The metabolic response of type i and ii muscle fibers during
repeated bouts of maximal exercise in humans.
Casey, A., D. Constantin-Teodosiu, S. Howell, E. Hultman, and P. L.
Greenhaff.
Department of Physiology and Pharmacology, University of Nottingham
Medical School, Queen's Medical Center, Nottingham NG7 2UH, United
Kingdom; Department of Clinical Chemistry, Huddinge University
Hospital, Karolinska Institute S-141 86, Huddinge, Sweden
APStracts 3:0063E, 1996.
Nine male subjects performed 2 bouts of 30 s maximal, isokinetic
cycling. Each bout of exercise was performed at 80 rev/min and
separated by 4 min recovery. Mixed muscle 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 utilisation was 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 utilisation was 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.
Received 21 August 1995; accepted in final form 7 February 1996.
APS Manuscript Number E406-5.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 20 March 96