Muscle shortens and develops tension so that movement is brought about. Muscles are divided into two types - striated muscle, smooth muscle: include skeletal and cardiac muscles. Characterised by alternating light and dark band. 40% of the body is skeletal muscle, 10% of the body is smooth and cardiac muscles. Skeletal muscles - attached to bones, they are under voluntary control. When contact move the body or part of the body their contraction depends on its nerve supply. The human body contains over 400 voluntary skeletal muscles. Functions: Force production for locomotion and breathing, force production for maintaining posture and stabilising joints, heat production, help venous return.