Precise quantification of the time course of voluntary activation capacity following Botulinum toxin injections in the biceps brachii muscles of chronic stroke survivors.
S Chandra, B Afsharipour, W Z Rymer and 1 others
PMID 32703213WHAT IT FOUND
Botulinum toxin injections in stroke survivors caused a 50% drop in elbow force within two weeks, with only partial recovery by twelve weeks.
Muscle electrical activity remained 35% below baseline, indicating lasting weakness that clinical spasticity scores missed.
Key findings
01Voluntary elbow flexion force dropped by an average of 50% in the first two to four weeks after injection and remained 35% lower than baseline at twelve weeks.
02Muscle electrical activity (sEMG) showed a greater reduction than force, remaining statistically significantly lower than baseline (within 40% of pre-injection value) at the end of twelve weeks.
03Clinical spasticity scores (Modified Ashworth) improved or returned to baseline faster than the underlying muscle weakness resolved, failing to track the time course of voluntary capacity loss.
STILL TO COME
How it was doneWhat they foundWhat it means for PTsWhat it means for OTs
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What it does not show
Very small sample size (n=8) limits generalizability. Participants did not receive concurrent physical or occupational therapy during the study, which may have influenced recovery rates. Botulinum toxin dosage and injection history varied among participants, introducing heterogeneity. The study observed a specific muscle (biceps brachii); results may not apply to other muscles treated for spasticity.
Declared interests
Funded by the National Institute on Disability, Independent Living, and Rehabilitation Research. No commercial conflicts of interest reported.
The easy way to misread this
Do not assume that improved spasticity scores (like the Modified Ashworth Scale) mean the patient's voluntary strength has recovered. The study shows that muscle weakness persists long after spasticity measures return to baseline or improve.