Moderate-intensity exercise-induced changes in lactate do not predict changes in corticospinal excitability

Aerobic exercise increases corticospinal excitability (CSE), creating an optimal environment for learning to occur. It has been hypothesized that this may be a result of lactate accumulation in the blood during exercise. However, while prior literature has linked moderate-intensity exercise with enhanced CSE, previous lactate-based work has mainly used maximal or fatiguing exercise. To date, the effect of lactate concentration on CSE during steady-state moderate-intensity exercise has not been investigated. Twenty-four participants (13F, mean age 23.7 ± 2.7) attended two separate study sessions. Session 1: Participants completed a maximal graded exercise test on a cycle ergometer. Session 2: Participants completed a moderate-intensity exercise session (20 min of cycling at 60% peak power output). Measures of CSE obtained from the first dorsal interosseous muscle were assessed via transcranial magnetic stimulation before, immediately after, and 10 min following the exercise session. Lactate was obtained via blood sample at these same timepoints. Linear regression demonstrated that lactate concentration did not predict an exercise-induced change in CSE immediately following exercise (R² = 0.02184, F(1, 22) = 0.4913, p = 0.4907) or 10 min post-exercise (R² = 0.02121, F(1, 22) = 0.4767, p = 0.4971). These results suggest that lactate is not the primary mechanism behind alterations in CSE driven by moderate-intensity exercise.