Abstract A new theory of the contraction of skeletal muscle is proposed. Myosin filaments are considered to rotate during contraction so that they have a screw motion relative to the actin filaments of each half sarcomere. A geometrical model of contraction is described in which projections on the myosin filament are repeatedly positioned for equivalent cross-bridge formation. A mechanical model is described in which rotation is caused by the formation of cross-bridges and is directly coupled to contraction by the winding-on of attached cross-bridges. The mechanism implies that cross-bridge cycles within each sarcomere are highly concerted. It also leads to a particularly simple description of the transduction of chemical energy (supplied by ATP hydrolysis) into mechanical energy. Possible ways of empirically testing the theory are discussed.