Video narration
What's happening inside you when you sprint across the PE field to catch up? At first, it feels like one simple action: you decide to run, and your legs move. But that run is a team effort. Your brain sends messages through nerves to the muscles in your legs. The muscles tighten and relax, pulling your bones so you can take each step. As you keep running, your lungs take in air and pass oxygen into your blood. Your heart pumps that blood around your body, carrying oxygen to the muscles doing the work. That's why your breathing gets quicker and your heartbeat speeds up: your working muscles need more oxygen-rich blood. So, what's happening inside you on that run? Your brain signals your muscles; your lungs put oxygen into your blood, and your heart pumps it to working muscles. One run, a whole team.