Cycling performance decrement is greater in hypobaric versus normobaric hypoxia

BACKGROUND: The purpose of this study was to determine whether cycling time trial (TT) performance differs between hypobaric hypoxia (HH) and normobaric hypoxia (NH) at the same ambient PO(2) (93 mmHg, 4,300-m altitude equivalent). METHODS: Two groups of healthy fit men were matched on physical performance and demographic characteristics and completed a 720-kJ time trial on a cycle ergometer at sea level (SL) and following approximately 2 h of resting exposure to either HH (n = 6, 20 ± 2 years, 75.2 ± 11.8 kg, mean ± SD) or NH (n = 6, 21 ± 3 years, 77.4 ± 8.8 kg). Volunteers were free to manually increase or decrease the work rate on the cycle ergometer. Heart rate (HR), arterial oxygen saturation (SaO(2)), and rating of perceived exertion (RPE) were collected every 5 min during the TT, and the mean was calculated. RESULTS: Both groups exhibited similar TT performance (min) at SL (73.9 ± 7.6 vs. 73.2 ± 8.2), but TT performance was longer (P < 0.05) in HH (121.0 ± 12.1) compared to NH (99.5 ± 18.1). The percent decrement in TT performance from SL to HH (65.1 ± 23.6%) was greater (P < 0.05) than that from SL to NH (35.5 ± 13.7%). The mean exercise SaO(2), HR, and RPE during the TT were not different in HH compared to NH. CONCLUSION: Cycling time trial performance is impaired to a greater degree in HH versus NH at the same ambient PO(2) equivalent to 4,300 m despite similar cardiorespiratory responses.