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

di Prampero PE, Salvadego D, Fusi S, Grassi B. A simple method for assessing the energy cost of running during incremental tests. J Appl Physiol 107: 1068-1075, 2009. First published August 6, 2009; doi:10.1152/japplphysiol.00063.2009.-The energy cost of running (Cr) is classically determined from steady-state oxygen consumption (VO(2)) 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 VO(2max) and related parameters as follows. Assume that the running speed is increased by a constant amount (Delta v) at regular short intervals (T) and that, during each intensity transient below the gas exchange threshold, VO(2) increases exponentially, without time delay, toward the steady state. If VO(2) is averaged over homologous times within each speed step, neglecting the initial 10 s, the VO(2) 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 VO(2) 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 Delta v and T were constant, the relationship between VO(2) 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 (R(2) 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 O(2)/(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 O(2)/(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.