Sliding filament theory is the theory which has been accepted for explaining the contraction of muscles. According to this theory, contractions of muscles is considered as the cycle of molecular events. During the muscle contraction, the thin actin and thick myosin filaments slide past each other. The process is done by cross-bridges which is extended from the myosin filaments. The contractile unit of muscle is said to be sarcomere. At the end of the sarcomere, actin filaments are attached to the Z disc. The Z disc then further pulled by the sliding filament which results in the shortening of sarcomere and muscle contraction.