The Effect of Paired Associative Stimulation on the Speed–Strength Parameters of Human Voluntary Movement

The successful performance of various coordination complexitysports’ motor actions is largely determined by the functional interactionbetween neurons of the primary motor cortex and spinal cord, realizedthrough anatomical and physiological connections between these structures.In experimental studies, it was shown that such functional connectionscan be targetly changed using the method of paired associative stimulation(PAS). The main goal of our research was to determine the effectsof the PAS with stimuli combining at the spinal motor neurons onthe speed-strength characteristics of human’s voluntary movement.The study involved 10 healthy male subjects engaged in sports games, aged18 to 22. The PAS session involved 100 pairs of associative stimulicombined at the spinal motor neurons. Corticospinal excitabilityusing the transcranial magnetic stimulation (TMS) method, the spinalmotor neurons’ excitability through transcutaneous electrical spinalcord stimulation (tSCS), and the speed-strength characteristicsof the maximum voluntary contraction (MVC) of the shin muscles (plantarflexion) were recorded before and after the PAS. Data analysis showedPAS led to an increase in corticospinal excitability, an increasein the torque achieved during 50, 100, 150 and 200 ms of MVC, an increasein the rate of contraction and relaxation of muscles during MVC.These PAS session effects are probably due to the involvement ofa larger number of fast motor units (MU) during MVC and an increasein the efficiency of inhibitory processes in the motor cortex duringmuscle relaxation.