## 2 Materials & Methods
### Measurements  
The two iPads (6 th generation, iOS 14.4), one with My Jump 2 and another one with HomeCourt and the TVJM, were used to assess jump height. The jumping height (cm) of each jump was recorded and used for data analysis. Participants stood on the TVJM's rubber mat with the belt around their waist and hands on their hips. Two iPad devices were placed on two foldable tablet stands without protective cases and were placed three meters in front of the participant side by side (Figure 2). The foldable tablet stands were set with a standardized angle of elevation at 75\({}^{\circ}\) in order to capture the entire body during the jumps using both mobile applications. This equipment setup was determined by the researchers to minimize measurement error.  
My Jump 2 is a video frame identification mobile application that provides a portable approach for measuring vertical jump performance. It uses the high-speed camera (at least \(\geq\)120 fps) of smart devices and adopts the HSC-Kinovea method to record the flight time and calculate jump height [17]. Almost perfect agreement (ICC > 0.99) and correlation (\(r>0.99\)) in CMJ height were found with the force platform [11]. The inter-rater reliability is also close to perfect (ICC = 0.97) [14]. Previous studies suggested that My Jump 2 was a valid and reliable tool for evaluating a wide range of populations (elderly: ICC = 0.95 [23]; children: ICC > 0.89 [9]; trained athletes: ICC > 0.97 [18]), showing its ability to assess participants with various CMJ performances. In this study, the My Jump 2 application was installed on an iPad. Before the jump assessment, (i) leg length from the greater trochanter to the lateral malleolus, (ii) from the lateral malleolus to the tip of toes, and (iii) vertical distance between the greater trochanter and the ground in a parallel squat position were measured and entered in the application for calculation. The jumps were recorded by the 120 Hz high-speed camera of the iPad with a quality of 720 p. The frames of take-off and landing were marked manually by one researcher, and the jump height was calculated automatically using this equation:  
\[h=t^{2}\times 1.22625\]  
where \(h\) was the jump height in meters, and \(t\) was the flight time in seconds [10]. The record would be shown on the screen, and the smallest measurement unit was 0.01 cm.  
HomeCourt (NEX Team Inc., San Jose, CA, USA, and Hong Kong) was a mobile application that was originally developed for tracking basketball shooting. Additionally, the latest iOS version includes the features of augmented reality and body segments for tracking a person's movements through the camera of the smart devices. This new addition empowers the development of HomeCourt to recognize objects and track human and ball movements. Apart from tracking basketball shooting, it allows users to assess vertical jump height using its AI. Each jump record would be shown on the screen, and the smallest measurement unit was 1 cm. Before the jump assessment, the application automatically measured users' wingspans, standing reach, and seated height for reference, which took about 30 s.  
The TVJM (T.K.K. 5406 Jump MD, Takei Scientific Instruments Co., Ltd., Niigata, Japan) is a linear position transducer with a wire-type linear encoder. [PERSON] and his colleagues [24; 25; 26] first used this instrument for CMJ assessment and reported high reliability (\(r=0.90\)). In this study, participants stood on the Takei rubber mat (approximately 380 mm in diameter and 3 mm in thickness, weighted at 0.4 kg) with a belt around the waist. The belt weighs only 0.2 kg and is connected to the mat with a measurement cord which initially represents the distance between the waist and the ground. The cord elongated during a jump. The height of each jump was displayed on the LCD screen on the belt. The smallest measurement unit was 1 cm, and its error was up to \(\pm 2\) cm.