[RECRUITMENT PATTERNS OF HOMOLOGOUS MUSCLES DURING UNILATERAL MOVEMENT IN HEMIPARETIC SUBJECTS].

BACKGROUND

The presence of unintentional muscular activity, with or without overt movement, in the homologue muscle contralateral to the limb being activated voluntarily, has been documented in both healthy and hemi-paretic populations. This activity has been termed contra-lateral motor irradiation (CMI), mirror movement, associated movement, motor overflow or synkinesis.

OBJECTIVE

To characterize the CMI phenomenon amongst healthy controls and patients with varying degrees of motor ability and also to assess the ability to consciously control this phenomenon.

METHODS

A cross-sectional design was used to study sub-acute (within 6 weeks of the insult) stroke patients; assessments were performed within two weeks of commencing rehabilitation and again after 4 weeks. Healthy controls were assessed once. A simple motor task, unilateral extension of wrist and fingers, was examined. Concomitant muscular activity of the homologue muscle on the contralateral upper limb was the focus of interest; EMG activation was monitored on both sides. The Fugl-Meyer test was used to assess the residual motor capacity of the upper limb.

RESULTS

CMI was demonstrated only in the non-paretic hand during voluntary activation of the paretic hand. The study group, unlike the control group, was unable to consciously reduce CMI.

CONCLUSIONS

Although the mechanisms underlying CMI are poorly understood, they reflect an important aspect of inter-hemispheric relationship in motor control. In stroke patients, CMI monitoring by surface EMG can be used to assess its characteristics following damage to different elements of the motor system.