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Intermittent altitude exposures improve muscular performance at 4,300 m

¹Biophysics and Biomedical Modeling Division and ²Thermal and Mountain Medicine Division, United States Army Research Institute of Environmental Medicine, Natick 01760; and ³Department of Health Sciences, Sargent College of Health and Rehabilitation Sciences, Boston University, Boston, Massachusetts 02215

Submitted 18 December 2002 ; accepted in final form 17 June 2003

Chronic altitude residence improves muscular performance at altitude, but the effect of intermittent altitude exposures (IAE) on muscular performance at altitude has not been defined. The purpose of this study was to determine the effects of 3 wk of IAE, in combination with rest and cycle training, on muscular performance at altitude. Six lowlanders (23 ± 2 yr, 77 ± 6 kg; means ± SE) completed a cycle time trial and adductor pollicis endurance test at sea level and during a 30-h acute exposure to 4,300 m altitude equivalent (barometric pressure = 446 mmHg) once before (pre-IAE) and once after (post-IAE) a 3-wk period of IAE (4 h/day, 5 days/wk, 4,300 m). During each IAE, three subjects cycled for 45–60 min/day at 60%-70% of maximal O₂ uptake and three subjects rested. Cycle training during each IAE did not appear to affect muscular performance at altitude. Thus data from all six subjects were combined. Three weeks of IAE resulted in 1) a 21 ± 6% improvement (P < 0.05) in cycle time-trial performance (min) from pre-IAE (32.8 ± 3.7) to post-IAE (24.8 ± 1.2), 2) a 63 ± 26% improvement (P < 0.05) in adductor pollicis endurance (min) from pre-IAE (9.2 ± 2.8) to post-IAE (14.8 ± 4.2), and 3) a 10 ± 4% increase (P < 0.05) in resting arterial O₂ saturation (%) from pre-IAE (82 ± 2) to post-IAE (90 ± 1). These improvements in muscular performance after IAE correlated strongly with increases in resting arterial O₂ saturation and were comparable to those reported previously after chronic altitude residence. IAE may therefore be used as an alternative to chronic altitude residence to facilitate improvements in muscular performance in athletes, soldiers, mountaineers, shift workers, and others that are deployed to altitude.

hypobaric hypoxia; ventilation; maximal O₂ uptake; submaximal work