## 4 Discussion  
In this study, we present a passive gait assist device that can be attached to a conventional rollator. Our device assists the user's natural muscular activities, which in turn results in trajectory assistance because the force pulls from the front of the user. This is a considerable improvement when compared to traditional rollators where it is common for the user to drag their feet. Furthermore, unlike rigid exoskeletons, our device allows for relatively free movement in space. This may in turn result in a safer gait rehabilitation environment. We provided both simulated and empirical, via load cells, force profiles that reside within the elastic cord, strap 1, and strap 2. The analysis of EMG data obtained from the SL and TA suggests that our device successfully reduces the lower limb demands without disrupting the user's natural gait patterns. While the configuration was not tested, our system is able to change the stiffness of the spring-bar system, the width at which the elastic cords are anchored, the spring constant of the elastic cord, and the length of strap 1 and strap 2. This suggests that this system is highly adjustable and can be set up according to the user's needs. For instance, we would be able to lessen the elastic force as increases in the user's lower limb functions occur. Also, because we can independently configure each limb, we believe that it is possible to aid  
Figure 4: SL and TA EMG WL analysis during gait. (**a**) Typical pattern of the SL and TA EMG WL during the stance and swing phases. The mean and S.D. are plotted as a line and shaded area, respectively. (**b**) The relative difference in SL EMG WL during the stance phase and (**c**) the TA EMG WL during the swing phase for all subjects. Data are presented as the median (25%, 75%), *_p_ < 0.05, assessed using the Wilcoxon signed-rank test. stroke patients. Moreover, we would be able to adjust the length of strap 1 and strap 2 to provide more dorsiflexion torque during the swing phase for the afflicted limb. There are some limitations that need to be addressed. The experiments were performed by community-dwelling elder adults without any gait impairments. In order to confirm that our passive gait assist device works in practice, further studies with gait-impaired populations such as bedridden, post-stroke, and post-surgery patients need to be conducted. Also, because our device attaches to a conventional rollator, it may be difficult to ambulate non-level surfaces. This hindrance could be inconvenient in real-world situations. Moreover, the EMG levels of only the SL and TA were examined. In order to assess lower-limb gait patterns, a more extensive investigation of the lower limb muscles when using our devices, such as the rectus femoris, vastus medialis, biceps femoris, and gluteus maximus, should be performed. By comparing the SL and TA EMG patterns during gait with the passive gait assist system with that of rollator gait conditions, we were able to observe that, at least for the tibia muscles, the overall patterns were similar. While conserved, we observed decreases in SL during the stance phase and TA during the swing phase, which is where the respective muscles are active. This decrease in tibia muscle demand should benefit subjects with weakened lower limb functions to perform gait without the help of a physiotherapist. This would allow for more frequent training, as resources are limited, which would in turn result in higher rehabilitative efficacy. Conceptualization, J.K., N.K. and S.-J.K.; methodology, J.K., S.K. and S.P. ; software, Y.K. and J.M. ; validation, J.K., Y.K., S.K. and S.-J.K.; formal analysis, J.K.; investigation, Y.K. ; resources, S.-J.K.; data curation, J.K. and Y.K. ; writing--original draft preparation, J.K.; writing--review and editing, J.K. and S.-J.K.; visualization, Y.K. and J.M. ; supervision, S.-J.K.; project administration, S.-J.K.; funding acquisition, S.-J.K. All authors have read and agreed to the published version of the manuscript.