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Related Experiment Videos

Stretch reflex dynamics in spastic elbow flexor muscles.

R K Powers1, D L Campbell, W Z Rymer

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

Annals of Neurology
|January 1, 1989
PubMed
Summary

Spastic hypertonia may stem from a lower stretch reflex threshold, not increased velocity-dependent responses. This finding challenges previous notions about stretch reflex dynamics in spastic muscles.

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Area of Science:

  • Neuroscience
  • Human Physiology
  • Rehabilitation Medicine

Background:

  • Spastic hypertonia is often characterized by exaggerated stretch reflexes.
  • Previous research highlighted the dynamic nature of stretch reflex output in spasticity.

Purpose of the Study:

  • To investigate the velocity dependence of stretch reflex dynamics in spastic elbow flexor muscles.
  • To test the hypothesis that spastic hypertonia is primarily caused by a decreased stretch reflex threshold.

Main Methods:

  • Studied stretch reflex dynamics in the elbow flexor muscles of 14 hemiparetic subjects.
  • Measured stretch-evoked torque and electromyographic activity in response to varying stretch velocities.

Main Results:

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  • Stretch-evoked torque showed weak dependence on stretch velocity in spastic muscles.
  • Dynamic and static reflex outputs were not preferentially enhanced in spasticity.
  • Stretch reflex dynamics were similar in voluntarily activated spastic and normal muscles.

    • Conclusions:

    • Spastic hypertonia may result from a reduced stretch reflex threshold.
    • Observed velocity dependence in electromyographic activity might be due to a velocity-dependent decrease in reflex threshold, not abnormal responsiveness.