Biomechanical and physiological responses to allowable load handling limits in Iranian female workers

In 2017, load limit values for manual material handling (MMH) tasks were confirmed to protect workers from low back disorders without prior validity investigation for Iranian workers. The present study investigated the applicability and feasibility of the Washington State Department of Labor and Industries (WISHA) lifting method as an occupational exposure limit (OEL) for the MMH tasks in a sample of young Iranian female workers using biomechanical and physiological criteria. A laboratory study was conducted with 10 female participants performing lifting tasks as described in the Iranian OEL for the MMH tasks based on the WISHA checklist. Each participant completed 21 lifting task combinations that varied in height and reach with the maximal allowable load. To test the applicability of the WISHA method, the maximum aerobic capacity and the equivalent heart rate (EHR) were estimated for 10 young Iranian female workers using an ergometer and Astrand protocol. Moreover, spinal loads for each lifting task were calculated using a static biomechanical model. From a physiological point of view, approximately 38% of the lifting tasks resulted in an increase in the physical workload. For 33% of the lifting trials, the estimated compression loads exceeded 3400 N. The findings revealed that the weight and lift height of the loads affected the lifting capacity of the participants. It seems that the allowable weight limits for manual lifting are not matched to the biomechanical and physiological capacities of the Iranian women. Therefore, the Iranian guideline for manual lifting is recommended to be revised based on the physiological and biomechanical capacities of the Iranian women.