## 3 Results
### Validity
indicated an excellent model fit (R = 0.972, R\({}^{2}\) = 0.944, \(p\) < 0.001 \(\mid\) ANOVA F-value = 323, \(p\) < 0.001), suggesting that MyJump explained 94.4% of the variance in Chronojump measurements (Table 6, Figures 5 and 6). The slope coefficient (\(\beta\) = 0.970, \(p\) < 0.001) suggested that for every 1 cm increase in MyJump CMJ height, the Chronojump measurement increases by 0.970 cm, indicating an \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Predictor** & **Estimate** & **SE** & \begin{tabular}{c} **95\% CI** \\ **Lower** \\ \end{tabular} & \
\begin{tabular}{c} **95\% CI** \\ **Upper** \\ \end{tabular} & **t** & \(p\) &
\begin{tabular}{c} **Standardized** \\ **Estimate** \\ \end{tabular} \\ \hline Intercept & 0.184 & 2.019 & \(-\)4.041 & 4.41 & 0.091 & 0.928 & — \\ CMJ MyJump (cm) & 0.97 & 0.054 & 0.857 & 1.08 & 17.96 & 0.001 & 0.972 \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Regression coefficients and confidence intervals for the CMJ. Figure 5: Q-Q plot of standardized residuals for CMJ regression model. The Q-Q plot assessed the normality of the standardized residuals from the linear regression model for CMJ height measurements (MyJump vs. Chronojump). The data points align closely with the diagonal reference line, indicating that the residuals follow an approximately normal distribution. Minor deviations at the extremes suggest slight departures from normality but do not significantly impact model validity. Figure 6: Scatter plot with regression line: CMJ MyJump vs. Chronojump. The scatter plot illustrated the relationship between countermovement jump (CMJ) height measurements obtained using MyJump and Chronojump. The solid black regression line represents the linear relationship between the two measurement methods, while the shaded area indicates the 95% confidence interval. almost perfect linear agreement between the two methods. The 95% confidence interval (CI: 0.857-1.08) further confirmed the stability of this estimate. The estimated marginal means (EMM) for the countermovement jump (CMJ) measurements obtained via MyJump indicate a mean jump height of 36.1 cm (95% CI: 35.6-36.7 cm). The estimated marginal mean for one standard deviation below the mean was 31.4 cm (95% CI: 30.6-32.1 cm), while one standard deviation above the mean was 40.9 cm (95% CI: 40.2-41.7 cm), demonstrating a consistent distribution of jump heights across participants. These results indicated that MyJump served as a highly accurate alternative to Chronojump for CMJ measurement, with minimal systematic bias and near-perfect predictability. The strong correlation, minimal residual error and excellent model fit suggested that MyJump could be reliably used for assessments of CMJ performance with a high degree of confidence. A linear regression analysis was also performed to assess the predictive relationship between squat jump (SJ) height measurements from MyJump and Chronojump (Table 7, Figures 7 and 8). The model demonstrated excellent fit with R = 0.955, R\({}^{2}\) = 0.912, \(p<0.001\), indicating that 91.2% of the variance in Chronojump SJ measurements was explained by MyJump (ANOVA F-value = 197, \(p<0.001\)). The slope coefficient (\(\beta\) = 0.920, \(p\) < 0.001) suggested that for every 1 cm increase in MyJump SJ height, the Chronojump measurement increases by 0.920 cm, demonstrating a strong predictive relationship between the two methods. The 95% confidence interval (CI: 0.783-1.060) further reinforces the reliability of this estimate. The estimated marginal mean (EMM) for squat jump (SJ) heights obtained through MyJump provided further insight into the distribution of performance among participants. The average jump height recorded was 34.6 cm (95% CI: 34.1-35.0 cm). A one standard deviation decrease from the mean corresponded to an estimated marginal mean of 31.8 cm (95% CI: 31.2-32.4 cm), whereas a one standard deviation increase resulted in an estimated marginal mean of 37.3 cm (95% CI: 36.7-37.9 cm).