Adaptive responses of hypertrophying skeletal muscle to endurance
training.
Stone, J., T. Brannon, F. Haddad, A. Qin, and K. M. Baldwin.
Department of Physiology and Biophysics, University of California,
Irvine, Irvine, CA 92717
APStracts 3:0168A, 1996.
We determined the effects of six weeks of endurance running on citrate
synthase (CS) activity and myosin heavy chain (MHC) expression in
bilateral surgical-overloaded rodent fast-plantaris and slow-soleus
muscles. The overload induced significant hypertrophy in both muscle
types, and this response was enhanced by endurance training. The
overload-induced compensatory hypertrophy was accompanied by a
proportional increase in muscle CS content. Although endurance
training produced significant increases in CS concentration in either
muscle type of the normal-trained groups (p<0.05), it was not
effective in causing similar changes in the overloaded-trained
muscles. Also, overload of either the sedentary or trained groups
produced an increase in slower MHC isoforms (i.e., type I in the
soleus; type I and IIa in the plantaris) and a concomitant decrease
in the faster MHC isoforms (IIa in the soleus; IIb in the plantaris;
p<0.05); whereas, endurance training alone produced the opposite
effect, especially in the plantaris. Collectively, these data
suggest: 1) increments in muscle oxidative enzyme content due to
endurance training are compromised when a hypertrophying process is
occurring concomitantly; and 2) the relative loading state imposed on
the muscle during repetitive locomotor activity is critical in
regulating the pattern of MHC plasticity.
Received 31 January 1996; accepted in final form 19 March 1996.
APS Manuscript Number A106-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 1 April 96