Impairment of voluntary control of finger motion following stroke: Role ofinappropriate muscle coactivation

Subjects with chronic hemiplegia following stroke attempted to perform volu ntary isometric, isokinetic, and free contractions of the extensor muscles of the metacarpophalangeal (MCP) joints. We recorded torque, metacarpophala ngeal joint angle and velocity, and electromyographic (EMG) activity of the extrinsic extensors and flexors and the first dorsal interosseous (FDI), W e found that voluntary MCP joint extension in hemiparetic subjects was grea tly impaired in comparison with control subjects: only two of the 11 stroke subjects were able to generate even 0.21 N-m of isometric extension torque , only two could produce positive finger extension with no load, and none c ould develop an isokinetic concentric extension. Deficits seemed to result from a combination of coactivation of the finger flexor and extensor muscle s and decreased voluntary excitation of the extensors, as normalized flexor and FDI EMG activity were greater for stroke than for control subjects (P < 0,001), but normalized extensor activity was reduced (P < 0,001), (C) 200 1 John Wiley & Sons, Inc.