Skeletal muscle strength during exposure to hypobaric hypoxia.

To assess the effects of acute exposure to hypobaric hypoxia and acute mountain sickness (AMS) on skeletal muscle strength, 10 healthy young men were studied before, during, and after a 48-h sojourn at a simulated altitude of 4,572 m (15,000 feet). Measurements were made of isokinetic (180 degrees, 36 degrees, and 0 degrees/s) knee extensor strength; isometric strength of upper torso, knee, and trunk extensor muscles; and strength endurance of knee extensor and elbow flexor muscles during a bout of repeated isokinetic contractions. There were no significant differences between strength measurements at sea level and after 2 and 24 h of hypoxic exposure. After 48 h of exposure, means of strength measurements were increased relative to sea-level values but the difference was statistically significant in the case of only one test; namely, isometric strength of the upper torso. Strength endurance was unchanged throughout the exposure. Symptoms of AMS were absent after 2 h, most pronounced after 24 h, and although somewhat reduced, still present to a significant extent after 48 h of hypoxia. Thus, despite the occurrence of AMS, muscle strength was unimpaired during acute hypoxic exposure.