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 ( \({\dot{V}}\textrm{O}_{2_\textrm{peak}}\) ), fractional utilization of \({\dot{V}}\textrm{O}_{2_\textrm{peak}}\) (% \({\dot{V}}\textrm{O}_{2_\textrm{peak}}\) ), 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 ( \({\dot{c}}La_\textrm{max}\) ) 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, \({\dot{V}}\textrm{O}_{2_\textrm{peak}}\) [mean ± SD]: 59.2 ± 6.5 mL⋅kg–1⋅min–1) performed an incremental test to determine power at LT2, \({\dot{V}}\textrm{O}_{2_\textrm{peak}},\) % \({\dot{V}}\textrm{O}_{2_\textrm{peak}}\) at LT2, and Cc (assessed at 3 W⋅kg–1, 75% \({\dot{V}}\textrm{O}_{2_\textrm{peak}},\) and 90% LT2).
Results
Modeled and experimentally determined power at LT2 demonstrated excellent agreement for all, male and female athletes (ICC \(\ge\) 0.961), with Cc at 90% LT2 providing the highest accuracy (ICC \(\ge\) 0.986). The three physiological determinants explained \(\ge\) 98% of the variance in power at LT2, with the largest unique contribution from \({\dot{V}}\textrm{O}_{2_\textrm{peak}}\) (62 and 67% of total \(R^2\) ), followed by Cc (8 and 34%) and % \({\dot{V}}\textrm{O}_{2_\textrm{peak}}\) at LT2 (5 and 12%) in males and females, respectively, while \({\dot{c}}La_\textrm{max}\) did not improve the regression.
Conclusion
\({\dot{V}}\textrm{O}_{2_\textrm{peak}}, \) % \({\dot{V}}\textrm{O}_{2_\textrm{peak}}\) 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 \({\dot{V}}\textrm{O}_{2_\textrm{peak}}\) contributes most to LT2 in both sexes, Cc appears more important in young females.
