Author: Cheng, Yung-wa Irene
Title: Effects of lifting posture on the lumbar spine under an unexpected unloading condition
Degree: M.Phil.
Year: 2002
Subject: Hong Kong Polytechnic University -- Dissertations
Lumbar vertebrae -- Movements
Spine -- Mechanical properties
Lifting and carrying -- Physiological aspects
Department: Jockey Club Rehabilitation Engineering Centre
Pages: xvi, 174, 10, 21 leaves : ill. (some col.) ; 30 cm
Language: English
Abstract: Nurses and physical therapists working with patients (such as athetoid) are frequently exposed to sudden loads. Many researchers have investigated the effects of sudden load application. However, little is known about the effects of sudden release of load. It has been proposed that a sudden release of load, for instance, when a load slips, can generate an unexpected acceleration and very large muscle forces, which may reach a level sufficient to damage the soft tissues of the spine. In addition, when the externally applied load is suddenly released, the exerted muscle force created to maintain equilibrium would generate an unexpected acceleration and unbalance the body. The purpose of this study is therefore to investigate the response of trunk and leg muscles under sudden release during lifting and to determine whether a proper lifting posture could reduce the risk of injury to the back. Ten normal and healthy male volunteers aged from 22-35 were recruited in this study. None of the subjects had any history of back injuries or significant back pain for the last two years. It was predicted that a subject would lose balance under a sudden unload condition if squat lifting with the lifting weight over 114N, asymmetric stoop lifting with the lifting weight over 173N, or symmetric stoop lifting posture with the lifting weight over 205N. Squat lifting was found to have longer response duration and longer co-contraction time compared to symmetric and asymmetric stoop lifting, meaning less stability under sudden unloading and also imposing larger forces on the spine. It was found that asymmetric stoop lift had the highest peak axial rotation moment and peak lateral bending moment in comparison with symmetric squat and stoop lift; however, symmetric stoop had highest peak flexion-extension moment in comparison with symmetric squat and asymmetric stoop lift. Results also showed that squat lift had the highest absolute rate of change of moment, implying that it may be more difficult to preserve balance when encountering sudden release of load in squat lifting than in the other two lifting postures. The safety limit for squat lifting is lower than others, but it has been commonly adopted as the preferred posture for lifting, and therefore the current ergonomic guidelines for proper lifting should be carefully addressed if sudden release conditions are to be taken into account. Nevertheless, the results of this study are valuable for establishing guidelines for manual material handling workers, who are exposed to sudden unload such as garbage collectors, truck unloaders and luggage dispatchers. Further biomechanical studies are required to determine the force generated by each muscle, and therefore the load on the lumbar spine under different lifting conditions can be studied quantitatively.
Rights: All rights reserved
Access: open access

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