Altered force perception in stroke survivors with spastic hemiplegia.

OBJECTIVE

To investigate the effect of spasticity and involuntary synergistic activation on force perception during voluntary activation of spastic paretic muscles.

METHODS

Eleven stroke subjects with spastic hemiparesis performed various isometric elbow-flexion force-matching tasks. Subjects were instructed to generate a target reference force with visual feedback using one arm (impaired or non-impaired) and then to produce a force with the other arm to match the magnitude of the reference force without visual feedback. The reference arm was at rest in unilateral exertion trials and maintained contraction in bilateral exertion trials during the matching force-production period.

RESULTS

Both force and effort mismatches occurred in most conditions, and there were asymmetries in force perception. When the non-impaired arm was the matching arm, effort and force overestimation occurred, but effort was matched better than force. When the impaired arm was the matching arm, force underestimation and effort overestimation occurred, but force was matched better than effort. No difference in matching performance was found between unilateral and bilateral exertion-matching tasks.

CONCLUSION

Overall, both force and effort misperceptions occur in stroke survivors with spasticity. Spasticity and spastic synergistic activation probably contribute to force and effort misperception during voluntary activation in chronic stroke.