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How do muscles work?

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Quick answer

Muscles work by contracting — shortening to pull on bones and create movement. When a nerve signal arrives, tiny protein filaments inside the muscle slide past each other, pulling the muscle tight, and let go when the signal stops. A nerve signal tells the muscle to contract.

Step by step

  1. A nerve signal tells the muscle to contract.
  2. Inside, protein filaments (actin and myosin) ratchet past each other.
  3. This sliding shortens the muscle, pulling on the bone it's attached to.
  4. Muscles can only pull, not push, so they work in opposing pairs.
  5. Contracting uses energy (ATP) from the food you eat.

People also ask

How do muscles create movement?
They contract, pulling on bones across a joint; because muscles only pull, pairs work in opposition — one bends a joint, the other straightens it.
Why do muscles get tired?
Sustained contraction uses up energy stores and builds byproducts faster than the body clears them, reducing force until you rest.
How do muscles get stronger?
Exercise causes tiny damage that the body repairs by adding muscle protein, gradually making the fibers thicker and stronger.
Why do muscles work in pairs?
Muscles can only pull, not push, so one muscle bends a joint and its partner straightens it.
What makes muscles tired?
Sustained effort depletes energy and builds up byproducts, reducing the muscle's ability to contract.

Part of the guide: How Your Body Works →