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A simple method for assessing the energy cost of running during incremental tests

Department of Biomedical Sciences and Technologies, University of Udine, Udine, Italy

Submitted 22 January 2009 ; accepted in final form 31 July 2009

The energy cost of running (Cr) is classically determined from steady-state oxygen consumption (O₂) at constant speed, divided by running speed. In the present study, Cr was determined during incremental treadmill tests in the course of the assessment of O_2max and related parameters as follows. Assume that the running speed is increased by a constant amount (v) at regular short intervals (T) and that, during each intensity transient below the gas exchange threshold, O₂ increases exponentially, without time delay, toward the steady state. If O₂ is averaged over homologous times within each speed step, neglecting the initial 10 s, the O₂ difference between corresponding time values becomes constant and equal to the difference between the appropriate steady states. Thus Cr was obtained from the ratio of the difference between the O₂ averages for any two homologous times, within subsequent periods, to the corresponding speed difference. Since in aerobic conditions, Cr on the treadmill is independent of the speed, and since v and T were constant, the relationship between O₂ and speed is described by straight lines, where the slope yields Cr above resting. This was indeed experimentally observed, the slopes of the linear regressions (R² range: 0.78 to 0.97 n = 9 to 16) within the three time windows being essentially equal. In six subjects, the grand-average of Cr amounted to 0.177 ± 0.011 ml O₂/(kg·m) [3.70 ± 0.23 J/(kg·m)]. This value is essentially equal to that obtained for the same subjects by applying the "classical" procedure [0.177 ± 0.015 ml O₂/(kg·m); 3.70 ± 0.31 J/(kg·m)], so confirming the validity of the incremental approach for assessing the energy cost of treadmill running.

treadmill running; incremental exercise; oxygen consumption; energy requirement