Energy Systems and Metabolism

Energy metabolism is how muscle regenerates adenosine triphosphate (ATP), its energy currency, fast enough to meet the demand of exercise, using 3 overlapping energy systems fuelled mainly by carbohydrate and fat.

Which system predominates depends on how hard and how long the effort is, from a few seconds of maximal power to hours of steady endurance.

For sport and exercise medicine (SEM) this physiology underpins how athletes fuel and recover, explains fatigue and 'hitting the wall', and sits behind conditions such as low energy availability.