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

The successful performance of various coordination complexity sports’ motor actions is largely determined by the functional interaction between neurons of the primary motor cortex and spinal cord, realized through anatomical and physiological connections between these structures. In experimental studies, it was shown that such functional connections can be targetly changed using the method of paired associative stimulation (PAS). The main goal of our research was to determine the effects of the PAS with stimuli combining at the spinal motor neurons on the speed-strength characteristics of human’s voluntary movement. The study involved 10 healthy male subjects engaged in sports games, aged 18 to 22. The PAS session involved 100 pairs of associative stimuli combined at the spinal motor neurons. Corticospinal excitability using the transcranial magnetic stimulation (TMS) method, the spinal motor neurons’ excitability through transcutaneous electrical spinal cord stimulation (tSCS), and the speed-strength characteristics of the maximum voluntary contraction (MVC) of the shin muscles (plantar flexion) were recorded before and after the PAS. Data analysis showed PAS led to an increase in corticospinal excitability, an increase in the torque achieved during 50, 100, 150 and 200 ms of MVC, an increase in the rate of contraction and relaxation of muscles during MVC. These PAS session effects are probably due to the involvement of a larger number of fast motor units (MU) during MVC and an increase in the efficiency of inhibitory processes in the motor cortex during muscle relaxation.