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 ([Formula: see text] ), its fraction (LT2(%)), and cost of running (C(R)), for calculating running speed at lactate threshold 2 (vLT2) in young athletes. 2. The impact of different C(R) determination methods on the accuracy of the model. 3. The contributions of [Formula: see text] , LT2(%), and C(R) to vLT2 in different sexes. METHODS: 45 male and 55 female young squad athletes from different sports (age: 15.4 ± 1.3 years; [Formula: see text] : 51.4 ± 6.8 [Formula: see text] ) performed an incremental treadmill test to determine [Formula: see text] , LT2(%), C(R), and vLT2. C(R) was assessed at a fixed running speed (2.8 [Formula: see text] ), at lactate threshold 1 (LT1), and at 80% of [Formula: see text] , respectively. RESULTS: Experimentally determined and modeled vLT2 were highly consistent independent of sex and age (ICC [Formula: see text] 0.959). The accuracy of vLT2 modeling was improved by reducing random variation using individualized C(R) at 80% [Formula: see text] (± 4%) compared to C(R) at LT1 (± 7%) and at a fixed speed (± 8%). 97% of the total variance of vLT2 was explained by [Formula: see text] , LT2(%), and C(R). While [Formula: see text] and C(R) showed the highest unique (96.5% and 31.9% of total [Formula: see text] , 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 C(R) to accurately predict vLT2. 3. The largest contribution of [Formula: see text] and C(R) to vLT2, the latter being more important in female athletes than in males, and the least contribution of LT2(%).