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Biomechanical Effects of a Personal Weight Transfer Device in the Stooped Posture

Repetitive work in the stooped posture is a known risk factor for developing low back disorders (LBDs). Use of the stooped posture in the workplace is widespread throughout the world in agriculture, construction, and mining. In California alone, hundreds of thousands of agricultural field workers routinely utilize the stooped posture. The purpose of this study is to evaluate if a personal weight transfer device as a possible intervention to reduce the load on the lumbar spine, thereby reducing the risk of developing LBDs. Eighteen healthy subjects performed stoop posture tasks in a laboratory study designed to simulate harvesting of low-growing crops. Results showed that when wearing the device in the static stooped posture, biceps femoris activity was reduced by 17%, lumbar flexion was reduced by 12%, ankle plantar-flexion increased by 5%, and the lumbar erector spinae of those subjects who did not experience flexion-relaxation of the erector spinae was reduced by 26%. Hip and knee flexion were not significantly altered. The device was effective in reducing the back muscle activity in those subjects who did not experience flexionrelaxation. Low back pain sufferers have reduced, or no, relaxation of back muscles during stoop. Therefore, the device may be beneficial for those with existing LBDs, and who use the stooped posture routinely. By limiting lumbar flexion, and consequently reducing loads on the lumbar intervertebral discs, the device may reduce the risk of developing LBDs in the population of people who use the stooped posture.