Effect of sensory feedback from the proximal upper limb on voluntary isometric finger flexion and extension in hemiparetic stroke subjects

Abstract

This study investigated the potential influence of proximal sensory feedback on voluntary distal motor activity in the paretic upper limb of hemiparetic stroke survivors and the potential effect of voluntary distal motor activity on proximal muscle activity. Ten stroke subjects and 10 neurologically intact control subjects performed maximum voluntary isometric flexion and extension, respectively, at the metacarpophalangeal (MCP) joints of the fingers in two static arm postures and under three conditions of electrical stimulation of the arm. The tasks were quantified in terms of maximum MCP torque [MCP flexion (MCP(flex)) or MCP extension (MCP(ext))] and activity of targeted (flexor digitorum superficialis or extensor digitorum communis) and nontargeted upper limb muscles. From a previous study on the MCP stretch reflex poststroke, we expected stroke subjects to exhibit a modulation of voluntary MCP torque production by arm posture and electrical stimulation and increased nontargeted muscle activity. Posture 1 (flexed elbow, neutral shoulder) led to greater MCP(flex) in stroke subjects than posture 2 (extended elbow, flexed shoulder). Electrical stimulation did not influence MCP(flex) or MCP(ext) in either subject group. In stroke subjects, posture 1 led to greater nontargeted upper limb flexor activity during MCP(flex) and to greater elbow flexor and extensor activity during MCP(ext). Stroke subjects exhibited greater elbow flexor activity during MCP(flex) and greater elbow flexor and extensor activity during MCP(ext) than control subjects. The results suggest that static arm posture can modulate voluntary distal motor activity and accompanying muscle activity in the paretic upper limb poststroke.

Figures

Fig. 1.

Schematic representation of the 2 arm postures used in the study. The thick black vertical line symbolizes where the subjects' fingers were coupled to the shaft of the servomotor, the thick black horizontal line symbolizes the surface of the experimental table, and the small gray rectangle symbolizes the cushioned support used to support the subjects' arm.

Fig. 2.

Effect of arm posture on maximum normalized metacarpophalangeal flexion (MCPflex; A) and MCP extension (MCPext; B) torque in stroke subjects and control subjects. For each subject group, each box represents the mean value of MCPflex or MCPext, respectively, for the corresponding arm posture (dark gray: posture 1; light gray: posture 2). Bars represent 95% confidence intervals. Asterisks indicate a statistically significant difference between posture 1 and posture 2 (***P < 0.001).

Fig. 3.

Differences between arm postures in net electromyography activity (EMGnet) of the 9 upper limb muscles during the MCPflex (A and C) and MCPext (B and D) trials in stroke subjects (A and B) and control subjects (C and D). For each subject group, each box represents the mean value of EMGnet for the corresponding muscle and the corresponding arm posture (dark gray: posture 1; light gray: posture 2). Bars represent 95% confidence intervals. FDS, flexor digitorum superficialis; EDC, extensor digitorum communis; FCU, flexor carpi ulnaris; B, brachioradialis; BB, biceps brachii; TB, triceps brachii; PM, pectoralis major; LD, latissimus dorsi; DM, deltoideus medius.

Fig. 4.

Differences between stroke subjects and control subjects in net EMG activity (A and B) and coactivation between the targeted muscle and nontargeted muscles (C and D) during the MCPflex (A and C) and MCPext (B and D) trials. Each box represents the mean value for the corresponding subject group (dark gray: stroke subjects, light gray: control subjects) of EMGnet (A and B) for the corresponding muscle or of the coactivation between FDS and each nontargeted muscle X during MCPflex [Xnet/(net FDS activity + Xnet); FDSandX; C] or the coactivation between EDC and each nontargeted muscle X during MCPext [Xnet/(net EDC activity + Xnet); EDCandX; D], respectively, for the corresponding pair of muscles. Bars represent 95% confidence intervals. A and B: asterisks indicate a statistically significant difference between stroke subjects and control subjects (*P < 0.017; **P < 0.01).