When a skeletal muscle relaxes,myosin head attach to actin by breaking down ATP to ADP and phosphate with the help of myosin ATPase. The myosin head forms the cross -bridges on the active site of the actin.The cross-bridge pulls the actin which slide over the myosin. The release of ADP completes the cross-bridge movements . ATP attaches to myosin, and break the actin -myosin cross-bridge. Thus breaking of ATP into ADP and phosphate help the thin filament to return to their original position.