Author: Tse, Tao-kan Alex
Title: Effects of sudden release on the electromyographic activities of the trunk during pulling
Degree: M.Sc.
Year: 2000
Subject: Back -- Wounds and injuries -- Prevention
Leg -- Muscles
Leg -- Muscles -- Contraction
Muscle contraction
Hong Kong Polytechnic University -- Dissertations
Department: Multi-disciplinary Studies
Jockey Club Rehabilitation Engineering Centre
Pages: 73 leaves : ill. (some col.) ; 30 cm
Language: English
Abstract: The effects of sudden release of load on the response of the trunk and leg muscles during pulling were investigated in this study. Ten normal males without history of back injuries or back pain in the past two years were recruited. Each subject was asked to stand on a forceplate and perform a series of pulling trials with different loads (20, 40 and 60N) in an erect standing posture with his inter-foot distance at shoulder width. For each pulling trial, the subject was asked to perform six repetitions. A sudden release of load was randomly triggered at the beginning of the 3rd, 4th or 5th repetition using a specially designed pulley mechanism. An accelerometer was used to register the onset of the release. Electromyoelectric activities of the subject's right latissimus dorsi, erector spinae, external oblique, rectus abdorminis, hamstrings, quadriceps, gastronemius and tibialis anterior were monitored. Response times of the trunk and leg muscles due to the sudden release of loads were determined and compared. It was shown that the erector spinae, biceps femoris and the gastronemius responded by relaxation while the rectus abdominis, external oblique, quadriceps and the tibialis anterior responded by contraction. An inconsistent response was observed for the latissimus dorsi. However, it mainly responded by contraction when the sudden release load was 60N. The response times of the relaxation muscles were found to increase with increased sudden release load. It was demonstrated that co-contraction of muscles were usually started from the distal lower limbs and then to the trunk in order to stabilize the body. It is proposed that the transient co-contraction may constitute an overload to the lumbar spine due to the sudden release. Moreover, it was found that the excursion of the center of pressure was more proximal to the heels with increased sudden release load. This suggests that the tendency of fall was more prone to occur with increased sudden release load. By means of extrapolation method, the maximum allowable limit of sudden release load was predicted to be equal to 95N. It is also recommended that sudden release condition should be taken into consideration in any program of preventive measures for ergonomic injury.
Rights: All rights reserved
Access: restricted access

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