40% of mass in men and 32% in women. 10% muscle and cardiac together: characterizations. Single muscle cell= muscle fiber: large and elongated cylinder. Longest 50 cm: fibers grouped together by ct to make muscle, cell is a bunch of myoblasts that come together during embryonic development. Myofibrils make up muscle fiber: 80% of muscle fiber, has thick and thin filaments, thick filaments. Ct: collagen and elastin surrounds muscle, provides structure and transfer of force to bones, epimysium. Divides muscle fibers into bundles: endomysium. A band: dark, thick filament along with portions of thin filaments that overlap, h zone. Middle of a band where thin filament does not reach: m line. Vertical line of protein keeping thick filaments together. I band: light, thin filament only, z line. In middle of i band filaments of adjacent sarcomeres: sarcomere. One a band, 2 halves of i bands: muscle growth. Flexibility is achieved by adding sarcomeres: titin.