Critical power and work-prime account for variability in endurance training adaptations not captured by V̇o.

Responses to exercise at a given percentage of one's maximum rate of oxygen consumption (V̇o), or percentage of the power associated with V̇o during a graded exercise test (i.e., P), vary. The purpose of this study was to determine if differences in critical power (P, maximum metabolic steady state) and work-prime (W', the amount of work tolerated above steady state) are related to training-induced changes in endurance. P, W', V̇o, and other variables were determined before and after 22 adults completed 8 wk of either moderate-intensity continuous training (MICT) or high-intensity interval training (HIIT) performed at fixed percentages of P. On average, P increased to a greater extent following HIIT (MICT: 15.7 ± 3.1% vs. HIIT: 27.5 ± 4.3%; = 0.03), but the magnitude of change varied widely within each group (MICT: 4%-36%, HIIT: 4%-61%). The intensity of the prescribed exercise relative to pretraining P, not P, accounted for most of the variance in changes to P in response to a given protocol ( = 0.61-0.64; < 0.01). Although P and V̇o were related before training ( = 0.92, < 0.01), the training-induced change in P was not significantly related to the change in V̇o ( = 0.06, = 0.26). Before training, time-to-failure at P was related to W' ( = 0.52; < 0.01), but not V̇o ( = 0.13; = 0.10) Training-induced changes in time-to-failure at the initial P were better captured by the combined changes in W' and P ( = 0.77, < 0.01), than by the change in V̇o ( = 0.24; = 0.02). Differences in P and W' account for some of the variability in responses to endurance exercise. As the highest percentage of V̇O at which steady state conditions can be achieved, a person's critical power (P) strongly influences the metabolic strain of a given exercise. In this study we demonstrate that training-induced changes in endurance are more strongly related to the intensity of an exercise training program, relative to P than relative to V̇o. Thus, exercise may be more homogenously and effectively prescribed in relation to P than traditional factors like V̇o.