The modulation of myosin isoform expression by mechanical loading:
the role of stimulation frequency.
Caiozzo, Vincent J., Michael J. Baker, and Kenneth M. Baldwin.
Departments of Orthopaedics and Physiology and Biophysics, College
of Medicine, University of California, Irvine, CA 92717
APStracts 3:0452A, 1996.
This study tested the hypothesis that mechanical loading, not
stimulation frequency per se, plays a key role in determining the
plasticity of MHC protein isoform expression in muscle undergoing
resistance training. Female Sprague-Dawley rats were randomly
assigned to resistance training programs that employed active: i)
shortening (n=7); or ii) lengthening contractions (n=8). The medial
gastrocnemius (MG) muscles in each group trained under loading
conditions that approximated 90-95% of Po, but were stimulated at
frequencies of 100 and 25 Hz, respectively. Lengthening and
shortening contractions were produced using a Cambridge ergometer
system. The MG muscles trained every other day, performing a total of
16 training sessions. Both training programs produced significant
(P<0.01) and similar reductions in the fast Type IIB MHC
protein isoform in the white MG muscle, reducing its relative content
to 50% of the total MHC protein isoform pool. These changes were
accompanied by increases in the relative content of the fast Type IIX
MHC protein isoform that were of similar magnitude for both groups.
The results of this study clearly demonstrate that stimulation
frequency does not play a key role in modulating MHC isoform
alterations that result from high resistance training.
Received 21 February 1996; accepted in final form 17 September
1996.
APS Manuscript Number A164-6.
Article publication pending Journal of Applied Physiology.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 5 November 1996