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16 September 2014
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You are here: BBC Science > Human Body & Mind > The Body > Muscles
Fact files

Muscles - Tone

Toning: Nerve impulses trigger contractions that tone your muscles

No control: You're not in control of muscle toning nerve impulses

Firm muscles

Your muscles are in a constant state of partial contraction, which keeps them firm, healthy and ready for action at all times. This is called muscle tone and it's the only aspect of skeletal muscle activity that you cannot control voluntarily. Even when a muscle is relaxed, nerve impulses from your brain stimulate groups of muscle fibres within it to contract and keep your muscle toned.

Flaccid muscles

If the nerve supply to a muscle is destroyed, for example in an accident, its muscle fibres are no longer stimulated to contract in this way. This will cause the muscle to lose its tone and become flaccid. Eventually the muscle will start to waste away.

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