Bioenergetics of Training: 3 Energy Systems | CSCS Chapter 3

Bioenergetics governs the conversion of macronutrients into ATP, the body's primary energy currency, through continuous catabolic and anabolic reactions. Human movement relies on three overlapping energy systems—phosphagen, glycolytic, and oxidative—which shift dominance based on exercise intensity and duration. The phosphagen system facilitates immediate, high-intensity bursts lasting up to 15 seconds, while glycolysis provides intermediate energy for efforts up to two minutes. The oxidative system, utilizing carbohydrates and fats, sustains long-duration, lower-intensity activity with significantly higher ATP yields. These systems do not operate in isolation but function in a constant ebb and flow. Coaches and sports scientists leverage this physiological framework to implement training methods that target specific metabolic pathways, optimizing performance by matching exercise demands with the appropriate energy system's capacity for ATP resynthesis.