Reply to Comments from P. M. Smith and M. J. Price

 

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The purpose of the present study was to compare the responses of physiological parameters when the crank rates were chosen spontaneously or set at ± 10 % of the freely chosen rate during two upper body exercises in well trained kayakers: a submaximal test in which intensities ranged from 50 to 80 % of maximal power (MP) and a supramaximal test where power output was set at 110 and 120 % of MP.

For the submaximal test the net energy expenditure (EE) was calculated. The estimation of net energy expenditure was based on measurement of whole-body oxygen consumption (V˙O₂ measured during exercise minus V˙O₂ measured during rest) and its caloric equivalent. Resting V˙O₂ was measured prior to exercise as the subjects sat quietly on the cycle ergometer, and one fixed mean value of resting V˙O₂ for all the calculations was used (0.446 ± 0.069 l × min^-1). The respiratory exchange ratio (R) was not used to estimate caloric output because R was sometimes higher than 1 during upper body exercise bouts, in the present study. A mean caloric equivalence of 4825 Kcal × L^-1 oxygen consumed was used to calculate the net energy expenditure during submaximal exercise.

i.e.: EE (watts) = ([[V˙O₂ - 0.446] l × min^-1 × 4825 Kcal × L^-1] × 4185 J)/60 s

We are in agreement with Smith and Price. A caloric equivalence of oxygen consumption equal to 5189 Kcal × L^-1 instead of 4825 Kcal × L^-1 could be used in this study. Indeed the respiratory exchange ratio reported during the different tests performed with upper body was sometimes equal to or higher than 1. However, given that the same caloric equivalence was used for all the subjects and measures, the results and particularly the conclusions can not be influenced.

Moreover, the results reported in Table [2] (p242) and concerning energy expenditure are inaccurate. In order to clarify the inaccuracies, an example has been taken.

EE (watts) = ([[V˙O₂ - V˙O_2REST] l × min^-1 × 4825 Kcal × L^-1] × 4185 J)/60 s

For T_SUB-10% at 50 % of MP:

EE = (2.1 - 0.446 l × min^-1) × 4825 Kcal × L^-1 = 7.98 Kcal × min^-1

When V˙O₂ was converted with the caloric equivalence of oxygen consumption, the unit × min^-1 was forgotten. So the values of EE were equal to one third of what they should be because subjects performed the exercise bout during 3 min.

→ EE = 7.98 Kcal/3 = 2.66 Kcal × min^-1 = 185 watts as reported in Table [2].

The new values are presented in Table [1] with the use of 4825 Kcal × L^-1 or 5189 Kcal × L^-1 as oxygen caloric equivalents. These values are different and lower than those reported by Smith and Price because in their calculations the mean values of V˙O₂ included the V˙O₂ at rest.

Using one mean value of V˙O₂ minus V˙O₂ at rest, recorded for example during T_SUB-10% at 50 % of maximal power and for one subject, the new reported values of EE were calculated as follows:

i.e. EE₄₈₂₅ = ([1.6 l × min^-1 × 4825 Kcal × L^-1] × 4185 J)/60 s = 538.5 watts

i.e. EE₅₁₈₉ = ([1.6 l × min^-1 × 5189 Kcal × L^-1] × 4185 J)/60 s = 579.1 watts

Gross (GE) and net (NE) efficiencies presented in Table [2] were calculated from equations presented in efficiency measurements section (p240). These data are valid because these parameters have been calculated from the oxygen consumption and power output values and not from the energy expenditure values.

New values of GE and NE are presented in Table [2] with either the use of 4825 Kcal × L^-1 or 5189 Kcal × L^-1 as oxygen caloric equivalents.

P. Pelayo

Faculté des Sciences du Sport et de l'EP Université de Lille 2

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