According to the sources, a myofibril has alternate dark and light bands caused by the proteins myosin (thick filaments) and actin (thin filaments) . In a resting muscle fibre, the thin actin filaments extending from opposite 'Z' lines only partially overlap the thick myosin filaments . The central part of the thick filaments not overlapped by thin filaments is called the H-zone . Therefore, the H-zone exists because of the central gap between the set of actin filaments in the A-band .