Isometric Force-Frequency and Dynamic Power-Frequency Relationships in Human Knee Extensors
Notice bibliographique
Résumé
Under voluntary control the neuromuscular system grades contractile output of recruited motor units by modulating discharge frequency. Electrically evoked (i.e., involuntary) contractions have been used to assess relationships between frequency input and contractile output. During an isometric contraction (i.e., no joint rotation) it is well-established that the force-frequency relationship is sigmoidal. However, there are few data describing the relationship between evoked input and dynamic (i.e., joint rotation) contractile parameters. Thus, the purpose was to examine the relationships between stimulated frequencies and dynamic power (i.e., product of concentric torque and angular velocity) during an isotonic contraction in comparison to an isometric force-frequency relationship. Knee extensors of 7 healthy young adult males were tested in a Cybex dynamometer. The right knee was at 90° and hip at 110°. Seat belts secured to the dynamometer were strapped across the hips and shoulders, and a non-elastic strap was secured across the thigh to avoid extraneous movement. Two stimulation electrodes, which consisted of aluminum wrapped in a conductive gel-soaked cloth were secured transversely to the proximal and distal portion of the knee extensors. For dynamic contractions the dynamometer was set to the “isotonic mode” and range of motion was 60°. The muscles were stimulated at 1, 5, 7.5, 10, 12, 15, 17, 20, 25, 30, 40, 50, 75 and 100 Hz. Besides the 1 Hz (i.e., single pulse) all frequencies during isometric contractions were 2s in duration. During isotonic contractions with the load set to 7.5% maximal voluntary contraction (MVC), pulses were programmed to terminate once range of motion was complete or until full range of motion was unachievable. Electrical current for all frequencies was determined from that required at 100 Hz to produce 50% isometric MVC force. Stimulation was done in ascending order with 20s rest between. The order between contraction modes was randomized and a 5-minute rest was given between modes. Results are presented as a percentage of relative peak force or peak power for 100 Hz during isometric or isotonic contractions, respectively. Both isometric force-frequency and dynamic power-frequency relationships were sigmoidal. During stimulation of increasing frequencies peak power was lower than isometric force by ~82%, ~47%, ~43%, ~38%, ~32%, ~25%, ~30%, ~23%, ~17%, ~12%, ~8% at ascending frequencies from 1 Hz to 40Hz, respectively. From 50 Hz to 100 Hz there were minimal differences (0-4%). These data indicate for the same stimulation frequencies the power-frequency relationship of a moderately loaded isotonic contraction is shifted rightward relative to an isometric force-frequency relationship. Therefore, isometric force-frequency and dynamic power-frequency relationships are not equivalent, and assessments of both relationships may be required to adequately characterize contractile function depending on the task. Supported by NSERC. This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.
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Prédiction distillée sur la base complète
Imitation des enseignantsNi prévalence calibrée, ni vérité terrain. Validation humaine à venir. Apprise à partir de 10 348 étiquettes directes de Codex et de 10 348 étiquettes directes de Gemma. Le mode candidate est l'union des têtes enseignantes seuillées; le consensus est leur intersection. Ces sorties portent le statut machine_predicted_unvalidated et ne sont ni des étiquettes humaines ni des étiquettes directes de modèles de pointe.
Scores Codex et Gemma par catégorie
| 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 | 0,001 | 0,002 |
| 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) | 0,000 | 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 tête enseignante, pas un consensus.
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