Cycling performance decrement is greater in hypobaric versus normobaric hypoxia

Abstract

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 PO2 (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 (SaO2), 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 SaO2, 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 PO2 equivalent to 4,300 m despite similar cardiorespiratory responses.

Keywords: Altitude; Endurance performance; Hypobaric hypoxia; Resting ventilation; Time trial performance.

Figure 1

Study design indicating timing of baseline, SL, and HYP measurements in either HH or NH. One preliminary peak oxygen uptake, two preliminary cycle endurance tests consisting of two steady-state exercise bouts followed by a cycle time trial test, and five cycle exercise training sessions occurred during baseline testing. Prior to each cycle endurance test in SL and HYP, resting ventilatory, cardiovascular, and hematologic responses were measured.

Figure 2

Time trial performance data. (a) Cycle time trial performance at sea level (SL) and hypoxia (HYP) in a group of men exposed to either hypobaric hypoxia (HH) or normobaric hypoxia (NH). Each man exposed to HH demonstrated a greater decrement in TT performance in hypoxia (HYP) than each man exposed to NH at an ambient PO₂ equivalent to 4,300 m in each condition. (b) For each matched pair, their sea level (SL) TT performance fell closely on the line of identity, but their performance in HH fell below their matched pair in NH on the line of identity. *P < 0.05 from SL; ^†P < 0.05 between groups.