It is well-reported that the morphological properties of skeletal muscles or muscle fibers, which are influenced by the level of protein synthesis and/or degradation, are regulated in response to mechanical load. However, the precise mechanism responsible for such phenomena is not fully understood yet. Changes of the distribution of satellite cells and/ or myonuclei have been also noted in atrophied or hypertrophied skeletal muscle fibers, suggesting that the number and/or function of these

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... meters play essential roles in the regulation of morphological properties of muscle and muscle fibers. Thus, the roles of satellite cells and/or myonuclei in the regulation of morphological properties of anti-gravitational muscle, soleus and adductor longus, in response to the level of mechanical stress, with or without association of macrophage-related factors, were briefly reviewed. It was suggested that a regulatory network among macrophage, interleukin-6, heat shock transcription factor 1, and activation of transcription factor 3 may play a crucial role for the modulation of skeletal muscle mass and function, which are also influenced by activation of satellite cells and distribution of myonuclei.