Characterization of Differences in the Time Course of Reflex and Voluntary Responses following Botulinum Toxin Injections in Chronic Stroke Survivors

Babak Afsharipour*, Sourav Chandra, Guijin Li, William Z. Rymer, Nina L. Suresh

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

1 Scopus citations


Spasticity is a major impairment that can occur following a hemispheric stroke and is often treated with injections of botulinum toxin, a neurotoxin that impairs transmission at the neuromuscular junction. Hyperreflexia is a defining feature of spasticity. Our main objective here was to quantify the time course of changes in the deep tendon reflex (DTR) responses and voluntary activation capacity following BT injection as well as to track changes in a clinical assessment of spasticity. Four chronic stroke survivors, scheduled to receive BT in their Biceps Brachii(BB) as part of their clinical care plan, were recruited for repeated testing sessions over the course of 4 months post injection. Both surface BB EMG reflex response to bicipital tendon taps as well as signals of applied tendon tap forces were recorded before and up to 18 weeks post-BT. Voluntary force and biceps EMG signals were also recorded during maximum voluntary (isometric) contractions (MVC) at each testing session. Our results show major reductions (up to 75%) in voluntary sEMG and force arising between 11 to 35 days post-BT-injection. The stretch reflex gain declined two weeks after the maximal reductions in voluntary EMG and force. Paradoxically, there was a short-term increase in stretch reflex gain, in three out of four participants, approximately 11-35 days post BT. The time course of recovery of voluntary MVC and reflex responses varied considerably with a longer recovery time for the reflex responses.

Original languageEnglish (US)
Article number9099202
Pages (from-to)1642-1650
Number of pages9
JournalIEEE Transactions on Neural Systems and Rehabilitation Engineering
Issue number7
StatePublished - Jul 2020
Externally publishedYes


  • Botulinum toxin
  • hyper-excitability
  • hyperreflexia
  • spasticity
  • stroke
  • surface EMG
  • tendon tap

ASJC Scopus subject areas

  • Rehabilitation
  • Neuroscience(all)
  • Internal Medicine
  • Biomedical Engineering


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