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

To study fusimotor function in stroke patients, we compared the amplitude of stretch reflexes elicited in flexor carpi radialis (FCR) after contraction 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 performed isometric wrist flexions with the wrist alternately in 15 degrees of flexion or extension. After contractions the wrist was moved passively to the mid-position, and stretch reflexes were elicited via controlled mechanical taps delivered over the FCR tendon. For both groups, the amplitude of the stretch reflex was greater after 'hold-short' than 'hold-long' contractions. This finding is consistent with the 'after-effects' of intrafusal fibre activation, and suggests that fusimotor neurones are activated during voluntary contractions of the paretic limb, just as in the limb of a healthy subject.