What effect does muscle relaxation have on the Z lines within a sarcomere?

During muscle relaxation, the Z lines within a sarcomere move farther apart. This occurs because, in a relaxed state, the actin filaments that are attached to the Z lines are not being pulled toward the center of the sarcomere by the myosin filaments. When a muscle contracts, the myosin heads bind to the actin, resulting in a sliding motion that brings the Z lines closer together—a process known as the sliding filament theory. However, once the muscle relaxes, there is a loss of tension and the actin filaments return to their resting state, leading to the Z lines moving further apart as the sarcomere lengthens. This increase in distance between the Z lines represents the return to a baseline muscle length, highlighting the dynamic nature of muscle contraction and relaxation.