The Effect of Upper Limb Exhaustive Activity on Corticospinal Excitability and Motoneuron Responsiveness of Lower Limb

The aim of the present study was to investigate the effect of upper limb exhaustive activity on corticospinal excitability and motoneuron responsiveness of lower limb. Ten active males (Age 28.1 ± 2.99yr, Height 1.77 ± 4.1 cm, Weight 75.7 ± 4.98) volunteered to participate in this study and visited the laboratory on three different occasions. After measuring anthropometric features and familiarization with the pull up (exhaustive task) and magnetic and electrical stimulations in the session one, in the second and third visits, motor evoked potential (MEP), cervicomedullary motor evoked potential (CMEP) and maximum direct motor response (Mmax) were assessed immediately, 10 and 20 minutes after the termination of the exhaustive protocol ( perform pull ups until exhaustion,7 sets with 1min rest intervals) ,by the use of magnetic stimulation over the motor cortex and spinal routes and electrical stimulation of peripheral nerve, respectively. The results showed that MEP in the Tibialis Anterior muscle (remote muscle) significantly decreased immediately (P₌0.001) and 10 minutes (P₌0.001) after performing the fatiguing task compared to the resting values. Also, no significant changes in CMEP and Mmax were observed in Tibialis Anterior muscle at any time points relative to the baseline (P= 0.5, P= 0.07). Based on the data obtained in this study, it looks that supraspinal centers account for the spreading of fatigue from the upper limb to the lower limb. Besides, such a supraspinal fatigue needs a considerable time to be recovered.