Muscle synergy analysis yields an efficient and physiologically relevant method of assessing stroke

Area of Science:

• Neuroscience
• Rehabilitation Medicine
• Biomechanics

Background:

• The Fugl-Meyer Assessment (FMA) is a standard clinical tool for evaluating motor function post-stroke, relying on subjective clinician ratings.
• The physiological underpinnings and objective relevance of individual FMA task items remain underexplored.

Purpose of the Study:

• To objectively evaluate the physiological relevance of FMA upper extremity tasks using muscle synergy analysis.
• To compare muscle activation patterns between healthy individuals and stroke survivors during FMA tasks.
• To identify FMA tasks most sensitive to muscle coordination impairments in stroke.

Main Methods:

• Electromyography (EMG) was used to record activity from 41 upper body muscles in healthy participants and stroke survivors performing 37 FMA upper extremity tasks.
• Muscle synergy analysis was applied to quantify and compare muscle coordination patterns between groups.
• The relationship between muscle synergy merging and stroke severity was investigated.

Main Results:

• Thirteen 'standard' muscle synergies were identified in healthy individuals, capable of reconstructing all observed muscle activity.
• Posterior trunk muscle synergies were consistently activated in healthy participants but often inactivated in stroke survivors with severe impairments.
• Stroke survivors exhibited 'merged' muscle synergies, with merging rates increasing with impairment severity, particularly evident in 26 specific FMA tasks.

Conclusions:

• The FMA captures aspects of physiological motor function and muscle coordination deficits.
• Posterior trunk muscle activity and stability are critical for motor control and recovery after stroke.
• A subset of 26 FMA tasks may be sufficient for evaluating muscle coordination impairments in stroke survivors, suggesting potential for FMA refinement.