Slow and Fast Muscles

Slow and Fast Muscles

slow and fast

Depending on the system of respiration they use and how quickly they contract, muscles are classified as either:

  • slow-twitch (type I)
  • fast-twitch (type II)

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.