Item – Thèses Canada

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Numéro d'OCLC
465562027
Lien(s) vers le texte intégral
Exemplaire de BAC
Exemplaire de BAC
Auteur
Di Domizio, Jennifer,1981-
Titre
The effects of posture and force coupling on upper extremity muscle activity.
Diplôme
M. Sc. -- York University, 2006
Éditeur
Ottawa : Library and Archives Canada = Bibliothèque et Archives Canada, [2008]
Description
2 microfiches
Notes
Includes bibliographical references.
Résumé
In the upper extremity, external risk factors of force, repetition and/or joint posture have been associated with a higher incidence of musculoskeletal disorders. Although research is limited to findings from one study, it was shown that higher cumulative finger flexor tendon loading was associated with jobs of high force and high repetition, thus implicating load exposure as a risk factor for injury. Further insight into load accumulation in the upper extremity is needed to identify possible mechanisms of tissue injury and ultimately determine acceptable standards for cumulative loading. Thus this thesis examined estimates of load accumulation by measuring muscle activity during static and force varying tasks combining factors of force, repetition, forearm posture, multiple joint force coupling and dynamometer orientation performed over short and longer durations. Twelve healthy, right-hand dominant volunteers performed five tasks (isolated hand grip, isolated shoulder push, isolated shoulder pull, a hand grip with a push and a band grip with a pull) using a grip dynamometer mounted to a tri-axial force transducer. Tasks were examined in three forearm postures (supination, neutral and pronation) over a short exposure (10 s) and in a neutral posture over a longer exposure (3 min). To study the effect of an assisted grip force generation, all push or pull tasks were repeated with the dynamometer orientation rotated (180°) while maintaining a neutral forearm posture. Objective data included surface EMG from eight upper extremity muscles (flexors carpi radialis and ulnaris, flexor digitorum superficialis, extensors carpi radialis and u1naris, extensor digitorum communis, anterior deltoid and posterior deltoid), hand grip force, triaxial forces and moments and wrist angles, while subjective measures included ratings of perceived exertion and discomfort. Findings revealed that forearm muscle activity increased under conditions of multiple joint force coupling involving pull tasks performed over a short (61-110%) or longer exposure (1-21%) (all p < 0.017). When adding a push exertion to a grip task, forearm extensor muscle activity elevated (short exposure: 27-79% and longer exposure: 6-22%), however, flexor activity decreased (short exposure: 11-20% and longer exposure: 23-40%). Postural changes during grip tasks (with and without a push or pull exertion) increased forearm extensor activity when progressing from supination (8.3-35.2% MVE) to neutral (12.0-49.6% MVE) to pronation (16.8-58.4% MVE) (all p < 0.017). Decreased forearm muscle activity resulted when the dynamometer orientation "assisted" with grip force generation (short exposure: 12-50% decrease and longer exposure: 2-34% decrease). These results suggest that occupational tasks should be designed with considerations of force coupling, forearm posture and tool orientation in an effort to decrease forearm muscle load accumulation and ultimately reduce the incidence of work-related musculoskeletal disorders.
ISBN
9780494295588
0494295589