The aim of this study was to determine the muscle load reduction of the upper extremities and lower extremities associated with wearing an exoskeleton, based on analyses of muscle activity (electromyography: EMG) and the AnyBody Modeling System (AMS). Twenty healthy males in their twenties participated in this study, performing bolting tasks at two working heights (60 and 85 cm). The muscle activities of the upper trapezius (UT), middle deltoid (MD), triceps brachii (TB), biceps brachii (BB), erector spinae (ES), biceps femoris (BF), rectus femoris (RF), and tibialis anterior (TA) were measured by EMG and estimated by AMS, respectively. When working at the 60 cm height with the exoskeleton, the lower extremity muscle (BF, RF, TA) activities of EMG and AMS decreased. When working at the 85 cm height, the lower extremity muscle activity of EMG decreased except for TA, and those of AMS decreased except for RF. The muscle activities analyzed by the two methods showed similar patterns, in that wearing the exoskeleton reduced loads of the lower extremity muscles. Therefore, wearing an exoskeleton can be recommended to prevent an injury. As the results of the two methods show a similar tendency, the AMS can be used.

The aim of this study was to confirm the effect of a lift-assist device when performing a patient-lifting task. Ten working caregivers participated in this experiment, and lifting patients from bed to wheelchair (B2C) and wheelchair to bed (C2B) was performed for manual care (MC) and lift-assist device (robot) care (RC). EMG sensors and IMU motion sensors were attached as indicators of the assistive device’s effectiveness. EMG was attached to the right side of eight muscles (UT, MD, TB, BB, ES, RF, VA, and TA), and flexion/extension angles of the neck, shoulder, back, and knee were collected using motion sensors. As a result of the analysis, both B2C and C2B showed higher muscle activities in MC than RC. When using a lift-assist device to lift patients, the RC method showed reductions in muscle activities compared to MC. As a result of the work-posture analysis, both the task type and the task phase exhibited pronounced reductions in shoulder, back, and knee ROM (range of motion) compared to those of MC. Therefore, based on the findings of this study, a lift-assist device is recommended for reducing the physical workloads of caregivers while performing patient-lifting tasks.

Introduction: Research and development efforts regarding passive lower-limb exoskeletons are actively ongoing to reduce work-related musculoskeletal disorders (WMDSs) from improper and prolonged posture. The aims of this study were to evaluate the effects of passive lower-limb exoskeletons and working heights on muscle activity and subjective comfort ratings. Methods: In this study, 20 males performed a 10-min drilling task for three levels of working height (60, 85, and 110 cm), and three levels of intervention (WO: without exoskeleton, W_CEX, and W_CC) were used as independent variables. The EMG data of eight muscles and subjective discomfort ratings in each of the six body parts were analyzed in this study. Results: The results of this study confirm that the effect of wearing a lower-limb exoskeleton device may vary depending on the muscle type and working height. Overall, the positive effects of wearing were generally observed in the lower-limb muscles, whereas the muscle activity of the upper limbs showed an increasing trend when wearing the device at a height of 85 cm or more. Conclusions: Therefore, to obtain positive effects in both the upper- and lower-limb muscles, using the lower-limb exoskeletons at a working height of 85 cm or less is recommended.