Effects of changing wrist positions on finger flexor hypertonia in stroke survivors

Sheng Li*, Derek G. Kamper, William Zev Rymer

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

25 Scopus citations

Abstract

We sought to establish whether spastic hypertonia results from changes in intrinsic muscle properties or from altered stretch reflex properties. We hypothesized that finger flexor spastic hypertonia is primarily of neural origin, and that the dynamics of spastic muscle responses to stretch should therefore reflect the dynamics of muscle spindle receptor responses. In 12 stroke survivors, we recorded torque and electromyographic (EMG) responses of extrinsic finger flexors to constant-velocity rotation of the metacarpophalangeal (MCP) joints of the affected hand, over a range of initial muscle lengths. Stretch velocity was set to 6°, 50°, 150°, or 300° per second. Muscle length changes were imposed by changing wrist angle between 0°, 25°, and 50° of flexion. We found that reflex torque and EMG responses exhibited both velocity and length dependence, and there were significant interactions between velocity and length, replicating known characteristics of muscle spindle receptors. Our results support the hypothesis that finger flexor hypertonia is primarily of neural origin, and that it accurately reflects spindle receptor firing properties.

Original languageEnglish (US)
Pages (from-to)183-190
Number of pages8
JournalMuscle and Nerve
Volume33
Issue number2
DOIs
StatePublished - Feb 1 2006

Keywords

  • Length dependence
  • Muscle spindle
  • Spasticity
  • Stretch reflex
  • Stroke
  • Velocity dependence

ASJC Scopus subject areas

  • Physiology
  • Clinical Neurology
  • Cellular and Molecular Neuroscience
  • Physiology (medical)

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