## 4 Discussion
### Vertical Ground Reaction Forces  
Our findings revealed that both groups exhibited similar magnitudes and patterns of vGRFs across all foot regions and walking conditions, with some notable exceptions. Subjects with hyperpronated feet demonstrated greater vGRFs in the midfoot region compared to those with neutral feet. Additionally, significantly lower vGRFs were exerted on the lateral forefoot and, occasionally, on the medial forefoot by subjects with hyperpronated feet compared to their neutral foot counterparts in nearly all tested gait conditions  
Similarly to our findings, some researchers have reported increased forces on the entire midfoot region [68] or the medial midfoot region [24] in hyperpronated feet, as well as weak to fair relationships between peak pressure exerted on the medial midfoot and various indices used in the classification of hyperpronation [69]. Other investigators have also reported lower forces and/or pressures under the fourth and fifth metatarasophalangeal joints, anatomical structures located in the lateral forefoot region, thereby supporting our results [24; 26; 27; 48; 51]. Our findings did not confirm previous observations of increased peak pressure under the middle region of the forefoot, which includes the second and third metatarasophalangeal joints [48; 70], and decreased forces on either the entire or the lateral region of the rearfoot [26; 27]. Some researchers have shown greater forces and pressures under the hallux [26; 28; 48; 69] and the second toe [48], but these findings could not be supported by our data due to the inability to distinguish between the various regions of the toes. The increased forces in the midfoot are likely due to the misalignment of the subtalar joint and the associated collapse or flattening of the medial longitudinal arch. Kinematic studies have demonstrated significantly higher peak rearfoot version [17; 51; 52] and an increased medial deviation in the trajectory of the center of pressure [29; 48]. Furthermore, the ligament laxity resulting from repetitive stress on plantar ligaments, such as the spring ligament [67], may allow the medial longitudinal arch to collapse more easily during gait, as evidenced by the increased relative vertical displacement of the navicular bone [71]. These changes may explain the redistribution of plantar loads, placing greater stress on the midfoot region as the foot compensates for the altered joint alignment and reduced stability. Additionally, as the medial longitudinal arch collapses and the foot excessively pronates, the structures in the inner region of the foot, such as the second and third metatarsophalangeal joints, may become overburdened. This diminishes the forces exerted on structures located in the medial region (first metatarsophalangeal joint) and, more notably, the lateral regions (fourth and fifth metatarsophalangeal joints) of the forefoot [24; 26; 27] and, consequently, reducing their contribution in supporting body weight during gait. Comparisons between slopes revealed that midfoot forces were lower during uphill and level walking compared to downhill walking. Excessive pronation facilitates forefoot contact with the ground and, by increasing the relative distance between the calcaneus and metatarals, imposes greater strain on the plantar fascia while impairing the efficient function of the windlass mechanism [72]. However, increased ankle dorsiflexion during uphill walking facilitates the windlass mechanism by enhancing plantar fascia tension through the stretch of the Achilles tendon, whose collagen fibers envelop calcaneus and integrate into its superficial layers [62; 72; 73]. These responses may be even more pronounced in individuals with hyperpronated feet, as plantar fascia tension is likely to increase more due to passive stretching of a tighter Achilles tendon, as indicated by the reduced range of motion of ankle dorsiflexion exhibited by these individuals compared to those with neutral foot posture in this study.