| Objective: For individuals with hemiparesis, weight bearing is commonly used as one of the most effective means to facilitate extensors. There is little direct evidence validating the therapeutic effect of weigt bearing for exciting muscles of the lower extremity, though positive loading response hans been comfirmed in locomotion. Besides, as we kown individuals with hemiparesis, their gravity center often shift, whether the situation link with the motoneuronal excitability is unclear. Spinal motoneurons supplied by the vestibulospinal pathway can be modulated differently in response to postural changes, in normal human, the TS H reflex amplitude is lower when standing than sitting. While for person with Hemiparesis, it remains unclear whether constraint in supraspinal excitation exerts a measurable effect on spinal reflex when the posture is change. This paper uses surface EMG to collect data of triceps surae (TS) H reflex, and to study: 1. The response of H reflex to change of the loading of the involved side immediately and long term exercise; 2. Whether the response of H reflex modulation to the change of posture standing and sitting is alter in person with hemiparesis; 3. Whether long term weight bearing exercise can improve gravity center, and whether the graty center is associated with the situation of the H reflex. To depict the change of H reflex and to clarify the clinical sense is the main purpose of this study.Subjects and methods: 13 strokes and 9 normals are involved in this study. Before test, all the patients accept BRSS. The patients are divided into two groups randomly: Group1-common rehabilitation for 4 weeks; Group2-wearing special shoe more than 3 hours per day in addition. We choose 9 normals as controls. The experiment is divided into two period. The first term record the gravity center of patients. Then all the people were instructed to stand upright on two calibrate scales in three loading conditions by shifting 10%, 50%, 90% of his/her body weight on the test leg and to sit relax with the test leg straight. The distance between each participant's feet was about shoulder width. Neck movement was limited by waering a sponge collar. The subject were encouraged to shift body eight gradually to the test leg without bending the hip and knee joints. Then we elicited TS H reflexs and recorded. The second term (4 weeks later) repeated the operation.We use DNI-200P EMG machine and Ag-Agcl surface electrodes. Deal with the skin carefully when place electrodes and collect the EMG signals of TS H reflex.Use SPSS 11.5 to analyse the data. Use one way ANAVO or two way ANAVO to analyse the difference between groups, Use paired t test to analyse the difference within the groups. The significance is P <0.05, bilateral tested.Results: At the beginning, the H reflex of group1 and 2 is much higher than the normals (P<0.05); Within the groups, normals stanceH reflex is lower than sit (P<0.05), the group1 and 2 did not represent the difference. After 4 weeks treatment, though H reflex is lower than before within the group (P<0.05), here was still no difference between group1 and 2, and they were still higher than the normals. The shift of gravity center was much more better than before in both group1 and 2 within the groups, and group2 is better than group1 (P<0.05).Conclusion: Our results found that, though long term weight bearing exercise of involved side was good for situation of gravity center, which is prerequisite for achieving better balance and ambulation, there was no support for immediate and long term load effect on motoneuronal excitability in standing. This indicates that joint compression with body weight may not be effective for facilitation in the lower extremity. Postural modulation of the H reflex was absent in patients with post-stroke hemiparesis, and failure of H reflex depression of the affected TS in standing appears to be a menace of postural stability. Whether H reflex as a parameter of motoneuronal excitability, can be used a parameter of postural stability of stroke people, the research should be going step futher about its use.
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