###### Abstract  
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\({}_{\text{CEX}}\), and W\({}_{\text{CC}}\)) 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. passive lower-limb exoskeleton; leg assist device; work-related musculoskeletal disorders (WMSDs); ergonomic intervention +
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0000-0002-0001-9300-0000-0002-000 result, the passive lower-limb exoskeleton device, which can be used for both standing and sitting postures, has recently received much attention [5,6]. A passive exoskeleton device is a mechanical device to assist human joints or movements without an external power source or battery. Although it is true that there are still several barriers to applying the exoskeletons directly to the workplace, the passive exoskeleton is relatively easier to apply to the field without significant changes in the work environment than the active exoskeleton. Thus, the passive exoskeleton is being considered in various fields to reduce physical fatigue by reducing muscle activity [7,8]. Among the passive exoskeletons, the lower-limb exoskeleton is an auxiliary device that allows the user to maintain a sitting position without a chair. The passive lower-limb exoskeleton, as an alternative to an active exoskeleton, does not require an external power source or battery and also has the advantage of being relatively lightweight and easy to wear using a belt or buckle [9]. Several studies have evaluated the effects of passive lower-limb exoskeleton devices. For example, [PERSON] et al. (2020) [10] tested the squatting posture while working before and after wearing a passive leg assist device and reported that the activity of the rectus femoris (RF) muscle significantly decreased when wearing the device, while that of the tibialis anterior (TA) muscle increased slightly. [PERSON] and [PERSON] (2013) [11] showed that wearing a lower-limb assistive device reduced the floor reaction force when caregivers assisted in transferring elderly or physically challenged patients. [PERSON] et al. (2019) [12] reported that studies on the stress applied to other joints were necessary, although lower-limb devices effectively reduced lower-limb muscle activity. As such, wearing lower- and upper-limb exoskeleton devices can have both positive [13,14,15] and negative [16,17,18,19] effects, and, in particular, the effect of wearing an exoskeleton device may vary depending on the working environment, so further research is needed. Although there are several studies on lower-limb exoskeleton devices, there are limitations in that more studies are needed on the differences in effectiveness when applying them to various working heights and muscles.