## 2 Materials and Methods
### Experimental Conditions and Procedure  
Comparisons were made for four orthosis conditions (Figure 1): prefabricated arch-support orthoses [2-mm (D2), 6-mm (D6), and 10-mm (D10) heel lift] versus control condition (2-mm flat control). The three arch-support orthoses (D2, D6 and D10) had the same arch-support of 25 mm, which was made of Polyurethane (PU) as specified with the off-the-shelf orthosis (Arch-support series-Universal II, Dr. Kong Footwear Ltd., Hong Kong), while the control orthosis did not have medial arch-support. The D2 orthosis had the same heel lift as the original prefabricated orthosis, while the D6 and D10 conditions were modified by adding the same PU material at the heel regions, respectively. The information on stack height and heel lift is provided in Figure 1. All arch-support orthoses were fit into the identical neutral running shoe (ARBN023, [PERSON], Beijing, China). Ten holes with a diameter of about 15 mm were cut in the shoe to allow direct placement of the reflective markers on the skin to assess forefoot and rearfoot kinematics.  
After anthropometrical measurements were taken, a total of 28 reflective markers (diameter 14 mm) were placed on the skin according to the modified Oxford Foot Model [42]: four pelvis markers (left and right anterior and posterior superior iliac spines), medial and lateral femoral cordyles, medial and lateral malleolus, 1 st and 5 th metatarsal heads, and triads markers on middle thigh, middle shank, posterior heel, and forefoot. The Oxford Foot Model is a multi-segment foot model used to calculate forefoot and rearfoot kinematics and it has been shown to have reliable gait measurements in various populations [42; 43; 44]. The foot markers were attached to the skin via a magnetic base that attached to the skin using strong adhesive tape [36] (Figure 2). This allowed markers to be attached to and detached from the foot through holes in the shoe, and ensured that the marker placement kept consistent among all test conditions since the magnetic bases stayed attached to the foot during the entire data collection session. The markers on the medial and lateral epitondyles were used during the static trial and then removed before commencing with the movement trials. The markers were placed by the same experimenter to ensure consistency across the participants.  
The participants were instructed to run at their selected speeds (2.65 \(\pm\) 0.45 m/s) in four tested orthoses (D2, D6, D10, and control) on an instrumented treadmill with force plate embedded (Bertec Corp, Columbus, Ohio, sampling at 1000 Hz). At first, the preferred speed of each participant was determined while running on the treadmill by gradually increased the running speed [45]. Briefly, while gradually increasing the treadmill speed, the participants were instructed to identify their preferred speed for their regular running. A synchronized 10-camera motion capturing system (Vicon MX, Vicon Motion System Ltd., Oxford, England, sampling at 200 Hz) was used to record kinematic data for the study. Running test for each condition lasted 1 min to achieve stable gait before data  
Figure 1: The four experimental orthoses.  
Figure 2: Marker placements: (a) marker set, (b) magnetic base, and (c) marker placement on foot.  
collection [29; 46]. The last 10 footfalls from each condition were extracted for subsequent analysis. The testing order was randomly assigned across participants using an online program (www.random.org, accessed on 1 December 2018). To avoid any fatigue, they were required to rest unshod (i.e., barefoot) for 5 min between orthosis conditions [29; 45].