Dynamic Muscle Fatigue and Potentiation in Human Plantar Flexors
Bibliographic record
Abstract
Activation history can enhance or impair subsequent contractile responses. Following a brief high‐intensity voluntary contraction, the contractile response for the same submaximal input stimulus will be enhanced (post‐activation potentiation; PAP). However, prolonged voluntary activation can impair contractile responses due to neuromuscular fatigue. Because both effects are dependent on immediate prior activation, a co‐existence between these two competing processes is observed. Specifically, submaximal frequencies are enhanced (PAP) while maximal frequencies are simultaneously depressed (fatigue). Due to preferential enhancement of low frequency activation, PAP can mitigate the effects of prolonged low‐frequency force depression (PLFFD), ‐ a long‐lasting reduction of force evoked at low‐frequencies following fatiguing exercise. Usually, this relationship has been evaluated using isometric contractions. The purpose was to assess the relationship between PAP, muscle fatigue and recovery during and following an isotonic (dynamic) fatiguing protocol through which power (force and velocity) are assessed. It is hypothesized that PAP will attenuate PLFFD during the fatiguing protocol and throughout 30 minutes of recovery. The plantar flexors of 5 healthy young adult males (n=4) and females (n=1) to date have been tested while lying prone in a Cybex dynamometer. The ankle was at 90° and knee joint at 180° (straight leg). Inelastic large Velcro straps firmly secured the hips, shoulders and thighs to the dynamometer. Participants performed isotonic plantar flexion contractions over a 20° range of motion (90° to 110°) of the ankle joint with a load of 20% of maximal voluntary isometric contraction (MVC) until peak power was reduced by 20%, 50% and 75% of baseline values. At these intervals of power loss, electrical stimulation of the tibial nerve in the popliteal fossa was done to record unloaded power responses at 10 Hz and 50 Hz. Following task failure (75% power loss), recovery was assessed immediately and at 3, 5, 10, 20 and 30 minutes. For these, voluntary contractions (10 concentric at 20% MVC) were done to induce PAP. Evoked unloaded dynamic measurements were done prior to and following the 10 concentric contractions to assess any effect of PAP. PLFFD is a preferential loss of low frequency force assessed by comparing a stimulated force ratio between responses at 10 Hz to 50 Hz. During dynamic contractions we used a peak power 10:50 Hz ratio to incorporate the factor of velocity. During fatigue the peak power 10:50 Hz ratio was enhanced by ~35% at 20% power loss, by ~15% at 50% power loss, and minimally enhanced (~9%) at task failure (75% power loss). During recovery this ratio was enhanced follow the potentiating contractions compared to non‐potentiated; task failure (~3%), 3 min (~26%), 5 min (~45%), 10 min (~20%), 20 min (~25%) and 30 min (~38%). These results indicate that during dynamic muscle fatigue and recovery, PAP may mitigate PLFFD to varying degrees.
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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".