The In Vivo Dynamic Response of the Human Spine to Rapid Lateral Bend Perturbation
Notice bibliographique
Résumé
STUDY DESIGN: A repeated measures design was used to determine the effects that combinations of two preloads and two added loads have on spine mechanics both before and during the response to the added load. OBJECTIVE: To investigate the effects of varying initial isometric and added step input load magnitudes on mechanical and electromyographic responses of the trunk during sudden loading that causes lateral bending moments. SUMMARY OF BACKGROUND DATA: Cocontractions of the antagonistic and agonistic muscles of the trunk are required for stability during loading of the spine. In several in vivo studies, it was observed that trunk muscle cocontraction serves a functional role before the application of unexpected or sudden loads. The response of agonistic and antagonistic trunk muscles to rapid lateral bend moments would provide further insight into the dynamic stability mechanisms of the spine. METHODS: In this study, 13 men maintained an upright standing posture while resisting the application of lateral bend moments produced by four different loading conditions comprising combinations of two preloads (5% or 15% of the maximum isometric lateral bend moment) and two added loads (20% or 30%). The preloading was used to develop different initial levels of trunk stiffness before the application of the added loads. The lateral bend moment and angular rotation of the trunk were measured, as well as the surface electromyogram amplitudes of the bilateral internal oblique, external oblique, rectus abdominus, lumbar erector spinae, and thoracic erector spinae muscles. Dependent measures were recorded during the steady state preload conditions, and peak values were recorded after the load was added. RESULTS: Higher added loads resulted in higher peak lateral bend rotations, and higher preloads resulted in lower rotations. The patterns of response were similar for the peak lateral bend moments and the electromyogram amplitudes from four of the five agonistic muscles. The thoracic erector spinae excepted, each of the other four muscles demonstrated larger responses in the agonistic muscles. However, all of the antagonistic muscles showed some increase in electromyogram activity in response to the added load. The thoracic erector spinae appeared to have the role of counteracting the flexor moments created by the abdominal muscles and the maintenance of spine stability. The agonistic external obliques and lumbar erector spinae had the largest responses to the added load. A comparison of the 35% loading conditions showed an increased response of the trunk to the 5% + 30% condition (with lower initial trunk stiffness), as compared with the 15% + 20% condition. CONCLUSIONS: The findings from this study show that higher levels of preactivation can serve to increase spine compression and trunk muscle stiffness, thereby attenuating the lateral displacements caused by rapid loading. Furthermore, antagonistic muscles were observed to respond rapidly to such perturbations with large increases in activation when preactivation and spine stability were low. The trunk muscles monitored all were larger, multisegmental muscles. The results from this study lend support to previous studies suggesting that the larger multisegmental muscles make a significant contribution to spinal stability.
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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 | 0,001 |
| 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 ».