In normal excitation of the muscle fibres, the action potential arising from the neuromuscular junction (end-plate) propagates along the surface of the muscle fibre. When the depolarization induces a marked increase of the permeability in the muscle membrane, the action potential is manifested reflecting a rapid entry of sodium into the cell followed by an outflow of potassium (Hodgkin, 1951; Hodgkin & Huxley, 1952). It, however, is stated by many authors that there is no direct essential links between the action potential and the initiation of the contractile mechanism, but unknown physiological intermediate steps between them (Excitation-Contraction Coupling. Sandow, 1952). Hill & Howarth (1957), Hodgkin & Horowicz (1960) suggested that a depolarization, somewhat less than required to cause contraction, can release some chemical reactions that has been physiologically produced by excitation. In this paper, the author reviewed results of the study on the E-C coupling which recently has been reported.