Contractile properties of rat, rhesus monkey, and human type i muscle fibers. Widrick, Jeffrey J., Janell G. Romatowski, Miloslav Karhanek, and Robert H. Fitts. Department of Biology, Marquette University, Milwaukee, WI 53201
APStracts 3:0280R, 1996.
It is well known that skeletal muscle intrinsic maximal shortening velocity is inversely related to species body mass. However, there is uncertainty regarding the relationship between the contractile properties of muscle fibers obtained from commonly studied laboratory animals and those obtained from humans. In this study we determined the contractile properties of single chemically skinned fibers prepared from rat, rhesus monkey, and human soleus and gastrocnemius muscle samples under identical experimental conditions. All fibers used for analysis expressed type I myosin heavy chain as determined by SDS-PAGE. Allometric coefficients for type I fibers from each muscle indicated that there was little change in peak tension (force/fiber cross-sectional area) across species. In contrast, both soleus and gastrocnemius type I fiber Vo (maximal unloaded shortening velocity), Vmax (the y-intercept of the force-velocity relationship), peak power per unit fiber length, and peak power normalized for fiber length and cross-sectional area were all inversely related to species body mass. The present allometric coefficients for soleus fiber Vo ( -0.18) and Vmax (-0.11) are in good agreement with published values for soleus fibers obtained from common laboratory and domesticated mammals Taken together, these observations suggest that the maximal shortening velocity of slow fibers from quadrupeds and humans scale similarly and can be described by the same quantitative relationships. These findings have implications in the design and interpretation of experiments, especially those that use small laboratory mammals as a model of human muscle function. 

Received 2 February 1996; accepted in final form 1 July 1996.
APS Manuscript Number R68-6.
Article publication pending Am. J. Physiol. (Regulatory Integrative
Comp. Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 July 1996