| Cross education refers to the casual muscle contractions caused by a long-term training or unilateral electrical stimulation on human body, or even imagination about sports, which increased the strength of both the training mucles and their contralateral counterparts. Most studies confirmed that the reason for strength cross transfer after a long-term strength training or unilateral electrical stimulation was not the hypertrophy of muscle structure, but the neurogenic changes mainly. That is to say no changes in strength origin of muscles. To further clarify the cross education of central mechanism caused by the electrical acupuncture stimulation, this study put forward the following hypothesis: a long-term unilateral electrical acupuncture was significantly effective for increasing the strength of tibialis anterior muscle, in which the adaptive change of the excitability of cerebral cortex and corticospinal played an important role. Thus, a four-week long experiment was designed to observe the muscle strength of the bilateral tibialis anterior in maximum casual isometric contractions by the unilateral electroacupuncture on the right lower limb Zusanli(ST36) and Xiajuxu(ST39), in which the MEP of tibialis anterior muscle was evoked by a single-pulse transcranial magnetic stimulation and the related indicators that represented the adaptive changes of the excitability of motor cortex were recorded. This study further explored the central mechanism of cross education phenomenon by unilateral electroacupuncture acupoints and provided a theoretical basis for the rehabilitation of stroke patients with hemiplegia and postoperative fracture braking as well as muscle dysfunction caused by severe skin damages and so on.Objectives To examine the adaptive changes of the excitability of motor cortex and corticospinal before and after electroacupuncture on the Zusanli(ST36) and Xiajuxu(ST39) of the right tibialis anterior muscle by transcranial magnetic stimulation(TMS), and explore the adaptive regulation mechanism of the central nervous system caused by the increased strength cross education of unilateral limb after electroacupuncture.Methods Participants were 21 right foot boys from Tianjin university of sports, all non-sport professionals, who were randomly divided into 2 groups: 11 of them in the electric acupuncture acupoints group(E- ACUP group)and the other 10 participants in the control group(CON group). The acupoints were the Zusanli(ST36) and Xiajuxu(ST39) on the tibialis anterior muscle of the right leg.The current was an intermittent constant flow with a 5s intermittent cycle. The electroacupuncture frequency was 50 Hz and the pulse width was 0.5 ms. The advisable current was the maximum tolerance which could cause muscle contractions. 20 stimulations were conducted in 4 weeks with five times each week, and 30 mins each time. The maximum voluntary contraction(MVC) of the bilateral tibialis anterior muscle, the resting motor threshold(r MT), motor evoked potential(MEP) of the tibialis anterior muscle area and cortical silent period(CSP) before and after the experiment were examined.Results 1. The MVC of the left and right tibialis anterior muscle in E – ACUP group before the experiment were 257.01±31.06 and 264.58±19.69, and after the experiment were 302.5±19.69 and 295.35±17.61, which increased by 17.69% and 11.62% respectively, thus there was a significant difference in their increasements(P < 0.001); The MVC of the left and right tibialis anterior muscle in CON group before the experiment were 282.15±16.77 and 282.34±15.87, and after the experiment were 291.14±19.50 and 290.84±19.19,thus there was no significant difference in their increasements(P > 0.05); there was a significant difference in the increasements of MVC percentages between these two groups(P < 0.01). 2. The resting motor threshold of the left motor cortex in E- ACUP group before and after the experiment were 75.18±11.98 and 72.45±11.32, with a significant decrease of 3.63%(P < 0.05); The resting motor threshold of the right motor cortex in E- ACUP group before and after the experiment were 67.82±12.56 and 67.36±12.49, and no significant difference(P > 0.05) occured, but a decreasing trend. The resting motor threshold of the left and right motor cortex in CON group before the experiment were 74.60 ±12.08 and 72.90±10.81, and after the experiment were 74.80±12.27 and 72.90±10.34, with no significant changes(P > 0.05). There was a significant difference in the decreases of the r MT percentages of left cortext between the CON group and the E- ACUP group(P < 0.05). There was no significant difference in the decreases of the r MT percentages of right cortext between the CON group and the E- ACUP group(P > 0.05). 3. In the E- ACUP group, the latency of motor evoked potentials of left motor cortex before and after the experiment were 27.78±2.44 and 25.46±1.91, which was significantly shortened by 8.35%(P < 0.01); and the latency of motor evoked potentials of right motor cortex before and after the experiment were 26.71±3.04 and 26.06±2.87, with no significant changes(P > 0.05) but a trend of shortening. In the CON group, no significant changes occurred in the latency of motor evoked potentials of left and right motor cortex before and after the experiment(P > 0.05). There was no significant difference in the decreases of the percentages of motor evoked potentials latency between the CON group and the E- ACUP group(P > 0.05). 4. There was no significant change of percentages in the amplitude of motor evoked potential of left and right motor cortex before and after the experiment between the CON group and the E- ACUP group(P > 0.05).5. The cortical silent period(CSP) of the left and right motor cortex in E – ACUP group before the experiment were 132.84±28.14 and 138.30±22.21, and after the experiment were 117.27±28.68 and 122.94±24.44, which were shortened by 1.17% and 1.11% respectively, and there was a significant difference in their changes(P < 0.05). The cortical silent period(CSP) of the left and right motor cortex in CON group before and after the experiment had no significant differences(P > 0.05); There was a significant difference in the decreases of the percentages of CSP of the left and right motor cortex between the CON group and the E- ACUP group(P < 0.01).Conclusion By examine the TMS, it was found out that the potential central adaptive mechanism of the cross education of muscle strength increasement after a four-week long continuous unilateral electroacupuncture may be that more excitability of interneurons were activated and suppressed the inhibitory interneurons or inhibitory interneurons excitability, which promoted the signal transmition between the two hemispheres of the brain, thus speeded up the nerve conduction of the bilateral corticospinal tract. The plasticity of corticospinal tract contributed to the neurophysiological mechanism of the strength growth cross education caused by the stimulation of unilateral electroacupuncture in human acupoints. |
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