International Journal of Exercise Science 8(3): 202-212, 2015. The critical power (CP) concept enables the calculation of time to exhaustion (tLIM) for a given power output above CP using the equation of tLIM = W’/(power – CP), where W’ is the curvature constant, and CP is the asymptote for the power-tLIM relationship. The CP concept offers great promise for prescribing high-intensity interval training (HIIT); however, knowledge on the concept’s sensitivity is lacking (i.e., how much of a difference in W’ expenditure is needed to evoke different metabolic responses). We tested if two different power-tLIM configurations expending identical proportions of W’ would evoke different end-exercise oxygen uptake (VO2) and heart rate (HR) values. Five men and five women completed a graded exercise test, 3-min all-out exercise tests, and intervals prescribed to deplete either 70 or 80% of W’ on separate visits. Consistency statistics of intraclass correlation (ICC a), standard error of measure (SEM), and coefficient of variation (CV) were calculated on end-exercise values. End-exercise VO2 were similar for the 3.5- and 5-min bouts, depleting 70% of W’ (ICC a = 0.91, SEM = 3.23 mL·kg-1·min-1, CV = 8.1%) and similar for the 4- and 5-min bouts, depleting 80% of W’ (ICC a = 0.95, SEM = 2.34 mL·kg-1·min-1, CV = 8.1%). No VO2 differences were observed between trials or conditions (p = 0.58). Similarly, HR values (~181 b·min-1) did not differ between trials or conditions (p = 0.45). Use of the CP concept for HIIT prescriptions of different power-tLIM configurations evokes similar end-exercise VO2 values on a given day. Our findings indicate that \u3e10% W’ depletion is necessary to evoke different metabolic responses to HIIT
