Sports movements such as jumping and sprinting and daily movements such as going up and down stairs and getting up from a chair are generated by skeletal muscle contractions. Therefore, elucidation of the mechanism of skeletal muscle contractions is essential to improve sport performance and acquire smooth daily movements. Thus, I am working on visualization of the contractile apparatus (skeletal muscle) in living human bodies using ultrasonography and magnetic resonance imaging (MRI) and on the mechanical testing to verify the behavior of actin and myosin at a molecular level, targeting single muscle cells and single myofibrils.