A correction equation for jump height measured using the just jump system

McMahon, JJ; Jones, P; Comfort, P

Abstract

Purpose: To determine the concurrent validity and reliability of the popular Just Jump system (JJS) for determining jump height and, if necessary, provide a correction equation for future reference. Methods: Eighteen male college athletes performed 3 bilateral countermovement jumps (CMJs) on 2 JJSs (alternative method) that were placed on top of a force platform (criterion method). Two JJSs were used to establish consistency between systems. Jump height was calculated from flight time obtained from the JJS and force platform. Results: Intraclass correlation coefficients (ICCs) demonstrated excellent within-session reliability of the CMJ height measurement derived from both the JJS (ICC = .96, P < .001) and the force platform (ICC = .96, P < .001). Dependent t tests revealed that the JJS yielded a significantly greater CMJ jump height (0.46 ± 0.09 m vs 0.33 ± 0.08 m) than the force platform (P < .001, Cohen d = 1.39, power = 1.00). There was, however, an excellent relationship between CMJ heights derived from the JJS and force platform (r = .998, P < .001, power = 1.00), with a coefficient of determination (R2) of .995. Therefore, the following correction equation was produced: Criterion jump height = (0.8747 × alternative jump height) – 0.0666. Conclusions: The JJS provides a reliable but overestimated measure of jump height. It is suggested, therefore, that practitioners who use the JJS as part of future work apply the correction equation presented in this study to resultant jump-height values.

Citation

McMahon, J., Jones, P., & Comfort, P. (2016). A correction equation for jump height measured using the just jump system. International Journal of Sports Physiology and Performance, 11(4), 555-557. https://doi.org/10.1123/ijspp.2015-0194

• Journal Article Type: Article
• Acceptance Date: Sep 2, 2015
• Online Publication Date: Sep 21, 2015
• Publication Date: May 1, 2016
• Deposit Date: May 13, 2016
• Publicly Available Date: May 13, 2016
• Journal: International Journal of Sports Physiology and Performance
• Print ISSN: 1555-0265
• Publisher: Human Kinetics
• Volume: 11
• Issue: 4
• Pages: 555-557
• DOI: https://doi.org/10.1123/ijspp.2015-0194
• Publisher URL: http://dx.doi.org/10.1123/ijspp.2015-0194
• Related Public URLs: http://journals.humankinetics.com/ijspp