Exercise physiology

Exercise physiology is the way the whole body responds when it is put to work. During exercise, energy demand rises substantially compared with rest. To meet it, the sympathetic nervous system, a part of the nervous system that works without conscious control, kicks in, and the body mounts an integrated response, meaning one coordinated across several organs, that helps maintain homeostasis, its internal balance.

As the workload increases, cardiac output, the amount of blood the heart pumps in one minute, rises. That blood is also distributed differently: it is preferentially diverted from the digestive tract and the kidneys to the muscles that are working. And the lungs respond immediately: pulmonary ventilation, the air moving in and out, increases.

In muscle, work is paid for with ATP, the molecule cells use as their energy currency. But the ATP the muscle has stored is only enough for a few seconds of contraction. It is like the loose change in your pocket: it works for a quick purchase, but not for a big shopping trip. For sustained exertion, such as jogging, the muscle typically uses another pathway, oxidative phosphorylation, which takes place inside the mitochondria, the cell's tiny power plants.