**1. Introduction**

Football is the most popular sport in the world, has the largest number of participants, and is associated with a high risk of injury at the professional, amateur, and youth levels during practices and matches [1–5]. It is estimated that somewhere between 13 and 35 players ge<sup>t</sup> injured every 1000 competitive hours. The most common incidence of injuries occurs in the lower limbs, mostly ankle sprains [1,5,6]. Dvorak et al. studied injury incidences in the 2010 International Federation of Association Football World Cup. They found that ankle sprains were the most prevalent injury in practices or matches [6]. The impacts of ankle sprains can be severe and include considerable

medical expenses, decreased fitness or endurance levels, and missed matches. Furthermore, a common complication of ankle sprains is chronic ankle instability, which results in episodes of the ankle giving way, recurrent sprains, and persistent symptoms such as pain, swelling, limited motion, weakness, and diminished self-reported function. This includes functional and mechanical impairments in isolation, or both [7].

In order to lower football injury risk, shoe manufacturers have attempted to design di fferent cleat configurations that can handle a variety of field conditions, such as turf or grass. In an early study, researchers reported that decreasing the number of cleats and their size may reduce the risk of knee injury [8]. Queen et al. determined that turf cleats could decrease the pressure and force beneath the forefoot, compared to other types of cleats that might minimize metatarsal injury risk on grass [9]. However, Torg et al. examined the mechanical properties of rotational torsion resistance to explain the relation between turf shoes and surface conditions at five temperatures, suggesting that only flat turf football shoes could lower the sprain risk incidence under all conditions [10]. Adjusting cleat configurations could potentially minimize the risk of injuries such as knee sprains and stress fractures on specific field conditions. However, at present, no clear experimental evidence exists to determine the positive e ffect of cleat configurations on improved ankle stability or decreased ankle sprains.

Increased ankle stability and the prevention of ankle sprains by increasing the shoe collar height have been examined for basketball shoes [11–15]. High collar basketball shoes exhibit a smaller ankle inversion range of motion (ROM), smaller ankle inversion and external rotation at initial contact, and smaller peak inversion velocity, compared to low collar shoes, but no significant di fference in kinetic parameters during side-step cutting are observed [11,12]. During jumping tasks, research has revealed that ankle joints show a smaller peak plantarflexion moment and power when wearing basketball shoes with high collars, compared to low collars [13]. According to other research, high collar basketball shoes result in delayed pre-activation timing and decreased amplitude of muscle activity [14]. Therefore, high collar basketball shoes are one factor used to reduce injury potential [16].

Based on the experience with basketball shoes, similar footwear technology has been implemented in football shoes in an attempt to mitigate injury risk. Researchers have observed the ankle inversion between high and low collar football shoes using an inversion platform, which can be rotated 35◦ to induce a sudden ankle inversion [17]. This research has indicated that high collar shoes significantly reduce the amount and rate of inversion. Additionally, using an arthrometer foot plate, researchers have found that high collar shoes are more e ffective in decreasing inversion ROM and velocity [18]. However, the research method employed in these previous studies does not accurately portray real-world practices and matches when only the ankle inversion is available. Additionally, although the peak ankle plantarflexion moment and power are significantly smaller in high collar, compared to low collar basketball shoes during landing jumps [13], knowledge of the e ffects of football shoe collar types on ankle dorsiflexion/plantar flexion movement is currently limited. Furthermore, according to previous studies, around 31% to 46% of football injuries, especially for the knee and ankle, are induced by losing balance or inducing a sprain after landing [19,20]. Hence, for football shoes, questions remain regarding how ankle kinematics and kinetics behave in both dorsiflexion-plantarflexion and inversion-eversion dynamic movements when performing jumping and landing maneuvers.

It should be noted that postural stability has been used to examine the risk of ankle sprain [21,22], and a deficiency in postural stability could play a significant role in increasing ankle sprain risk [20]. A study has found that high collar boots have smaller postural sway, compared to low collar boots, and thereby collar height might have a positive e ffect on postural control [23]. In a recent study, however, a high collar football shoe did not enhance static postural stability, compared to a low collar shoe [18]. Thus, limited research is available regarding the e ffects of shoe collars on postural stability. Evidence from a psychological study shows that elastic ankle taping or sti ff ankle bracing provides beneficial e ffects by increasing the feeling of confidence and stability during dynamic-balance tasks [24]. However, direct evidence is conflicting on the beneficial impact on dynamic balance [25–28]. The lack of consistent findings may be due to a lack of measuring more sensitive parameters. The dynamic postural

stability index (DPSI) measures three directional components of the ground reaction force during single-leg jump landings. Furthermore, DPSI and its directional components can detect differences in dynamic stability in different football collar types [29]. Therefore, DPSI provides a measure of dynamic stability that has high precision and reliability [30].

Determining the effect of high collar football shoes on ankle biomechanics and DPSI during single-leg jump landings might provide further insight into the biomechanics and dynamic stability of playing football. The purpose of the study aims to determine differences in shoe collar types (i.e., low collar, elastic collar, and high collar) on ankle biomechanics and DPSI during anterior and lateral single-leg jump landings. Our first hypothesis was that smaller ankle ROM, moment, and joint stiffness would result from the high collar football shoe, compared to the elastic or low collar shoes, in both tasks. Our second hypothesis was that dynamic stability would improve when wearing a high collar football shoe, compared to an elastic or low collar shoe, in both tasks.

#### **2. Materials and Methods**
