We investigate the molecular mechanisms of the morphological and functional changes of skeletal muscles in response to several situations such as overload, disuse, pathology, exercise, aging, etc. in vivo. For example, we are interested in the physiological roles of aquaporin 4 (AQP4) in the regulation of morphological and functional changes of skeletal muscles. AQP4 is a selective water channel that is located on the plasma membrane of myofibers in skeletal muscle, and involved in the modulation of homeostasis in myofibers through the regulation of water transport and osmotic pressure. But it remains unclear the physiological roles of AQP4 in the regulation of the morphological and functional changes of skeletal muscles. We hope to provide useful basic findings to understand molecular mechanisms of regulation of the health of skeletal muscles, through the elucidation of the physiological roles of AQP4 in the adaptive changes of skeletal muscles.