Sports Physiology is how the human body adapts to exercise. For the body to perform in sport there are a number of energy systems
the alactic anaerobic system is used by 100m sprinters, producing explosive, short duration, high intensity movements using energy already in the muscles
the lactic anaerobic system is used by 400m runners, producing sustained, high intensity movement
the aerobic system is used by distance runners, energy demands are lower but it is sustained longer