) amounted to 91.9±20.5 (peak) and 61.0±4.7 (mean).

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The energy cost of running (Cr) is classically determined from steady-state oxygen consumption (Vo2) 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 (Deltav) at regular short intervals (T) and that, during each intensity transient below the gas exchange threshold, Vo2 increases exponentially, without time delay, toward the steady state. If Vo2 is averaged over homologous times within each speed step, neglecting the initial 10 s, the Vo2 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 Vo2 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 Deltav and T were constant, the relationship between Vo2 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 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 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.

The purpose of this study was to investigate the effects of a 120 km desert running race (5 stages over 4 days) on the main physiologic parameters related to the individual aerobic work capacity. Incremental treadmill tests were carried out on 7 recreational long-distance runners (age: 50.4±11.8 years; body mass: 76.0±8.5 kg; mean±SD) before and 3-5 days after the competition. Maximal oxygen consumption (V O 2max ), ventilatory threshold and heart rate were obtained by standard methods; the mean energy cost of running (Cr) above resting was calculated during the same protocol from the slope of the oxygen consumption versus running speed. After the race, the subjects exhibited significant (p<0.05) reductions only in VO 2max (averaging 7%; from 46.7±5.1 to 43.2±4.4 ml ⋅ kg -1 ⋅ min -1 ) and in maximal heart rate (averaging 3%; from 172.4±14.1 to 166.7±14.5 beats ⋅ min -1 ). Knowledge of Cr (3.78±0.31 J ⋅ kg -1 ⋅ m -1 and 3.74±0.48 J ⋅ kg -1 ⋅ m -1 , before and after the race respectively) allowed us to estimate the overall daily energy requirement, about 20 850 kJ. VO 2max and the maximal heart rate seem to be the main variables affected by prolonged strenuous runs followed by insufficient rest periods.