Fast twitch and slow twitch muscles are types of muscle fiber used to perform different kinds of physical activity. For example, slow twitch muscles in the lower leg aid in standing, while fast twitch muscles in the eyelid enable blinking.
Slow twitch muscles have the capacity to work for a long time while tiring slowly, so they are used in endurance activities such as walking and marathon running. Because these muscles use oxygen as fuel, they are red in color. Fast twitch muscles tire quickly because they consume energy at a high rate and make sprinting, jumping and other explosive movements possible. These muscles are anaerobic and are lighter in color.