Innervation zone distribution of the biceps brachii muscle examined using voluntary and electrically-evoked high-density surface EMG.
Chengjun Huang, Cliff S Klein, Zhaojian Meng and 3 others
PMID 31186009WHAT IT FOUND
Electrical pulses found the same nerve entry spots in the biceps across intensities, while voluntary contraction shifted them toward the shoulder as force increased.
Low voluntary effort matched electrical pulses.
Key findings
01Increasing electrical stimulation intensity did not significantly change the average biceps nerve entry spot location.
02Increasing voluntary contraction level significantly shifted the biceps nerve entry spot toward the shoulder, with significant differences at 60% and 80% of maximum voluntary contraction compared with 20%, but not at 100% compared with 20%.
03The nerve entry spot from 20% voluntary contraction was similar to that from electrical stimulation, but spots from 60, 80 and 100% voluntary contraction were more toward the shoulder than electrical stimulation.
STILL TO COME
How it was doneWhat they foundWhat it means for PTs
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What it does not show
Only eight healthy men were studied, so the findings do not show what happens in patients with spasticity, paralysis, or stroke. Each participant was tested only once, so the repeatability of the maps was not checked. The electrode spacing was 8 mm, giving 4 mm resolution, so smaller differences in the nerve entry spot may have been missed. Four outer columns were removed because of poor signal, so the analysis covered only part of the muscle surface. The study did not test botulinum toxin injection or clinical function, only EMG maps in healthy muscle.
Declared interests
The supplied text states funding by the National Institutes of Health. It does not report author conflicts of interest.
The easy way to misread this
Do not conclude that this method can guide botulinum toxin injection in patients. The study was done in healthy men with no spasticity, no injection, and no clinical outcomes.