Proceedings of The Physiological Society
University of Oxford (2011) Proc Physiol Soc 23, PC85
The decrease of FiO2 was not a limiting factor of endurance at VO2 max
H. Petot1, R. Meilland1, M. Landrain1, V. Billat1
1. UBIAE U902 INSERM, University d'Evry Val d'essone, Evry, France.
VO2max and endurance at VO2max are currently used as markers for trainning prescription and to evaluate the physical fitness and health. If the limiting factors of VO2max are well understood as is the effect of acute hypoxia, then the limiting factors of endurance at VO2max need to be clarified. Thus, the purpose of this study was to demonstrate that 1) hypoxia decrease the VO2max plateau amplitude but not the VO2max plateau duration 2) was caused by the fact that the first power elicited VO2max ( PVO2max) was decreased by hypoxia and consequnetly this decrease of power output in hypoxia allowed to maintain the same VO2max plateau duration than in normoxia. Ten subjects performed four cycling tests at three days interval: 1) Two incrementals tests in normoxia (IncN) ( FiO2 = 20.93 %) and in acute hypoxia (FiO2 = 14.5 %) to determine VO2max, the power at VO2max (PVO2max) and the lactate threshold (PLT) in both conditions 2) two time limit (tlim) at VO2max in both condition in witch the power was decreased just after the subject reached VO2max to determine the endurance at VO2max (tlim@VO2max). The result showed that tlim@VO2max were not significantly different between the two conditions ( 702.5 ± 572.5 s in N vs. 869.5 ± 782.5 s in H, p= 0.18) whereas VO2max decreased by 9.6 ± 5.6 % and PVO2max decreased by 17 % in hypoxia. tlim@VO2max in hypoxia was correlated with tlim@VO2max in normoxia (p = 0.0004 with r = 0.9). tlim@VO2max was correlated with the number of power waves during the plateau ( p = 0.007 with r = 0.78) but not with the delta VO2max ( p = 0.94), the delta PVO2max ( p=0.69) or the delta of oxygen blood desaturation ( p=0.58) between N and H. In conclusion, the study showed that the decrease of FiO2 was a limiting factor of the VO2max amplitude but not of the endurance at VO2max and that the endurance at VO2max in hypoxia depend on the power varaition during the VO2max plateau but not on the subjects physical fitness.
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