It is traditionally assumed that exhaustion during high-intensity aerobic exercise occurs because the fatigued neuromuscular system is not able to maintain the power output (PO) required by the task despite maximal levels of voluntary effort (1). Marcora & Staiano (2) challenged this assumption by showing that exhausted subjects can produce a PO much higher than the PO required by the task. Criticisms were raised for failing to account for the power-velocity relationship due to ergometer set up (3). In the present study, after a maximal incremental test on a cyclosimulator (Velotron, Racer Mate®) to obtain the peak PO (PPO), the volunteers [n=18; PPO=273 (29)W] performed a constant workload test (CONST) until exhaustion defined as cadence < 90 rpm despite strong verbal encouragement. Each subject had his respective gear ratio defined so that, at the cadence of 90 rpm, the PO of CONST would equal 80% PPO and any increase in the CAD would result in an increased PO due the fixed length of the crank arm and gear ratio. Upon exhaustion, subjects were required to quickly increase their cadence maximally over 10 s (MAXCAD). This all-out effort was unknown by volunteers prior to testing. During CONST, electromyography of the quadriceps muscle (VL+VM+RF) (QEMG) was recorded. The rating of perceived exertion (RPE) was obtained every minute. Repeated measures ANOVA with Bonferroni’s post hoc test was used to analyze the data (p<0.05). CONST lasted 498 (213)s, with high RPE [20 (0.5)] at the end of the test. Albeit lower than MAXCAD before const, PO, cadence, and QEMG during MAXCAD after CONST were significantly higher than PO, cadence, and QEMG during CONST (Table 1). These results show that, albeit significant, the effects of fatigue on the ability to recruit (QEMG) and shorten the locomotor muscles against a given load (cadence) cannot explain why subjects terminate high-intensity aerobic exercise. Indeed, immediately after exhaustion, all subjects were able to achieve during MAXCAD a PO higher than the PO required by the CONST. Therefore, as previously suggested, neuromuscular fatigue does not seem to cause task failure during high-intensity aerobic exercise. High perception of effort appears to be the key factor limiting exercise tolerance in well-motivated subjects.