| Description: |
Quantifying oxidative, glycolytic, and phosphagen energy system contributions during exercise is challenging due to their simultaneous activation and reliance on indirect estimation. This narrative review critically examines the methodological foundations, assumptions, and practical implications of current approaches used to estimate energy system contributions during continuous and intermittent exercise, with the aim of clarifying how these methods shape the interpretation of bioenergetic responses. Oxidative contribution, primarily estimated through oxygen uptake (VO2) integration, typically exceeds (~75–88%) in continuous efforts longer than 6 min and can reach values above ~87% when exercise duration allows full development of VO2 kinetics, particularly in trained young adult cohorts. In contrast, supramaximal efforts shorter than 30–90 s involve markedly lower oxidative contribution, commonly below ~50% and as low as ~8–19%. Glycolytic contribution is inferred from net blood lactate concentration accumulation and increases with exercise intensity, ranging from ~3–5% in longer severe-intensity efforts to values up to ~60% during brief maximal tasks lasting 15–30 s. Phosphagen contribution is estimated using the fast component of post-exercise VO2 recovery or theoretical phosphocreatine breakdown models, and can reach ~39–48% in maximal efforts lasting 10–15 s, while declining to values below ~10% in prolonged exercise. Each method is shaped by exercise duration, intensity, structural format, and physiological assumptions, contributing to methodological heterogeneity and limiting direct comparability between studies. Advances in portable gas analyzers, near-infrared spectroscopy, and biosensing technologies have improved temporal resolution and ecological validity. To enhance the accuracy and practical application of energy system profiling, standardized and integrative frameworks are urgently required. |