Geometrical restrictions on cross-bridge motion and sliding filament dynamics

To ensure asynchronous motion and continuous force development in a sliding filament mechanism when the cross-bridge configurational cycle is geometrically constant and uniform, the repeat distances of the cross-bridge set and the active site set must be different. When the two sets overlap they will then form an interference pattern—the elements are in phase in some regions, out of phase in others. The geometrical restrictions that this puts on the cross-bridge cycle are discussed. One consequence may be that only a discrete set of modes of motion are possible in active filament sliding, the number of modes being determined by the energy supply rate and the internal friction in the system.