*2.2. Equipment*

Three commercially available football shoes (U.S. size 8, Vapor Untouchable 3; Nike, Portland, OR, USA), which are very popular for football players, were tested in the current study. All shoes were built on the same shoe platform and had identical lightweight upper sections, carbon fiber, thermoplastic polyurethane plates, and cleats, but different shoe collar types: high collar (mass: 300 g; collar height: 70 mm; material: high intensity knitted fabric), elastic collar (mass: 310 g; collar height: 35 mm; material: low intensity knitted fabric), and low collar (mass: 300 g; collar height: 0 mm, material: nil) (Figure 1).

**Figure 1.** Football shoes used in the current study. (**a**) high collar shoe, (**b**) elastic collar shoe, (**c**) low collar shoe.

The testing environment was an indoor artificial turf-top football ground. The three-dimensional kinematics were measured using a ten-camera Vicon Vantage motion capture system (Vantage 8; Vicon, Oxford, UK), which was arranged around the artificial turf football ground, at a sampling rate of 200 Hz. These cameras are widely used to capture motion trajectory in sports science and biomechanics to optimize human movement [31,32]. The ground reaction force, which was measured for the dominant lower limb, was collected simultaneously using a 600 × 900 mm force plate (9287C; Kistler, Winterthur, Switzerland), which was recessed in the middle of the artificial turf football ground, at a sampling rate of 1000 Hz. The force plate was also used to record the forces exerted by the foot when standing, walking, or running [31,32]. A 900 × 600 × 10 mm artificial turf cover was fixed on the surface of the force plate through screws at each corner (Figure 2). The kinematics and kinetic data were collected and synchronized using a Nexus Lock (Lock +; Vicon, Oxford, UK) with Nexus software (Nexus 2.6.1; Oxford, UK). The Nexus Lock is Vicon's control box for connecting, integrating, and synchronizing third-party devices with the Vicon motion capture system.

**Figure 2.** Experimental setup.

Thirty-six retroreflective markers (diameter: 14 mm) were attached to the lower limbs using bio-adhesive tapes. The reflective markers were placed on both the right and left limbs of the iliac crest; anterior superior iliac spine; posterior superior iliac spine; lateral/medial prominence of the lateral femora epicondyle; proximal tip of the head of the fibula; anterior border of the tibial tuberosity; lateral/medial prominence of the lateral malleolus; dorsal margin of the first, second, and fifth metatarsal head; and four four-marker rigid clusters were attached bilaterally onto the thigh and shank.
