The body during exercise
Physical Education · Key Stage 3 · The School
Immediately
Heart rate and breathing rate rise, stroke volume increases, blood is redirected to working muscles, and body temperature climbs so you sweat. All of it serves one purpose: deliver more oxygen and remove more carbon dioxide. Every short-term response answers that single demand.
Over months
Train regularly and the heart muscle thickens, so RESTING HEART RATE FALLS — the same blood moved in fewer beats. Muscles gain capillaries and mitochondria, bones grow denser, tendons strengthen. These take weeks, which is why consistency beats intensity for a beginner.
Systems together
The respiratory system takes oxygen in, the cardiovascular system carries it, the muscular system uses it, and the skeletal system provides the levers. Naming the interaction is what turns a list into an explanation, and it is what the mark scheme rewards.
SHORT-TERM, within minutes: heart rate rises, breathing deepens, you get warm and sweat, muscles feel heavy. All reverse within an hour. LONG-TERM, over months of training: resting heart rate FALLS, the heart wall thickens, more capillaries grow in the muscles, lung capacity rises, bones get denser. A single hard session gives you only the first list — the second is what turning up repeatedly buys.
Why you keep breathing hard after you stop
Finish a hard sprint and your breathing does not settle for a minute or two, even though you are standing still and using almost no energy. That is because your body is paying back what it borrowed: during the sprint it produced energy faster than oxygen could be delivered, and afterwards it has to catch up — restoring the muscles, clearing what built up, cooling you down. The heavier the effort, the longer the repayment. Noticing how long it takes you to settle is one of the more honest measures of fitness available without any equipment.