A Lactate Kinetics Method for Assessing the Maximal Lactate Steady State Workload

Abstract

During a continuously increasing exercise workload (WL) a point will be reached at which arterial lactate accumulates rapidly. This so-called lactate threshold (LT) is associated with the maximal lactate steady state workload (MLSS_W), the highest WL, at which arterial lactate concentration [LA] does not change. However, the physiological range in which the LT and the MLSS_W occur has not been demonstrated directly. We used minor WL variations in the MLSS_W range to assess arterial lactate kinetics in 278 treadmill and 148 bicycle ergometer exercise tests. At a certain workload, minimal further increment of running speed (0.1-0.15 m/s) or cycling power (7-10 W) caused a steep elevation of [LA] (0.9 ± 0.43 mM, maximum increase 2.4 mM), indicating LT achievement. This sharp [LA] increase was more pronounced when higher WL increments were used (0.1 vs. 0.30 m/s, <i>P</i> = 0.02; 0.15 vs. 0.30 m/s, <i>P</i> < 0.001; 7 vs. 15 W, <i>P</i> = 0.002; 10 vs. 15 W, <i>P</i> = 0.001). A subsequent workload reduction (0.1 m/s/7 W) stopped the [LA] increase indicating MLSS_W realization. LT based determination of running speed (MLSS_W) was highly reproducible on a day-to-day basis (<i>r</i> = 0.996, <i>P</i> < 0.001), valid in a 10 km constant velocity setting (<i>r</i> = 0.981, <i>P</i> < 0.001) and a half marathon race (<i>r</i> = 0.969, <i>P</i> < 0.001). These results demonstrate a fine-tuned regulation of exercise-related lactate metabolism, which can be reliably captured by assessing lactate kinetics at the MLSS_W.