The authors present a synthesis on the mechanism of muscle contraction. Firstly they establish the concept of polarizated and depolarizated membrane. They emphasize the importance of the contractile substance (actomyosin) and of the energy furnished by the adenosinetriphosphate. They also discuss on the chemical reactions which take place to form these substances, as well as on the part played by the myohaemoglobin in the muscular contraction.