Modeling lactate threshold in young squad athletes: influence of sex, maximal oxygen uptake, and cost of running

Purpose This study aimed to investigate: 1. The influence of sex and age on the accuracy of the classical model of endurance performance, including maximal oxygen uptake ($$\dot{V}\mathrm{O}_{2}\mathrm{peak}$$ V ˙ O 2 peak ), its fraction (LT2%), and cost of running (CR), for calculating running speed at lactate threshold 2 (vLT2) in young athletes. 2. The impact of different CR determination methods on the accuracy of the model. 3. The contributions of $$\dot{V}\mathrm{O}_{2}\mathrm{peak}$$ V ˙ O 2 peak , LT2%, and CR to vLT2 in different sexes. Methods 45 male and 55 female young squad athletes from different sports (age: 15.4 ± 1.3 years; $$\dot{V}\mathrm{O}_{2}\mathrm{peak}$$ V ˙ O 2 peak : 51.4 ± 6.8 $$\hbox {mL} \cdot \hbox {kg}^{-1} \cdot \hbox {min}^{-1}$$ mL · kg - 1 · min - 1 ) performed an incremental treadmill test to determine $$\dot{V}\mathrm{O}_{2}\mathrm{peak}$$ V ˙ O 2 peak , LT2%, CR, and vLT2. CR was assessed at a fixed running speed (2.8 $$ \hbox {m} \cdot \hbox {s}^{-1} $$ m · s - 1 ), at lactate threshold 1 (LT1), and at 80% of $$\dot{V}\mathrm{O}_{2}\mathrm{peak}$$ V ˙ O 2 peak , respectively. Results Experimentally determined and modeled vLT2 were highly consistent independent of sex and age (ICC $$\ge$$ ≥ 0.959). The accuracy of vLT2 modeling was improved by reducing random variation using individualized CR at 80% $$\dot{V}\mathrm{O}_{2}\mathrm{peak}$$ V ˙ O 2 peak (± 4%) compared to CR at LT1 (± 7%) and at a fixed speed (± 8%). 97% of the total variance of vLT2 was explained by $$\dot{V}\mathrm{O}_{2}\mathrm{peak}$$ V ˙ O 2 peak , LT2%, and CR. While $$\dot{V}\mathrm{O}_{2}\mathrm{peak}$$ V ˙ O 2 peak and CR showed the highest unique (96.5% and 31.9% of total $$R^2$$ R 2 , respectively) and common (– 31.6%) contributions to the regression model, LT2% made the smallest contribution (7.5%). Conclusion Our findings indicate: 1. High accuracy of the classical model of endurance performance in calculating vLT2 in young athletes independent of age and sex. 2. The importance of work rate selection in determining CR to accurately predict vLT2. 3. The largest contribution of $$\dot{V}\mathrm{O}_{2}\mathrm{peak}$$ V ˙ O 2 peak and CR to vLT2, the latter being more important in female athletes than in males, and the least contribution of LT2%.