Skeletal, striated or “voluntary” muscles: all muscles anchored to bones and aponeuroses and used for locomotion and maintaining posture. Posture is generally maintained as an unconscious reflex, but all skeletal muscles react to conscious control.
Every skeletal muscle has both fast and slow fibers:

  • Fast twitch fibers are “white”, they have an anaerobic functioning: they are faster but can only contract a few times before they tire. They use glucose (derived from glycogen) to work.
  • Slow twitch fibers are “red”, they have an aerobic functioning: they are slower but can contract for very long periods before they tire. They can work using both glucose and fat.