Muscles and Movement

Muscles are stretchy bundles of fibres attached to your bones. When your brain tells a muscle to work, it gets shorter — that is called contracting — and pulls the bone it is attached to. That pull is what makes your body move.

Here is something surprising: muscles can only pull, they can never push. So how do you straighten your arm after bending it? The answer is teamwork. Muscles are arranged in pairs, and they take turns pulling in opposite directions.

Bend your arm and feel the muscle on top, the bicep, become firm and round. It is contracting to lift your forearm. Now straighten your arm: the bicep relaxes and the triceps underneath contracts to pull your arm back down. One pulls while the other rests, then they swap.

Not all muscles are ones you choose to move. Your heart is a special muscle that beats on its own without you thinking about it. The muscles in your stomach and intestines squeeze food along automatically too. These are called involuntary muscles, and they keep you alive every second.