Test Re-Test Reliability of Countermovement Jump Testing in Academy Rugby League Environments: Establishing Thresholds for Minimum Detectable Change to Guide Longitudinal Development

Abstract

League wide profiling is well established in rugby league academy pathways, however the understanding of between-session reliability of assessments completed in applied settings is unknown. This study aimed to determine the between-session reliability of force-time characteristics of the countermovement jump (CMJ) in academy rugby league players. Forty-one academy rugby league players performed three separate CMJ trials on two occasions, separated by 48 hours prior to their resistance training session. Between session reliability was determined by calculating the intraclass correlation coefficient (ICC) and coefficient of variation (CV) with 95% confidence intervals, standard error of measurement (SEM) and minimal detectable change (MDC) from the mean of three trials. Analysis reported moderate to excellent reliability (ICC_-95 ≥ 0.5) for 33 out of 37 variables for profiling lower body ballistic force capabilities. Jump height and jump momentum reported good to excellent reliability (ICC_-95 = 0.78, CV = 6.64% and ICC_-95 = 0.90, CV = 3.58% respectively). League wide profiling assessments undertaken within club environments result in reliable insights of CMJ performance and associated force-time characteristics. Although reliable, future improvements to league wide profiling protocols should remove the club environment as a factor with centralised testing at a singular time in the season to improve data quality of large sample normative datasets.