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Stroke-Related Changes in Tonic and Phasic Muscle Recruitment During Reaching Reveal Pathway-Specific Motor Deficits
Anna S Korol1, Amelia Adcock2, Valeriya Gritsenko3
1Neuroscience, West Virginia University, Morgantown, WV, USA.
Journal of Central Nervous System Disease
|November 17, 2025
Summary
Stroke survivors show abnormal muscle recruitment, with overactive proximal muscles and reduced distal muscle activation. These neuromuscular deficits impact movement efficiency and may require tailored rehabilitation strategies focusing on both gravity support and coordination.
Area of Science:
- Neuroscience
- Rehabilitation Medicine
- Biomechanics
Background:
- Upper limb motor deficits are common after stroke, persisting despite rehabilitation.
- Current clinical assessments do not fully capture underlying neuromuscular impairments, especially in mild cases, hindering personalized treatment.
- Understanding specific muscle recruitment changes is crucial for developing effective stroke rehabilitation.
Purpose of the Study:
- To characterize stroke-related changes in muscle recruitment during reaching.
- To differentiate tonic (gravity-compensating) and phasic (dynamics-related) electromyography (EMG) activity components.
- To investigate how these components are altered in individuals post-stroke.
Main Methods:
- Surface EMG was recorded from 12 upper limb muscles during reaching tasks in stroke survivors and control groups.
- Principal component analysis was used to extract and compare tonic and phasic EMG components.
- Statistical analyses, including generalized linear mixed-effects models, evaluated group differences.
Main Results:
- Individuals with stroke exhibited abnormal muscle recruitment, including overactivated proximal muscles and reduced phasic activation of distal muscles.
- Muscle activation patterns were altered, with reduced phasic activation worsening over time post-stroke.
- Hemisphere-specific coactivation patterns were observed, correlating with impaired intersegmental dynamics compensation.
Conclusions:
- Stroke leads to distinct but interacting deficits in tonic and phasic muscle recruitment.
- Persistent overactivation of proximal muscles and reduced distal phasic activation are key findings.
- Rehabilitation should target both inefficient antigravity support and impaired intersegmental coordination for improved movement efficiency.
