Objective: 

The accumulation of lactate in the blood after an high-intensity exercise is associated to an increase of lactate extractions by the CNS. However, no information has been yet provided about the influences of blood lactate levels on excitability of the cerebral cortex, in particular, of the motor cortex. The aim of the present study was to examine the effects of high blood lactate levels, induced with a maximal cycling or with an intravenous infusion, on motor cortex excitability.

Materials and Methods: 

The study was carried out on 23 male athletes from the Track and Field Team of the University. Seventeen subject performed a maximal cycling test on a mechanically braked cycloergometer, whereas 6 of them were submitted to the intravenous infusion of a lactate solution (3 mg/kg in 1 min). Before the exercise or the injection, at the end as well as 5 and 10 minutes after the conclusion, blood lactate was measured and excitability of the motor cortex of each subject were evaluated by using the transcranial magnetic stimulation (TMS).

Results: 

In both these experimental conditions, it was observed that an increase of blood lactate is associated with a decrease of motor threshold, i.e. an improvement of motor cortex excitability.

Discussion and Conclusion: 

The main findings of this study were that, after an acute exhaustive exercise, the strong increase of blood lactate is associated with a significant decrease of the motor threshold, i.e. an increase of blood lactate is associated with an improvement of the motor cortex excitability evaluated with TMS. Since we observed that an intravenous infusion of lactate, in subjects not performing any exercises, is associated with a significant decrease of motor threshold, it can be concluded that the raise of blood lactate levels during a maximal exercise is per se capable to improve the excitability of motor cortex.