Slow & Fast Skeletal Muscles (AQA A Level Biology): Revision Note

Slow & fast skeletal muscle fibres

• There are two types of muscle fibres in skeletal muscles

  • Fast fibres

  • Slow fibres

• The two fibre types have different properties, so the relative proportion of each present in muscle tissue determines the properties of the muscle

Fast muscle fibres

• Fast muscle fibres:

  • contract rapidly

  • rely on anaerobic respiration for ATP supply

  • fatigue quickly due to lactate production

  • are pale in colour

    • They have few capillaries and are low in myoglobin due to their low oxygen requirements

• Fast fibres are suited to short bursts of high-intensity activity, e.g. in:

  • the limbs of animals that flee predators or hunt prey at high speeds

  • human eyelid muscles

  • biceps and triceps in the upper arms of humans

Slow muscle fibres

• Slow muscle fibres:

  • contract more slowly

  • rely on aerobic respiration for ATP

  • fatigue slowly due to reduced lactate production

  • are darker in colour

    • They have a dense capillary network and are high in myoglobin and haemoglobin due to their demand for oxygen

• Slow fibres are suited to sustained, low intensity activities, e.g. in

  • the limbs of animals that migrate or stalk prey over long distances

  • human back and leg muscles