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.
Active transporters or ion pumps are transporters that convert energy from various sources—including adenosine triphosphate (ATP), sunlight, and other redox reactions—to potential energy by pumping an ion up its concentration gradient.