Multiple variables explain the variability in the decrement in V˙O2max during acute hypobaric hypoxia. Med. Sci. Sports Exerc., Vol. 30, No. 6, pp. 869-879, 1998.
Purpose: We used multiple regression analyses to determine the relationships between the decrement in sea level (SL, 760 Torr) V˙O2max during hypobaric hypoxia (HH) and variables that could alter or be related to the decrement in V˙O2max.
Methods: HH conditions consisted of 682 Torr, 632 Torr, and 566 Torr, and the measured independent variables were SL-V˙O2max, SL lactate threshold (SL-LT), the change in hemoglobin saturation at V˙O2max between 760 and 566 Torr (ΔSaO2max), lean body mass (LBM), and gender. Male (N = 14) and female (N = 14) subjects of varied fitness, training status, and residential altitude (1,640-2,460 m) completed cycle ergometry tests of V˙O2max at each HH condition under randomized and single-blinded conditions.
Results: V˙O2max decreased significantly from 760 Torr after 682 Torr (∼915 m) (3.5 ± 0.9 to 3.4 ± 0.8 L·min−1, P = 0.0003). Across all HH conditions, the slope of the relative decrement in V˙O2max (%V˙O2max) during HH was −9.2%/100 mm Hg (−8.1%/1000 m) with an initial decrease from 100% estimated to occur below 705 Torr (610 m). Step-wise multiple regression revealed that SL-V˙O2max, SL-LT, ΔSaO2max, LBM, and gender each significantly combined to account for 89.03% of the variance in the decrement in V˙O2max (760-566 Torr) (P < 0.001).
Conclusions: Individuals who have a combination of a large SL-V˙O2max, a small SL-LT (V˙O2, L·min−1), greater reductions in ΔSaO2max, a large LBM, and are male have the greatest decrement in V˙O2max during HH. The unique variance explanation afforded by SL-LT, LBM, and gender suggests that issues pertaining to oxygen diffusion within skeletal muscle may add to the explanation of between subjects variability in the decrement in V˙O2max during HH.