The highest work rate associated with a predominantly aerobic contribution coincides with the highest work rate at which VO2max can be attained.

Purpose: To estimate the highest power output at which predominant energy contribution is derived from the aerobic system (aerobic limit power: ALP) and to compare ALP with the upper boundary of the severe intensity exercise domain.

Methods: Fifteen male individuals participated in this study. The upper boundary was estimated using i) linear relationship between time to achieve $\dot{\text{V}}$ O_2max and time to task failure (P_UPPERBOUND), ii) hyperbolic relationships between time to achieve $\dot{\text{V}}$ O_2max vs. power output, and time to task failure vs. power output (P_UPPERBOUND´), and iii) precalculated $\dot{\text{V}}$ O_2max demand (I_HIGH). ALP was estimated by aerobic, lactic, and phospholytic energy contributions using $\dot{\text{V}}$ O₂ response, blood [lactate] response, and fast component of recovery $\dot{\text{V}}$ O₂ kinetics, respectively.

Results: ALP was determined as the highest power output providing predominant aerobic contribution; however, anaerobic pathways became the predominant energy source when ALP was exceeded by 5% (ALP + 5%) (from 46 to 52%; p = 0.003; ES:0.69). The $\dot{\text{V}}$ O₂ during exercise at ALP was not statistically different from $\dot{\text{V}}$ O_2max (p > 0.05), but $\dot{\text{V}}$ O_2max could not be attained at ALP + 5% (p < 0.01; ES:0.63). ALP was similar to P_UPPERBOUND and P_UPPERBOUND´ (383 vs. 379 and 384 W; p > 0.05). There was a close agreement between ALP and P_UPPERBOUND (r: 0.99; Bias: - 3 W; SEE: 6 W; TE: 8 W; LoA: - 17 to 10 W) and P_UPPERBOUND´ (r: 0.98; Bias: 1 W; SEE: 8 W; TE: 8 W; LoA: - 15 to 17 W). ALP, P_UPPERBOUND, and P_UPPERBOUND´ were greater than I_HIGH (339 ± 53 W; p < 0.001).

Conclusion: ALP may provide a new perspective to intensity domain framework.