Aberrant co-contraction of agonist and antagonist muscles in post-stroke hemiparetic patients : relation to motor impairment

Abstract EN

Background: Impairment of upper limb function is a common problem following hemiplegic stroke.

The aim of this study is to assess the extent of aberrant co-contraction of agonist/antagonist muscles during voluntary movement of the paretic upper extremity and its relation to motor abilities assessed by motor scales.

Methodology: Twenty post-stroke hemiparetic patients were evaluated.

Modified Ashworth Scale was used as a measure of spasticity.

Upper limb motor impairment was assessed with the Fugl-Meyer motor assessment scale (FMS).

Integrated electromyographic activities (IEMG) of wrist extensors and flexors were simultaneously recorded during isometric wrist extension (WE) and were simultaneously recorded during isometric wrist flexion (WF).

The degree of co-contraction and the strength of contraction were assessed.

Co-contraction was calculated as ratio of antagonist to agonist IEMG.

Strength of contraction was calculated as ratio of affected to non-affected IEMG.

The affected and the non-affected side were compared.

Results: Significant differences were found between the affected and the unaffected sides regarding the measured parameters.

The degree of co-contraction was significantly greater in the affected limb during WE (p<0.001) and WF (p<0.001) and was found to correlate significantly with FMS during WE (r=-0.847, p<0.001) and WF (r=-0.736, p<0.001).

The degree of co-contraction measured during WE and WF correlated with the degree of spasticity (r=0.841, p<0.001 and r=0.480, p<0.001 respectively).

It was also found to correlate with strength of contraction of wrist extensors (r=-0.654, p=0.002) and flexors (r=-0.737, p<0.001).

Conclusions: Co-contraction is a manifest phenomenon in paretic upper extremity.

Its degree correlates significantly with motor impairment.

Antagonist co-contraction can contribute, in part, to weak agonist activity further contributing to impaired functional abilities of post-stroke hemiparetic patients.