Author: Cheng, Chun-shing Aldous
Title: The effects of sudden release height and load on the lumbar spine during lifting
Degree: M.Sc.
Year: 2002
Subject: Hong Kong Polytechnic University -- Dissertations
Back -- Wounds and injuries
Lifting and carrying -- Physiological aspects
Lumbar vertebrae -- Movements
Department: Multi-disciplinary Studies
Jockey Club Rehabilitation Engineering Centre
Pages: xi, 81 leaves : col. ill. ; 30 cm
Language: English
Abstract: The effects of sudden release load and height on the response of the trunk and leg muscles during lifting were investigated in this study. Ten normal males without history of back injuries that warranted medical treatment in the past one year were recruited. Each subject was asked to stand on a forceplate and perform a series of stoop lifting trials with different loads (20, 40, 60 and 80N) and different release height (one-quarter and three quarter of distance from knee to shoulder level) in erect standing posture with his inter-foot distance at shoulder width. For each lifting trial, the subject was asked to perform maximum six repetitions. A sudden release of load was randomly triggered at the selected release height of the 3rd, 4th and 5th repetition using a specially designed pulley mechanism. An accelerometer was used to register the onset of the release. Electromyographic (EMG) activities of the subject's right rectus abdominis, external oblique, internal oblique, erector spinae, multifidus, latissimus dorsi, rectus femoris, biceps femoris, tibialis anterior and gastroenemius were monitored. Reaction times of the trunk and leg muscles due to the sudden release of loads at two different release heights were determined and compared. It was shown that the erector spinse, multifidus, latissimus dorsi, biceps femoris and gastroenemius reacted by relaxation while the rectus abdominis, external oblique, internal oblique, rectus femoris and tibialis anterior resacted by contraction. The recruitment pattern of individual muscles was more consistent with higher sudden release load and less consistent with the sudden release load of 20N. The recovery time of the erector spinae and multifidus were found to be longer at low release height. More muscle co-contractions involved and longer co-contraction duration after sudden release were found at low release height. It is proposed that more transient co-contraction with sudden release at the low release height may constitute a higher risk of overload to the lumbar spine. Moreover, it was found that the excursion of the center of pressure was more proximal to the heels at low release height. This suggests that the tendency of fall is more prone to occur at low release height comparing to high release height. By means of extrapolation method, the maximum allowable limit of sudden release load was predicted to be 224N at the high release height but it was reduced by 43% and only 127N at the low release height. It is recommended that sudden release condition should be taken into consideration in any program of preventive measures for ergonomic injury. In addition, the risk of injury is significantly higher when the sudden release is occurred at low level comparing to high level.
Rights: All rights reserved
Access: restricted access

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