Purpose Understanding physiological determinants of lactate threshold 2 (LT2) is crucial for tracking adaptations and deriving individualized training recommendations in cycling. Therefore, the study investigated: 1. the accuracy of modeling power output at LT2 in young athletes of both sexes using maximal oxygen uptake (VO2peak), fractional utilization of VO2peak (%VO2peak), and oxygen cost of cycling (Cc); 2. the influence of Cc determination on the model accuracy; 3. the influence of the model predictors and inclusion of maximal lactate accumulation rate (cLamax) on power at LT2 depending on sex. Methods Eighty-three cyclists and triathletes (22 females, 61 males; age [median and IQR]: 14.6 [13.8-17.6] years, VO2peak [mean ± SD]: 59.2 ± 6.5 mL·kg¹·min¹) performed an incremental test to determine power at LT2, VO2peak, %VO2peak at LT2, and Cc (assessed at 3 W·kg-1, 75% VO2peak, and 90% LT2). Results Modeled and experimentally determined power at LT2 demonstrated excellent agreement for all, male and female athletes (ICC = 0.961), with Cc at 90% LT2 providing the highest accuracy (ICC = 0.986). The three physiological determinants explained = 98% of the variance in power at LT2, with the largest unique contribution from VO2peak (62 and 67% of total R²), followed by Cc (8 and 34%) and %VO2peak at LT2 (5 and 12%) in males and females, respectively, while cLamax did not improve the regression. Conclusion VO2peak, %VO2peak at LT2 and Cc accurately predict power at LT2 in young cycling athletes independent of sex, with determination of Cc at 90% LT2 providing the highest accuracy. While VO2peak contributes most to LT2 in both sexes, Cc appears more important in young females.
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