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 (~1100 m) performed three cycling ramp-incremental exercise tests (with verification stages performed at 110 % of peak power output (PPO)) in simulated altitudes of 0m (SL), 1111m (MILD), and 2222m (MOD), in a randomized order. There were significant effects of condition (i.e., fraction of inspired oxygen [(FIO2]) 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, moderate altitude 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 FIO2.

Supramaximal Testing to Confirm the Achievement of V̇O2max in Acute Hypoxia

“…Few studies (10,14) have investigated the ability of supramaximal verification testing to verify VO 2max in individuals residing at altitude. However, our study is unique by questioning the effect of acute hypoxia in lowlanders in terms of supramaximal exercise's ability to verify VO 2 .…”

“…To make inferences on interchangeable methodology, equivalence testing was used to determine the similarity of V ̇O2 between incremental and supramaximal tests in acute hypoxia and normoxia. Our sample size justification is grounded in established precedents from previous relevant research regarding supramaximal exercise testing and draws upon the extensive body of existing research within our field (3)(4)(5)(6)(9)(10)(11)13,14,(29)(30)(31). Equivalence testing rejects the presence of a difference that is large enough to be relevant practically, defined by the upper and lower equivalence margin.…”

“…Conducting the incremental and the supramaximal tests in the same visit may provide increased likelihood of verifying VO 2 because a priming bout of exercise has shown to improve the ability to identify a VO 2 plateau (8). Overall, supramaximal testing to confirm the achievement of V ̇O2max has been successful across different ages (9), fitness levels (3,10), clinical populations (11)(12)(13), and acclimatized athletes at 1111, 2222 (14), and 2350 m (10).…”

“…The reduction in V̇O 2max and performance in acute hypoxia can be attributed to reduced blood oxygen content (23). Recently, others investigated V̇O 2max verification testing in individuals acclimated to mild altitude (1111 m) by conducting supramaximal testing at 110% peak power output in simulated altitudes of 0, 1111, and 2222 m (14). The verification V̇O 2max values were lower than the incremental V̇O 2max values in each condition; however, verification testing was not altered in hypoxia (14).…”

“…Recently, others investigated V̇O 2max verification testing in individuals acclimated to mild altitude (1111 m) by conducting supramaximal testing at 110% peak power output in simulated altitudes of 0, 1111, and 2222 m (14). The verification V̇O 2max values were lower than the incremental V̇O 2max values in each condition; however, verification testing was not altered in hypoxia (14). Similarly, others investigated V̇O 2max verification testing in endurance trained runners residing at altitude (2,350 m) and found that verification in all athletes produced a similar V̇O 2max (less 3% difference) (10).…”