Aim: 

The aim was to assess, in healthy humans, the effects of high blood lactate levels, induced with a maximal cycling, on the excitability of brainstem motoneurons, tested by using the Blink Reflex (BR) recovery cycle.

Methods: 

The study was carried out on 10 male athletes from the Track and Field Team of the University. The study previewed the assessment of BR excitability after an exhaustive exercise. Capillary blood lactate and glucose levels as well as BR excitability were measured before, at the end and 10 minutes after the conclusion of the exercise. The BR elicited by electric stimulation of supraorbital nerve consists of two main responses in orbicularis oculi muscles: the early response, R1, ipsilateral to the side of stimulation, and the late response, R2, bilaterally expressed. The stimulus intensity was adjusted to obtain a well-defined and reproducible ipsi and contralateral R2 in five consecutive trials. The recovery cycle of the R2 component of the reflex was obtained using the paired-stimulus paradigm (conditioning and test electric pulse of equal intensity), at ISI of 100, 600, 1000 and 1500 ms.

Results and Conclusion: 

In these experimental conditions, it was observed that an increase of blood lactate is associated with a significant decrement of R2 component (ipsi- as well as contralateral) at ISI 1000 and 1500 ms. Since impulses that induce R2 component descend to the facial nuclei through a polisynaptic pathway in medulla, an abnormal recovery cycle of the R2 component probably indicate a decreased excitability of interneurons subserving this part of the reflex.