Prolonged exhaustive submaximal exercise in humans induces marked
metabolic changes, but little is known about effects on muscle Na+, K+ATPase
activity and sarcoplasmic reticulum (SR) Ca2+ regulation. We therefore investigated
whether these processes were impaired during cycling exercise at 74.3±1.2% v02
peak (mean±SEM) continued until fatigue, in eight healthy subjects (v02 peak
3.93±0.69 l.min-1). A vastus lateralis muscle biopsy was taken at rest, at 10 and 45
min of exercise and at fatigue. Muscle was analysed for in-vitro Na+,K+ ATPase
activity (maximal K+ -stimulated 3-0-methylfluorescein phosphatase, 3-0-MFPase
activity), Na+K+ATPase content (3[H] ouabain binding sites), SR Ca2+ release rate
induced by 4 chloro-m-cresol and Ca2+ uptake rate.