1.5.5

Slow & Fast Twitch Fibres

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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.

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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.
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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.
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Energy source

  • Slow twitch fibres -
    • Rely on energy released through aerobic respiration.
  • Fast twitch fibres -
    • Rely on energy released through anaerobic respiration.
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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).
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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.

Jump to other topics

1Principles of Science I

1.1Structure & Bonding

1.2Properties of Substances

1.3Cell Structure & Function

1.4Cell Specialisation

1.5Tissue Structure & Function

1.6Working with Waves

1.7Waves in Communication

2Practical Scientific Procedures and Techniques

3Science Investigation Skills

4Principles of Science II

4.1Extracting Elements

4.2Relating Properties to use of Substances

4.3Organic Chemistry

4.4Energy Changes in Industry

4.5The Circulatory System

4.6Ventilation & Gas Exchange

4.7Urinary System

4.8Cell Transport

4.9Thermal Physics

4.10Materials

4.11Fluids

5Contemporary Issues in Science

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