Comparative analysis of lumbar load across delivery truck designs during loading and unloading tasks

BackgroundParcel loading and unloading often involve deep trunk flexion and external loads, elevating lumbar stress.ObjectiveTo 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.MethodsTen 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 (α = 0.05).ResultsTruck 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.ConclusionsThe 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.