Summary Objectives The aim of this study was to determine the physiological responses and time to exhaustion, at critical power and 5% above, in trained cyclists. Equipments and methods Eleven male cyclists completed an incremental test, three constant work rate tests to exhaustion to determine critical power (CP), and finally two tests until exhaustion at CP and CP plus 5%. Results The modeling of the power-inverse time relationship provided a mean critical power of 295 ± 39 W. Time to exhaustion at critical power was significantly higher than 5% above (22.9 ± 7.5 min versus 13.3 ± 5.8 min). Oxygen uptake, pulmonary ventilation, and blood lactate obtained at the end of the CP plus 5% exhaustion trial were not significantly different from the maximal variables. However, the physiological end values during the CP test were significantly lower compared to the incremental test. Conclusions These data support the idea that CP in trained cyclists is the physiological index that estimates the boundary between heavy to severe exercise domains. Thus, when cyclists exercised at a power output 5% higher than CP, the VO2max was reached at the end of exercise.