Assessing Jump Performance: Intra- and Interday Reliability and Minimum Difference of Countermovement Jump and Drop Jump Outcomes, Kinetics, Kinematics, and Jump Strategy

Understanding the reliability of jump testing is essential to determine the neuromuscular progress of athletes and make informed decisions. This study aimed to assess the reliability of several countermovement jump (CMJ) and drop jump (DJ) test metrics in female volleyball players. Sixteen (n = 16) semi-professional female volleyball players participated in this test-retest study. Intrasession and intersession reliability of CMJ and DJ metrics were evaluated using a randomized cross-over design. A dual force platform was used to collect CMJ and DJ data, and several dependent variables were calculated using forward dynamics. Intraclass correlation coefficients (ICC), coefficients of variation (CV), and minimum difference (MD) were calculated to assess intra- and interday reliability. During the same testing, the third attempt consistently yielded the highest values for both tests in jump height but presented excellent reliability (CMJ: ICC [95%CI] = 0.97 [0.93-0.99]; CV [95%CI] = 4.1% [1.2-7.0]; MD95 = 3.5 cm; MD90 = 2.9 cm; DJ: ICC [95%CI] = 0.91 [0.77-0.97]; CV [95%CI] = 6.7% [1.9-11.5]; MD95 = 6.0 cm; MD90 = 5.0 cm). CMJ height exhibited excellent reliability between sessions (ICC [95%CI] = 0.93 [0.81-0.97]; CV [95%CI] = 3.8% [1.1-6.4]; MD95 = 3.5 cm; MD90 = 3.0 cm), whereas DJ height demonstrated slightly lower but still acceptable intersession reliability (ICC [95%CI] = 0.81 [0.55-0.93]; CV [95%CI] = 6.1% [1.7-10.4]; MD95 = 5.2 cm; MD90 = 4.4 cm). Intersession reliability for CMJ kinetics and kinematics was excellent for 13 of the 24 metrics assessed. For DJ, only concentric (ICC [95%CI] = 0.91 [0.76-0.97]; CV [95%CI] = 3.0% [0.9-5.2]; MD95 = 15 Ns; MD90 = 12.6 Ns) and eccentric impulses (ICC [95%CI] = 0.99 [0.96-0.99]; CV [95%CI] = 1.7% [0.5-2.9]; MD95 = 9.2 Ns; MD90 = 7.7 Ns) demonstrated excellent intersession reliability. Most CMJ variables showed excellent reliability within sessions, while DJ had lower reliability in most metrics. These findings provide valuable information to physical trainers to select the metrics to assess athletes' performance as well as to identify a minimum cut-off value that serves as a reference for each of the metrics reported in both tests.