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Genetic determinism of fiber type proportion in human skeletal muscle

Genetic determinism of fiber type proportion in human skeletal muscle,JEAN-AIME SIMONEAU,CLAUDE BOUCHARD

Genetic determinism of fiber type proportion in human skeletal muscle   (Citations: 36)
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Skeletal muscle fiber type distribution is quite heterogeneous, with about 25% of North American Caucasian men and women having either less than 35% or more than 65% of type I fiber in their vastus lateralis muscle. To what extent human skeletal muscle fiber type proportion is under the control of genetic factors is examined in this paper. The results summarized here suggest that about 15% of the total variance in the proportion of type I muscle fibers in human is explained by the error component related to muscle sampling and technical variance, that about 40% of the phenotype variance is influ- enced by environmental factors, and the remaining variance (about 45%) is associated with inherited factors. These estimates suggest that a difference of about 30% in type I fibers among individuals could be explained exclusively by differences in the local environment and level of muscular contractile activ- ity. However, unidentified genetic factors would have to be invoked to account for the observation that the skeletal muscle of about 25% of the North American Caucasian population have either less than 35% or more than 65% of type I flbers.-Simoneau, J.-A., Bouchard, C. Genetic determinism of fiber type pro- portion in human skeletal muscle. FASEB J. 9, 1091-1095 (1995) muscle fibers. However, the vast majority of functional studies of human subjects have established the distinction between muscle fiber types from fibers stained with the use of myofibrillar adenosine triphosphatase (mATPase) histo- chemistry. Staron (5) has shown that the staining intensity of mATPase stained fibers was correlated with the myosin heavy chain composition and Reiser et al. (6) have shown that this characteristic was correlated with shortening ve- locity. Studies reveal that skeletal muscle can exhibit a high or a low percentage of type I fibers. Based on a large sample (more than 400), we have shown that the vastus lateralis muscle of about 25% of North American Caucasian men and women has either less than 35% or more than 65% of type I fibers (7), thus demonstrating that the number of individuals in the population with a low or a high proportion of muscle type I fibers is not negligible. An important ques- tion then becomes to what extent these human skeletal muscle characteristics are under the control of genetic fac- tors. In popular textbooks on exercise physiology, one finds two major and different points of view typically expressed: either the percentage of type I fibers in human skeletal muscle is set by the genes (8, 9) or fiber type distribution is partly genetically determined and thus perhaps amenable to change with exercise training (10). In a recent review paper, the concept was put forward that the proportion of
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