# Morphology-Related Foot Function Analysis: Implications for Jumping and Running
## 1 Introduction  
Human feet are the basic terminal structures that support human walking, running, jumping, and other locomotion. The foot is a complex structure that controls balance and movement [1; 2]. Foot morphology has been studied since the early 20 th century [3]. Previous studies have demonstrated that the foot differs significantly between habitually barefoot and shed people [4; 5; 6], and differences in the kinetics of walking, running, and jumping have been observed [7; 8; 9].  
Different foot morphology may also be a contributory factor for injury during motion [10], and may also influence physical activity performance [11; 12]. There are many reasons for morphological differences in humans, which include disease, foot malfunctions, genetics, and deformity [13]. Research findings have indicated that external factors, such as footwear, may deform foot structure, and result in conditions such as hallux valgus (HV) [3; 14]. HV could induce foot dysfunction [15], influence foot morphology [16], and may impair quality of life [17], which may result in depression and pain [18].  
In addition, when compared to habitually shed populations, habitually barefoot populations demonstrate more toe separation [3; 4; 14]. Studies on foot morphology have focused on the width and length of the foot [6], and several studies have investigated the morphological differences between the hallux and other toes [4; 14]. However, whether these differences influence the motions needed for physical activity is unclear.  
Jumping is a typical movement in many sports, and has attracted much attention from the research community [19; 20]. Jumping performance has been evaluated using a one-foot and a two-feet jump [19], and toe flexor function has also been examined [20]. Furthermore, the countermovement jump has been important to support clinicians in the medical diagnosis of muscle power during prolonged recoveryperiods following ankle injuries [21]. The contribution of the forefoot and toes has been evaluated while performing the vertical jump, and kinematics, kinetics, and spatiotemporal parameters have been recorded and analyzed [22].  
[PERSON] et al. [23] indicated that habitually barefoot populations and shed populations present different foot strike patterns. Habitually barefoot populations land on the forefoot, then bring down the heel, and have been observed landing with a flat foot, but seldom on the heel. Habitually shed populations mostly land with a rearfoot strike. The elevated and cushioned heel of the modern running shoe may be a contributory factor that has facilitated the differences in the strike patterns observed. However, strike patterns have been observed to be variant, even between shed or barefoot populations, in recent studies [2; 7; 8; 24]. In spite of the conflicting opinions about barefoot locomotion, it has gained in popularity in recent years, and is now included in athletic training [25], recreational running [26], and rehabilitation [27]. A previous study has revealed the foot shape and function differences in native barefoot walkers [5] and runners [24]. The morphological differences between habitually barefoot and shed runners were found to exist in the forefoot and toe regions [4]. However, morphology based on the functions of the forefoot and toes while performing vertical jumping and running has not been investigated.  
Therefore, the purpose of this study was to examine morphology-related performance differences while conducting vertical jumping and running tasks between habitually barefoot males and shed males. A further aim was to explore any functional differences in the forefoot and toes, based on foot morphological characteristics. It was hypothesized that the lower extremity kinematics and plantar forefoot loading distribution would be different due to the morphological differences in the forefoot and toes region.