External Trunk Support with Industrial Benchwork
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Standing at a workbench is required for manual work including sorting and assembly. When work heights and reach distances are not matched to stature or arm length, the trunk assumes a partially bent position, which increases the postural effort required to stand or to reach to far distances. As a result, the biomechanical load on the lumbar spine is raised, which contributes to a higher risk for back pain. In ergonomics, assistive devices are being developed to counter this effect. A new leaning device was tested in the laboratory with forward-bent standing and reaching where the trunk was bent forward and twisted to reach to a far target 45° from the center. This device supported the trunk at the upper chest. With leaning, back muscle activity decreased by ~ 60% with forward-bent standing and ~ 23-30% with the off-center reach, depending on reach height. Because leaning changed how standing remained balanced, ~12° less bending was required to reach the target. Therefore, upper-trunk support may be helpful for benchworkers when ergonomic design is not possible; some product development and testing is still needed to provide the right amount of support at the right time and to ensure there is no rib joint irritation. An interesting outcome from these previous studies was related to workers’ posture when they leaned against a workbench that was adjusted for heavier work (hip height). Low back muscle activity was unchanged with forward-bent standing, but decreased by ~ 23-30% with the off-center reach. This reduction was accompanied by greater twist at the mid back as a way of compensating for a loss of hip rotation. Three different heights for bench leaning were compared in a third study: elbow height, hip height and below hip height. The results showed that leaning at elbow height lowered the work demand by ~16-24% for far reach, partially due to changed motions consistent with greater mid back movement and coincided with ~ 8% increase in work demands at the mid-back and greater scapular recruitment. Therefore, more research is needed to establish work height guidelines for use when leaning against a workbench.