The body relies on three integrated bioenergetic systems—the phosphagen, glycolytic, and oxidative phosphorylation pathways—to regenerate ATP during exercise. Their relative contributions depend on exercise intensity and duration, with anaerobic metabolism predominating in short maximal efforts and aerobic metabolism becoming the primary supplier during longer efforts. The crossover between anaerobic and aerobic predominance occurs at approximately 75–80 s of maximal exercise.

Quantifying anaerobic energy release during whole-body maximal exercise remains challenging. As direct invasive measures are impractical, researchers rely on indirect approaches such as oxygen deficit, mixed metabolite-based methods, and theoretical models. Each approach incorporates assumptions and methodological variations that contribute to inconsistencies in reported values.

Oxygen uptake increases more rapidly during high-intensity exercise than traditionally appreciated, making a meaningful aerobic contribution even in brief maximal efforts. Faster oxygen kinetics can enhance speed-endurance, delay fatigue, and improve performance, particularly when supported by effective pacing strategies.

Athletes, coaches, and practitioners can optimize performance by tailoring training intensity, work–rest ratios, and pacing strategies to the specific energy system demands of their event. Appropriately prescribed high-intensity training can enhance both anaerobic and aerobic pathways, supporting performance across a wide range of sports.