According to Muscle Physiology from the University of California, San Diego, ATP supplies the energy needed by muscles to contract. Ironically, ATP is also needed for muscle relaxation. The chemical stimulates muscle relaxation by disconnecting myosin and actin.
ATP, also known as adenosine triphosphate, is the primary source of energy for many body functions, muscle contraction included, notes Wikipedia. According to Muscle Physiology, muscle contraction and relaxation are achieved through the Lymn-Taylor actomyosin ATPase hydrolysis mechanism. Scientists have yet to fully uncover the link between the Lymn-Taylor actomyosin ATPase hydrolysis mechanism and the mechanical cross-bridge function that also plays a critical role in muscle contraction. However, Lymn and Taylor, the scientists behind the discovery of the Lymn-Taylor actomyosin ATPase hydrolysis mechanism theorize that ATP plays its role through a process that is broken into four parts.
First, ATP binds to myosin, breaking down an actin-myosin bridge and causing muscle contractions to stop. The free myosin and its bridge then move to a point where they can attach to actin. At this point, ATP is broken down into adenosine diphosphate and Pi, generating energy, explains Muscle Physiology. ADP, Pi and the myosin bridge then attach to actin, causing muscle contraction. During the muscle relaxation phase, actin displaces ADP and Pi at the myosin cross bridge. ADP and Pi are then reconstituted into ATP by the body, and the process starts again. Muscle contraction also requires the brain, the nervous system and other body systems to function properly.