Interlimb interactions during bilateral voluntary elbow flexion tasks in chronic hemiparetic stroke

Area of Science:

• Neuroscience
• Rehabilitation Medicine
• Motor Control

Background:

• Hemiparetic stroke frequently impairs motor function, affecting interlimb coordination.
• Understanding interlimb interactions is crucial for developing effective stroke rehabilitation strategies.

Purpose of the Study:

• To systematically investigate interlimb interactions in individuals with chronic hemiparetic stroke.
• To examine force production and muscle activation patterns during unilateral and bilateral tasks.

Main Methods:

• Fourteen chronic hemiparetic stroke subjects performed unilateral and bilateral elbow flexion tasks at various force levels (20-100% MVC).
• Elbow flexion force and biceps electromyogram (EMG) were measured bilaterally.
• Tasks were performed without visual feedback, with force output targeted to a visual display.

Main Results:

• Asymmetrical motor overflow (increased EMG in the contralateral limb) was observed during unilateral tasks of the non-impaired limb.
• During bilateral submaximal contractions, the impaired limb exhibited a force deficit (FD), compensated by the non-impaired limb.
• The non-impaired limb's force contribution decreased as contraction intensity increased, and FD appeared in the non-impaired limb during bilateral MVC.

Conclusions:

• Interlimb interactions in chronic stroke are activation level-dependent and involve asymmetrical motor overflow.
• Ipsilateral corticospinal projections from the non-lesioned hemisphere contribute to compensatory mechanisms in interlimb coordination.
• Unbalanced interhemispheric inhibition also plays a role in altered motor control post-stroke.