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The Muscular System

Muscle fibre types and sporting activity

  • 3 things to know
  • A2 2

Overview

Type I, IIa and IIb fibres, their speed, force, colour and fatigue, motor neurones, fibre mixes for midfielders and rowers, inheritance and training, biopsies and fibre type testing.

What you need to know

Answer each one before you reveal it.

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Evaluation

Evaluate the use of fibre type testing to choose a sport for a young athlete.

Key term

Name the three main types of skeletal muscle fibre.

Key term

Compare the speed of contraction and force of type I and type IIb fibres.

Questions from this subtopic

Each one with the model answer underneath.

  1. 1

    Name the three main types of skeletal muscle fibre.

    Model answer

    The three types are slow twitch type I, fast oxidative glycolytic type IIa and fast glycolytic type IIb. Each fibre type suits a different kind of activity.

  2. 2

    Compare the speed of contraction and force of type I and type IIb fibres.

    Model answer

    Type I fibres contract slowly and produce low force. Type IIb fibres contract fastest and produce the greatest force.

  3. 3

    Which features of type I fibres give them high resistance to fatigue?

    Model answer

    Type I fibres contain many mitochondria and a lot of myoglobin and have a dense capillary supply. The fibres make ATP aerobically, producing little lactic acid.

  4. 4

    Why are type I fibres red and type IIb fibres white?

    Model answer

    Type I fibres contain a lot of myoglobin, a red pigment, and many capillaries. Type IIb fibres have little myoglobin and few capillaries, so they look pale.

  5. 5

    How do type IIb fibres produce energy?

    Model answer

    Type IIb fibres rely on anaerobic energy from large stores of phosphocreatine and glycogen. Type IIb fibres fatigue quickly as hydrogen ions accumulate.

  6. 6

    Describe type IIa fibres.

    Model answer

    Type IIa fibres contract fast and produce high force. Type IIa fibres can work both aerobically and anaerobically and resist fatigue better than type IIb fibres.

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The change is called cardiac .
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AThe target heart rate is about 168 bpm.
BMaximum heart rate is 220 − 18 = 202 bpm.
CThe working is 0.75 × (202 − 65) + 65 = 167.75 bpm.

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