Beidleman, B. A., Staab, J. A., Fulco, C. S., Cymerman, A., & Murza, S. R. (2012). Time-trial performance is impaired to a greater degree in hypobaric versus normobaric hypoxia at the same ambient PO2. Presentation 2155 at the 59th Annual Meeting of the American College of Sports Medicine, San Francisco, California; May 29-June 2, 2012.

This study determined whether time-trial performance differed between hypobaric hypoxia and normobaric hypoxia at the same ambient oxygen pressure (92 mmHg, ~4,300 m equivalent). Volunteers (N = 17) were exposed to hypobaric hypoxia and six volunteers were exposed to normobaric hypoxia. They completed a 720-kJ time-trial on a cycle ergometer both at sea-level and following ~1 hour of exposure to the same ambient oxygen pressure (92 mmHg, ~4300 m equivalent) in either hypobaric hypoxia or normobaric hypoxia conditions. Ss were free to manually increase or decrease the work rate on the cycle ergometer by 5 watt increments. Heart rate, SaO2 (percentage of available hemoglobin that is saturated with oxygen), and rating of perceived exertion were collected every five minutes during the time-trial and mean values were calculated.

Five Ss (29%) were unable to complete the 720-kJ time-trial in hypobaric hypoxia so only the remaining 12 Ss were included in the data analysis. Both groups exhibited nearly identical time-trial performances at sea-level (~73.3vs. ~73.2 minutes) but time-trial performance was significantly longer in hypobaric hypoxia (~120.4 minutes) compared to normobaric hypoxia (~99.5 minutes). Similarly, the % decrement in time-trial performance from sea-level to hypobaric hypoxia (~65.4 minutes) was significantly greater than the % decrement from sea-level to normobaric hypoxia (~35.5 minutes). In hypobaric hypoxia, heart rate and SaO2 were not statistically different. There were no differences in rating of perceived exertion during the time-trial in hypobaric hypoxia or normobaric hypoxia.

Implication. Time-trial performance is impaired to a greater degree in hypobaric compared to normobaric hypoxia at the same ambient oxygen pressure (equivalent to 4,300 m) despite similar cardiorespiratory responses. Performances are not highly related to physiological measures.

Performances in hypobaric and normobaric experiments should not be compared or equated.

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