Maximal exercise cardiorespiratory responses of men and women during acute exposure to hypoxia.

Three male and four female subjects were acutely exposed to normoxic and hypoxic gas mixtures (FIO2 = 17.39%, 14.40%, 11.81%) in a single-blind randomized fashion during four treadmill runs to volitional exhaustion. Maximal scores for oxygen consumption (VO2), carbon dioxide production and heart rate decreased linearly (p less than 0.01) with increasing hypoxia. Conversely, maximal scores for ventilation, ventilatory equivalent (VE/VO2) and R increased linearly (p less than 0.01) with decreasing FIO2. During hypoxia, no significant differences in work time or respiratory compensation threshold were evident. However, female subjects had significantly higher (p less than 0.05) VE/VO2 scores and showed a relative decrease in VO2max that was significantly less (p less than 0.01) than male subjects. It was concluded that young highly active females, when compared to males of similar age and relative condition, have a stronger adaptive response to acute hypoxia during a maximal treadmill run.