Relaxation of muscles happens, when actin and myosin filaments slide away from each other. The striations appear in the striated muscles, due to the alternate bands of myosin and actin. The band of actin, i.e. the I band, is light in colour and with an elastic band called Z line, it is held in the middle. The myosin band has a darker colour and is called the A band and by an elastic band called M line, it is held in the middle.

During contraction, the position of Z line changes in relation to M, line making the muscle fibre shorter. During relaxation, the actin filaments move to their original position and the muscle fibre becomes longer.