## 3 Results  
The means and standard deviations of the MH of the CMJ are presented in Figure 2. The results of [PERSON]'s test were W = 0.344 and \(p\) = 0.01. Therefore, the violation of sphericity was corrected by adjusting the degrees of freedom using the Greenhouse-Geisser adjustment (epsilon = 0.639). The value of \(\eta^{2}\) = 0.898 at \(\text{F}_{2,38}\) = 175.8 and \(p\) < 0.001 (significant within-subject effect) indicated a large effect size for the MH results when comparing the four measurement tools. The statistical power for the MH values in CMJ was 1.0 (with a sample size of 21 subjects). Pairwise comparisons between the measurement tools revealed (1) a significant 27.7% (\(p\) < 0.001) lower mean MH value for the My Jump 2-FT than the force platform, and (2) non-significant differences (below 1.0%) between the My Jump 2-DT and force platform (\(p\) = 1.0), and between the mo-cap system and force platform (\(p\) = 1.0). The results of the ICC and 95% CI are presented in Table 1. The ICCs showed a poor agreement between the My Jump 2-FT and force platform (\(p\) < 0.001), a good agreement between the My Jump 2-DT and force platform (\(p\) < 0.001), and excellent agreement between the mo-cap system and force platform (\(p\) < 0.001). Considering the Bland-Altman plots (Figure 3), the following bias was observed: 12.4 cm for the My Jump 2-FT vs. force platform (Figure 3a), \(-\)0.2 cm for the My Jump \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Variable**} & **My Jump 2-FT** & **My Jump 2-DT** & **Mo-Cap System** \\  & **vs. Force Platform** & **vs. Force Platform** & **vs. Force Platform** \\ \hline ICC (–) & 0.362 & 0.858 & 0.955 \\
95\% CI (–) & \(-\)0.050–0.762 & 0.648–0.943 & 0.891–0.982 \\ \hline \hline \end{tabular} Notes: My Jump 2-FT—My Jump 2 app for the flight time of the jumper, My Jump 2-DT—My Jump 2 app for the displacement time of the marker placed on the jumper’s sacrum (new method), mo-cap—motion capture, ICC—intradass coefficient correlation, CI—confidence interval.  
\end{table} 
Table 1: The concurrent validity of the My Jump 2 app and mo-cap system compared to the force platform for estimating the maximum height in a counter-movement jump. Figure 2: Means of the maximum height in a counter-movement jump, obtained using four testing methods. My Jump 2-FT—My Jump 2 app for the flight time of the jumper, My Jump 2-DT—My Jump 2 app for the displacement time of the marker placed on the jumper’s sacrum (new method), mo-cap—motion capture, *—significant difference between the force platform and My Jump 2-FT.  
2-DT vs. force platform (Figure 3b), and \(-0.4\) cm for the mo-cap system vs. force platform (Figure 3c). Furthermore, the ranges between the upper LOA and lower LOA were 14.0 cm for the My Jump 2-FT vs. force platform, 19.3 cm for the My Jump 2-DT vs. force platform, and 10.8 cm for the mo-cap system vs. force platform. Figure 3: [PERSON] plots for the following: (**a**) the My Jump 2-FT and force platform; (**b**) the My Jump 2-DT and force platform; (**c**) the mo-cap system and force platform. My Jump 2-FT—My Jump 2 app for the flight time of the jumper, My Jump 2-DT—My Jump 2 app for the displacement time of the marker placed on the jumper’s sacrum (new method), mo-cap—motion capture, SD—standard deviation for the average difference between the two instruments, +1.96*SD—upper limit of agreement, \(-1.96\)*SD—lower limit of agreement, bias—average difference between the two instruments. In addition, there was a very large correlation (0.7 \(<\) \(r\) \(<\) 0.9) between the My Jump 2-FT and force platform (\(p\) \(<\) 0.001) (Figure 4a), between the My Jump 2-DT and force platform (\(p\) \(<\) 0.001) (Figure 4b), and between the mo-cap system and force platform (\(p\) \(<\) 0.001) (Figure 4c). Figure 4: Correlation between the following: (**a**) the My Jump 2-FT and force platform; (**b**) the My Jump 2-DT and force platform; (**c**) the mo-cap system and force platform.