Characterization of the coordination of agonist and antagonist muscles among stroke patients, healthy late middle-aged and young controls using a myoelectric-controlled interface.

Objective: The coordination of agonist and antagonist muscles around a single joint plays an important role in daily activities. The aim of this study was to apply a myoelectric-controlled interface (MCI) with different dimensions to investigate stroke- and aging-induced deteriorations in the coordination of agonist and antagonist muscles.

Approach: Eight stroke patients (affected sides), ten healthy late middle-aged controls and eighteen healthy young controls were enrolled to perform tracking tasks during voluntary isometric elbow flexion and extension by modulating their biceps and triceps activities with 1D or 2D MCI. The root mean square error (RMSE) between actual and target agonist activations, normalized agonist and antagonist activations, and co-contraction index (CI) and normalized elbow torque were used to quantify the movement performance.

Main Results: During elbow extension, significant increases in RMSE were identified in stroke patients with increasing MCI dimensionality, whereas significant decreases in normalized agonist and antagonist activations and normalized elbow torque were observed in all three groups. In addition, significant decreases in CI were observed in both control groups (P  <  0.05). During elbow flexion and extension, RMSE increased in the following order: young controls  <  late middle-aged controls  <  stroke patients. By contrast, CI was significantly higher in stroke patients and late middle-aged controls than in young controls, possibly due to stroke- and aging-induced loss of skill in modulating the coordination of agonist and antagonist muscles when meeting the demands of a changing environment.

Significance: This study suggests that 2D MCI might be applied as a rehabilitation tool to achieve fine control of abnormal muscle coordination.