Adenosine Triphosphate (ATP) is a high-energy compound formed from the oxidation of fat and carbohydrate. It is used as the energy supply for muscles and body functions.
When a muscle contracts and exerts force, the energy used to drive the contraction comes from ATP. However, since the amount of ATP immediately available to the muscle is small, your body begins to produce more ATP by breaking down carbohydrate and fat. Otherwise, the duration of activity would be severely limited. ATP is ultimately the body’s only energy source, and is supplied both aerobically and anaerobically.
ATP is produced aerobically with oxygen throughout the day via the Krebs Cycle. As exercise intensity increases, the muscles demand more energy in the form of ATP, which results in an increased heart rate to delivery oxygen via blood for the production of ATP. Under short-term, high intensity exercise, ATP can be produced anaerobically without oxygen by utilizing Creatine Phosphate store in the muscles.