Exploring Predictors and Patterns of Acceleration in an Elite Male Rugby Union Season

Background: Physical testing and monitoring are widely used in elite sport, generating a multitude of data. While this information can be valuable, its utility requires careful scrutiny. In particular, muscular power is vital for success in rugby union but the relationship between power testing, particularly preseason jump testing, and the on-field expression of power as acceleration, is unclear. Initially, this study sought to determine theoretical peak acceleration (a_peak) in an elite rugby union season via in-situ Acceleration-Speed (A-S) profiles. Following this, the study aimed to (a) determine whether a_peak was predicted by preseason countermovement jumps (CMJ); (b) investigate differences in A-S Profiles between playing positions and (c) investigate differences in CMJ discrete variables and force-time series between playing positions. Methods: The main dependent variable, a_peak, was defined as acceleration at 3 m·s^-1 derived from A-S profiles (Morin et al., 2021). Preseason CMJ performance was quantified using common practitioner-utilised variables, which were used to predict a_peak from in-season A-S profiles for the entire squad and between the Forwards and Backs positions. Participants were grouped into either Forwards (n = 23) and Backs (n = 16) depending on their playing position. The effects of each CMJ variable and position were investigated by fitting multiple linear regression models, with the associated Type III ANOVA used to partition between- and within-group variance. A-S profile characteristics and discrete CMJ variables were compared between positions using Welch’s Two Sample t-tests and effect sizes, and Statistical Parametric Mapping (SPM) was used to analyse respective force curves. Results: Of the preseason CMJ variables, relative concentric peak force significantly predicted the in-season a_peak. (R² = 0.29, F(3, 22) = 3.43, p = 0.013), whereas there was no evidence that jump height, concentric peak velocity, and absolute concentric peak force did. The Backs exhibited greater maximal theoretical speed and greater predicted accelerative ability at higher speeds, although there was no clear difference in a_peak between playing position groups. The Forwards produced significantly greater absolute concentric peak force, in addition to absolute force late in the concentric phase of the CMJ (81–94%), although only in proportion to their higher bodyweight. Conclusion: These findings provide further insight into the physical demands, output, and novel profiling of elite rugby union players. Selection of variables when testing physical qualities should be systematically considered and understood before undertaking testing. Relative peak force in the CMJ may predict peak acceleration to a greater extent than CMJ peak velocity, and therefore may inform training prescription to a greater proportion. Analytical methods such as A-S Profiles and SPM show promise but require further development in elite sport. Practitioners should continue to be critical when selecting testing and measurement tools and not measure variables due largely to availability.