ScholarWorks@성균관대학교

초록

Background: Parcel loading and unloading often involve deep trunk flexion and external loads, elevating lumbar stress. Objective: To compare lumbar load across delivery truck types (Conventional, Low-entry, Newly designed) and task types (loading, unloading) using erector spinae electromyography, lumbar flexion angle, and L5/S1 compressive force. Methods: Ten delivery workers performed standardized loading and unloading cycles in each truck. Electromyography was normalized to maximal voluntary contraction; lumbar kinematics were recorded with an inertial measurement unit system; and L5/S1 compression was estimated frame by frame with a biomechanical model using a 98 N hand load. For each variable, the 50th and 90th percentiles were computed. Effects of truck type and task type, as well as their interaction, were analyzed using a two-way repeated-measures analysis of variance (alpha = 0.05). Results: Truck type significantly influenced lumbar flexion. At the 50th percentile, the newly designed truck showed 24.0% less flexion than the conventional and 43.9% less than the low-entry; at the 90th percentile, reductions were 19.6% and 30.6% (p < 0.05). L5/S1 compression also varied by truck type: at the 50th percentile, the newly designed truck was 21.6% lower than the low-entry and 13.8% lower than the conventional; at the 90th, it was 7.9% lower than the low-entry (p < 0.05), while the conventional showed no significant differences. EMG showed no significant effects, and task effects were minimal. Conclusions: The newly designed truck reduced lumbar flexion and L5/S1 compression relative to the low-entry and conventional trucks, demonstrating a clear ergonomic benefit for parcel handling.

키워드