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.
