The effects of exercise on the body
Biology · Key Stage 2 · The School
Your body works harder
When you exercise, your muscles work harder than usual. Working muscles need more oxygen. They need more energy too. Your body has to respond quickly. It changes how it works, to keep up with that extra demand. These changes happen automatically. You do not have to think about them at all.
Heart rate and breathing rate rise
To send more oxygen to your muscles, your HEART RATE goes up. It beats faster than when you rest. Your BREATHING RATE goes up too. Each breath brings in more oxygen. Both changes happen for the very same reason. You can feel both changes yourself, right after a short run.
Why the changes happen
Working muscles need extra oxygen. That oxygen helps release energy. A faster heart moves blood around the body more quickly. That blood carries the oxygen with it. Faster breathing puts more oxygen into that blood in the first place. Without both changes happening together, working muscles would quickly run short of what they need.
Two people run the same short race. Straight after, both have a fast heart rate and fast breathing. A few minutes later, the fitter person's heart rate has dropped back close to normal. The less fit person's heart is still beating fast. A fitter heart is stronger, so it can pump more blood with each beat. That means it does not need to beat as fast, either during exercise or while recovering afterwards. Regular exercise, over weeks and months, is what makes a heart stronger in this way.