Why does your heart beat faster when you exercise?

The longer answer

Every beat is your heart squeezing, pushing blood out through tubes called blood vessels, then relaxing to fill up again. It does this all day and all night, even while you sleep, without you ever having to think about it.

Muscles use oxygen to make the energy they need to move. Sitting still, they need only a little. Running, jumping or dancing, they need lots, so your brain tells your heart to beat faster and your lungs to breathe harder.

Exercise is good for your heart. Because it is a muscle, using it hard makes it stronger, just like your legs or arms.

Three things to know

• Your heart is about the size of your fist. Make a fist and hold it in the middle of your chest, a little to the left. That is about how big your heart is, and where it sits.
• A hummingbird's heart beats faster than a drum roll. Its wings flap so fast they hum, and its little heart beats many times every second to keep up.
• You can feel your heartbeat in your wrist. Rest two fingers gently on your wrist, just below the thumb, and you will feel a soft tap, tap, tap.

Try it at home: Feel your heartbeat change

1. Sit quietly, then find the beat in your wrist with two fingers, or put your hand on your chest.
2. Count the taps for 15 seconds while a grown-up watches the clock.
3. Now jump, dance or run on the spot until you are puffed out.
4. Count again for 15 seconds. How many more beats did you count?

Sit and rest for a little while, then count once more to feel your heart slow back down.