Evaluating Novel Methods of Classifying Interlimb Asymmetries Within Collegiate American Football Players

Over the last few years, researchers and sport scientists have expressed an increased interest in the effects of interlimb asymmetry on aspects of sport performance such as jumping, sprinting, and changing direction. This study aimed to evaluate the diagnostic utility of three different means of classifying asymmetry to highlight if a 6-week resistance training intervention can meaningfully reduce levels of asymmetry, and to determine the relation between asymmetry reduction and improvements in change of direction (CoD) performance, if any. Eighteen, division-two collegiate American football skill position players completed all pre- and post-intervention procedures. These procedures involved the completion of the Bulgarian Split Squat (BSS) exercise from which asymmetries in relative average power (Rel.AP), and relative peak power (Rel.PP) were derived. Additionally, participants completed three repetitions within the 505 and L-drill tests to quantify CoD performance. Results from our study show that participants classified as asymmetrical, exhibiting observed asymmetry in Rel.PP scores larger than the sample mean plus one standard deviation, had the greatest likelihood of reducing asymmetry (OR = 6.99, 95% CI: 1.4, 12.5) and improving L-drill performance (OR = 1.33, 95% CI: -2.1, 4.8). Further, our training intervention meaningfully reduced Rel.AP asymmetry (p = 0.027, Cohen's d = 0.73). At the group level, these reductions in asymmetry were accompanied by improvements in L-drill performance that were larger than the sample smallest worthwhile change (SWC). At the individual level, however, change scores in asymmetry and change scores in CoD performance only showed small, non-significant correlations.