Progress toward motor recovery with active neuromuscular stimulation: muscle activation pattern evidence after a stroke

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Abstract

Chronic cerebrovascular accident individuals with partial paralysis in an upper extremity typically demonstrate difficulty in voluntarily controlling movement initiation. This study investigated patterns of electromyogram (EMG) activation levels while stroke subjects voluntarily initiated their impaired wrist and finger extensor muscles. Twenty subjects were randomly assigned to either a unilateral movement/stimulation group or a bilateral movement/stimulation group. Participants completed 4 days (6 h over 2 weeks) of active neuromuscular stimulation (i.e., 5 s/trial, 90 trials/day, biphasic waveform) on the wrist and finger extensors according to group assignments. The EMG activation levels were analyzed with a three-factor mixed design Motor recovery protocol×Session block×Trial block (2×2×3) ANOVA with repeated measures on the second and third factors. This robust analysis revealed higher EMG activation levels for the coupled bilateral movement/stimulation group than the unilateral movement/stimulation group. In addition, higher muscle activation levels were found for the second session block as well as trial blocks 2 and 3. Overall, these findings indicated improved motor capabilities of the impaired muscles as evidenced by the higher voluntary EMG activation levels.

Introduction

Neuromuscular stimulation is a promising protocol for the motor recovery and relearning required after a cerebrovascular accident (CVA). Motor relearning has become a focal point to neurologists, physiatrists and stroke rehabilitation specialists for two reasons: (a) recent survival rates have increased the number of individuals attempting to cope with partial paralysis and (b) 66% of the survivors display distinct motor disability characteristics 1-year post-CVA [1], [2], [3]. Once spontaneous recovery plateaus in the first year poststroke, then assistance such as active neuromuscular stimulation becomes imperative for upper extremity movements to be executed. Indeed, numerous neuromuscular stimulation studies have reported improved motor capabilities for individuals beyond the first year poststroke [4], [5], [6], [7]. Moreover, Cauraugh and Kim [5] report that when electromyogram (EMG)-triggered neuromuscular stimulation is coupled with bilateral movements, greater improvements in functional motor capabilities accrue (e.g., higher number of blocks moved, faster movement onset in a chronometric reaction time task and less variability in a sustained contraction task).

Despite the continued development in the neuromuscular stimulation and motor relearning literature, Nudo [3] recently stated that the optimal frequency, intensity and timing of motor recovery training protocols remain to be determined. Moreover, the above points were reiterated by Burridge and Ladouceur [6] in a critical review of the clinical and therapeutic applications of neuromuscular stimulation. Most importantly, both sets of prominent researchers agree that the optimal intensity and frequency of the neuromuscular stimulation for motor relearning have not been empirically resolved.

Given that no previous studies have empirically quantified the efforts to initiate and execute voluntary motor actions by individuals with chronic hemiparesis, a first step in determining the optimal intensity and frequency of neuromuscular stimulation is to investigate the pattern of voluntary EMG activation levels for active neuromuscular stimulation. Specifically, what is the effect of 4 days (6 h) of active neuromuscular stimulation (i.e., 5 s/trial, 90 trials/day, biphasic waveform) on the muscle activation patterns of the wrist and fingers during extension movements? For the neuromuscular frequency and intensity tested in Cauraugh and Kim's [5] study, two specific motor recovery protocols were examined: (a) EMG-triggered neuromuscular stimulation provided by surface electrodes on the impaired wrist and finger muscles and (b) EMG-triggered neuromuscular stimulation on the impaired wrist/finger muscles coupled with bilateral movements with the unimpaired wrist and fingers. This training effect study on voluntary muscle activation levels compared activation (initiation) patterns for the unilateral movement/stimulation and bilateral movement/stimulation motor recovery protocols. Moreover, the objectives of this study were consistent with the suggestion by Chae and Yu [7] that researchers should determine and confirm the efficacy of motor recovery protocols.

Section snippets

Subjects

Twenty participants, 4 females and 16 males (M age=63.03 years), volunteered to participate in the motor recovery study. All subjects were more than 1 year post-CVA and the average length of time since stroke onset was 33.86 months. Eleven of the subjects had a left hemisphere CVA (six unilaterals and five bilaterals) and nine had a right hemisphere CVA (four unilaterals and five bilaterals). Chronic hemiparesis was a common problem for each subject. Participants were randomly assigned to one

Results

The Motor recovery protocol×Session block×Trial block (2×2×3) ANOVA with repeated measures on the last two factors revealed three significant main effect findings. As seen in Fig. 1, the reliable motor recovery protocol effect [F(1,18)=5.86, p<0.03] indicated higher EMG activation levels during training for the bilateral movement/stimulation group in comparison to the unilateral/stimulation group. Further, a measure of the magnitude of the effect indicated that a relatively large amount of the

Discussion

Determining whether a training effect was evident in the pattern of voluntary EMG activation levels for two stroke motor recovery protocols was the primary purpose of this study. The three significant main effect findings provide evidence favoring an EMG activation level training effect. Specifically, the higher activation levels produced by subjects in the bilateral movement and stimulation group indicate an increased ability to voluntarily turn on the wrist and finger extensors in comparison

Acknowledgements

An award to the first author from the American Heart Association, Florida/Puerto Rico Affiliate, supported this work.

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