Final answer:
Cross-bridge release during muscle contraction occurs when ATP binds to the myosin head, causing it to detach from actin and allowing the muscle to relax before the next contraction cycle.
Step-by-step explanation:
In muscle contraction, cross-bridge release is a critical step which occurs when a new molecule of ATP binds to the myosin head. This binding of ATP causes the myosin head to detach from the actin filament, effectively breaking the actin-myosin cross-bridge. After detachment, the ATP is then hydrolyzed (broken down) into ADP and inorganic phosphate (Pi), which energizes the myosin head, cocking it into a position ready for another cycle of cross-bridge formation and power stroke, thus enabling continuous muscle contraction and relaxation.