Musculoskeletal Modeling of a Hinge-Type Back-Support Exoskeleton: A Simplified Approach for Practical Assessment

To promote the adoption of exoskeletons in industries aiming to prevent work-related musculoskeletal disorders, it is essential to demonstrate their positive impact for specific tasks and users through practical evaluation methods. This study assessed four methods, each with a different level of detail, for modeling the support provided by a hinge-type back-support exoskeleton in OpenSim. Methods 1 and 2 simulated support as a pure torque applied at the hip joint, with Method 1 relying on user kinematics, and Method 2 using exoskeleton movement data to estimate the torque profile. Method 3 estimated supporting force vectors based on user kinematics and exoskeleton configuration, assuming the user's body and the exoskeleton moved together. Method 4 incorporated the movement of the exoskeleton to simulate support as force vectors and was used as the reference for comparison. Results for back muscle activity and L5-S1 joint reaction forces were compared across the four modeling methods using data from fourteen participants performing squatting and stooping tasks with the exoskeleton. Statistical parameter mapping revealed significant differences in L5-S1 joint reaction forces between Methods 1 and 2 compared to Method 4 throughout the exoskeleton engagement period during squatting, and at the peak trunk angle during stooping. In contrast, minimal differences were observed between Method 3 and Method 4. These findings suggest that modeling exoskeleton support as force vectors based on user kinematics (Method 3) provides reasonable accuracy, demonstrating the feasibility of evaluating exoskeleton support with reduced data collection complexity and enabling an efficient assessment process.