Are running, speed change and kicking metrics during football training associated with reductions in hip adductor strength?

Purpose This observational repeated-measures study quantified the associations between running, speed change (accelerations and decelerations), and kicking metrics and acute hip adductor strength from football training. Methods Twelve trained youth football players (34 observations) wore foot-mounted inertial measurement units during training to estimate football actions. Maximal isometric hip adductor strength test was performed pre- and post-training to quantify changes. Results Linear mixed models revealed moderate to very large associations for all running and speed change metrics (β = −0.48 to −0.73, p ≤ 0.004) while associations were small and not statistically significant for the kicking metrics: ball releases, release index, and high speed releases (β = −0.25, −0.26, 0.13, respectively, p > 0.05). The largest strength reductions were associated with distances of high intensity accelerations (Β = −0.31% per meter, 95% CI = −0.47%;−0.15%), high intensity decelerations (Β = −0.30% per meter, 95% CI = −0.50%;−0.12%), and counts of high intensity speed changes (Β = −0.40% per count, 95% CI = −0.57%;−0.23%). Conclusions In conclusion, running and speed change metrics (accelerations, decelerations) as opposed to kicking metrics displayed significant associations with acute hip adductor strength reductions. As high intensity speed change metrics were associated with the largest reductions to hip adductor strength, practitioners may monitor and manipulate the programming of these actions within training to manage external loading and fatigue.