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 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.


CONCLUSIONS
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.
Thermal and Mountain Medicine Division, United States Army Research Institute of Environmental Medicine, Kansas St., Bldg 42, Natick, MA 01760, USA.
Beth A
BA
Beidleman
Thermal and Mountain Medicine Division, United States Army Research Institute of Environmental Medicine, Kansas St., Bldg 42, Natick, MA 01760, USA.
Charles S
CS
Fulco
Thermal and Mountain Medicine Division, United States Army Research Institute of Environmental Medicine, Kansas St., Bldg 42, Natick, MA 01760, USA.
Janet E
JE
Staab
Thermal and Mountain Medicine Division, United States Army Research Institute of Environmental Medicine, Kansas St., Bldg 42, Natick, MA 01760, USA.
Sean P
SP
Andrew
Thermal and Mountain Medicine Division, United States Army Research Institute of Environmental Medicine, Kansas St., Bldg 42, Natick, MA 01760, USA.
Stephen R
SR
Muza
Altitude; Endurance performance; Hypobaric hypoxia; Resting ventilation; Time trial performance