As a new ATP molecule attaches to the head of the myosin molecule, the cross-bridge is released,the ATP is broken down to ADP and P, which both remain bound to the myosin hesd, and the myosin head is restored to its original position, where it can attach to the next attachment site. As long as Ca2+ remain attached to troponin, and as long as ATP remains available, the cycle of cross-bridge formation, movement, and release is repeated. A new ATP must bind to myosin befrom the cross-bridge can be released. When ATP is not available after a person dies, the cross-bridges that have formed are not released, causing muscles to become rigid.