Direction-Specific Instability Poststroke Is Associated With Deficient Motor Modules for Balance Control.

Area of Science:

• Neuroscience
• Biomechanics
• Rehabilitation Science

Background:

• Deficits in muscle coordination contribute to balance impairment and falls in stroke survivors.
• Understanding muscle coordination during postural control is crucial for stroke rehabilitation.

Purpose of the Study:

• To investigate muscle coordination deficits for postural control in stroke survivors.
• To associate these deficits with body sway following balance perturbations.

Main Methods:

• Compared automatic postural responses of leg and trunk muscles in unimpaired individuals and stroke survivors.
• Elicited responses using unexpected floor translations in 12 directions.
• Extracted muscle synergies using nonnegative matrix factorization and assessed body sway.

Main Results:

• Stroke survivors displayed atypically structured paretic motor modules (muscle synergies) with long latency responses, suggesting direct cerebral involvement.
• Other paretic motor modules showed intact structure but poor recruitment, indicating indirect cerebral control.
• Paretic deficits strongly correlated with direction-specific postural instability.

Conclusions:

• Muscle coordination deficits in the paretic limb cause direction-specific postural instability in stroke survivors.
• These findings highlight the need for targeted interventions addressing patient-specific balance impairments.
• Cerebral lesion location influences the heterogeneity of balance control deficits.