## 4 Discussion
The TA, the largest dorsiflexor of the ankle joint, plays an important role in foot stabilization and postural control during walking [26]. The significant increase in TA activity that occurred with the use of the RHH in the OT is thought to be due to increased sagittal motion of the ankle using the lift pedal to overcome an obstacle [27]. On the other hand, it is estimated that the relatively large wheel compared to the RBH affected the reduction in muscle activation while facilitating movement on uneven ground such as UT. Interestingly, TA activity decreased in the DS when using both types of rollators. Previous studies have confirmed that sloped walking leads to altered lower limb muscle forces [28]. The balance is to keep the center of mass (CoM) within the limits of the base of support (BoS). Accordingly, it is presumed that the use of a rollator increases BoS during walking and maintains proper balance, contributing to a significant reduction in TA activity [29]. The BF is mainly involved in the knee flexion [11]. The increased muscle activity in the OT and UT measured when using the RBH is thought to ensure gait stability in environments with obstacles or uneven ground. Our findings are commonly in line with a previous study which found that BF plays an important role in maintaining dynamic postural stability in older adults during walking [30]. It is suggested that the significant decrease in BF activity during the use of the RHH was influenced by the structural characteristics of the walker, which has a lift pedal and relatively large wheels. A previous study has reported that the elderly need more lower extremity muscle activity when walking on an uphill slope than on a flat road [31]. Therefore, it can be considered that the activity of the BF was higher in the US when walking with the RHH, which is heavier than the RBH. The GM not only acts as a plantar flexor in the late stance phase but also as a knee flexor, performing as an antagonist during knee extension [32]. In this study, GM showed similar activity patterns in both the RBH and RHH depending on the walking environment. The significant increase in GM activity in the FT when using the RHH is thought to be due to the increased weight of the rollator requiring more forward propulsion. The biggest activity of GM can be found in the US. This is consistent with previous findings that observed greater activation of the gastrocnemius muscle in the elderly group during uphill walking [33; 34]. It is believed that this rapid increase is also caused by generating additional force to push the rollator forward during uphill walking. Walking on an inclined terrain is a locomotion activity that requires complex adaptations to maintain stability [35]. In addition, it was found that inclined walking was associated with a higher risk of falling in the elderly than walking on stairs with a similar inclination [36]. Accordingly, increased muscle activity during uphill walking is thought to maintain a stable posture on an incline. As a result of comparing the mean force, peak pressure, and contact area measured when using two types of rollators in various walking environments, similar patterns were found in the H and LT regions. The mean force, peak pressure, and contact area all decreased in the OT, UT, and US compared to the FT, while significant differences were most evident in mean force. This means that a large reduction in mean force has a direct effect on peak pressure and contact area. Decreased plantar pressure distribution in the H, LT, and FF regions could be associated with the lowest GM activity in the UT. During walking, the foot contributes to generating propulsion to move forward while adapting to the irregular surface [37]. Balance and gait are very important considerations for the health of older adults [38]. When walking using a walking aid, if there is an obstacle, deformation, or slope in the ground, the elderly use a walking strategy to keep the stability and postural balance for avoiding falling.