## 4 Discussion  
This study was a timely and novel validation study to examine the concurrent validity and test-retest reliability of the three selected possible remote assessments for CMJ, namely My Jump 2, a popular and valid mobile application, and HomeCourt, a mobile application with AI, and the TVJM, a portable jump assessment tool. So as to provide references to practitioners on the meaningful changes in performance, this study provided the MDC of each device, which is the minimal number of measured changes that fell outside measurement error. This study provided evidence and information to researchers and practitioners to select devices for CMJ remote assessment. All selected devices showed good to excellent test-retest reliability (ICC\({}_{3,1}\): 0.82-0.97). In general, variabilities in CMJ outputs were low (CV: 2.58-6.45%), and all measurement systems appeared to be sufficiently reliable. Jump height values recorded varied among different technologies from trivial to moderate effect size. Sufficient concurrent validity between My Jump 2 and the TVJM (\(r\) = 0.93, \(d\) = 0.15) was found, but not between My Jump 2 and HomeCourt (\(r\) = 0.85, \(d\) = 0.68). In comparison, HomeCourt in this study was the last valid system because it registered 12.85% and 9.71% higher than the average jump heights measured by My Jump 2 and the TVJM, respectively, for the total 180 jumps. Vertical jump tests have been investigated for more than 50 years to determine lower-body maximal explosive strength. There are various ways to define jump height. Force platform measurement [6; 29] has been widely considered the gold-standard test but requires several instruments for recording and processing the data. It calculates the vertical displacement of an individual's center of mass (CoM) using the measured kinetic data. To our best knowledge, measuring flight time to determine jumping performance was first reported in the 1980s [30]. At that time, the flight time was measured by electronic apparatus, which consisted of a digital timer (\(\pm\)0.001 s) and a resistive platform, while the jumps were performed with hands on the hip and minimal horizontal and lateral displacements. In fact, the technology and principle behind My Jump 2, a mobile application, were similar to those of [PERSON]'s study. My Jump 2 used video frame identification to recognize the flight time [17], the time difference between the two frames marked at take-off and landing. The mobile apparatus makes the assessment portable and user-friendly. The TVJM is a type of linear position transducer [8]. A cord is attached to a rubber mat on the ground, and the belt at the athlete's waist is pulled out of its housing when the athlete jumps. This device assumes that the change in length of the cord is the change of the \begin{table}
\begin{tabular}{c c c c c c c} \hline  & \multicolumn{2}{c}{**CMJ [Mean \(\pm\) SD (cm)]**} & \multicolumn{2}{c}{**ICC\({}_{3,1}\) (95\%**} & \multirow{2}{*}{**CV\%**} & \multirow{2}{*}{**SEM**} & \multicolumn{1}{c}{**MDC**} \\ \cline{2-2} \cline{5-7}  & **Day 1** & & & **Day 2** & & **CI** \\ \hline My Jump 2 & 40.91 \(\pm\) 7.75 & 40.79 \(\pm\) 7.44 & 0.93 (0.87–0.97) & 3.68 & 1.95 & 5.41 \\ HomeCourt & 45.58 \(\pm\) 7.50 & 46.62 \(\pm\) 6.83 & 0.89 (0.77–0.94) & 4.31 & 2.42 & 6.71 \\ TVJM & 41.80 \(\pm\) 8.02 & 42.23 \(\pm\) 8.05 & 0.97 (0.93–0.98) & 2.58 & 1.46 & 4.05 \\ \hline \end{tabular} Note: CMJ: Countermovement jump; TVJM: Takei Vertical Jump Meter; CI: confidence interval; CV: coefficient of variation; ICC: intraclass correlation coefficient; MDC: minimal detectable change; SD: standard deviation; SEM: standard error of measurement; TVJM: Takei Vertical Jump Meter.  
\end{table} 
Table 4: Between-day test–retest reliability of CMJ measurement devices.