How do muscles change their shape?
The muscle cells move by contraction and relaxation by utilizing the energy in the form of ATP. Muscle contraction is initiated by the signal sent by the CNS to the muscle fibres. During contraction, the muscles fibres shorten, the muscle pulls on the ligaments that connect the bones and the movable body parts. During relaxation the muscle fibres come to their original position. This movement of muscles cells or the muscle fibres results in the movement of the body parts.