Tennis player video showing the muscles of the body doing a forehand stroke and muscles fade out. The average adult human skeleton has around 206 bones. These bones meet at joints, the majority of which are freely movable. The skeleton also contains cartilage for elasticity. Ligaments are strong strips of fibrous connective tissue that hold bones together at joints, thereby stabilizing the skeleton during movement. Muscles of the body are predominately powered by the oxidation of fats and carbohydrates, but anaerobic chemical reactions are also used, particularly by fast twitch fibers. These chemical reactions produce adenosine triphosphate (ATP) molecules which are used to power the movement of the myosin heads. Skeletal muscle anatomy royalty free videos from medical animation experts Polymime.