## 4 Discussion  
The goal of this study was to establish the test-retest reliability of a newly developed tennis-specific 77 COD test incorporating vertical jump tests (SJ-CMJ) among adolescent tennis athletes. All jump tests and the 77 COD tests had high within-subject reliability variance. CMJ and SJ are among the most commonly applied test methods for assessing the mechanical capacities of the lower body [43,44]. Since CMJ height can reflect lower extremity muscle power, a significant positive correlation exists between the CMJ and SJ [45]. The within-subject variances (CV) in the present study are acceptable. These results demonstrated stable repeatability across all protocols (CV < 10%) [41]. [PERSON] et al. and [PERSON] et al. reported CV values for the SJ and CMJ of 5.4-3.3% and 6.3-2.8%, respectively [43,46]. The CV values in the current study are higher than those reported in other studies. However, studies on reliability in jump height among young athletes and children (CMJ, ICC = 0.90, CV% = 7.1) [47] (SJ, ICC = 0.97, CV% = 4.9) [48] are similar to our findings. Excellent reliability (ICC > 0.91) was achieved across all protocols performed in this study. The SJ, CMJ, and 77 COD tests had similar within-subject reliability, as indicated by the values of ICC and Cronbach's \(\alpha\). Both CMJ and SJ tests are considered reliable and valid [43] in children [49]. \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Variables** & **Test \(\pm\) SD** & **Retest \(\pm\) SD** & \(p\) &
\begin{tabular}{c} **95\% CI** \\ **(Lower \(\pm\) Upper)** \\ \end{tabular} & **ICC** & **95\% CV** & \(\alpha\) \\ \hline CMJ (cm) & 23.23 \(\pm\) 3.51 & 23.41 \(\pm\) 3.07 & 0.396 & \(-\)0.59 \(\pm\) 0.24 & 0.938 & 7.0\% & 0.93 \\ \hline SJ (cm) & 22.77 \(\pm\) 2.83 & 23.04 \(\pm\) 2.46 & 0.176 & \(-\)0.66 \(\pm\) 0.12 & 0.914 & 6.8\% & 0.91 \\ \hline
77 COD (s) & 9.76 \(\pm\) 1.38 & 9.74 \(\pm\) 1.40 & 0.460 & \(-\)0.09 \(\pm\) 0.19 & 0.959 & 6.1\% & 0.95 \\ \hline \hline \end{tabular} SD = standard deviation; CI = confidence interval; ICC = intraclass correlation coefficient; CV = coefficients of variation; \(\alpha\) = [PERSON]’s alpha reliability coefficients.  
\end{table} 
Table 2: Descriptive and reliability statistics for all the tests. Figure 3: Bland–Altman plots of test-retest scores. Most of the scores were close to the average of the differences between the two tests in the Bland-Altman graphs, and the test-retest results were consistent. The relationship of COD to performance parameters in adolescent athletes depends on age, body composition, maturity status, and years of training experience [33]. These results suggest that repeated attempts should be made until the researcher's judgment is satisfied or the subject's true performance is revealed for a consistent COD performance (mean \(\pm\) 3-4 repetitions). SJ and CMJ vertical jumps are commonly used to measure explosive muscle power and jump height [50]. Similar to our study, CMJ height is generally superior to SJ performance [38]. Minor differences in performance between SJ and CMJ are thought to result from the effective use of the stretch-shortening cycle [50; 51]. In a study conducted by [PERSON] et al. on male athletes, 30 m CODS1-2 tests were found to have a weak correlation with CMJ (r = -0.00, r = -0.16) heights [52]. Similarly, [PERSON] et al. demonstrated that, in soccer players, COD tests (pro-agility shuttle and T-tests) were weakly correlated with SJ (r = -0.32, r = -0.23) and CMJ (r = -0.30, r = -0.16) heights, with the relationships being weaker in male athletes compared to female athletes. It has been suggested that the more consistent relationship between COD performance and vertical jump in female athletes, compared to males [53; 54], is determined by factors such as explosive strength, the stretch-shortening cycle (SSC), and the use of elastic energy [38]. The findings of our study indicate that sport-specific COD tests, such as the 77 COD test, are more strongly correlated with vertical jumps.