## 4 Discussion
These changes contribute to decreased plantar pressure in the feet and and a slower walking speed. In particular, on irregular road surfaces, the elderly show a cautious gait pattern with slow gait speed, decreased stride length, and increased variability in stride timing [39]. So, it is believed that the pressure in the H, LT, and FF regions was affected as the walking speed and forward propulsion force decreased to maintain balance on rough ground. Additionally, when using the RHH, the LT and FF regions showed an increase in mean force and peak pressure compared to the RBH. These results are thought to be due to the changes in plantar pressure distribution in the elderly, whose weight shifts to the lateral side of the foot during walking while the weight of the rollator affects forward movement or direction control [40]. When walking on a downhill slope using two types of rollators, mean force, peak pressure, and contact area in the H and LT regions significantly increased compared to other walking environments. In previous research, as a result of analyzing the peak pressure of the foot according to the slope during downhill walking, it was reported that the pressure of the hallux region increased while the pressure of the lesser toes region decreased as the slope increased [41]. The plantar pressure in the H, LT, and FF regions significantly increased during downhill walking, which may be related to the result of increased upper and lower extremity muscle activity. That is, when walking downhill using a rollator, it can be considered that stability is maintained by using a gait strategy in which muscles of the upper and lower limbs are activated, and force is applied to the toes until the moment the foot leaves the ground. Furthermore, forefoot pain, which is common in older people, is often caused by high pressure under the forefoot [42]. In particular, the peak pressure on the hallux region is the highest compared to other regions when walking downhill, which means that continuous use of a walker can cause foot injuries or pain of the elderly. Therefore, it is necessary to design the structure of the rollator to reduce forefoot pain by redistributing high forefoot plantar pressure. For the results in the MF and HF regions, the mean force, peak pressure, and contact area measured in the OT and UT all increased. Previous studies analyzing the gait characteristics of the elderly reported an increase in support time and a decrease in movement speed from the initial stance phase to the middle stance phase for stable gait [43]. Accordingly, it could be confirmed that total plantar pressure distribution, not local pressure, increased while using the cautious gait strategy to stably maintain dynamic balance in an environment with obstacles or uneven ground. This gait strategy involves lower extremity muscle outcomes in which RF and BF are activated to maintain postural stability. When using the RHH in the OT, the significant increase in mean force and peak pressure in the MF region compared to the RBH is thought to be due to the use of the \"lift pedal\" mounted on the RHH. It is also thought that the reduced RF and TA activity during walking using the RHH with large wheels in the UT affected the mean force, peak pressure, and contact area between the hindfoot and the ground. In the elderly, downhill walking is a challenging daily mobility activity that requires complex adaptions to maintain gait stability [44]. From the results of the foot region, it can be confirmed that the mean force, peak pressure, and contact area when walking on a downhill terrain are relatively low compared to other walking environments. It has been found that walking downhill is associated with a higher risk of falling than walking up stairs because it significantly reduces walking stability [45]. The significantly lower plantar pressure distribution in the HF region may be considered to be due to the decrease in dorsiflexion and TA activity while reducing the stride length to ensure gait stability.