam A, Juneau M, Bherer L, Bosquet L. Comparison of the 9

metabolic energy cost of overground and treadmill walking in older adults. European journal 10

of applied physiology 2012;112(5):1613-20 doi: DOI 10.1007/s00421-011-2102-11

1[published Online First: Epub Date]|. 12











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15



Health Care 2001 5:189-93 3




7

8

9

10

11

Figure legends. 12

Figure legends 13



16



0.05. 19

20




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16

1



4




ACSM [6] 8

9

10

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90x70mm (300 x 300 DPI)

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Figure 2 Metabolic power above rest (PN) of treadmill-walking (black line) and shuttle-walking (grey line) at each of the seven stages, * = treadmill-walking different from shuttle walking, p < 0.05.

90x71mm (300 x 300 DPI)

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90x71mm (300 x 300 DPI)

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STARD checklist for reporting of studies of diagnostic accuracy

(version January 2003)

Section and Topic Item

#

On page #

TITLE/ABSTRACT/

KEYWORDS

1 Identify the article as a study of diagnostic accuracy (recommend MeSH

heading 'sensitivity and specificity').

2

INTRODUCTION 2 State the research questions or study aims, such as estimating diagnostic

accuracy or comparing accuracy between tests or across participant

groups.

3

METHODS

Participants 3 The study population: The inclusion and exclusion criteria, setting and

locations where data were collected.

5

4 Participant recruitment: Was recruitment based on presenting symptoms,

results from previous tests, or the fact that the participants had received

the index tests or the reference standard?

5

5 Participant sampling: Was the study population a consecutive series of

participants defined by the selection criteria in item 3 and 4? If not,

specify how participants were further selected.

5

6 Data collection: Was data collection planned before the index test and

reference standard were performed (prospective study) or after

(retrospective study)?

5

Test methods 7 The reference standard and its rationale. 5

8 Technical specifications of material and methods involved including how

and when measurements were taken, and/or cite references for index

tests and reference standard.

5

9 Definition of and rationale for the units, cut-offs and/or categories of the

results of the index tests and the reference standard.

5, 9, 10

10 The number, training and expertise of the persons executing and reading

the index tests and the reference standard.

5

11 Whether or not the readers of the index tests and reference standard

were blind (masked) to the results of the other test and describe any

other clinical information available to the readers.

5

Statistical methods 12 Methods for calculating or comparing measures of diagnostic accuracy,

and the statistical methods used to quantify uncertainty (e.g. 95%

confidence intervals).

6,7,10

13 Methods for calculating test reproducibility, if done. -

RESULTS

Participants 14 When study was performed, including beginning and end dates of

recruitment.

6

15 Clinical and demographic characteristics of the study population (at least

information on age, gender, spectrum of presenting symptoms).

6

16 The number of participants satisfying the criteria for inclusion who did or

did not undergo the index tests and/or the reference standard; describe

why participants failed to undergo either test (a flow diagram is strongly

recommended).

6

Test results 17 Time-interval between the index tests and the reference standard, and

any treatment administered in between.

5

18 Distribution of severity of disease (define criteria) in those with the target

condition; other diagnoses in participants without the target condition.

5,10

19 A cross tabulation of the results of the index tests (including

indeterminate and missing results) by the results of the reference

standard; for continuous results, the distribution of the test results by the

results of the reference standard.

Table 1,

P10

20 Any adverse events from performing the index tests or the reference

standard.

6

Estimates 21 Estimates of diagnostic accuracy and measures of statistical uncertainty

(e.g. 95% confidence intervals).

9,10,11

22 How indeterminate results, missing data and outliers of the index tests

were handled.

10

23 Estimates of variability of diagnostic accuracy between subgroups of

participants, readers or centers, if done.

-

24 Estimates of test reproducibility, if done. -

DISCUSSION 25 Discuss the clinical applicability of the study findings. 10,11,12

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Journal: BMJ Open

Manuscript ID: bmjopen-2014-005216.R2


Date Submitted by the Author: 09-Aug-2014


Taylor, Matthew; Universiity of Essex, Biological Sciences Sandercock, Gavin; University of Essex, Biological Sciences






BMJ Open on D



jopen.bmj.com

/B

MJ O


eptember 2014. D

ownloaded from



1



3


2., Cardoso, F

1., Taylor, MJD.

1 Sandercock, GRH

1 * 4

5





Germany. 10

11

12

13



Word Count: 2498 16

17

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2

Abstract 1


the same as treadmill-walking or predicted values walking speed equations. 3



years. 6





0.55 J.kg

.m


.kg

.m


effects at 0.67 m.s

-1 (p < 0.004) and 0.84 m

.s

-1 (p < 0.001), where the energy cost of treadmill-12

walking was significantly higher than that of shuttle-walking. This pattern was reversed at 13

walking speeds 1.52 m·s-1

(p < 0.042) and 1.69 m·s-1

(p < 0.007) where shuttle-walking had a 14

greater energy cost per meter than treadmill-walking. At all walking speeds, the energy cost of 15

shuttle-walking was higher than predicted using the American College of Sports Medicine 16

walking equations. 17


of treadmill walking and should not be directly compared. We warn against estimating the 19

metabolic cost of the incremental shuttle-walking test using the current walking-speed equations. 20

21

22

23

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3

1






We warn against risk stratification of cardiac patients based on estimated oxygen costs using the 7

American College of Sports Medicine walking equations during the incremental shuttle-walking 8

test. 9


higher walking speeds – a larger study of metabolic cost of the incremental shuttle-walking test 11

is warranted. 12

13

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4

INTRODUCTION 1







questionable.[4] 8













combine data from these tests in our multicentre study. We also compared metabolic cost of the 21

ISWT with values predicted from treadmill-walking equations[6] and published estimates [4 7]. 22

23

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5

METHODS 1


community-based rehabilitation following elective cardiac revascularization. The study was 3

approved by the Faculty ethics board at The University of Essex. All patients gave written, 4

informed consent. 5

Equipment 6







Protocol 13




(1.12 mph) and 16







We assumed a standard resting metabolic rate of 4 ml.kg

-1.min

-1 based on reference standards[9]. 22

Metabolic power was then calculated via indirect calorimetry from and above rest 23 &VO2 &VCO2

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6

and from body mass: metabolic power [W.kg

-1] = ( - rest) [ml

.kg

-1.s

-1]

. respiratory 1


-1]. [10 11] To analyse the relationship between 2

speed and metabolic power of walking the metabolic power was predicted as a quadratic function 3

of speed: metabolic power = a + b v² [10 12-16]. The energy cost of walking per metre distance 4

was calculated by: energy cost [J.kg

-1.m


.kg

-1]

. speed

-1 [m

.s

-1]. [10 11 17] 5

6










16

RESULTS 17

Figure 1 shows the oxygen uptake at each of seven stages completed by at least 7 patients. There 18




(p=0.006; n=8) and 0.84 m·s-1

(p=0.003; n 21

= 8) but the significantly steeper increases in oxygen demand during shuttle-walking meant the 22

opposite was true at 1.69 m·s-1

(p < 0.006; n = 7). 23

&VO2 &VO2

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7


2





1.115 v² and power-shuttle walking on the ground = 1.126 + 1.665 v² where 99% of the variance 7





(p < 0.004; n = 8) and 0.84 m·s-1

(p < 0.001; n = 8). Due to the steeper 11

increase observed in shuttle-walking the metabolic power was significantly higher at 1.52 m⋅s-1

12

(p=0.042; n=7) and 1.69 m⋅s-1

(p=0.007; n=7) compared with treadmill-walking. 13

14

**Insert Figure 2 here** 15







20



0.67 m·s-1

(p < 0.004; n=8) and 0.84 m·s-1

(p < 0.001; n=8), where the energy cost of treadmill-22

walking was higher than that of shuttle-walking. Again, this pattern was reversed at higher 23

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8

walking speeds of 1.52 m·s-1

(p < 0.042) and 1.69 m·s-1


greater energy cost per meter (for the n=7 patients achieving this level) than treadmill-walking. 2

3


DISCUSSION 5







as they are most affected by oxygen kinetics and patients’ unusually long stance phase during 12

their gait cycle at this very slow walking speed and were excluded from our figures. The change 13

in walking energy cost per metre on the treadmill show the expected pattern. Slow speeds are 14

associated with higher cost per metre which decreases as optimal (comfortable) walking speed 15

approaches. Continuing to increase walking speed above this pace requires a greater cost per 16

metre. In contrast to this, the energy cost per metre in shuttle-walking decreases only very little 17

and only following the first (very slow) walking pace in the initial stage. The energy cost then 18

increases stage-by-stage throughout the protocol. The cost is only consistent between treadmill 19

and shuttle-walking between 1.2 - 1.4 m·s-1

(close to comfortable walking speed) and the 20

increase in energy requirements is much greater in shuttle walking. Based on these pilot data, we 21

intend to report cardiorespiratory fitness values separately according to test modality and 22

recommend this practice to others. 23

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speeds (0.6-0.8 m.s


.s

-1). As walking 4





-1 and 7



speeds (0.50-0.84 m.s










·min-1



·min-1


fitness from ISWT performance[4]. In addition to differences in oxygen requirements of ground 18

and treadmill walking, shuttle-walking may have a higher cost due to repeated acceleration, 19

deceleration phases or the negotiation of turns[7]. We propose, therefore that any clinical cut-20

offs for walking tests should be developed using the same testing modality as that for which they 21

are proposed for use in (i.e. treadmill or ground). 22

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(METs). We calculated metabolic cost in METs (Gross [ml.kg

-1.min

-1] /3.5) and compared 2

MET values at all ISWT stages with those reported previously[4] and the ACSM-predicted 3

values (Table 1). It should be noted that the values predicted using the ACSM walking equations 4

by Woolf-May and Ferret[4] are incorrect. The MET values they reported in cardiac patients are 5

almost double the predicted values using the ACSM equations and much higher than those 6

reported presently. Woolf-May and Ferrett’s [4] MET values further appear anomalous as they 7

are more than double that age-matched controls and significantly higher than recently-reported 8

values in cardiac patients during the ISWT [7]. These latter values [7] do, however, broadly 9

agree with those reported presently. 10





elicits a 5 MET energy cost in cardiac patients is inconsistent with more-recent data from Woolf-15

May & Meadows [7] and those of the present study; both of which suggest the 5 MET threshold 16

is nearer Level 7 or 8. 17

18







&VO2

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4





practice. We omitted to do this for comparability with previous work. [4 6] The accuracy of 9


exercise instead of an assumed value of 4 ml.kg

-1.m

-1. [9] 11

12



cardiorespiratory fitness in cardiac patients. Importantly, the ACSM walking equations grossly 15

underestimate the actual energy cost of shuttle-walking and should not be used in research or 16

clinical practice. Our comparison using metabolic equivalents (METs) also reveals that some 17

published [4] estimates of the ISWT’s energy cost in cardiac patients appear erroneously high. 18

Given these two shortcomings, we strongly warn against clinical decision-making or patient risk 19

stratification based on achieving the 5 MET threshold estimated using the ISWT. We 20

recommend a more accurate assessment of the ISWT’s energy cost be performed in a larger, 21

more generalisable sample of cardiac patients. 22

23

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Almodhy & Cardoso collected and analysed the data. Beneke performed the metabolic modeling 2

and advanced statistical analysis. Sandercock and Taylor drafted the manuscript. Beneke, 3

Almodhy and Cardoso revised the manuscript. All authors contributed to the final preparation 4

and drafting of the manuscript. 5


Funding. None. 7


9

10

11

12

13

14

15

16

17

18

19

20

21

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References 1

2

3



2010;96(3):222-7 6



e12 9





5. Sandercock GR, Cardoso F, Almodhy M, et al. Cardiorespiratory fitness changes in patients 14

receiving comprehensive outpatient cardiac rehabilitation in the UK: a multicentre study. 15

Heart 2012 doi: 10.1136/heartjnl-2012-303055[published Online First: Epub Date]|. 16







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14

9. Wissenschaftliche Tabellen Geigy Teilband Körperflüssigkeiten. (Scientific Tables Geigy, 1

Volume Body Fluids.) In: Lentner C, ed. Giegy Scientific Tables. 7th ed. Basel: Ciba-Geigy, 2

1985:225-28. 3







1960;15:1015-21 10



83 13






1974;33(4):293-306 19



1991;62(6):385-9 22

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Physiol 1986;61(4):1369-74 2



20. Mian OS, Thom JM, Ardigo LP, et al. Metabolic cost, mechanical work, and efficiency 5

during walking in young and older men. Acta Physiol (Oxf) 2006;186(2):127-39 doi: 6

10.1111/j.1748-1716.2006.01522.x[published Online First: Epub Date]|. 7

21. Berryman N, Gayda M, Nigam A, et al. Comparison of the metabolic energy cost of 8

overground and treadmill walking in older adults. European journal of applied physiology 9

2012;112(5):1613-20 doi: DOI 10.1007/s00421-011-2102-1[published Online First: Epub 10

Date]|. 11











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Health Care 2001 5:189-93 3




7

8

9

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17

Table 1. 1 2 3 ISWT

Protocol

Level

Walking

Speed

(m·s-1

)

ACSM

Predicted

METs

Published

ISWT

METs

Recorded METs:

Treadmill Walking.

Mean (Range)

Recorded METs:

Shuttle Walking.

Mean (Range)

1 0.50 1.9 3.0 2.3 (1.6-2.6) 2.0 (1.6-2.2)

2 0.67 2.1 3.7 3.3 (2.8-4.0) 2.7 (2.5-3.1)

3 0.84 2.4 4.4 3.6 (3.1-4.3) 3.1 (2.8-3.3)

4 1.01 2.7 5.1 3.8 (3.2-4.6) 3.6 (3.2-3.8)

5 1.18 3.0 5.9 4.0 (3.6-4.7) 4.0 (3.6-4.6)

6 1.35 3.3 6.6 4.4 (4.3-5.9) 4.4 (4.0-4.9)

7 1.52 3.6 7.3 5.0 (4.6-6.2) 5.3 (4.8-5.6)

8 1.69 3.9 8.0 5.5 (5.0-6.7) 6.1 (5.7-6.6)

9 1.86 4.2 8.7 -- --

10 2.03 4.5/7.9** 9.4 -- --

11 2.20 4.8/8.5** 10.2 -- --

12 2.37 5.1/9.1** 10.9 -- --

4 5

6

7

8

9

10

11

12

13

14

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Figure legends 1



4



0.05. 7

8




12

Table 1. Comparison of predicted values, published values and measured metabolic cost (METs) 13

of the incremental shuttle-walking test. 14

15

Legend: MET – Metabolic Equivalent (calculated as: gross [ml.kg

-1.s

-1]/3.5) ISWT – 16

Incremental Shuttle Walking Test, ACSM – American College of Sports Medicine [6]. Published 17

ISWT METs in cardiac patients from Woolf-May & Ferrett [4]. 18


ACSM [6] 20

21

&VO2

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3


2., Cardoso, F

1., Taylor, MJD.

1 Sandercock, GRH

1 * 4

5





Germany. 10

11

12

13



Word Count: 2498 16

17

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2

Abstract 1


the same as treadmill-walking or predicted values walking speed equations. 3



years. 6





0.55 J.kg

.m


.kg

.m


effects at 0.67 m.s

-1 (p < 0.004) and 0.84 m

.s

-1 (p < 0.001), where the energy cost of treadmill-12

walking was significantly higher than that of shuttle-walking. This pattern was reversed at 13

walking speeds 1.52 m·s-1

(p < 0.042) and 1.69 m·s-1


greater energy cost per meter than treadmill-walking. At all walking speeds, the energy cost of 15

shuttle-walking was higher than predicted using the American College of Sports Medicine 16

walking equations. 17


of treadmill walking and should not be directly compared. We warn against estimating the 19

metabolic cost of the incremental shuttle-walking test using the current walking-speed equations. 20

21

22

23

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3

1






We warn against risk stratification of cardiac patients based on estimated oxygen costs using the 7

American College of Sports Medicine walking equations during the incremental shuttle-walking 8

test. 9


higher walking speeds – a larger study of metabolic cost of the incremental shuttle-walking test 11

is warranted. 12

13

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4

INTRODUCTION 1







questionable.[4] 8













combine data from these tests in our multicentre study. We also compared metabolic cost of the 21

ISWT with values predicted from treadmill-walking equations[6] and published estimates [4 7]. 22

23

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5

METHODS 1


community-based rehabilitation following elective cardiac revascularization. The study was 3

approved by the Faculty ethics board at The University of Essex. All patients gave written, 4

informed consent. 5

Equipment 6







Protocol 13




(1.12 mph) and 16







We assumed a standard resting metabolic rate of 4 ml.kg

-1.min

-1 based on reference standards[9]. 22

Metabolic power was then calculated via indirect calorimetry from and above rest 23 &VO2 &VCO2

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6

and from body mass: metabolic power [W.kg

-1] = ( - rest) [ml

.kg

-1.s

-1]

. respiratory 1


-1]. [10 11] To analyse the relationship between 2

speed and metabolic power of walking the metabolic power was predicted as a quadratic function 3

of speed: metabolic power = a + b v² [10 12-16]. The energy cost of walking per metre distance 4

was calculated by: energy cost [J.kg

-1.m


.kg

-1]

. speed

-1 [m

.s

-1]. [10 11 17] 5

6










16

RESULTS 17

Figure 1 shows the oxygen uptake at each of seven stages completed by at least 7 patients. There 18




(p=0.006; n=8) and 0.84 m·s-1

(p=0.003; n 21

= 8) but the significantly steeper increases in oxygen demand during shuttle-walking meant the 22

opposite was true at 1.69 m·s-1

(p < 0.006; n = 7). 23

&VO2 &VO2

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7


2





1.115 v² and power-shuttle walking on the ground = 1.126 + 1.665 v² where 99% of the variance 7





(p < 0.004; n = 8) and 0.84 m·s-1

(p < 0.001; n = 8). Due to the steeper 11

increase observed in shuttle-walking the metabolic power was significantly higher at 1.52 m⋅s-1

12

(p=0.042; n=7) and 1.69 m⋅s-1

(p=0.007; n=7) compared with treadmill-walking. 13

14








20



0.67 m·s-1

(p < 0.004; n=8) and 0.84 m·s-1

(p < 0.001; n=8), where the energy cost of treadmill-22

walking was higher than that of shuttle-walking. Again, this pattern was reversed at higher 23

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8

walking speeds of 1.52 m·s-1

(p < 0.042) and 1.69 m·s-1


greater energy cost per meter (for the n=7 patients achieving this level) than treadmill-walking. 2

3


DISCUSSION 5







as they are most affected by oxygen kinetics and patients’ unusually long stance phase during 12

their gait cycle at this very slow walking speed and were excluded from our figures. The change 13

in walking energy cost per metre on the treadmill show the expected pattern. Slow speeds are 14

associated with higher cost per metre which decreases as optimal (comfortable) walking speed 15

approaches. Continuing to increase walking speed above this pace requires a greater cost per 16

metre. In contrast to this, the energy cost per metre in shuttle-walking decreases only very little 17

and only following the first (very slow) walking pace in the initial stage. The energy cost then 18

increases stage-by-stage throughout the protocol. The cost is only consistent between treadmill 19

and shuttle-walking between 1.2 - 1.4 m·s-1

(close to comfortable walking speed) and the 20

increase in energy requirements is much greater in shuttle walking. Based on these pilot data, we 21

intend to report cardiorespiratory fitness values separately according to test modality and 22

recommend this practice to others. 23

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9





speeds (0.6-0.8 m.s


.s

-1). As walking 4





-1 and 7



speeds (0.50-0.84 m.s










·min-1



·min-1


fitness from ISWT performance[4]. In addition to differences in oxygen requirements of ground 18

and treadmill walking, shuttle-walking may have a higher cost due to repeated acceleration, 19

deceleration phases or the negotiation of turns[7]. We propose, therefore that any clinical cut-20

offs for walking tests should be developed using the same testing modality as that for which they 21

are proposed for use in (i.e. treadmill or ground). 22

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10


(METs). We calculated metabolic cost in METs (Gross [ml.kg

-1.min

-1] /3.5) and compared 2

MET values at all ISWT stages with those reported previously[4] and the ACSM-predicted 3

values (Table 1). It should be noted that the values predicted using the ACSM walking equations 4

by Woolf-May and Ferret[4] are incorrect. The MET values they reported in cardiac patients are 5

almost double the predicted values using the ACSM equations and much higher than those 6

reported presently. Woolf-May and Ferrett’s [4] MET values further appear anomalous as they 7

are more than double that age-matched controls and significantly higher than recently-reported 8

values in cardiac patients during the ISWT [7]. These latter values [7] do, however, broadly 9

agree with those reported presently. 10





elicits a 5 MET energy cost in cardiac patients is inconsistent with more-recent data from Woolf-15

May & Meadows [7] and those of the present study; both of which suggest the 5 MET threshold 16

is nearer Level 7 or 8. 17

18







&VO2

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11




4





practice. We omitted to do this for comparability with previous work. [4 6] The accuracy of 9


exercise instead of an assumed value of 4 ml.kg

-1.m

-1. [9] 11

12



cardiorespiratory fitness in cardiac patients. Importantly, the ACSM walking equations grossly 15

underestimate the actual energy cost of shuttle-walking and should not be used in research or 16

clinical practice. Our comparison using metabolic equivalents (METs) also reveals that some 17

published [4] estimates of the ISWT’s energy cost in cardiac patients appear erroneously high. 18

Given these two shortcomings, we strongly warn against clinical decision-making or patient risk 19

stratification based on achieving the 5 MET threshold estimated using the ISWT. We 20

recommend a more accurate assessment of the ISWT’s energy cost be performed in a larger, 21

more generalisable sample of cardiac patients. 22

23

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12


Almodhy & Cardoso collected and analysed the data. Beneke performed the metabolic modeling 2

and advanced statistical analysis. Sandercock and Taylor drafted the manuscript. Beneke, 3

Almodhy and Cardoso revised the manuscript. All authors contributed to the final preparation 4

and drafting of the manuscript. 5


Funding. None. 7


9

10

11

12

13

14

15

16

17

18

19

20

21

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13

References 1

2

3



2010;96(3):222-7 6



e12 9





5. Sandercock GR, Cardoso F, Almodhy M, Pepera G. Cardiorespiratory fitness changes in 14

patients receiving comprehensive outpatient cardiac rehabilitation in the UK: a multicentre 15

study. Heart 2012 doi: 10.1136/heartjnl-2012-303055[published Online First: Epub Date]|. 16







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14

9. Wissenschaftliche Tabellen Geigy Teilband Körperflüssigkeiten. (Scientific Tables Geigy, 1

Volume Body Fluids.) In: Lentner C, ed. Giegy Scientific Tables. 7th ed. Basel: Ciba-Geigy, 2

1985:225-28. 3







1960;15:1015-21 10



83 13






1974;33(4):293-306 19



1991;62(6):385-9 22

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15


Physiol 1986;61(4):1369-74 2



20. Mian OS, Thom JM, Ardigo LP, Narici MV, Minetti AE. Metabolic cost, mechanical work, 5

and efficiency during walking in young and older men. Acta Physiol (Oxf) 6

2006;186(2):127-39 doi: 10.1111/j.1748-1716.2006.01522.x[published Online First: Epub 7

Date]|. 8

21. Berryman N, Gayda M, Nigam A, Juneau M, Bherer L, Bosquet L. Comparison of the 9

metabolic energy cost of overground and treadmill walking in older adults. European journal 10

of applied physiology 2012;112(5):1613-20 doi: DOI 10.1007/s00421-011-2102-11

1[published Online First: Epub Date]|. 12











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16



Health Care 2001 5:189-93 3




7

8

9

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17

Table 1. 1 2 3 ISWT

Protocol

Level

Walking

Speed

(m·s-1

)

ACSM

Predicted

METs

Published

ISWT

METs

Recorded METs:

Treadmill Walking.

Mean (Range)

Recorded METs:

Shuttle Walking.

Mean (Range)

1 0.50 1.9 3.0 2.3 (1.6-2.6) 2.0 (1.6-2.2)

2 0.67 2.1 3.7 3.3 (2.8-4.0) 2.7 (2.5-3.1)

3 0.84 2.4 4.4 3.6 (3.1-4.3) 3.1 (2.8-3.3)

4 1.01 2.7 5.1 3.8 (3.2-4.6) 3.6 (3.2-3.8)

5 1.18 3.0 5.9 4.0 (3.6-4.7) 4.0 (3.6-4.6)

6 1.35 3.3 6.6 4.4 (4.3-5.9) 4.4 (4.0-4.9)

7 1.52 3.6 7.3 5.0 (4.6-6.2) 5.3 (4.8-5.6)

8 1.69 3.9 8.0 5.5 (5.0-6.7) 6.1 (5.7-6.6)

9 1.86 4.2 8.7 -- --

10 2.03 4.5/7.9** 9.4 -- --

11 2.20 4.8/8.5** 10.2 -- --

12 2.37 5.1/9.1** 10.9 -- --

4 5

6

7

8

9

10

11

12

13

14

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18

Figure legends 1



4



0.05. 7

8




12

Table 1. Comparison of predicted values, published values and measured metabolic cost (METs) 13

of the incremental shuttle-walking test. 14

15

Legend: MET – Metabolic Equivalent (calculated as: gross [ml.kg

-1.s

-1]/3.5) ISWT – 16

Incremental Shuttle Walking Test, ACSM – American College of Sports Medicine [6]. Published 17

ISWT METs in cardiac patients from Woolf-May & Ferrett [4]. 18


ACSM [6] 20

21

&VO2

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90x70mm (300 x 300 DPI)

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90x71mm (300 x 300 DPI)

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STARD checklist for reporting of studies of diagnostic accuracy

(version January 2003)

Section and Topic Item

#

On page #

TITLE/ABSTRACT/

KEYWORDS

1 Identify the article as a study of diagnostic accuracy (recommend MeSH

heading 'sensitivity and specificity').

2

INTRODUCTION 2 State the research questions or study aims, such as estimating diagnostic

accuracy or comparing accuracy between tests or across participant

groups.

3

METHODS

Participants 3 The study population: The inclusion and exclusion criteria, setting and

locations where data were collected.

5

4 Participant recruitment: Was recruitment based on presenting symptoms,

results from previous tests, or the fact that the participants had received

the index tests or the reference standard?

5

5 Participant sampling: Was the study population a consecutive series of

participants defined by the selection criteria in item 3 and 4? If not,

specify how participants were further selected.

5

6 Data collection: Was data collection planned before the index test and

reference standard were performed (prospective study) or after

(retrospective study)?

5

Test methods 7 The reference standard and its rationale. 5

8 Technical specifications of material and methods involved including how

and when measurements were taken, and/or cite references for index

tests and reference standard.

5

9 Definition of and rationale for the units, cut-offs and/or categories of the

results of the index tests and the reference standard.

5, 9, 10

10 The number, training and expertise of the persons executing and reading

the index tests and the reference standard.

5

11 Whether or not the readers of the index tests and reference standard

were blind (masked) to the results of the other test and describe any

other clinical information available to the readers.

5

Statistical methods 12 Methods for calculating or comparing measures of diagnostic accuracy,

and the statistical methods used to quantify uncertainty (e.g. 95%

confidence intervals).

6,7,10

13 Methods for calculating test reproducibility, if done. -

RESULTS

Participants 14 When study was performed, including beginning and end dates of

recruitment.

6

15 Clinical and demographic characteristics of the study population (at least

information on age, gender, spectrum of presenting symptoms).

6

16 The number of participants satisfying the criteria for inclusion who did or

did not undergo the index tests and/or the reference standard; describe

why participants failed to undergo either test (a flow diagram is strongly

recommended).

6

Test results 17 Time-interval between the index tests and the reference standard, and

any treatment administered in between.

5

18 Distribution of severity of disease (define criteria) in those with the target

condition; other diagnoses in participants without the target condition.

5,10

19 A cross tabulation of the results of the index tests (including

indeterminate and missing results) by the results of the reference

standard; for continuous results, the distribution of the test results by the

results of the reference standard.

Table 1,

P10

20 Any adverse events from performing the index tests or the reference

standard.

6

Estimates 21 Estimates of diagnostic accuracy and measures of statistical uncertainty

(e.g. 95% confidence intervals).

9,10,11

22 How indeterminate results, missing data and outliers of the index tests

were handled.

10

23 Estimates of variability of diagnostic accuracy between subgroups of

participants, readers or centers, if done.

-

24 Estimates of test reproducibility, if done. -

DISCUSSION 25 Discuss the clinical applicability of the study findings. 10,11,12

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BMJ Open · For peer review only 2 Abstract Incremental shuttle-walking and treadmill-walking tests...

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