Investigating Premotor Cortical And Motoneuronal Excitability In Fast And Slow Voluntary Contractions Of The Elbow Flexors
Bibliographic record
Abstract
Corticospinal excitability (CSE) increases prior to a voluntary contraction; however the contributions of cortical and spinal mechanisms are not well understood. It is also unknown whether the intended contractile rate affects the change in CSE. PURPOSE: To assess premotor cortical and motoneuronal excitability prior to fast (ballistic) vs. slow (ramp) contractions. METHODS: Eighteen young, healthy participants (9 M; 9F) were positioned supine with the non-dominant arm flexed to ∼90° at the elbow joint. They completed 72 isometric elbow flexion contractions targeting 50% maximal voluntary contraction (MVC) torque. In a randomized order, contractions were completed at a fast (as fast as possible) and slow (25% MVC/s) contractile rate. Participants were also cued to contract with warning (red) and “GO” (green) visual signals. Stimulation was applied over the motor cortex, corticospinal tract, and brachial plexus to elicit motor evoked potentials (MEPs), cervicomedullary evoked potentials (CMEPs), and M-waves, respectively, in the surface electromyogram (EMG) recorded over the biceps brachii. With the muscle relaxed, stimulation intensities elicited MEPs and CMEPs of ~10% maximal M-wave (Mmax). MEPs and CMEPs were collected at 0, 25, 50 and 75% of premotor reaction time (RT) following the “GO” signal. Baseline MEPs and CMEPs were elicited at rest between trials, without being preceded by the visual signals. Cortical and motoneuronal excitability were evaluated by ratios of MEP/CMEP and CMEP/Mmax amplitude at 0, 25, 50, 75% RT compared to resting baseline. RESULTS: CMEP/Mmax amplitude was 45% greater in the ballistic condition (p < 0.001) and 42% greater in the ramp condition at 0% RT (p < 0.001) compared to baseline. CMEP/Mmax amplitude increased progressively closer to EMG onset, reaching 63% greater than baseline in the ballistic condition (p < 0.001) and 64% greater in the ramp condition at 75% RT (p < 0.001). Normalized to the CMEP, there were no differences in MEP amplitudes from baseline in either contractile condition across all RT points (all p > 0.05). CONCLUSIONS: These data indicate that increases in premotor CSE are mediated by spinal mechanisms rather than cortical mechanisms. Furthermore, the increase in premotor CSE does not appear to be influenced by the intended contractile rate. Supported by NSERC. NSERC
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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".