## 4 Discussion

Table 3: Values of the different methods for measuring CMJ jump height. between jumps was not specified in the previous study [19], so it is not possible to know if fatigue could have affected their results through the FT method (i.e., Different joint position between take-off and landing), whilst our subjects rested 60 s between trials and three minutes between each jump test. Despite these methodological differences, their results comparing the FP through the TOV versus a smartphone application (FT method) regarding only CMJ did not differ with our CMJ results. Based on the present study and the literature [19; 20], it seems that the flight time method, independent of the technology used (e.g., FP, contact mat, smartphone application), is an imprecise means of assessment. On the other hand, there is a high correlation and good reliability between the JH SJ+CMJ measured through the FT with the FP and the APP (r = 0.872, \(p<\) 0.01, ICC = 0.843, CV = 4.88%). These results are in accordance with other studies that compare the SJ+CMJ+CMJ+AE bright using a FP and a contact mat (both through FT) (r = 0.99, \(p<\) 0.001, ICC = 0.985, CV% = 2.7) [21]. Additionally, the mean comparison of the present study shows that the JH analyzed with the FP through the FT and the APP did not differ (\(p\) = 0.457). Therefore, the APP and the contact mat seem to equal the accuracy of the FP with the FT method. However, it is important to highlight the fact that some studies compare the My Jump APP based on FT, with other instruments also based on FT (i.e., contact mat or FP through the FT) [21; 30; 31], instead of comparing it with the FP through the TOV (gold standard) [16]. Therefore, all these technologies that use the FT method are not as precise as the TOV method. Bearing in mind that the most accurate and considered the gold standard method to measure the height of the jump is the FP based on the TOV [19; 20], these are the results that should be trusted. Analyzing specifically the different jumps, it was found in SJ significant differences between the JH measured with the FP through the TOV and the FP and the APP through the FT (\(p<\) 0.01 in both cases). However, we found no significant difference comparing the JH measured with the FP and the APP (both through the FT) (\(p\) = 0.826). Further, CMJ data showed no significant differences among the three methods (i.e., FP through the TOV versus the FP and the APP through the FT) (\(p>\) 0.05 in both cases). Our results are in line with the only one previous study that researched the differences between the FP through the TOV versus a smartphone application (FT method) [19], and it showed near perfect correlations (ICC = 0.996; \(p<\) 0.001). Results of the reliability and validity obtained in the present study comparing the CMJ height through the FT with the FP and the APP (r = 0.872, \(p<\) 0.01, ICC = 0.843 and CV = 4.88%) are in accordance with the first validation study of My Jump App [30] that compare the CMJ height using a FP through FT (r = 0.995, \(p<\) 0.001, ICC = 0.997, CV% = 3.5), and other study that compare the CMJ height using a contact mat and the My Jump App (both through FT) (r = 0.999, \(p<\) 0.001, ICC = 0.948, CV% = 10.096) [21]. Despite the differences between the sampling frequency of the devices (i.e., FP \(\approx\)1000 Hz and the smartphone camera \(\approx\) 240 Hz), the height values obtained were very similar between the two methods, as reflected by the ICC. The literature that evaluates the smartphone applications in this area has analyzed the CMJ as the only vertical jump option discarding the SJ [19; 21]. However, with this study it has been demonstrated that the results of the CMJ cannot be extrapolated to the SJ. The height of the SJ and CMJ is defended by several authors as a method to detect fatigue and individualize load prescriptions, so the reduction of the height of the VJ can be interpreted as evidence of the deterioration of neuromuscular function (i.e., fatigue, neuromuscular overload) [12].