Muscle contraction results from an attachmentdetachment cycle between the myosin heads extending from myosin filaments and the sites on actin filaments.
When a muscle contracts, the actin is pulled along myosin toward the center of the sarcomere until the actin and myosin filaments are completely overlapped.
As a result of the high calcium concentration, actin and myosin filaments will bind stronger, unable to relax properly to make a new contraction possible.
The overall process is initiated by an external signal, typically through an action potential stimulating the muscle, which contains specialized cells whose interiors are rich in actin and myosin filaments.