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Stroke-Related Changes in Tonic and Phasic Muscle Recruitment During Reaching Reveal Pathway-Specific Motor Deficits
Anna S Korol1, Amelia Adcock1, Valeriya Gritsenko1
1West Virginia University, Morgantown, WV.
Biorxiv : the Preprint Server for Biology
|July 15, 2025
Summary
Stroke survivors show abnormal muscle recruitment affecting both gravity compensation and movement dynamics. These distinct, interacting neuromuscular deficits impact upper limb function and may require tailored rehabilitation strategies.
Area of Science:
- Neuroscience
- Biomechanics
- Rehabilitation Medicine
Background:
- Upper limb motor deficits are common after stroke, persisting despite rehabilitation.
- Clinical assessments often miss underlying neuromuscular impairments, especially in mild stroke cases.
Purpose of the Study:
- To characterize stroke-induced changes in muscle recruitment during reaching.
- To differentiate tonic (gravity-compensating) and phasic (dynamics-related) electromyography (EMG) activity components.
Main Methods:
- Surface EMG was recorded from 12 upper limb muscles in 8 stroke survivors and 9 controls during reaching tasks.
- Principal Component Analysis (PCA) was used to extract tonic and phasic EMG components.
- Statistical analyses (GLMMs, regression, correlation) compared component amplitudes, tuning, and coactivation patterns.
Main Results:
- Individuals with stroke, even mild, displayed abnormal muscle recruitment and altered directional tuning in proximal muscles.
- Phasic activation of distal muscles was reduced and worsened over time post-stroke (R² = 0.52, p = 0.002).
- Hemisphere-specific alterations in tonic and phasic coactivation were observed, correlating with impaired intersegmental dynamics compensation (R² = 0.67, p = 0.013).
Conclusions:
- Stroke causes distinct yet interacting tonic and phasic muscle recruitment deficits.
- Findings suggest shared disruption of corticospinal and reticulospinal pathways.
- Results support developing neuromechanically-informed tools for personalized stroke rehabilitation.
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