Physiological responses to ramp-incremental cycling tests performed at three simulated altitudes: a randomized crossover trial

Abstract

Hypoxia negatively impacts aerobic exercise, but exercise testing in hypoxia has not been studied comprehensively. To determine the effects of simulated altitude on the gas exchange threshold (GET), respiratory compensation point (RCP), and maximal oxygen uptake (V̇O₂max), 24 participants (mean [SD]; 26 [4] years; 171.6 [9.7] cm; 69.2 [11.9] kg) acclimatized to mild altitude (MILD; ∼1100 m) performed three cycling ramp-incremental exercise tests (with verification stages performed at 110% of peak power output (PPO)) in simulated altitudes of 0 m (sea level, SL), 1111 m (MILD), and 2222 m (moderate altitude, MOD), in a randomized order. There were significant effects of condition (i.e., fraction of inspired oxygen [F_IO₂]) for GET (p = 0.001), RCP (p < 0.001), V̇O₂max (p < 0.001), and PPO (p < 0.001). The V̇O₂ corresponding to GET and RCP (mL·kg^-1·min^-1) in MOD (24.1 [4.3]; 37.3 [5.1]) were significantly lower (p < 0.05) compared to SL (27.1 [4.4]; 41.8 [6.6]) and MILD (26.8 [5.7]; 40.7 [7.3]) but similar (p > 0.05) between SL and MILD. For each increase in simulated altitude, V̇O₂max (SL: 51.3 [7.4]; MILD: 50.0 [7.6]; MOD: 47.3 [7.1] mL·kg^-1·min^-1) and PPO (SL: 332 [80]; MILD: 327 [78]; SL: 316 [76] W) decreased significantly (p < 0.05 for all comparisons). V̇O₂max values from the verification stage were lower than those measured during the ramp-incremental test (p = 0.017). Overall, a mild simulated altitude had a significant effect on V̇O₂max and PPO but not GET and RCP, MOD decreased all four variables, and the inclusion of a verification stage had little effect on the determination of V̇O₂max in a group of young healthy adults regardless of the F_IO₂. Trial registration: Open Science Framework 10.17605/OSF.IO/ZTC9E.

Keywords: consommation maximale d'oxygène; exercise testing; gas exchange threshold; high altitude physiology; hypoxie normobare; maximal oxygen uptake; normobaric hypoxia; physiologie de haute altitude; point de compensation respiratoire; respiratory compensation point; seuil d'échange gazeux; test d'effort.