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

BACKGROUND

Vertical stiffness (K) 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 in male college players.

METHODS

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 tests, intraclass correlation coefficient (ICC), coefficient of variation (CV), Pearson product moment correlation coefficient (), Bland-Altman plots, and one-way regression.

RESULTS

There was almost perfect agreement between measurement instruments for the K value (ICC > 0.972, 95% CI = 0.954-0.992,  < 0.01). Almost perfect agreement was observed between evaluators (ICC > 0.989, 95% CI = 0.981-0.997,  < 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, < 0.001). The My Jump 2 showed good variability when measuring K 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 ( > 0.9655,  < 0.001).

CONCLUSION

The My Jump 2 smartphone application showed excellent reliability and intra-rater consistency in measuring K 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 in college players with careful consideration of its limitations, particularly at higher jump heights.