Validity and reliability of My Jump 2 app for estimating maximum height in counter-movement jump according to new method

The study aimed to determine the validity of My Jump 2 app compared to the force platform, and the reliability of this measurement tool for estimating the maximum height (MH) in the counter-movement jump (CMJ). Twenty-one untrained male students (age: 21.0 ± 1.9 years) participated in the study. The MH was estimated based on: (1) the displacement of the jumper’s center of mass (force platform), (2) the displacement time (DT) of the reflective marker stuck on the jumper’s sacrum according to the new concept and the flight time (FT) of the jumper (smartphone with My Jump 2 app), and (3) displacement of the reflective marker stuck on the jumper’s sacrum (mo-cap system). The analysis included intraclass correlation coefficient (ICC), Pearson correlation coefficient ( r ), Bland-Altman systematic bias and Cronbach’s alpha ( α ). Assessment of the concurrent validity showed a poor agreement (ICC = 0.362; bias = 12.4 cm) at r  = 0.849 between the My Jump 2 app for FT and force platform ( p  < 0.001), a good agreement (ICC = 0.858; bias = -0.3 cm) at r  = 0.763 between the My Jump 2 app for DT and force platform ( p  < 0.001) and an excellent agreement (ICC = 0.955; bias = -0.4 cm) at r  = 0.913 between the mo-cap system and force platform ( p   0.9) indicated a very good reliability of all measurement tools. Findings revealed a high accuracy of the MH estimation method in CMJ based on the displacement of the marker stuck on the sacrum using the My Jump 2 app and mo-cap system.