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Bones and muscles work together — Biology, 7–10 years

Bones support and protect the body, while muscles pull on them to make movement possible. Biology, 7–10 years.

A moving body is a team

Bones form a strong framework, protect important organs and meet at joints such as the elbow. Muscles are attached to bones by tough cords called tendons; when a muscle shortens, it pulls a bone and a joint moves. Muscles work in pairs because they can pull, not push.

Why do we need this system?

An animal needs a firm body to stand, protect its organs and move towards food or safety. The problem is that one material cannot do all three jobs well: hard bones support and protect, while soft muscles pull them into action. Studying bodies revealed this partnership.

Bending an elbow

Try lifting a 500-gram book: 1) your upper-arm bone stays connected to the forearm at the elbow; 2) the biceps at the front shortens and pulls the forearm up; 3) the triceps at the back relaxes; 4) to lower the book, the pair changes roles. The bones act like levers around the joint.

Muscles pull

It is easy to imagine a muscle pushing a bone, because the arm moves out when a muscle tightens. In fact, a muscle can only shorten and pull; the opposite muscle helps return the joint or control the movement. This is why biceps and triceps are a pair rather than one muscle doing everything.

Movement in daily life

Every time you climb stairs, write, chew or catch a ball, bones, joints and muscles share the work. Knowing this helps people protect their bodies: strong bones need useful food and activity, while muscles need practice and rest. Physiotherapists use this knowledge after an injury to rebuild safe movement.

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