Biomechanical investigation of a passive upper-extremity exoskeleton for manual material handling – a computational parameter study and modelling approach

Passive upper-extremity exoskeletons may decrease the risk of developing work-related musculoskeletal disorders. This study examined how shoulder muscle forces and biomechanical loads in the glenohumeral and L4-L5 joint changed as different support torque (1.1-11.2 Nm) and angle settings (60-120°) of an exoskeleton were simulated during an overhead manual material handling task. Full-body kinematics of 15 grocery workers, who lifted a bread case (7.9 kg) onto shopping shelfs (145.5 cm), were captured on site. The kinematic data were used to drive a detailed human-exoskeleton model based on inverse dynamics. Generally, simulations with maximum torque combined with a peak angle setting between 75-105° reduced L4-L5 compression and anteroposterior shear forces, glenohumeral contact forces and shoulder flexor muscle forces. The exoskeleton therefore, seemed effective for reducing physical exposure during overhead handling. However, maximum torque with the lowest angle setting, 60°, increased musculoskeletal loading, suggesting that not adjusting the exoskeleton properly could be detrimental.