Use aerobic energy expenditure instead of oxygen uptake to quantify exercise intensity and predict endurance performance

Endurance performance depends on the body's ability to uptake and utilize oxygen to generate energy As such, scientists often determine exercise intensity and predict endurance performance using the percentage of an individual's maximum aerobic capacity (often expressed as %V O2max ) (4, 10, 12). Scientists calculate %V O2max using an individual's mode-specific, steady-state submaximal V O2 (a measure of exercise economy) and V O2max . However, V O2 is only a proxy for the rate of energy that an individual can generate via aerobic metabolism, because it does not account for substrate oxidation, which affects the energy yield per volume of O 2 uptake (1, 5, 16). The energy yield per volume of O 2 uptake is ~7% greater for carbohydrate versus fat oxidation ( Therefore, accounting for substrate oxidation leads to more accurate calculations of the rate of aerobic energy expended during physical activity and exercise. Accordingly, some recent studies have begun expressing exercise economy as the rate of aerobic energy expenditure (E aero ) (e.g., W/kg or kcalkg 1 min 1 ) rather than V O2 (e.g., ml O 2 kg 1 min 1 )