Voluntary co-contraction of ankle muscles alters motor unit discharge characteristics and reduces estimates of persistent inward currents
Bibliographic record
Abstract
ABSTRACT Motoneuronal persistent inward currents (PICs) are both facilitated by neuromodulatory inputs and highly sensitive to local inhibitory circuits (e.g., Ia reciprocal inhibition). Methods aimed to increase group Ia reciprocal inhibition from the antagonistic muscle have been successful in decreasing PICs, and the diffuse actions of neuromodulators released during activation of remote muscles have increased PICs. However, it remains unknown how motoneurons function in the presence of simultaneous excitatory and inhibitory commands. To probe this topic, we investigated motor unit (MU) discharge patterns and estimated PICs during voluntary co-contraction of ankle muscles, which simultaneously demands the contraction of agonist-antagonist pairs. Twenty young adults randomly performed triangular ramps (10s up and down) of both co-contraction (simultaneous dorsiflexion and plantarflexion) and isometric dorsiflexion to a peak of 30% of their maximum muscle activity from a maximal voluntary contraction. Motor unit spike trains were decomposed from high-density surface electromyography recorded over the tibialis anterior (TA) using blind source separation algorithms. Voluntary co-contraction altered motor unit discharge rate characteristics, decreasing estimates of PICs by 20% (4.47 pulses per second (pps) vs 5.57 pps during isometric dorsiflexion). These findings suggest that, during voluntary co-contraction, the inhibitory input from the antagonist muscle overcomes the additional excitatory and neuromodulatory drive that may occur due to the co-contraction of the antagonist muscle, which constrains PIC behavior. KEY POINTS Voluntary co-contraction is a unique motor behavior that concurrently provides increases in excitatory and inhibitory inputs to motoneurons. During co-contraction of agonist-antagonist pairs, agonist motor unit discharge characteristics are altered, consistent with reductions in persistent inward current magnitude. Reciprocal inhibition from the antagonist likely becomes proportional to the increase in neural drive to the agonist, dampening the magnitude of persistent inward currents.
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How this classification was reachedexpand
Full frame machine prediction
Teacher imitationNot calibrated prevalence, not ground truth. Human validation pending. The Gemma side is a direct model label for every work in the frame, read from the title-only record. The Codex side is a classifier learned from the 10,348 direct Codex labels and calibrated to design-weighted sample rates; fields without enough sample support carry no Codex call. Candidate is the union of the two sides; consensus is their intersection. These outputs are machine_predicted_unvalidated and are not human labels.
Distilled classifier scores by category (both heads)
| Category | Codex | Gemma |
|---|---|---|
| Metaresearch | 0.000 | 0.001 |
| Meta-epidemiology (narrow) | 0.000 | 0.000 |
| Meta-epidemiology (broad) | 0.000 | 0.000 |
| Bibliometrics | 0.000 | 0.000 |
| Science and technology studies | 0.000 | 0.000 |
| Scholarly communication | 0.000 | 0.000 |
| Open science | 0.000 | 0.000 |
| Research integrity | 0.000 | 0.000 |
| Insufficient payload (model declined to judge) | 0.001 | 0.000 |
Machine scores (provisional)
The two teacher heads of the student model, read on this work. A score orders the frame for review; it never asserts a category, and the validation status ships verbatim with every row.
Baseline scores from an immature model (maturity gate not passed, 7 training rounds). Scores rank; they never assert a category.
score_only:v0-immature-baseline · verbatim from the scoring run: score_only means the number may rank works, and no category label ships from itClassification
machine, unvalidatedMachine predicted; a candidate call from one source (direct Gemma or distilled Codex), not a consensus.
How this classification was reached, model by model and score by score, is at the end of the page under "How this classification was reached".