The study aimed to assess the reproducibility of power output during a 4 min (TT4) and a 20 min (TT20) time-trial and the relationship with performance markers obtained during a laboratory graded exercise test (GXT). Ventilatory and lactate thresholds during a GXT were measured in competitive male cyclists (n=15;VO2max 67±5 ml · min-1 · kg-1; Pmax 440±38W). Two 4 min and 20 min time-trials were performed on flat roads. Power output was measured using a mobile power-meter (SRM). Strong intraclass-correlations for TT4 (r=0.98; 95% CL: 0.92-0.99) and TT20 (r=0.98; 95% CL: 0.95-0.99) were observed. TT4 showed a bias±random error of - 0.8±23W or - 0.2±5.5%. During TT20 the bias±random error was - 1.8±14W or 0.6±4.4%. Both time-trials were strongly correlated with performance measures from the GXT (p<0.001). Significant differences were observed between power output during TT4 and GXT measures (p<0.001). No significant differences were found between TT20 and power output at the second lactate-turn-point (LTP2) (p=0.98) and respiratory compensation point (RCP) (p=0.97). In conclusion, TT4 and TT20 mean power outputs are reliable predictors of aerobic endurance. TT20 was in agreement with power output at RCP and LTP2.
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