investigation on a developed wearable assistive device (wad) on decreasing lumbar muscles activity during static holding tasks; emg analysis and biomechanical modeling

one of the most common diseases associated with musculo-skeletal ailment is low back pain which is epidemic among general public. if manual tasks are performed inappropriately by workers at workplaces, it may cause back pain in the lumbar spine. in recent years, a variety of assistive devices has been presented and used to utilize a passive force generator which has been effective in decreasing lumbar moments and the force requirements by erector spinae muscles. in forward flexion, trunk muscles balance the weight of upper body and external loads. regarding to small moment arm of these muscle, they create great forces that may lead to high intradiscal pressure and cause disc injury. the aim of this paper is to present a new wearable assistive device that decreases trunk muscle activity during static holding task. the performance of this device is simulated biomechanically with link-segment model. using anybody software, compressive and shearing forces and also muscle activity of lumbar were determined. to validate the results, electromyography (emg) of muscles of fifteen male participated in the study was analyzed.  results of link-segment model indicated that there was a reduction in the lumbar moment by 15 - 23% using wad. moreover anybody model demonstrated that compressive and shearing forces decreased by 24% and 29% respectively in average and muscle activities decreased by 18 - 25%, too. statistical analysis demonstrated that normalized electromyography of right and left lumbar, thoracic erector spinae and latissimus dorsi muscles significantly decreased (p<0.05) by 21.9%, 20.4%, 23.6%, 20.4%, 23.7%, and 16.7% respectively and electromyography of right and left external oblique, internal oblique and rectus abdominus muscles had significant change (p<0.05)