A field evaluation method for assessing whole body biomechanical joint stress in manual lifting tasks

Work-related musculoskeletal injuries are often associated with overexertion of the body at work. The manual materials handling activity of lifting is a major source of work-related musculoskeletal disorders. Biomechanical evaluation offers useful information about the physical stress imposed on the worker's body joints; however, biomechanical analysis is usually tedious and complex. For evaluation purpose, the biomechanical method needs to be easy to apply in a field environment. Manual lifting occurs as one of the most common manual materials handling tasks in the workplace. A biomechanical evaluation method was developed based on the ratio of joint moment to joint capacity. The method was applied to evaluate the physical stress of manual lifting in truck loading jobs using a nine-link whole body joint model. Thirty eight industrial tasks were evaluated using the developed joint moment ratio. The moment ratio was compared with subjectively rated body discomfort, overall workload, and the NIOSH lifting index. The moment ratio was found to have a high correlation with the NIOSH lifting index. The biomechanical method can be used with relatively simple equipment and procedure which may be suitable for on-site ergonomic evaluation.