Modeling lactate threshold in cycling—influence of sex, maximal oxygen uptake, and cost of cycling in young athletes

Abstract

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 (

$${\dot{V}}\textrm{O}_{2_\textrm{peak}}$$



V
˙


O

2
peak





), fractional utilization of

$${\dot{V}}\textrm{O}_{2_\textrm{peak}}$$



V
˙


O

2
peak





(%

$${\dot{V}}\textrm{O}_{2_\textrm{peak}}$$



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˙


O

2
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 (

$${\dot{c}}La_\textrm{max}$$



c
˙

L

a
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,

$${\dot{V}}\textrm{O}_{2_\textrm{peak}}$$



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peak





[mean ± SD]: 59.2 ± 6.5 mL⋅kg–1⋅min–1) performed an incremental test to determine power at LT2,

$${\dot{V}}\textrm{O}_{2_\textrm{peak}},$$



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˙


O

2
peak


,



%

$${\dot{V}}\textrm{O}_{2_\textrm{peak}}$$



V
˙


O

2
peak





at LT2, and Cc (assessed at 3 W⋅kg–1, 75%

$${\dot{V}}\textrm{O}_{2_\textrm{peak}},$$



V
˙


O

2
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

$${\dot{V}}\textrm{O}_{2_\textrm{peak}}$$



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˙


O

2
peak





(62 and 67% of total

$$R^2$$


R
2



), followed by Cc (8 and 34%) and %

$${\dot{V}}\textrm{O}_{2_\textrm{peak}}$$



V
˙


O

2
peak





at LT2 (5 and 12%) in males and females, respectively, while

$${\dot{c}}La_\textrm{max}$$



c
˙

L

a
max




did not improve the regression.


Conclusion



$${\dot{V}}\textrm{O}_{2_\textrm{peak}}, $$



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˙


O

2
peak


,



%

$${\dot{V}}\textrm{O}_{2_\textrm{peak}}$$



V
˙


O

2
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

$${\dot{V}}\textrm{O}_{2_\textrm{peak}}$$



V
˙


O

2
peak





contributes most to LT2 in both sexes, Cc appears more important in young females.