Are region-specific changes in fibre types attributable to nonuniform muscle hypertrophy by overloading? |
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Authors: | Kunihiro Sakuma Akihiko Yamaguchi Shigeru Katsuta |
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Affiliation: | (1) Doctoral programme in Health and Sport Sciences, University of Tsukuba, Tsukuba, Ibaraki 305, Japan;(2) Department of General Education, Health Sciences University of Hokkaido, 1757 Kanazawa, Ishikari-Tobetsu, Hokkaido 061-02, Japan;(3) Institute of Health and Sport Sciences, University of Tsukuba, Tsukuba, Ibaraki 305, Japan |
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Abstract: | Muscle fibre composition was compared among the proximal (25%), middle (50%) and distal (75%) regions of the muscle length to investigate whether compensatory overload by removal of synergists induces region-specific changes of fibre types in rat soleus and plantaris muscles. In addition, we evaluated fibre cross-sectional area in each region to examine whether fibre recruitment pattern against functional overload is nonuniform in different regions. Increases in muscle mass and fibre area confirmed a significant hypertrophic response in the overloaded soleus and plantaris muscles. Overloading increased the percentage of type I fibres in both muscles and that of type IIA fibres in the plantaris muscle, with the greater changes being found in the middle and distal regions. The percentage of type I fibres in the proximal region was higher than that of the other regions in the control soleus muscle. In the control plantaris muscle, the percentage of type I and IIA fibres in the middle region were higher than that of the proximal and distal regions. With regard to fibre size, type IIB fibre area of the middle and distal regions in the plantaris increased by 51% and 57%, respectively, with the greater changes than that of the proximal region (37%) after overloading. These findings suggest that compensatory overload promoted transformation of type II fibres into type I fibres in rat soleus and plantaris muscles, with the greater changes being found in the middle and distal regions of the plantaris muscle. |
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Keywords: | Fibre types Fibre area Compensatory overload Nonuniform change Plantaris muscle |
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