Beidleman, B. A., Muza, S. R., Fulco, C. S., Lammi, E., Staab, J. E., & Cymerman, A. (2009). Self-selected exercise intensity decreases but perception of effort remains constant during a cycle time-trial at altitude. ACSM 56th Annual Meeting, Seattle, Washington. Presentation number 2356.

This study determined whether a decrease in arterial oxygen saturation (SaO2) during an acute exposure to altitude affects self-selected exercise intensity and perception of effort during a cycle time-trial. Male lowlanders (N = 26) of similar age (~22 years), weight, and sea-level peak oxygen uptake first completed a maximal effort 720 kJ cycle time-trial at sea level and then again within four hours of exposure to either 3,000 m (N = 6), 3,500 m (N = 8) or 4,300 m (N = 12) altitude in a hypobaric chamber. Heart rate, SaO2, and rating of perceived exertion were measured every five minutes during the cycle time-trial and the respective overall means were calculated. The overall mean work rate and altitude-specific percent of maximum work rate maintained during the time-trial were calculated for each altitude.

Time-trial performance (in minutes) was impaired by ~32% from sea-level values at 3,000 m, by ~38% from sea level to 3,500 m, and by ~65% from sea level to 4,300 m. Arterial oxygen saturation was decreased from sea-level values at 3,000 m, 3,500 m, and 4,300 m. Heart rate did not change from sea-level values at 3,000 m or 3,500 m, but was decreased at 4,300 m. Percent of maximum work rate did not change from sea-level values at 3,000 m, but was decreased at 3,500 m and 4,300 m. Ratings of perceived exertion did not change from sea-level values at any altitude. The decrease in percent of maximum work rate was correlated with the decrease in arterial oxygen saturation with increasing altitude.

Implication. During an acute exposure to altitude, self-selected exercise intensity (e.g., percent of maximum work rate) decreased proportionally to the decrease in arterial oxygen saturation during a cycle time-trial but perceived exertion was maintained around 14 (i.e., somewhat hard) regardless of altitude.

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