Effects of Lactate on Corticospinal Excitability: A Scoping Review.

Aerobic exercise has been shown to impact corticospinal excitability (CSE), however the mechanism(s) by which this occurs is unclear. Some evidence suggests an increase in blood lactate concentration resulting from exercise may be what is driving these changes in corticospinal excitability. The extent of literature examining this effect and whether it is consistent across the literature is unknown. As such, the objective of this scoping review was to summarize the existing literature examining the effect of lactate on corticospinal excitability and to determine any trend(s) in the effect. Embase, CINAHL, Medline, SPORTDiscus, and PsycInfo were systematically searched to retrieve original research reporting on blood lactate concentration and measures of corticospinal excitability associated with aerobic or high intensity interval exercise. Two reviewers independently determined study eligibility, and one reviewer extracted data from all eligible studies. The database search yielded 717 papers of which 9 were determined eligible. Multiple studies in which participants completed high intensity and/or exhaustive exercise showed a correlation between large increases in blood lactate concentration and increased corticospinal excitability, however several other studies noted no difference in corticospinal excitability following an increase in blood lactate concentration. This review showed that the existing body of literature is small and highly variable in both methods and results, therefore we can draw limited conclusions about the role of lactate, however based on the evidence available lactate does not appear to be the key player in the modulation of CSE. In addition, evidence from other literature supports moderate intensity aerobic exercise as a modulator of neuroplasticity, suggesting that there may be other key factors contributing to the changes in the brain following exercise.