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## Description

Tolerance for high-intensity constant power exercise is dictated by the hyperbolic relationship between power and duration. This relationship is defined by two parameters: the asymptote, termed critical power, and the curvature constant (W′). Critical power distinguishes predictable tolerance to high-intensity work from power outputs resulting in unpredictable exercise tolerance. The amount of work that can be completed above critical power is W′. Interestingly, the pacing strategy for which the participant expends W′ affects exercise tolerance in short bouts. Purported mechanisms for this modulation in tolerance are speeding/slowing of oxidative metabolism. One result of speeded kinetics of metabolism could be the preservation of voluntary locomotor power. OBJECTIVE To measure locomotor muscle fatigue dynamics, oxidative kinetics and exercise tolerance during a fast- start pacing strategy compared to a constant power task. METHODS Sixteen volunteers (26 ± 4 yr, 176 ± 7 cm, 76 ± 12 kg, 3 women, 13 men) completed constant and fast-start exercise tasks to the limit of tolerance above critical power. Maximal isokinetic power was measured throughout as an index of locomotor fatigue. RESULTS Compared to constant power pacing, a fast-start pacing strategy resulted in augmented tolerance to supra-critical power exercise of 52 ± 48 s (X F [2] =12.29, p<0.01; CI95 26, 78 s). Tolerance to constant power exercise was reproducible and was not different before and after the fast-start strategy bout. The decline in maximal isokinetic power was not different during constant power and fast- start pacing strategies (F [1, 168] = 1.94, p=0.17), nor was there an interaction of pacing strategy and time (F [5, 168] = 0.48, p =0.79). There were no differences in the time constant for oxidative metabolism for the pacing strategies (p=0.35; CIDiff -9, 7 s). CONCLUSIONS While fast-start pacing improved exercise tolerance and augmented the supra-critical power work tolerance, the dynamics of locomotor fatigue and oxidative kinetics were not different between conditions. Our data argue against a fixed volume of work (W′) above critical power and lend more evidence to the modern view that W′ is a result of a complex conflation of fatigue-related processes rather than a simple work capacity or energy storage.