Evidence for fusimotor drive in stroke patients based on muscle spindle thixotropy

To study fusimotor function in stroke patients, we compared the amplitude o f stretch reflexes elicited in flexor carpi radialis (FCR) after contractio n of FCR with the wrist held flexed ('hold-short') or extended ('hold-long' ). Seven subjects with impaired hand function and spasticity due to stroke, and seven healthy subjects were investigated. Surface electrodes recorded electromyographic activity of wrist flexors and extensors while subjects pe rformed isometric wrist flexions with the wrist alternately in 15 degrees o f flexion or extension. After contractions the wrist was moved passively to the mid-position, and stretch reflexes were elicited via controlled mechan ical taps delivered over the FCR tendon. For both groups, the amplitude of the stretch reflex was greater after 'hold-short' than 'hold-long' contract ions. This finding is consistent with the 'after-effects' of intrafusal fib re activation, and suggests that fusimotor neurones are activated during vo luntary contractions of the paretic limb, just as in the limb of a healthy subject. (C) 1999 Published by Elsevier Science Ireland Ltd. All rights res erved.