<P> A muscle that fixes or holds a bone so that the agonist can carry out the intended movement is said to have a neutralising action . A good famous example of this are the hamstrings; the semitendinosus and semimembranosus muscles perform knee flexion and knee internal rotation whereas the biceps femoris carries out knee flexion and knee external rotation . For the knee to flex while not rotating in either direction, all three muscles contract to stabilize the knee while it moves in the desired way . </P> <P> Composite or hybrid muscles have more than one set of fibers that perform the same function, and are usually supplied by different nerves for different set of fibers . For example, the tongue itself is a composite muscle made up of various components like longitudinal, transverse, horizontal muscles with different parts innervated having different nerve supply . </P> <P> The insertion and origin of a muscle are the two places where it is anchored, one at each end . The tissue of the attachment is called an enthesis . </P> <P> The origin of a muscle is the bone, typically proximal, which has greater mass and is more stable during a contraction than a muscle's insertion . For example, with the latissimus dorsi muscle, the origin site is the torso, and the insertion is the arm . When this muscle contracts, normally the arm moves due to having less mass than the torso . This is the case when grabbing objects lighter than the body, as in the typical use of a lat pull down machine . This can be reversed however, such as in a chin up where the torso moves up to meet the arm . </P>

What is the only type of motion muscles perform