Slow-twitch muscle

Fast-twitch muscle

• Uses aerobic respiration which means it’s able to contract for long periods.
• Because it depends on an oxygen supply the contraction speed is slow.
• No lactate is produced as a waste product so the muscle doesn’t fatigue.
• It contains a lot of mitochondria and also myoglobin. This protein is similar to haemoglobin and stores energy in the muscles to be used during aerobic respiration. The cells are a red colour.
• It’s located in the heart and certain back and leg muscles.

• Uses anaerobic respiration which means it’s only used during short activity bursts.
  It doesn’t rely on the blood supply so its contraction speed is fast.
  Muscles fatigued, causing discomfort, due
• to a build of lactate and a decrease in pH.
• It contains a lot of glycogen and only a small amount of mitochondria (as they’re not required in anaerobic respiration) and myoglobin. The cells are a white colour.
• It’s located in the finger and arm muscles, the breast muscles of birds, and frog legs.