This is normal skeletal muscle. The thick myosin filaments interdigitate with the thin actin filaments. The thin filaments are anchored at the Z disk, which are the attachment points of adjacent myofibrils by intermediate filaments of desmin and vimentin. Dystrophin and other proteins bind actin and stabilize the sarcolemmal membrane. Thick myosin filaments are kept aligned by myomesin protein forming the M line in the middle of the H band.

Creatine phosphate supplies the energy for the first few seconds of muscle contraction, followed by energy generated from aerobic metabolism or anaerobic glycolysis. Mitochondria supply the ATP to power aerobic contraction. The myoglobin within the myofiber binds oxygen and aids in diffusion of oxygen into the fiber. More myoglobin and more mitochondria are found in type 1 ('slow twitch', oxidative) fibers for sustained contraction. More glycogen, but no myoglobin, provides fast ATP generation via glycolysis in type 2 ('fast twitch', glycolytic) fibers for rapid strength of contraction. Thus, type 1 fibers are more prominent in persons training for a marathon race, while type 2 fibers are prominent in persons training for the 100m dash.