Muscles and movement
The heart is made of a unique muscle type known as cardiac and it never tires. But the body also has many other paired muscles, some voluntary that are attached to the skeleton and help the body move, some involuntary that work the internal organs and cannot be controlled. Muscles and posture also go hand in hand, where regular exercise tones muscle and improves your posture to reduce strain on other parts of the body.
Cardiac muscle is unique to the heart. It never tires.
The body's involuntary muscles work our internal organs. They are outside our control.
Voluntary muscles make the body move. They are attached to the skeleton and can be controlled.
Voluntary muscles have fast twitch and slow twitch fibres. Fast twitch fibres contract quickly, but do not use oxygen well and tire quickly. Slow twitch fibres contract slowly, but use oxygen well and keep going for a long time. Top sprinters have more 'fast twitch' fibres. Endurance athletes tend to have more 'slow twitch' fibres.
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