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Relative proportions of hybrid fibres are unaffected by 6 weeks of running exercise in mouse skeletal muscles
Author(s) -
Glaser Brian W.,
You Geoffrey,
Zhang Min,
Medler Scott
Publication year - 2010
Publication title -
experimental physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.925
H-Index - 101
eISSN - 1469-445X
pISSN - 0958-0670
DOI - 10.1113/expphysiol.2009.049023
Subject(s) - myosin , muscle fibre , skeletal muscle , biology , fast twitch muscle , wheel running , anatomy , medicine , endocrinology , microbiology and biotechnology
Hybrid muscle fibres co‐expressing two or more myosin heavy chain (MHC) isoforms represent a significant proportion of fibres in many muscles, but the prevalence and precise composition of these fibres varies significantly among muscles and animal species. In the present study, we used a forced running protocol for 6 weeks to determine the effects of running exercise on the relative proportion of hybrid muscle fibre types in mouse muscles. In the course of this experiment, we also determined the relative proportions of these fibres in several different skeletal muscles, since data about hybrid fibres in the mouse are sparse. We found that the proportions of hybrid fibres in mouse muscles varied significantly among specific muscles (2–25%), but these proportions were unaffected by 6 weeks of forced running exercise. In contrast, weight‐bearing muscles significantly increased in mass in response to running. These data suggest that hybrid muscle fibres are relatively refractory to the effects of moderate exercise and represent a stable phenotype in normal mouse muscles. The precise nature and physiological function of these fibres remain incompletely understood, but it is clear that hybrid fibres represent a common phenotype in many muscles.