CHARACTERISTICS OF MUSCLE RELAXATION CONTROL IN STROKE HEMIPLEGIC PATIENTS

H. Matsumoto^1,2, Y. Takenaka², K. Sugawara²

¹Division of Rehabilitation, Shonan Keiiku Hospital, Kanagawa, Japan, ²Division of Physical Therapy Science, Graduate Course of Health and Social Work, Kanagawa University of Human Services, Kanagawa, Japan

Background: Spasticity in stroke patientsis accompanied by involuntary contractions, indicating voluntary muscle relaxation difficulties.

Purpose: The present study has been aimed at understanding the characteristics of voluntary muscle relaxation control ofthe spastic muscles of stroke hemiplegic patients. Additionally, we examined the repeated muscle relaxationeffects on muscle output and activity before and after relaxation practice to understand themechanisms of muscle relaxation control.

Methods: The subjects were 11 stroke patients with moderate-to-mild paralysis, as per theFugl-Meyer assessment scale. Electrodes were applied to the biceps brachii (BB), triceps brachii (TB), flexor carpi radialis (FCR), and extensor carpi radialis (ECR) muscles on the paralyzed side using surface electromyography (EMG). The exercise task was to perform isometric elbow flexion in a sitting posturewith the shoulder joint in a drooped position and the elbow joint flexed at 90°. The muscle output was determined based on the maximum voluntary contraction (MVC) and was set at 20% and 60% MVC. Muscle output wasvisually adjustedby checking the output meter. While maintaining this state, the subjects were asked to quickly relax their muscles to a randomly presented response signal 100 timesas a practice task.Before and after exercise, muscle tension changes and muscle activity due to muscle relaxation were recorded and measured 10 times each in the same manner at both 20% and 60% MVC outputs as the test was conducted. The waveforms of the surface EMG were rectified, root mean square (RMS) was performed, and the results were compared by dividing the waveforms by 100 ms before the response signal and 100-almost 1000 ms after the response signal (0 ms) as the base point.

Results: Muscle activity was significantly reduced (P <0.05) after repetitive exercises in the antagonist TB and ECR, the co-muscles of the antagonist muscles. This was more remarkable under the 60% MVC condition (P <0.001).In contrast, the BB, the main action muscle, showed a significant increase in muscle activity after repetitive movements and a significant decrease over time. FCR, the co-muscle of the main action muscle, decreased with time, but there was no significant difference before and after the repetitions (P <0.05).

Conclusions: In stroke patients, the activity of the antagonist muscle, TB, and its co-muscle, ECR, significantly decreased with repetitive exercises, suggesting that the effect was due to repetitive exercises and that voluntary smooth muscle relaxation could be performed. As a result, the joint contraction due to spasticity decreased, and the muscle activity of the BB, the main active muscle, increased. Also,60% MVC required stronger voluntary muscle activity, which suggests that the effect of 60% MVC was to enhance the control over the relaxation of the antagonist muscle, which resulted in a strong effect.

Implications: Involuntary co-contraction of antagonist muscles due to spasticity was reduced by performing repetitive movements in muscle relaxation exercises in stroke patients. We recognizethe need to investigate differences in conditions and methods to understand the kinetic characteristics of muscle relaxation control in stroke patients in the future.

Funding acknowledgements: The authors have no conflicts of interest directly relevant to the content of this article.

Keywords:
Stroke
Muscle relaxation
Motor control

Topics:
Neurology: stroke
Neurology
Musculoskeletal: upper limb

Did this work require ethics approval? Yes

Institution: Sho-nan Keiiku Hospital

Committee: Sho-nan Keiiku Hospital Ethics committee

Ethics number: 45160