Joint-Angle–Dependent Neuromuscular Dysfunctions at the Wrist in Persons After Stroke

The experiment setup. Abbreviations: A/D, analog-to-digital; EMG, electromyographic.

The representative wrist torques (dash-dot lines) and electromyographic signals (solid lines) of the (A) unaffected and (B) affected extensor carpi radialis muscles of a subject during wrist extension at wrist joint of 30°. T_TrialMax(30°) in B was the maximum torque value with respect to the initial resting offset level, T_rest(30°), that the subject could generate at position 30°.

The measured wrist torques during wrist extensions (Ext) and flexions (Fle) across the wrist angles. Torque values were represented by the mean (●, ▴) and standard deviation (error bars), for the unaffected (●) and the affected (▴) groups at different wrist angles during wrist flexion (—) and extension (---).

Normalized wrist torques during wrist extensions and flexions across the wrist angles. The normalized torque values were represented by the mean (●, ▴) and standard deviation (error bars), for (A) wrist flexion and (B) wrist extension of the unaffected group (●) and the affected group (▴) at different wrist angles.

Normalized mEMG of the flexor carpi radialis and extensor carpi radialis during (A, B) wrist flexions and (C, D) extensions across the wrist angles. mEMG was the ensemble mean of the moving-averaged electromyographic activity of a muscle over 100ms before the appearance of the maximal torque value during a wrist contraction.¹⁹ The normalized mEMG mean values were represented by the mean (●, ▴, ○, Δ) and standard deviation (error bars). The normalized mEMG mean values of the flexor carpi radialis were denoted by the unaffected (●), and the affected (▴); and the normalized mEMG mean values of the extensor carpi radialis were denoted by the unaffected (○) and the affected (Δ); the dashed lines with asterisks (--*--) were the mean values of the corresponding normalized wrist torques.

The overall muscle coactivations between different pairs of muscles during both wrist flexion and extension across all wrist angles, represented by the normalized mEMG/mEMG coactivating representations detected experimentally (+) and their linear regressions (red lines). mEMG was the ensemble mean of the moving-averaged electromyographic activity of a muscle over 100ms before the appearance of the maximal torque value during a wrist contraction.¹⁹ The muscle coactivations were illustrated by the correlation between the experimental data and the regression line with correlation coefficient (r); the probability confidence (P); and the slope of the regression line (s). Abbreviations: BIC, biceps brachii; ECR, extensor carpi radialis; FCR, flexor carpi radialis; TRI, triceps brachii.