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Clonus is explained from increased reflex gain and enlarged tissue viscoelasticity
Erwin de Vlugt1, Jurriaan H de Groot, Wessel H J Wisman
1Department of Mechanical Engineering, Laboratory of Neuromuscular Control, Delft University of Technology, Mekelweg 2, 2628 CD Delft, The Netherlands. e.devlugt@tudelft.nl
Journal of Biomechanics
|October 22, 2011
Summary
Ankle clonus in upper motor neuron diseases like stroke and spinal cord injury results from changes in muscle tissue properties and neural pathways. Understanding these factors is key for effective therapy.
Area of Science:
- Neuroscience
- Biomechanics
- Clinical Neurology
Background:
- Upper motor neuron diseases (UMND), including stroke and spinal cord injury (SCI), are associated with neural damage and muscle tissue alterations.
- Differentiating between neural and muscular contributions is crucial for selecting optimal therapeutic strategies for UMND patients.
Purpose of the Study:
- To investigate the influence of Ia reflex pathway gain and muscle tissue viscoelasticity on the development, frequency, and duration of ankle clonus.
- To model the mechanisms underlying ankle clonus in stroke and SCI patients.
Main Methods:
- Utilized Monte Carlo simulations with a nonlinear antagonistic muscle model of the human ankle joint.
- Varied Ia reflex gain by adjusting motor unit pool threshold and gain.
- Modified passive tissue viscosity and elasticity by altering optimal muscle length.
Main Results:
- Tissue viscoelasticity significantly impacted the emergence and persistence of ankle clonus.
- Model predictions accurately reflected observed ankle movement frequencies before and after a sudden damper intervention.
- Higher reflex gains correlated with greater tissue viscoelasticity in patients.
Conclusions:
- Ankle clonus in stroke and SCI arises from a combination of altered motor unit pool properties (decreased threshold, increased gain) and reduced optimal muscle length.
- Findings suggest a relationship between neural changes and muscle tissue properties in the development of ankle clonus.
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