Modification of Spastic Stretch Reflexes at the Elbow by Flexion Synergy Expression in Individuals With Chronic Hemiparetic Stroke.
Jacob G McPherson, Arno H Stienen, Justin M Drogos and 1 others
PMID 28751255WHAT IT FOUND
In stroke survivors, spastic stretch reflexes during functional arm lifting were no larger than reflexes seen in healthy people doing the same amount of voluntary muscle work.
This suggests the involuntary coactivation itself, not spasticity, drives reaching deficits.
Key findings
01Stretch reflexes in the paretic arm increased in direct proportion to the amount of shoulder abduction effort required, confirming that flexion synergy drives elbow flexor activity.
02When comparing stroke survivors expressing flexion synergy to healthy controls performing matched levels of voluntary elbow flexion, the magnitude of the stretch reflexes was statistically similar.
03Although stretch reflexes were exaggerated in stroke survivors at rest, they did not exceed those in healthy controls when both groups were actively pre-activating the elbow flexors.
STILL TO COME
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What it does not show
The study did not measure stretch reflexes during actual volitional elbow extension (reaching), which is the functional task most relevant to clinical practice. All perturbations started from the same angle, preventing the assessment of spatial reflex thresholds. The sample size was small (20 participants total), and the stroke cohort had a wide range of impairment severity. The comparison between synergy-driven reflexes in stroke patients and volitional reflexes in healthy controls relies on the assumption that the neuromodulatory environment is comparable, which may not be true post-stroke.
Declared interests
The study was supported by the National Institutes of Health (N.I.H.) and non-U.S. government sources. No commercial conflicts of interest are reported in the provided text.
The easy way to misread this
Do not conclude that spasticity is irrelevant to stroke recovery. This study shows that during *flexion synergy expression*, reflexes match those of voluntary effort, but it does not rule out spasticity's impact at rest or in other movement phases. The finding suggests synergy management may be a higher priority for reaching deficits, not that spasticity treatment is useless.