Metabolic response of type I and II muscle fibers during repeated bouts of maximal exercise in humans.
Nine male subjects performed two bouts of 30-s maximal isokinetic cycling. Each bout of exercise was performed at 80 revolutions/min and was separated by 4 min of recovery. Mixed-muscle phosphocreatine (PCr) resynthesis during recovery (88.1 +/- 6.1%) was positively correlated with the restoration of total work production during bout 2 (r = 0.80, P < 0.05). During bout 1, ATP and PCr utilization were greater in type II compared with type I fibers (P < 0.01 and P < 0.05, respectively). The subsequent 4-min period of recovery was insufficient to allow total restoration of ATP and PCr in type II fibers, but restoration of ATP and PCr in type I fibers was almost complete. During the second bout of exercise, ATP and PCr utilization were reduced in type II fibers (P < 0.01), without a corresponding change in type I fibers, and performance was also significantly reduced. The reduction in work capacity observed during bout 2 may have been related to a slower resynthesis, and consequently a reduced availability, of ATP and PCr in type II fibers.
Casey
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A
Department of Physiology and Pharmacology, University of Nottingham Medical School, Queen's Medical Center, United Kingdom.
Constantin-Teodosiu
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D
Howell
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Hultman
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E
Greenhaff
P L
PL
D000255:Adenosine Triphosphate / Q000378:metabolism; D000328:Adult; D019298:Glucose-6-Phosphate / Q000378:metabolism; D006801:Humans; D008297:Male; D018656:Muscle Fibers, Fast-Twitch / Q000378:metabolism*; D018657:Muscle Fibers, Slow-Twitch / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000378:metabolism / Q000502:physiology; D010725:Phosphocreatine / Q000378:metabolism; D010807:Physical Endurance
D010725:Phosphocreatine; D019298:Glucose-6-Phosphate; D000255:Adenosine Triphosphate