Effect of Maximal and Submaximal Muscle Activation on Corticospinal Excitability in Humans
Bibliographic record
Abstract
Introduction Following short duration (5‐10s), high intensity (≥70%MVC) muscle activation, there is an enhancement of muscle contractile properties, termed post action potentiation (PAP). During PAP induced by voluntary or electrically stimulated conditioning contractions (CC) it has been reported that the corticospinal silent period (SP), assessed by transcranial magnetic stimulation (TMS), is elongated. Although a coexistence between the two occurs, the direct effect of PAP on corticospinal excitability has not been systematically evaluated to help determine whether a direct link exists. The purpose was to assess SP duration following potentiating and non‐potentiating voluntary and electrically stimulated contractions. We hypothesized that maximal and submaximal CCs inducing PAP and those not inducing PAP enhancement, respectively, will prolong SP durations albeit to a lesser degree at submaximal intensities. Methods Ten healthy young (three females; 18‐35y) individuals free of neurological issues to date have participated in the study. Subjects were seated with their right forearm pronated and their hand was fixed to a custom finger abduction force dynamometer. Monopolar surface electromyography signals were recorded from the first dorsal interosseous muscle (FDI) with self‐adhering Ag/AgCl electrodes. Peripheral stimulated twitches and tetani (50Hz) were evoked over the ulnar nerve at the wrist via a pair of small readjustable electrodes. Maximal M‐waves (M‐max) and baseline levels of (voluntary and stimulated) PAP and force were obtained for each subject. Electrically stimulated and voluntarily induced CCs of 10s were performed at ~95% MVC and ~35% MVC for a total of four contraction conditions. Before and after these contractions SP times were obtained during the plateau of ~25% MVC held for three seconds. To obtain SP times the TMS output was set to elicit a response ~75% of M‐max. The four conditions of voluntary or stimulated, maximal and submaximal CCs were pseudo‐randomized and repeated four times per subject. The nearest three values from each subject were averaged and compared as a normalized percent change from baseline. Results Following both maximal voluntary and stimulated CCs, mean twitch torque was enhanced similarly (PAP ~180%) with no PAP at the submaximal levels. Mean change in SP duration following maximal voluntary CCs was ~14% longer than control values, while maximal tetanic CCs similarly prolonged the SP by ~13%. Both voluntary and stimulated submaximal contractions prolonged SP duration similarly by ~5% and ~6%, respectively. Conclusion These findings indicate that corticospinal inhibition assessed as SP elongation is present not only when the muscle is enhanced under PAP but also occurs following contractions inducing no PAP. This suggests that the muscle activation required to induce PAP likely causes the observed corticospinal inhibition, not the enhanced muscle properties of PAP per se.
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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 | 0.000 |
| 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) | 0.002 | 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".