The movement of parts of the body is accomplished
through a system of levers composed of skeletal
muscles and bones. In a lever, the muscle attached to
the bone provides the effort or force that moves the
bone. As the muscle contracts and relaxes, flexes or
extends, the bone rotates around a joint in the skeletal
system. In relation to the muscles, the bones, and the
body part being moved, the joint is the fixed point that
functions as the fulcrum for the lever. The body part
being moved is the load in the lever (Figure HM-7-1 on
page HM-7-1).