AUTHOR=Wang Yizhang , Wang Xintang , Luan Chenglin , Shan Wei , Gong Lijing 

TITLE=The validity and reliability of the My Jump 2 app for measuring vertical stiffness in male college players

JOURNAL=Frontiers in Sports and Active Living

VOLUME=6

YEAR=2024

URL=https://www.frontiersin.org/journals/sports-and-active-living/articles/10.3389/fspor.2024.1405118

DOI=10.3389/fspor.2024.1405118

ISSN=2624-9367

ABSTRACT=<sec><title>Background</title><p>Vertical stiffness (K<sub>vert</sub>) can be used to evaluate sports performance and injury risk in players. The My Jump 2 smartphone application (App), is increasingly being used by researchers, coaches, and players in the competitive sports field. We aimed to analyze the reliability and concurrent validity of the My Jump 2 app for measuring K<sub>vert</sub> in male college players.</p></sec><sec><title>Methods</title><p>Twenty male college players (10 soccer players, 10 basketball players; age, 20.2 ± 1.3 years old; weight, 76.4 ± 6.0 kg; height, 178.3 ± 4.7 cm) volunteered to take part in this study. Three drop jumps were performed by participants from 30 cm to 40 cm on a force platform and retested after three days. All the jumps were recorded by both the Force platform and the My Jump 2 app. Data obtained from the above two devices were compared using the paired <italic>t</italic> tests, intraclass correlation coefficient (ICC), coefficient of variation (CV), Pearson product moment correlation coefficient (<italic>r</italic>), Bland-Altman plots, and one-way regression.</p></sec><sec><title>Results</title><p>There was almost perfect agreement between measurement instruments for the K<sub>vert</sub> value (ICC &gt; 0.972, 95% CI = 0.954–0.992, <italic>P</italic> &lt; 0.01). Almost perfect agreement was observed between evaluators (ICC &gt; 0.989, 95% CI = 0.981–0.997, <italic>P</italic> &lt; 0.05). Also, the My Jump 2 app showed excellent intra-rater reliability in all participants (ICC = 1.000, 95% CI = 1.000–1.000, <italic>P </italic>&lt; 0.001). The My Jump 2 showed good variability when measuring K<sub>vert</sub> at T1 30 cm (CV = 5.4%), T1 40 cm (CV = 6.7%), T2 30 cm (CV = 5.0%), and T2 40 cm (CV = 10.3%). The test-retest reliability of My Jump 2 was moderate to good at 30 cm (ICC = 0.708, 95% CI = 0.509–0.827); however, it was lower to moderate at 40 cm (ICC = 0.445, 95% CI = 0.222–0.625). Very large correlations were observed between the force platform and the My Jump 2 for K<sub>vert</sub> (<italic>r</italic> &gt; 0.9655, <italic>P</italic> &lt; 0.001).</p></sec><sec><title>Conclusion</title><p>The My Jump 2 smartphone application showed excellent reliability and intra-rater consistency in measuring K<sub>vert</sub> in male college players. While demonstrating excellent intra-rater consistency and strong agreement with force platform measurements, it showed slightly lower reliability at higher jump heights. Overall, the My Jump 2 app is a valid tool for evaluating K<sub>vert</sub> in college players with careful consideration of its limitations, particularly at higher jump heights.</p></sec>