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Related Experiment Videos

Quantitative relations between hypertonia and stretch reflex threshold in spastic hemiparesis.

R K Powers1, J Marder-Meyer, W Z Rymer

  • 1Sensory-Motor Performance Program, Rehabilitation Institute of Chicago, IL 60611.

Annals of Neurology
|February 1, 1988
PubMed
Summary

Spasticity in hemiparetic subjects is primarily caused by a reduced stretch reflex threshold, not increased reflex stiffness. This finding highlights a key central nervous system disturbance in spastic muscles.

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Area of Science:

  • Neuroscience
  • Biomechanics
  • Motor Control

Background:

  • Spasticity is a common motor disorder following central nervous system injury.
  • It is characterized by velocity-dependent increases in muscle tone and exaggerated stretch reflexes.
  • The underlying mechanisms, specifically the contributions of stretch reflex excitability and muscle-tendon properties, remain debated.

Purpose of the Study:

  • To differentiate the roles of stretch reflex threshold and joint stiffness in generating torque in spastic elbow muscles.
  • To investigate whether altered reflex gain or altered reflex threshold is the primary contributor to spasticity.

Main Methods:

  • Evaluated 14 hemiparetic spastic subjects.
  • Measured stretch-evoked torque in elbow muscles following a constant angular deflection.

Related Experiment Videos

  • Assessed the relative contributions of variations in stretch reflex threshold and total joint stiffness.

    • Main Results:

    • Within-subject torque variations were mainly driven by changes in stretch reflex threshold, not reflex stiffness.
    • Between-subject comparisons showed stiffness differences, but reflex thresholds correlated with torque magnitude.
    • Reflex stiffness estimates were similar in voluntarily activated spastic and normal muscles.

    Conclusions:

    • The primary central disturbance in spasticity appears to be a reduction in the stretch reflex threshold.
    • There is no significant enhancement of reflex gain in spastic muscles.
    • These findings suggest that therapeutic strategies targeting reflex excitability may be beneficial for spasticity management.