Absence of stretch reflex gain enhancement in voluntarily activated spastic muscle

Wynne A. Lee, Ann Boughton, William Z. Rymer*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

100 Scopus citations


Static and dynamic stiffnesses of voluntarily activated elbow muscles were compared in spastic and contralateral arms of 15 subjects with spastic hemiparesis. Stiffnesses were estimated from the positional deflections induced by applying load perturbations to each forearm. In 11 15 subjects (73%), stiffnesses were comparable on the two sides. In the remaining 4 15 subjects (27%), stiffnesses were consistently greater on the spastic side, however, EMG recordings from these spastic muscles were of much smaller amplitude than those of the contralateral muscles, indicating that this increase was probably caused by changes in the mechanical properties of elbow muscles, rather than by stretch reflex enhancement. We conclude that for voluntarily activated muscles of spastic hemiparetic subjects, reflex stiffness (and presumably stretch reflex gain), of spastic and contralateral limbs is not significantly different. These findings impose important constraints upon theories attempting to explain spastic hypertonia, and they also provide guidelines for clinical quantification of spasticity.

Original languageEnglish (US)
Pages (from-to)317-335
Number of pages19
JournalExperimental Neurology
Issue number2
StatePublished - Nov 1987

ASJC Scopus subject areas

  • Neurology
  • Developmental Neuroscience


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