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When a person takes part in exercise the cardiovascular, respiratory, energy and muscular systems all work together to supply energy to the working muscles and remove waste products.

When the muscles start to work, they need more oxygen so the respiratory system responds by getting more oxygen into the lungs. The blood carries greater amounts of oxygen and the heart responds to pump more oxygenated blood around the body.

These effects are shown in the table:

After exercising, the muscles need to rest, adapt and recover. There is a risk of injury if the body is not rested for long enough after exercise. This concept can be better understood by studying the Principles of training.

Redistribution of blood flow

During exercise, the cardiovascular system redistributes the blood so that more of it goes to the working muscles and less of it goes to other body organs such as the digestive system. This redirection of blood flow is caused by a mechanism (or process) called the vascular shunt mechanism. It works a little bit like a railway terminal, where trains are directed on to some tracks and stopped from travelling on to others. The blood vessels allow lots of blood to travel to the working muscles but they don't allow much to travel to other organs. When the muscles stop working, the blood distribution returns to its normal route.

Warm up and warm down

Warming up before sport allows the body systems to make all these changes gradually, so they are fully prepared for the stresses placed upon them during the activity.