Purpose: To determine which laboratory measurement best predicts 40 km cycling time-trial (TT) performance. Methods: Fifteen male cyclists performed lactate-threshold (LT), ventilatory-threshold (VT), 5 km and 40 km TT. Key variables of interest were Watts at thresholds. For VT determination we used: breakpoint of ventilatory equivalent of oxygen (VE/VO2); breakpoint of ventilatory equivalent of carbon dioxide (VE/VCO2); V-slope; respiratory exchange ratio (RER)=1 and 0.95. For LT we used Stegmann's individual anaerobic threshold; the stage preceding the second 0.5 mmol L1 increase (Baldari); 4 mmol L1; 1 mmol L1 increase in 3 min; the stage preceding the first 1 mmol L1 increase as criterion methods (<1 mmol). Analyses also included peak power during the incremental threshold tests (MaxVTwatts, MaxLTwatts) and 5 km performance (5Kavgwatts). Results: Regression analyses between VT variables and 40Kavgwatts were significant for V-slope (r2=0.63), VE/VO2 (r2=0.64), RER0.95 (r2=0.53), RER1 (r2=0.57), and MaxVTwatts (r2=0.65). Regressions between LT variables and 40Kavgwatts were significant for Baldari (r2=0.52), 4 mmol L1 (r2=0.36), <1 mmol (r2=0.35), Keul (r2=0.34), and MaxLTwatts (r2=0.51). Regressions between 5K variables and 40Kavgwatts were significant for 5Kavgwatts (r2=0.58). Paired t-tests between these variables and the 40Kavgwatts indicated that absolute power outputs at VE/VO2 (P=0.33), RER0.95 (P=0.93), and 4 mmol L1 (P=0.39) were not significantly different from 40Kavgwatts. Conclusion: We conclude that VT-based variables are generally superior to LT variables relative to predicting 40Kavgwatts, the simplest of several valid measures appears to be VE/VO2.
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