# Long-Term Effects of a Soft Robotic Suit on Gait Characteristics in Healthy Elderly Persons
## 5 Discussion  
Motion ranges of hip, knee, and ankle joints increased in the PON condition compared with those in the POFF condition. Correspondingly, the walk ratio of the PON condition increased to 0.0057 m/steps/min from 0.0054 m/steps/min of the POFF condition, with an average increase of 6.9%. Toward this, we considered that the provided hip flexion assistance contributed to the hip flexion and consequently brought the swing leg to be positioned further forward compared with the case of the POFF condition. This result is consistent with our previous results [24] showing that the walk ratio in the PON condition was significantly increased to 0.0057 m/steps/min with an average increase of 8.9% compared with that in the POFF condition. It is recognized that healthy young persons walk at a walk  
Figure 11: Comparison of the walk ratio of each subject achieved in the POFF condition between Week 1 and Week 6. Figure 12: Comparison of the walk ratio achieved in the POFF condition between Week 1 and Week 6. On each bar chart, the error bar denotes one standard deviation. Figure 13: Comparison of the typical motions of the POFF condition around the timings of the toe off and the heel contact between Week 1 and Week 6.  
ratio of approximately 0.0065 m/steps/min [32]. Thus, it can be confirmed that, as immediate effects (i.e., comparison between the POFF condition and the PON condition), the robotic suit improved gait characteristics of the elderly persons to a level closer to a healthy gait pattern. On the other hand, after six weeks' use of the robotic suit, the walk ratio in the POFF condition reached \(0.0057\pm 0.0013\) m/steps/min from its initial state \(0.0052\pm 0.0009\) m/steps/min, with an average increase of 9.8%. Moreover, it was interestingly observed that elderly persons with a lower walk ratio may improve more by repeated use of the robotic suit. A similar study has also been conducted by [PERSON] et al. [28] to evaluate the long-term effects of a hip assistive device for three months. However, they reported that there was no increase of the walk ratio after three months' walking training with their device, while they found a significant increase of the walk ratio in an experiment for validating the immediate effects [33]. Thus, it can be argued that, as long-term effects (i.e., comparison in the POFF condition between Week 1 and Week 6), our device had the potential to make a contribution to gait rehabilitation of elderly persons. However, it is also found that, different from the immediate effect of the improved walk ratio by mainly increasing hip flexion, knee flexion, and ankle dorsiflexion, the walk ratio increased with reduced hip flexion, knee flexion, and ankle dorsiflexion, but increased hip extension, knee extension, and ankle plantar flexion in the case of long-term effects. Toward such a difference, we considered that the provided hip flexion assistance may indirectly influence the dynamics of the lower limbs. The most potential contributor could be the improved pelvic rotation. It is known [34; 35] that the pelvic rotation plays an important role in determining step length or, equivalently, the walk ratio. That is, the greater pelvic rotation allowed for a larger step length. It was also reported [36; 37; 38] that elderly persons walk in degraded pelvic rotation and hip extension, resulting in a declined walk ratio and walking speed. By considering these, in the case of using the device, we assumed that hip flexion assistance promoted the forward pelvis rotation of the elderly subjects. In turn, this promotion concurrently enhanced the standing leg muscles that were used for stabilizing the oppositely-rotating trunk, as pointed out in [39]. In such a way, after six weeks' repeated use of the device, it seems that muscles used for hip extension were reactivated and then softened, consequently leading to improved maximum hip extension. On the other hand, this improvement contributed to the improved gait characteristics with the increased walk ratio.