Diagram shows how ATP hydrolysis is transduced into motion. Myosin head attaches, detaches cyclically. ATP binding closes that cleft, opening actin binding cleft, weakening the affinity and breaking the attachment to actin. Because actin and myosin are bound, this causes relative motion of head along actin filament. If x-bridges produce the force and are uniformly distributed along thick myofilaments, then developed force should vary linearly with overlap of myofilaments.
Force correlates with all lengths of muscle.
Experiments demonstrate that the MHC does the job, with light chains modulating the interaction.