Sliding Filament Theory The sliding filament theory allows muscle contraction. According to the theory, during muscle contraction, a myosin head attaches to a binding site on the actin filament, forming a cross-bridge. This binding causes the head to bend, pulling on the actin filament, and moving it toward the center of the sarcomere. The head then releases, and attaches to the next binding site on the actin, pulling this site toward the center. As this occurs again and again, the filaments increase their overlap, and the sarcomere shortens from both ends. When many sarcomeres shorten at the same time, the muscle fiber shortens. Energy from the conversion of ATP to ADP is provided to the cross-bridges by the enzyme ATPase; ATP breakdown causes the heads to return to the “cocked” position, ready to bind to another actin binding site.