Quick revise

After studying this section you should know

There are 3 types of muscle:

1. Cardiac Muscle

  • Only found in the heart
  • Contract and relax continuously
  • Work without conscious effort

2. Involuntary Muscle

  • Around organs like the intestines
  • Work without conscious effort

3. Voluntary Muscles

  • Attached to the skeleton
  • Under your control

Muscle Diagram

Muscle Fibres

  • Muscles are made up of fibres, which are either fast twitch or slow twitch.
  • Everybody has a similar number of fibres, but different people have different proportions of fast twitch and slow twitch
  • People who are fit and have larger muscles have fatter fibres, so more are ready to be used.
  • Nerve impulses tell the muscle to contract when it needs to.
  • Complex movements are made by the coordination of nerve impulses sent to the muscle by the nervous system.
  • Fast twitch and slow twitch are good for different things.

Fast twitch fibres

  • Contract very quickly and powerfully, but get tired quickly.
  • Sprinters and shot-putters have lots of fast twitch fibres

Slow twitch fibres

  • Contract more slowly and with less force, but don’t get tired so quickly.
  • Long distance runners have more slow twitch fibres

Muscle Contraction

To make a joint move in two directions, you need two muscles that pull in the opposite direction.

Antagonistic muscles

  • Pairs pairs of muscles that work against one another
  • One muscle contracts (shortens) whilst the other relaxes (lengthens)
  • The muscle that is doing the work (contracting) is the agonist
  • The relaxing muscle is the antagonist

Synergists muscles -These hold the stationary bone still, so only one bone moves e.g. when the bicep contracts to bend the elbow, synergists stop the shoulder moving.

Isometric Contraction - The muscle stays the same length, so nothing moves

Isotonic Contraction - The muscle changes length, so moves

Muscle Fatigue – if you use your muscles a lot and they don’t get enough oxygen, they feel tired or fatigued

Muscle Atrophy – if you don’t use your muscles, they become smaller

Cramp – a sudden contraction of a muscle that won’t relax

Muscles never fully relax, they always have some tension in them. This is called muscle tone, which is improved by regular exercise.

Muscle Videos


Here are two videos with a good introduction to Muscles and what you will need to know.