PurposeThis study aimed to determine if durability can be predicted from laboratory measures in a professional cycling population.MethodsData were collected from 10 professional cyclists (age = 19.2 +/- 0.8 yr, body mass = 70.4 +/- 5.5 kg, height = 182.9 +/- 4.0 cm, body mass index = 21.0 +/- 1.3 kg center dot m(-2), V?O-2max = 74.4 +/- 4.8 mL center dot kg(-1)center dot min (-1), critical power [CP] = 5.6 +/- 0.6 W center dot kg(-1), W ' = 23.7 +/- 5.4 kJ). Participants completed a laboratory test and a CP test on two occasions. The second occasion was preceded by a novel fatiguing protocol, which consisted of five bouts of 8-min of exercise at 105%-110% of CP. CP in a fatigued state was expressed as a percentage of the fresh CP and coined delta CP ( increment CP). The Pearson product correlation analysis was conducted to determine the relationship between laboratory-based measures and increment CP.ResultsSignificant positive relationships were found between increment CP and relative peak power output (r = 0.891, P < 0.001), relative maximum oxygen uptake (r = 0.835, P = 0.003), relative power output at the second ventilatory threshold (r = 0.738, P = 0.015), power output at the first ventilatory threshold (r = 0.748, P = 0.013) and relative power output at the first ventilatory threshold (r = 0.826, P = 0.003), gross efficiency at 300 W (r = 0.869, P = 0.001), and at 200 W (r = 0.792, P = 0.006). Significant negative relationships were found between increment CP and carbohydrate oxidation at 200 W (r = -0.702, P = 0.024). A multiple linear regression demonstrated that increment CP can be predicted from laboratory measures (R-2 = 0.96-0.98, P < 0.001).ConclusionsThese findings demonstrate the physiological determinants of durability in a professional cycling population.