Muscle fatigue and exhaustion during dynamic leg exercise in normoxia and hypobaric hypoxia

Charles S. Fulco, Steven F. Lewis, Peter N. Frykman, Robert Boushel, Sinclair Smith, Everett A. Harman, Allen Cymerman, and Kent B. Pandolf Environmental Physiology and Medicine Directorate and Occupational Health and Performance Directorate, US Army Research Institute of Environmental Medicine, Natick 01760-5007; and Department of Health Sciences, Sargent College of Allied Health Professions, Boston University, Boston, Massachusetts 02215 Received 23 October 1995; accepted in final form 16 April 1996. Fulco, Charles S., Steven F. Lewis, Peter N. Frykman, Robert Boushel, Sinclair Smith, Everett A. Harman, Allen Cymerman, and Kent B. Pandolf. Muscle fatigue and exhaustion during dynamic leg exercise in normoxia and hypobaric hypoxia. J. Appl. Physiol. 81(5): 1891-1900, 1996. Using an exercise device that integrates maximal voluntary static contraction (MVC) of knee extensor muscles with dynamic knee extension, we compared progressive muscle fatigue, i.e., rate of decline in force-generating capacity, in normoxia (758 Torr) and hypobaric hypoxia (464 Torr). Eight healthy men performed exhaustive constant work rate knee extension (21 ± 3 W, 79 ± 2 and 87 ± 2% of 1-leg knee extension O 2 peak uptake for normoxia and hypobaria, respectively) from knee angles of 90-150° at a rate of 1 Hz. MVC (90° knee angle) was performed before dynamic exercise and during 5-s pauses every 2 min of dynamic exercise. MVC force was 578 ± 29 N in normoxia and 569 ± 29 N in hypobaria before exercise and fell, at exhaustion, to similar levels (265 ± 10 and 284 ± 20 N for normoxia and hypobaria, respectively; P > 0.05) that were higher ( P