Dynamic Muscle Fatigue and Potentiation in Human Plantar Flexors
Notice bibliographique
Résumé
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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Comment cette classification a été obtenuedéplier
Prédiction machine sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Le volet Gemma est une étiquette directe du modèle pour chaque travail de la base, lue sur la notice réduite au titre. Le volet Codex est un classifieur appris des 10 348 étiquettes directes de Codex et calibré sur les taux pondérés de l'échantillon; les champs sans appui suffisant ne portent aucun appel Codex. Le mode candidate est l'union des deux volets; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont pas des étiquettes humaines.
Scores du classifieur distillé par catégorie (deux têtes)
| Catégorie | Codex | Gemma |
|---|---|---|
| Métarecherche | 0,000 | 0,000 |
| Méta-épidémiologie (sens strict) | 0,000 | 0,000 |
| Méta-épidémiologie (sens large) | 0,000 | 0,000 |
| Bibliométrie | 0,000 | 0,000 |
| Études des sciences et des technologies | 0,000 | 0,000 |
| Communication savante | 0,000 | 0,000 |
| Science ouverte | 0,000 | 0,000 |
| Intégrité de la recherche | 0,000 | 0,000 |
| Charge utile insuffisante (le modèle a refusé de juger) | 0,002 | 0,000 |
Scores machine (provisoires)
Les deux têtes enseignantes du modèle étudiant, lues sur ce travail. Un score ordonne la base pour la relecture; il n'affirme jamais une catégorie, et le statut de validation accompagne chaque rangée tel quel.
Scores de référence d'un modèle non mature (critères de maturité non atteints, 7 itérations). Un score ordonne; il n'affirme jamais une catégorie.
score_only:v0-immature-baseline · tel quel depuis la passe de notation : score_only signifie que le nombre peut ordonner les travaux, et qu'aucune étiquette de catégorie n'en découleClassification
machine, non validéePrédiction automatique; un appel candidat d’une seule source (Gemma direct ou Codex distillé), pas un consensus.
Le détail, modèle par modèle et score par score, se trouve en fin de page sous « Comment cette classification a été obtenue ».