Effects of Functional Electromyographic Biofeedback Muscle Training on Cortical Excitability and Lower Limb Motor Function in Chronic Stroke
Background: Impaired force level control is a major deficit of motor control in people with stroke. Electromyograghic biofeedback (EMGBFB) has been suggested by researchers and clinicians to be an useful and effective tool for enhancing control of force level during motor skill learning for people with stroke, but research literatures thus far have yet to provide convincing evidences to support this claim. According to motor learning theory, task-oriented, active learning, feedback manipulation and practice variation are key components to enhance motor function recovery. Developing functional EMGBFB-assisted muscle training based on motor learning concept is important for stroke rehabilitation. In addition, neural imaging studies have shown corresponding brain reorganization and neural plasticity following physical practice of movement skills in people with stroke. It is curious whether EMGBFB augmented physical practice of motor skills enhances brain reorganization. Using brain mapping techniques, in particular, the transcranial magnetic stimulation (TMS), we could investigate neural plasticity accompanying motor function changes induced by physical training, and hence may help to develop safer and more effective training parameters. The purposes of this study are (1) to update recent evidences regarding the effects of EMGBFB in people with stroke with a special emphasis on the outcome in the activity level of ICF model; (2) to determine the effects of constant or variable force exertion practice with 6-week functional EMGBFB-assisted tibialis anterior (TA) muscle training, according to the principles of motor learning, on the TA muscle strength, balance, lower limb motor function, and cortical excitability in people with chronic stroke; (3) to explore the relationship among cortical excitability, TA muscle strength, and motor function in hope to clarify the mechanisms underlying motor improvements after muscle training in stroke patients; (4) to investigate the effects of different doses of EMGBFB-assisted TA muscle training on TA muscle strength in people with chronic stroke. Study Design and Methods: First, randomized control studies about EMGBFB training of stroke were searched in MEDLINE, PEDro, CINAHL and Cochrane Library databases (to October 2011). The effects of EMGBFB in lower limb motor function were compared with conventional physical therapy alone. Second, three participants were randomly assigned to one of the three exercises programs: constant, variable or control to conduct a case-serial report. The constant and variable groups practiced TA muscle contractions with EMGBFB during functional activities for 6 weeks, in 18 sessions of 40 minutes each. Participants in the constant group aimed to produce 100% force output for each movement. Participants in the variable group aimed to produce force output of 100%, 75%, 50%, or 25% in random order. The control participants practiced upper extremity exercises. All participants were evaluated at baseline and at 1 day, 2 weeks, and 6 weeks post-training. Motor outcomes included TA muscle strength, dynamic balance test, walking speed, Timed Up and Go test (TUGT), and Six-minute Walk test (6MWT). TMS was used to measure the motor threshold (MT) and motor evoked potential amplitude (MEP amp). Third, thirty-three stroke participants were randomly assigned to one of three exercise groups: constant, variable, or control to conduct a randomized control study. Study method was descripted in previous case-serial report. Forth, changes in cortical excitability (TMS induced motor threshold, MT), TA muscle strength, and dynamic balance (anterior or posterior weight shift range) were observed longitudinally at baseline, posttest, 2 weeks, and 6 weeks follow up. Fifth, in the analysis about different doses of EMGBFB-assisted TA muscle training, partial data was collected from my previous published EMGBFB study in 2006. Forty participants were classified to one of the three exercise programs: high-EMGBFB (N=13), low-EMGBFB (N=12), or control (N=15). Subjects in the high-MMGBFB group were from constant group in this study, low-EMGBFBE was from previous study, and control group was from control group in both studies, Each program was 4~6 weeks in length, 30 minutes/section, and 2 or 3 sections per week. Each subject in the high-EMGBFB group practiced a total of 1440 trials (80 trials per session for 18 sessions), and the low-EMGBFB group practiced only 240 trials (20 trials per session for 12 sessions) of isotonic contractions in the affected TA muscle. The control group received regular physical therapy emphasizing the upper extremity movement. Affected TA muscle strength was evaluated at baseline, post-training, 2-week and 6-week after training. SPSS 17.0 was used for statistical analysis. Results: Two published abstracts of conferences, one published scientific article, and two ongoing scientific manuscripts were included. First one was a published conference abstract, the purpose was to update recent evidences regarding the effects of EMGBFB in people with stroke with a special emphasis on the outcome in the activity level of ICF model. The main results indicated that EMGBFB used in a dynamic and functional training mode is superior to conventional physical therapy alone for improving walking speed in people with stroke. Details were reported in Chapter II. Second one was a published scientific article, the purpose was to determine the effects of constant or variable force exertion practice with 6-week functional EMGBFB-assisted TA muscle training by a case-serial report. The preliminary data showed that 6-week of EMGBFB-assisted TA muscle training helped to improve TA strength immediately after training. The constant EMGBFB program also enhanced cortical excitability lasting for 6 weeks after training in stroke patients. The EMGBFB is a feasible and potentially effective adjunct therapy for improving TA control after stroke. Details were reported in chapter III. Third one was an ongoing scientific manuscript, the purpose was to further investigate the effect of functional EMGBFB-assisted TA muscle training. Both constant and variable groups showed significant improvements in TA strength. The variable group also showed significant improvements in dynamic balance. All participants showed improvements in walking speed, TUGT and 6MWT. The constant group showed a corresponding significant MT decrement after training. Details were reported in Chapter IV. Forth one was an ongoing manuscript, the purposes were to explore the relationship among cortical excitability, TA muscle strength, and dynamic balance in hope to clarify the mechanisms underlying motor improvements after muscle training in stroke patients. Significant negative correlation between MT and TA muscle strength and between MT and anterior weight shift range were found after training and at follow up. Positive relationship was found between TA muscle strength and anterior weight shift range after training and at 2 weeks follow up. Details were reported in chapter V. Fifth one was a published abstract of a conference, the purpose was to report the effects of different doses of EMGBFB-assisted TA muscle training on TA muscle strength in people with chronic stroke. The high-EMGBFB group showed significant improvement on affected TA muscle strength (p=0.004) compared with the low-EMGBFB and the control groups at post-training and follow-up. Details were reported in chapter VI. Conclusion: (1) Functional EMGBFB-assisted TA muscle training helped to improve strength and facilitate cortical excitability in patients with chronic stroke. Practicing variable force output with augmented faded feedback from the EMGBFB during functional movement transferred the training effects to balance function. (2) Higher dose of EMGBFB-assisted TA muscle training led to immediate and long-term improvement in muscle strength in chronic stroke patients. (3) The relationship between MT and strength or MT and balance was not dependent on the association between strength and balance. This implies that improved cortical excitability may independently contribute to muscle strength and balance function. Thus exercise training specifically for improving strength or improving balance function should be independently designed in stroke rehabilitation. This study highlights the importance of task-related training, motor learning principles and high dosage in EMGBFB training and provides evidence to further understand about the mechanism of motor function recovery induced by exercise training.
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