The human body has a very large number of muscles throughout the body, about 639. Muscle consists of about 6 billion muscle fibers, the longest fiber may be up to 60cm and the shortest may be only about 1mm. Human muscles account for about 35%-45% of the body’s weight, and they contain a lot of water inside. Important muscles in the body include the masticatory and facial muscles of the face, and the sternocleidomastoid muscles of the neck. There are also the pectoralis major, pectoralis minor, latissimus dorsi, and deltoid muscles of the chest, and the rectus abdominis, external obliques, and internal obliques abdominis of the abdomen. The muscles of the limbs, mainly include the biceps, triceps and quadriceps, gastrocnemius and flounder muscles.