Effect of a Weight Transfer Device on Muscle Activities, Joint Flexions, and Low Back Loads in the Stooped Posture.

摘要

Repetitive work in the stooped posture is a known risk factor for developing low back disorders (LBDs). Use of the stooped posture is widespread throughout the world in the agriculture, construction, and mining industries. An on-body weight transfer device was tested as a possible intervention for reducing the risk of developing LBDs.;Eighteen healthy subjects (11 male and 7 female), with no history of LBDs, performed stooped posture tasks in a laboratory study designed to simulate harvesting of low-growing crops. Surface electromyograms of the erector spinae, rectus abdominis, biceps femoris, and tibialis anterior muscles were recorded. Total torso, lumbar, hip, knee, and ankle joint flexions were measured with a combination of inclinometers and electrogoniometers.;Results show that when wearing the device in the static stooped posture, biceps femoris activity was reduced by 17% (p0.0001), lumbar flexion was reduced by 12% (p0.01), ankle plantar-flexion increased by 5% (p0.05), hip and knee flexion were not significantly altered, and the lumbar erector spinae of those subjects who did not experience flexion-relaxation of the erector spinae was reduced by 26% (p0.01). During torso flexion and extension between stooped and upright when wearing the device, peak values of back muscle activity and lumbar flexion were significantly reduced and hip flexion significantly increased, while peak tibialis anterior activity significantly increased during extension only. Abdominal muscles had a low level of activity throughout the procedure.;Whole-body musculoskeletal models, which included individual passive torso stiffness and anthropometry, predicted that when wearing the device in the static stooped posture, compression and shear forces on the L5-S1 intervertebral disc were reduced by 13% and 12% respectively (p0.0001). Internal loads in the hip, knee, and ankle joints were also significantly reduced.;Many low back pain sufferers have reduced, or no, relaxation of back muscles in the stooped posture. Therefore, the device may be beneficial for those with existing LBDs. Furthermore, by limiting lumbar flexion, the device could reduce the risk of developing LBDs for those who work while adopting the stooped posture. Follow up field studies are needed to confirm the long-term potential benefits of such an intervention approach.