Longitudinal analysis of explosive physical performance outcomes of professional athletes across multiple football codes: An investigation of systematic change and relative variation

The aims of this study were to: 1) investigate the within- and across-season changes in explosive physical performance outcomes including jump height (JH), relative peak power, and sprinting velocity for different football codes; 2) estimate associations between time-lagged training load variables and JH; and 3) quantify levels of within athlete variability and differences between codes. Retrospective physical performance, on-field, and S Rugby Union: n = 34). Mixed models with fixed effects of time (season and season stage), code, and position combined with random effects (athlete intercepts and slopes) were used to model changes over time. Additionally, athlete level linear regressions were conducted to describe individual variability. Regression coefficients describing systematic change were small with the largest coefficient identified for within-season JH (β = 0.27 95%CI: 0.08 to 0.46 cm). Moderate to large negative correlations (r = -0.41 to -0.66) were obtained between random intercepts and slopes for all outcomes. Analysis of within athlete variability identified larger variation for Rugby Union and for latter stages of the season. Collectively, the findings show limited systematic changes in physical performance variables of professional football code athletes and any improvements may be dependent on baseline capacity.