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Many warehouse slotting algorithms have overlooked worker ergonomics. This research aimed to develop ergonomics slotting guidelines based upon the back and shoulder postures and electromyographic (EMG) responses of the deltoid and erector spinae muscles when individual items are picked from, or full cases replenished to, different shelf heights In the first study of two studies, participants lifted small items representative of piece-pick tasks from seven shelf heights. In the second study, participants performed a simulated full case replenishment task in which they lifted boxes weighing between 2.7 and 10.9 kg from a cart into a flow rack. Shelf height significantly affected all postural and EMG variables and there was a trade-off between back and shoulder muscle activity across the varying shelf heights. Together, these studies were used to develop some general ergonomic slotting guidelines that could be implemented to reduce biomechanical load exposures experienced by distribution center workers. 

One-handed picking tasks are frequently performed when workers are picking small products or smaller quantities of products to fulfill customer orders. Many slotting models have been developed that minimize travel distance based on individual item order frequencies. None of these models have considered the biomechanical costs associated with the item selection process. This project aimed to quantify the physical demands on the back and shoulders as participants performed simulated picking tasks from different shelf heights. In this study, 17 female participants lifted items of two different weights (0.45 and 0.90 kg) from seven shelf heights ( 10.8, 37.1, 63.5, 89.9, 116.2, 142.6, 168.9 cm) and either walked one step prior to picking up the item (lifting task 1) or lifted the item without needing to take a step (lifting task 2). Dependent measures included 90th percentile electro-myographic (EMG) signals from the anterior and lateral deltoid muscles, and the erector spinae muscles, as well as spine and shoulder kinematics, and task durations. EMG data were normalized to maximal voluntary exertions. The results indicated that shelf height has significant effect on the time required to complete both task 1 and task 2. The time of complete task 1, with the one meter travel, is larger than the time to complete task 2 at each layer, and time difference between tasks is relatively consistent, the average of which is 0.75 seconds. The lifting time for shelf heights from 63.5 to 116.2 cm is relatively shorter compared with that at lower and higher shelves. The total time for walking and lifting varies by nearly half a second between the slowest and fastest conditions. This study provides data that can be used to develop slotting guidelines for piece pick operations in distribution centers. Complimentary data are still needed for the full case replenishment tasks to ensure the ergonomic needs of those working the back side of the flow rack are also considered.