## 3 Results  
Prior to investigating the changes in muscle activation patterns elicited by the passive gait assist device, we needed to configure the ideal length of straps 1 and 2. For instance, if the difference between strap 1 and strap 2 is too small, tension will still reside in strap 2 even if the pulling angle of the elastic cord is high; this will cause plantar flexion torque to be present during the swing phase. For the opposite case, in which the difference between straps 1 and 2 is large, dorsiflexion torque will be applied during the late stance stage. This was confirmed by our simulation as seen in Figure 3a. The two black lines represent HO and TO during the gait cycle. The red lines represent the total pulling force by the elastic cord and the blue and green lines represent the tension present in straps 1 and 2, respectively. As seen in the bottom left panel of Figure 3a, when strap 2 (90 mm) is relatively shorter than strap 1 (160 mm), there is a significant amount of tension in strap 2 prior to HO. Also, in the top right panel, when strap 2 (130 mm) is comparable in length to strap 1 (140 mm), we observe plantar flexion torque after TO. Thus, our simulation results suggest that the optimal lengths are 160 mm and 110 mm for straps 1 and 2, respectively, with the base of the triangle being 150 mm.  
Once we had selected the lengths for straps 1 and 2, we verified whether the simulated tension profiles were indeed what was present in the straps during the gait cycle. We attached three load cells to our system, one at the end of the elastic cord and one on each strap (Figure 3b). We note that the lengths were adjusted such that the length of the strap was 160 mm and 110 mm for straps 1 and 2, including the load cell length. We found that the force profiles obtained from the load cells (Figure 3c, solid lines) and those from the simulated data (Figure 3b, dashed lines) qualitatively matched well with one another. Thus, with our system parameters, we can assert that plantar flexion torque is provided during the late stance and dorsiflexion torque is present during the swing phase.  
The next question one might ask is whether this system actually assists the user during gait. It is common for gait-assistive devices to impede the user's natural gait patterns. The goal is to reduce the amplitude of the EMG signals while maintaining the overall patterns. We evaluated the patterns of two lower-limb muscles (TA and SL) that have well-documented functions during gait. The EMG WL patterns during rollator walking (Figure 4a, black lines) and passive gait assist device-assisted gait (Figure 4a, red lines) qualitatively match each other well. More importantly, we observed a decrease in dorsiflexor EMG WL during the swing phase and the plantar flexor EMG WL during the late stance phase. This agrees well with the initial objective of our system. We went further and analyzed the average EMG WL for SL and TA for the stance and swing phases, respectively (Figure 4b). The results suggest that this effect is not confined to one subject but instead seen across the participant group.  
Figure 3: Force profiles of the passive gait assist device. (**a**) Simulation of the tension that resides in the elastic cord and straps 1 and 2. HO and TO represent heel-off and toe-off, respectively. (**b**) Image of load cells attached to the specialized shoe. (**c**) Data from load cells (solid lines) are plotted with simulated data (dashed lines).