FOOT STRIKE POSTURE AND LOWER-LIMB DYNAMICS DURING SIDESTEPPING AMONG ELITE FEMALE ATHLETES: IMPLICATIONS FOR ACL INJURY RISK Chamnan Chinnasee 1 , Gillian Weir 3 , Jacqueline Alderson 3 , Siriporn Sasimontonkul 2 , and Cyril J Donnelly 3 Faculty of Health and Sports Science, Thaksin University, Phatthalung, Thailand 1 Faculty of Sports Science, Kasetsart University, Nakornpathom, Thailand 2 School of Sport Science, Exercise and Health, The University of Western Australia, Perth, Australia 3 The purpose of this study was to compare the lower-limb dynamics between fore-foot (FF) and rear-foot (RF) strike patterns during unplanned sidestepping. Three-dimensional (3D) motion capture data were collected from 16 elite female hockey players. Ankle, knee, and hip: angle at initial foot contact (IC), range of motion (ROM), peak moment, and negative peak net joint power during weight acceptance phase were compared between athletes using natural RF and FF strike techniques. Results showed ankle and hip angle at IC, ankle ROM, peak ankle and knee extension moments, peak knee valgus moments, and ankle and knee negative peak net power between RF and FF strike patterns were significantly different (α < 0.05). These findings show foot strike technique during unplanned sidestepping can effect athlete lower-limb dynamics, where RF strike athletes may be at higher risk of ACL injury. KEY WORDS: rear-foot, fore-foot, knee loading INTRODUCTION: Non-contact sidestepping is a common movement pattern among team sport athletes, where over one-half of non-contact ACL injuries occur (Cochrane et al., 2007; Shimokochi and Shultz, 2008; Griffin et al., 2006). Peak knee valgus moments in combination with extension moments have been shown to elevate ACL strain more than either loading pattern in isolation (Markolf et al., 1995). Laboratory analysis of sidestepping have shown that peak valgus knee moments are significantly elevated when compared with straight line running and more than double than that performed during unplanned versus planned sidestepping scenarios (Besier et al., 2001). Female athletes have a higher rate of ACL injuries relative to their male counterparts (Arendt et al., 1999; Ireland, 1999) and interestingly, more experienced female athletes may be at greater risk of injury (Sigward and Powers, 2006). There is large amount of research investigating the influence of technique and injury risk during dynamic sporting tasks. Simulation research has highlighted the importance of appropriate upper body dynamics towards peak knee valgus moments and ACL injury risk during unplanned sidestepping (Donnelly et al., 2012). Foot placement close to the midline and an upright torso during cutting has been reported to reduce peak knee valgus moments (Jamison et al., 2012; Dempsey et al., 2009). A greater and rapid initial hip flexion, internal rotation, and larger initial knee valgus angle has also been shown to produce elevated peak knee valgus loading (McLean et al., 2005; Kipp et al., 2011). Finally, Kristianslund et al., (2012) in a study of cutting technique, reported that narrow cuts with low knee valgus angle and toe landing may decrease knee valgus moments. Though fore-foot landing a popular and common coaching technique recommendation that has been shown to redistribute lower limb loading during running (Stearne et al., 2014), the influence of foot strike posture on an athlete’s ACL injury risk during unplanned sidestepping has yet to be investigated. The purpose of this study was to compare differences in lower-limb dynamics and ACL injury risk variables among athletes who adopt a natural fore-foot and rear-foot strike technique during unplanned sidestepping.