Slow & Fast Twitch Fibres
Applied Science: BTEC Level 3 National Extended Diploma, topic 1.5.5
Slow and Fast Twitch Fibres
There are two types of skeletal muscle fibres: slow and fast twitch fibres. They differ in their location, structure and properties.
Location
- Slow twitch fibres -
- Found in muscles used for posture such as the back and neck.
- Fast twitch fibres -
- Found mainly in muscles such as the arms and legs.
Adaption to function
- Slow twitch fibres -
- Adapted for endurance and slow movement over long periods of time.
- Muscle fibres are long and thin.
- The muscles fatigue slowly and contract slowly.
- Fast twitch fibres -
- Adapted for fast or strong movement over short periods of time.
- Muscle fibres are short and wide.
- The muscles fatigue quickly and contract quickly.
Energy source
- Slow twitch fibres -
- Rely on energy released through aerobic respiration.
- Fast twitch fibres -
- Rely on energy released through anaerobic respiration.
Cell structure
- Slow twitch fibres -
- Lots of mitochondria to maintain aerobic respiration.
- Lots of capillaries to supply muscle fibres with oxygen.
- Low levels of glycogen.
- Low levels of phosphocreatine.
- Large stores of myoglobin (pigment that stores oxygen), so appear reddish.
- Less sarcoplasmic reticulum (contains calcium ions).
Cell structure (cont'd)
- Fast twitch fibres -
- Fewer mitochondria.
- Fewer capillaries.
- High levels of glycogen.
- High levels of phosphocreatine.
- Small stores of myoglobin.
- More sarcoplasmic reticulum.
Test yourself on Slow & Fast Twitch Fibres
What are the two types of skeletal muscle fibres?
Which of the following statements about slow and fast twitch fibres are true?
Which of the following are NOT true for fast twitch fibres?