Oxygen uptake response during maximal cycling in hyperoxia, normoxia and hypoxia

Background: Oxygen uptake ((V)over dot O-2) on-kinetics is decelerated in a cute hypoxia and accelerated in hyperoxia in comparison with normoxia durin g submaximal exercise. However, the effects of fraction of oxygen in inspir ed air (FIO2) an (V)over dot O-2 kinetics during maximal exercise are unkno wn. Hypothesis: The effects of FIO2 on (V)over dot O-2 on-kinetics during m aximal exercise are similar to submaximal exercise. Methods: There were 11 endurance athletes who were studied during maximal 7-min cycle ergometer ex ercise in hyperoxia (FIO2 0.325), hypoxia (FIO2 0.166) and normoxia (FIO2 0 .209). The individual (V)over dot O-2 data were fit to a curve by using a t hree exponential model. Results: In hypoxia, (V)over dot O-2 on-response am plitude during Phase 2 (similar to 20-100 s from the beginning of exercise) was lower (p < 0.05) when compared with hyperoxia; time constant of (V)ove r dot O-2 Phase 3 (beyond similar to 100 s after beginning of exercise) was shorter (p < 0.05) when compared with hyperoxia; and mean response time (M RT, O-63%) for (V)over dot O-2 peak was shorter (p < 0.05) when compared wi th normoxia and hyperoxia. (V)over dot O-2 peak was higher in hyperoxia (4. 80 +/- 0.48 L (.) min(-1), p < 0.05) and lower in hypoxia (4.03 +/- 0.46 L (.) min(-1), p < 0.05) than in normoxia (4.36 +/- 0.44 L (.) min(-1)). Conc lusions: Moderate hypoxia or hyperoxia do not affect Vo, time constants at the onset of maximal exercise. However, MRT for (V)over dot O-2 peak is sho rtened in hypoxia. It is suggested that the differences in (V)over dot O-2 peak and power output during the latter half of the test and the point that FIO2 was modified only moderately might explain most of the discrepancy wi th the previous studies.