Correlations Between Biomechanical Variables and Subjective Measures of Satisfaction While Using a Passive Upper-Limb Exoskeleton for Overhead Tasks in the Field

This article proposes a novel evaluation approach on wearing passive upper-limb exoskeletons for overhead tasks in real-world automotive manufacturing lines. We determined that wearing exoskeletons reduced the biomechanical efforts of workers measured by joint kinematics and electromyography as well as the estimated shoulder joint reaction forces and torques derived from simulation. These quantitatively measured variables were statistically associated with subjective measures collected through satisfaction questionnaires. We specifically found that participants increased the shoulder flexion and abduction angles as well as the shoulder range of motion while wearing exoskeletons. Participants also reduced muscle activities, joint torques for shoulder flexion, and reaction forces exerted on the shoulder joints while wearing exoskeletons. Interestingly, our analysis also found that the increased shoulder movement while wearing the device was negatively associated with the satisfaction level. This indicates that although the assistance provided by the device allows users to perform a wider range of arm lifting movements, the deviation from their original movement with the device may lead to decreases in satisfaction levels. This integrative approach using biomechanics and ergonomics suggests that we can potentially predict the subjective scale of satisfaction based on biomechanical variables and preliminarily evaluate the usability and comfort while wearing exoskeletons in real-world settings.