Mitochondrial enzymes increase in muscle in response to 7-10 days
of cycle exercise.
Spina, Robert J., Maggie M.-Y. Chi, Michael G. Hopkins, Patti M.
Nemeth, Oliver H. Lowry, and John O. Holloszy.
Section of Applied Physiology, Department of Internal Medicine and
Department of Molecular Biology and Pharmacology, Washington
University School of Medicine
APStracts 3:0151A, 1996.
Endurance exercise training induces a significant increase in the
respiratory capacity of skeletal muscle. This is reflected by a
training-induced increase in mitochondrial enzyme activity. One
consequence of this adaptation is that there is a decreased reliance
on carbohydrate utilization with a concomitant increase in fat
utilization resulting in an improvement in endurance capacity.
Recently it has been reported that 7-14 days of cycle ergometer
exercise training does not induce an increase in mitochondrial enzyme
levels in skeletal muscle, but nevertheless, results in smaller
decreases in phosphocreatine and glycogen and smaller increases in
organic phosphate and lactate in muscle in response to the same
exercise after, as compared to before, training. However, previous
studies on rats have shown that an adapttive increase in
mitochondrial enzymes is already evident after only 2 days of
exercise-training. In view of this discrepency, the present study was
performed to re-evaluate the effect of short-term training (7-10
days) on mitochondrial enzymes in skeletal muscle in humans. Twelve
subjects (6 men and 6 women; 27 +/- 5 yrs old; mean +/- SE) underwent
7d (n=5) or 10d (n=7) of cycle ergometer exercise for 2 h/day at 60
-70% of O2 peak. O2 peak was increased by 9% (from 2.97 +/- 0.16 to
3.24 +/- 0.17) in response to training. Blood lactate levels were
lower at the same absolute work rates after than before training. The
activities of citrate synthase, [beta]-hydroxyacyl-CoA dehydrogenase,
mitochondrial thiolase, and carnitine acetyltransferase were
increased by 30% in response to training. The results of the present
study provide evidence that in humans, as in rats, the adaptive
increase in mitochondrial enzymes in skeletal muscle occurs fairly
rapidly in response to exercise training. They provide no support for
the claim that this adaptive response is delayed for more than two
weeks after the onset of training.
Received 13 November 1995; accepted in final form 6 March 1996.
APS Manuscript Number A1191-5.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 27 March 96