Muscle anatomy. Illustration of the muscles of the human body (posterior view) in a standing adult male figure in classical pose. There are more than 600 muscles in the human body, the most prominent being skeletal (voluntary) muscles which make up 40 to 45% of body weight. Muscles seen here (red) are voluntary muscles in that they are under conscious control. They are composed of bundles of specialized cells capable of contraction & relaxation to create movement. They are attached to the human skeleton by tendons (white); in this way the limbs, spine, pelvis, shoulders and head can move in relation to each other.