HD-sEMG decoding of motoneuron activity in stroke (involuntary vs voluntary)

• High-density surface electromyography (HD-sEMG) of biceps brachii with motor-unit decomposition was used to assess whether spinal motoneurons received and sent the same neural information during involuntary (passive stretch) versus voluntary activation after stroke.¹
• Populational motor unit activity was extracted from HD-sEMG with decomposition algorithms; MU discharge rates were compared across conditions.¹
• Fourteen stroke survivors and 10 age-matched controls were studied; distinct neural information was found to be shared in spastic muscle through decoding motoneuron activity.^{1 1}

Gardner updates

• HD-sEMG of biceps brachii with motor unit decomposition assessed whether spinal motoneurons shared the same neural information during involuntary (passive stretch) and voluntary (active contraction) activation in 14 stroke survivors and 10 age-matched controls. ¹

• HD-sEMG of biceps brachii in 14 stroke survivors and 10 controls during passive stretch and active contraction, with MU decomposition, assessed whether spinal motoneurons received and sent the same neural information during involuntary vs voluntary activation. ¹

Weekly enrichment (2026-07-20)

• The primary study (Chen & Zhou, IEEE Transactions on Biomedical Engineering, 2025) recorded HD-sEMG from biceps brachii while 14 stroke survivors and 10 age-matched controls performed passive stretch (involuntary) and active contraction (voluntary), decomposing populational motor-unit (MU) activity to compare neural drive across conditions.²
• In stroke survivors, involuntary (reflex) activation showed a significantly higher MU discharge rate than voluntary activation (18.41 ± 2.05 Hz vs. 14.99 ± 1.50 Hz; p < 0.001, Cohen’s d = 1.392).²
• Discharge-rate variability was markedly lower during involuntary than voluntary activation (0.04 ± 0.02 vs. 0.12 ± 0.04; p < 0.001, d = 1.775), indicating more regular reflex firing.²
• The spatial distribution of MU action potentials was reversed between conditions (lateral-medial 3.91 ± 1.01 vs. 4.85 ± 0.57, p < 0.001, d = 1.304; distal-proximal 5.16 ± 0.80 vs. 4.01 ± 0.73, p = 0.001, d = 1.222), showing involuntary activity is more distally localized.²
• Common synaptic input (CSI), estimated by cross-correlation of MU discharge timings, was lower in involuntary than voluntary activation (0.42 ± 0.07 vs. 0.55 ± 0.08; p = 0.004), and discharge variability correlated positively with CSI.²
• The authors conclude that information flow between supraspinal centers and the spinal cord is unbalanced after stroke, and that reflex MU discharge depends more on intrinsic spinal motoneuron properties than on descending brain control.²
• A companion HD-sEMG mapping study found that spastic activity evoked by passive stretch is spatially heterogeneous and distinct from voluntary contraction, consistent with diminished inhibitory reflex regulation after loss of corticospinal input.³
• Related HD-sEMG work in 14 chronic stroke survivors showed depth-ordered MU recruitment is disrupted on the spastic side (no force-related change in MU depth) unlike the non-spastic side, attributed to denervation and collateral reinnervation after the upper-motor-neuron lesion.⁴
• Clinical/BCI implication: noninvasively separating reflex-driven from volitionally-driven motor-unit activity could improve objective spasticity quantification (versus subjective clinical scales) and inform EMG-driven neuroprosthetic and rehabilitation controllers that must reject involuntary drive.²³

Footnotes

1. http://ieeexplore.ieee.org/document/11142632 ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶

2. https://doi.org/10.1109/tbme.2025.3600863 ↩ ↩² ↩³ ↩⁴ ↩⁵ ↩⁶ ↩⁷

3. https://doi.org/10.1186/s12984-024-01376-z ↩ ↩²

4. https://doi.org/10.1088/1741-2552/ac86f4 ↩