What happens during the sliding filament theory of muscle contraction?

During the sliding filament theory of muscle contraction, actin and myosin filaments interact in a way that allows the muscle fibers to shorten and generate force. Specifically, actin slides over the myosin filaments, which pulls the Z-discs closer together, effectively shortening the sarcomeres—the basic functional units of skeletal muscle. This sliding action is facilitated by the cross-bridge cycling process where myosin heads attach to binding sites on the actin filaments, rotate, and pull the actin filaments inward.

This process does not involve the complete separation of the actin and myosin filaments or the dissolution of either filament. Instead, they remain closely associated during contraction. The sliding motion occurs repeatedly as long as ATP is available and calcium ions are present, thus producing sustained muscle contraction. Understanding this mechanism is crucial for grasping how muscles generate movement in response to neural signals and how training can affect muscle performance over time.