 Dear students, in this topic we shall discuss the production of force required for sliding of filaments. The cross bridges between myosin head and actin pull the thin filaments towards the center of sarcomere. The force for this pulling is produced because of partial rotation of the myosin head. Dear students, the rotation of myosin head is produced because the myosin head has four binding sites M1, M2, M3 and M4. These sites sequentially bind with the binding sites present on the actin filament. So myosin head has four binding sites and actin filament has binding sites. The binding sites of myosin head sequentially bind with the binding sites of actin as the myosin head rotates against the actin filaments. The link is stretched elastically. As a result, tension is developed in it. This tension produced in the link is transmitted to the thick myosin filament. This tension provides the force to pull the actin filaments and shorten the sarcomere. Dear students, when rotation of the head is complete, then it dissociates from the actin filament and rotates back to its relaxed position. This dissociation occurs when magnesium ions and ATP bind to the head. In this condition, ATP is hydrolyzed and myosin head also changes its conformation. After some time, the head binds again on the next site of the actin filament. This attachment of rotation and detachment of myosin head repeats in a cyclic manner. As a result, filaments slide past, all these work takes place in small steps. As a result, sarcomere contractions take place.