Human motor system plasticity under local physical load

The rearrangement of neuronal network interaction is observed in the motion control system under the influence of internal and external factors. This phenomenon is called plasticity. We found out that the stimulation of different levels of motor system could cause single involuntary muscle contractions and continued locomotion. Herein, reafference played a significant role. The objective of the study was to investigate different levels of the human motor system plasticity under local load-bearing motor activity. Materials and Methods. The study enrolled 5 volunteers, who conducted local-bearing motor activity for 7 days. Before and after the 7-day training, the authors registered motor responses of the right upper limb under transcranial magnetic stimulation, transcutaneous electric and electromagnetic spinal cord stimulation, and n.musculocutaneus electrical stimulation. Electromyographic and dynamometric characteristics of maximum voluntary contraction were also studied. Results. After a 7-day load-bearing training of the shoulder flexor muscles there were some changes in maximum voluntary contraction power of m. biceps brachii and the muscles motor responses parameters of the upper limb under the cortical, spinal and peripheral stimulations. At the cortical level there was observed an increase in motor cortex area, which caused the upper limbs muscles responses. At the spinal level there was an increase in excitability of afferent input. There were also some changes at a peripheral level. The study of m.biceps brachii motor responses revealed insignificant increase in the excitability of n.musculocutaneus on the first day of the experiment and its decrease on the seventh day as compared with the background. The results proved significant structural plasticity of all motor system levels, which control motion under the influence of load-bearing training.