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.

Muscles are joined to bones by tough, stringy cords called tendons. You can feel one at the back of your ankle — that strong cord is the Achilles tendon, and it helps you stand on tiptoes and push off when you run.

Just like the rest of your body, muscles get stronger when you use them. Running, climbing and playing all give your muscles a workout. Eating good food and resting afterwards lets them repair and grow, so you become a little bit stronger each time.