Is the Functional Threshold Power a Valid Metric to Estimate the Maximal Lactate Steady State in Cyclists?

Lillo-Bevia, JR, Courel-Ibanez, J, Cerezuela-Espejo, V, Moran-Navarro, R, Martinez-Cava, A, and Pallares, JG. Is the functional threshold power a valid metric to estimate the maximal lactate steady state in cyclists? J Strength Cond Res 36(1): 167-173, 2022-The aims of this study were to determine (a) the repeatability of a 20-minute time-trial (TT20), (b) the location of the TT20 in relation to the main physiological events of the aerobic-anaerobic transition, and (c) the predictive power of a list of correction factors and linear/multiple regression analysis applied to the TT20 result to estimate the individual maximal lactate steady state (MLSS). Under laboratory conditions, 11 trained male cyclists and triathletes (V?o(2)max 59.7 +/- 3.0 ml center dot kg(-1)center dot min(-1)) completed a maximal graded exercise test to record the power output associated with the first and second ventilatory thresholds and V?o(2)max measured by indirect calorimetry, several 30 minutes constant tests to determine the MLSS, and 2 TT20 tests with a short warm-up. Very high repeatability of TT20 tests was confirmed (standard error of measurement of +/- 3 W and smallest detectable change of +/- 9 W). Validity results revealed that MLSS differed substantially from TT20 (bias = 26 +/- 7 W). The maximal lactate steady state was then estimated from the traditional 95% factor (bias = 12 +/- 7 W) and a novel individual correction factor (ICF% = MLSS/TT20), resulting in 91% (bias = 1 +/- 6 W). Complementary linear (MLSS = 0.7488 x TT20 + 43.24; bias = 0 +/- 5 W) and multiple regression analysis (bias = 0 +/- 4 W) substantially improved the individual MLSS workload estimation. These findings suggest reconsidering the TT20 procedures and calculations to increase the effectiveness of the MLSS prediction.

Automated summary

This study aimed to investigate the accuracy and repeatability of functional threshold power in estimating the maximal lactate steady state in cyclists. The results showed that the 20-minute time-trial (TT20) had high repeatability but differed significantly from the maximal lactate steady state (MLSS). By applying correction factors and regression analysis, as well as individual characteristics, the estimation accuracy of MLSS can be improved.