## 1 Introduction  
The prevalence of diabetes mellitus (DM) has been reported to increase every year. Uncontrolled DM will increase morbidity, mortality, and economic burdens [1]. The prevalence of DM in 2019 was expected to be 463 million people, growing to 10.2% (578 million people) by 2030 and 10.9% (700 million people) by 2045 [2]. One of DM complications is diabetic foot ulcers (DFUs). It was predicted that one-third of people with DM will experience DFUs in their lives [3, 4] and will develop recurrent ulcers about 0.4 times in the first year [5]. Furthermore, the risk of DFUs will increase 3 times for those who have DM more than 10 years, 7 times higher for those who have a level of glycated hemoglobin (HbA1c) above 86 mmol/mL, and 10 times higher for those who have body mass index (BMI) above 25 kg/m\({}^{2}\)[6]. Moreover, the annual health expenses for DM, especially for diabetic foot ulcers treatment, was more than USD 10 billion in the United States [7]. Due to its high costs, DM prevention is a primary concern worldwide. Exercise plays an essential role in DM prevention [8]. The American Diabetes Association (ADA) [9] advises that people with DM should accomplish adequate exercise to decrease the high levels of HbA1c [10] or excess BMI [11]. Exercise has also demonstrated its importance in maintaining a healthy body weight [11], decreasing the risk of cardiovascular diseases [12], and improving glycemic management [10]. The ADA recommends people with DM engage in vigorous aerobic exercise for at least 75 min per week or perform moderate-intensity aerobic exercise for at least 150 min per week [13]. In addition, people may perform aerobic exercise regularly to improve their health. Healthcare professionals recommend walking as one aerobic exercise, as it is not limited by race, gender, and age [14]. For nearly four decades, walking has been the most popular exercise in physical activity [15; 16; 17]. There is a paradigm transformation regarding recommended walking to achieve health, from light-moderate exercise [16] to moderate-vigorous exercise [13]. Several studies have extensively documented that walking increases the incidence of DFUs in people with DM due to increased peak plantar pressure (PPP) [18; 19; 20]. Moreover, to resolve the increased PPP, several studies confirmed that wearing a proper inside decreases the PPP and thus the risk of DFUs [21; 22; 23]. However, as walking is performed to improve health, on the other hand, it increases the incidence of DFUs. This presents the need to decrease the PPP in walking exercises for people with DM [24]. As an answer, there are two often used strategies by researchers to decrease the PPP--namely, (1) suitable walking speed [25] and (2) suitable insole material [26]. The PPP in the plantar region may vary at different walking speeds [27]. For example, moving forward at faster walking speeds engages the plantar surface to a pronated position that might increase PPP under the forefoot [28; 29]. This condition is believed to be a significant factor in affecting abnormally high PPP and further developing to the DFUs [30]. However, [PERSON] et al. have shown that slower walking speed increases PPP in the forefoot [24]. Thus, one factor contributing to high PPP at slower walking speed was the increased foot-to-floor contact time, leading to increased PPP in the central and medial forefoot region [24; 27]. Furthermore, the issue of reducing PPP at the plantar region is essential for DFUs prevention. Therefore, appropriate walking speeds may decrease the PPP for DM subjects under the forefoot, midfoot, and rearfoot [31; 32]. The ethylene--vinyl acetate (EVA), Poron, Plastazote, and polyurethane were developed based on their function to reduce the PPP in the plantar region [33; 34; 35]. The insole has functions such as cushioning, resilience, and stiffness. The EVA has been used as an insole material in different plantar regions (forefoot, midfoot, and rearfoot) [36; 37; 38].