Supramaximal Testing to Confirm the Achievement of V̇O2max in Acute Hypoxia

Abstract

To confirm maximal oxygen uptake (V̇O2max), a bout of supramaximal exercise can be performed after maximal exercise. Supramaximal exercise verifies V̇O2max if the V̇O2max is similar to the incremental test. Acute hypoxia decreases V̇O2max due to decreases in arterial oxygenation which results in different determinants of V̇O2max. Purpose We sought to determine if supramaximal exercise testing confirms the achievement of V̇O2max in acute hypoxia. We hypothesized that the incremental and supramaximal V̇O2 will be sufficiently similar in acute hypoxia. Methods Twenty-one healthy adults (males n = 13, females n = 8) completed incremental and supramaximal exercise tests in normoxia and acute hypoxia (fraction inspired oxygen = 0.14) separated by at least 48 hours. Incremental exercise started at 80 and 60 W in normoxia and 40 and 20 W in hypoxia for males and females, respectively, with all increasing by 20 W each minute until volitional exhaustion. Following a 20 minute post-exercise rest period, a supramaximal test at 110% peak power until volitional exhaustion was completed. Results Supramaximal exercise testing yielded a lower V̇O2 than incremental testing in hypoxia (3.11 ± 0.78 vs. 3.21 ± 0.83 L min-1, p = 0.001) and normoxia (3.71 ± 0.91 vs. 3.80 ± 1.02 L min-1, p = 0.01). Incremental and supramaximal V̇O2 were statistically similar, using investigator-determined equivalence bounds ±150 mL min-1, in hypoxia (p = 0.02, 90% CI = [0.05 , 0.14]) and normoxia (p = 0.03, 90% CI = [0.01 , 0.14]. Likewise, using ±2.1 mL kg-1 min-1 bounds, incremental and supramaximal V̇O2 was statistically similar in hypoxia (p = 0.04, 90% CI = [0.70 , 2.0]) and normoxia (p = 0.04, 90% CI = [0.30 , 2.0]). Conclusions Despite differences in the oxygen cascade, the incremental and supramaximal V̇O2 were statistically similar in both hypoxia and normoxia, demonstrating the utility of supramaximal verification of V̇O2max in the setting of acute hypoxia.