On the mechanism of muscular contraction.

A thermodynamic analysis is presented for the energy conversion by muscle contraction. During the cyclic processes the major change in energy of the myosin-actin system is due to bond formation between myosin heads and actin. To account for the high efficiency of a working muscle the work done is connected directly to the formation of myosin-actin bond. It is suggested that successively stronger bonds are formed by a stepwise movement of myosin heads over an interval between two troponin molecules on the actin filament. At the end of the interval, where the bond has maximum strength, energy is supplied to break the bond. Here the work is not primarily connected to the 45 degrees rotation of myosin heads as is commonly done. A way of separating the different kinds of energy losses is presented.