Variability in submaximal lactate response is correlated with lactate at maximal lactate steady state

This study aimed to determine if individual blood lactate concentration ([BLa]) at maximal lactate steady state (MLSSc) is a repeatable trait and true interindividual variability in MLSSc exists. This study also aimed to determine why interindividual variability in MLSSc exists and whether large interindividual variability in MLSSc is responsible for the persistent variability in the [BLa] response to threshold-based prescription (THR) exercise. 29 participants (14F/15M) were included in the study. Repeated 30-minute constant-load exercise bouts were used to determine power at maximal lactate steady state (MLSSp). Participants completed three total bouts of exercise at MLSSp to determine repeatability and interindividual variability of MLSSc. Participants then completed a 15-minute bout of exercise at 80%MLSSp, to determine the [BLa] response to THR exercise. Large interindividual variability in MLSSc was observed (range= 3.6mmol/L - 12.0mmol/L). Interindividual variability in MLSSc was a repeatable trait, demonstrated by a small mean individual 95% confidence interval width for within-participant MLSSc values ([CIw] = 1.38mmol/L) and intraclass correlation coefficient showing strong absolute agreement in MLSSc across the three exercise sessions (ICC3,1= 0.754). A strong positive correlation was observed between MLSSc and the [BLa] response to THR exercise (80%MLSSp) (r2= 0.51, p< 0.001), however no relationship between aerobic fitness and MLSSc was observed (r2= 0.064, p= 0.18). The results demonstrate that repeatable interindividual variability in MLSSc exists, however the variability is not correlated to aerobic fitness. Furthermore, interindividual variability in MLSSc is in part responsible for the persistent interindividual variability in [BLa] response to THR exercise. (OSF registration: https://doi.org/10.17605/OSF.IO/8VH3Y).