Tolerance to high-intensity exercise is defined by the power-duration relationship rectangular hyperbola including an asymptote (critical power) and a curvature constant (W′). Critical power distinguishes two domains. Above the critical power, intolerance is predictable and reproducible. Power outputs less than or equal to critical power result in inherently unpredictable exercise tolerance. It is unclear whether or not the power-duration relationship can be manipulated through time deception. Morton (2009) reported improved exercise tolerance in participants viewing a clock calibrated 10% slow without their knowledge. However, the exercise task was inappropriately assigned without respect to the power duration relationship. Further, the time deception effect was only present in a small subsample of men. OBJECTIVE We aimed to measure the effect of time deception on exercise tolerance to a time-normalized supra-critical power task. METHODS Fourteen recreationally-active adults completed the study (22.5 ± 4.3 yr, 172.8 ± 7 cm, 73.6 ± 11 kg, 5 women, 9 men). Volunteers completed constant power bouts to the limit of tolerance while viewing a clock displaying elapsed time. The task was designed to bring about intolerance in 6 min, and therefore was a supra-critical power bout. Unbeknownst to the volunteers, the clock placed in front of the ergometer was randomly assigned to be calibrated correctly, 10% slow, or 10% fast. At the end of the trial participants were given standard encouragement and told their time. RESULTS There was no difference in peak V̇ O2 between the clock calibrations or during a ramp-incremental test (F[2.057, 26.74] =1.144, p=0.422), confirming that the participants were brought to the physiologic maximum in each experimental condition. There was no difference in exercise tolerance across the clock calibrations (F[1.564, 20.33] =1.141, p=0.3262). CONCLUSIONS Contrary to a report in the literature, time deception did not influence exercise tolerance to a supra-critical power task. This argues against exercise tolerance being defined by perceptual limits. Rather, supra-critical power exercise tolerance appears to be more closely related to predictable and reproducible bioenergetic processes.