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

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 (˙VO₂ max), 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_I O₂ ]) for GET (p = 0.001), RCP (p < 0.001), ˙VO₂ max (p < 0.001), and PPO (p < 0.001). The ˙VO₂ 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, ˙VO₂ max (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). ˙VO₂ max 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 ˙VO₂ max 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 ˙VO₂ max in a group of young healthy adults regardless of the F_I O₂. Trial registration: Open Science Framework 10.17605/OSF.IO/ZTC9E.