Differences in Kinematic Correlates of Impact Loading Between Rearfoot and Non-Rearfoot Strikers in Running Napier C1,2, MacLean CL2, Taunton JE2,3, Maurer J2, Hunt MA1 1Department of Physical Therapy, Faculty of Medicine, University of British Columbia, Vancouver, Canada 2Fortius Lab, Fortius Institute, Burnaby, Canada 3Division of Sports Medicine, Faculty of Medicine, University of British Columbia, Vancouver, Canada INTRODUCTION RESULTS Impact loading (in particular, average vertical loading rate (AVLR)) has been implicated in the development of several running-related injuries (RRIs)1,2. Some researchers have also suggested that overstriding (landing with the foot too far in front of the centre of mass (COM)) may be linked to increased loading rates and RRI3. There is no clear method for measuring overstriding. The purpose of the present study was to establish the relationship between kinetic outcomes (vertical impact peak (VIP), instantaneous vertical loading rate (IVLR), and AVLR) and five kinematic measures of overstriding (angle of shank at initial contact (IC); horizontal distance from heel to COM at IC; horizontal distance from centre of pressure (COP) to COM at IC; angle between COP, COM, and vertical projection of the COM; percent of step length anterior to COM). Twelve RFS and six NRFS healthy, female runners between the ages of 18 and 60 years were analyzed (Table 1). RFS and NRFS groups displayed opposing relationships between the kinematic measures of overstriding and kinetic outcomes (Table 2). RFS showed a moderate positive correlation between horizontal distance from heel to COM at IC and AVLR (r = 0.62, p = 0.037) as well as IVLR (r = 0.64, p = 0.039) (Table 2; Figure 2). Conversely, NRFS displayed moderate to strong negative correlations between kinetic outcomes and several kinematic measures, with percent of step length anterior to COM showing the strongest association (VIP r = -0.80, p = 0.016; AVLR r = -0.56; p = 0.031; IVLR r = -0.65, p = 0.009) (Table 2; Figure 3). Table 1. Description of participants. Table 2. Pearson’s correlation (r) values for rearfoot strike (RFS) and non-rearfoot strike (NRFS). Group Age (years) BMI (kg/m2) RFS (n = 12) 38.2 (11.1) 21.7 (1.2) NRFS (n = 6) 40.4 (8.1) 23.2 (2.9)   Shank Angle Heel to COM COP to COM Angle between COP-COM-vertical projection of COM Percent step length anterior to COM RFS (n=12) VIP 0.38 0.46 -0.37* -0.35* -0.45* AVLR 0.02 -0.62* -0.23* -0.26* -0.52* IVLR 0.10 -0.64* -0.28* -0.47* NRFS (n=6) -0.25* -0.53* -0.55* -0.80* -0.40* -0.21* -0.16* -0.14*  -0.56* -0.33* -0.27*  -0.65* METHODS Twenty-three healthy, novice female runners between the ages of 18 and 60 years who had no history of lower extremity joint surgery and no current lower extremity pain were recruited. Three-dimensional kinetic and kinematic data were collected over three trials of 15 seconds at the participant’s preferred speed on an instrumented treadmill. The first 10 stance phases from each trial were processed and assessed for a VIP. Only participants who displayed a VIP at least 2/3 of the time (n = 18) were included in the analysis. For the purpose of analysis, participants were divided into two groups: rearfoot strikers (RFS, n = 12) and non- rearfoot strikers (NRFS, n = 6). Angle of shank at IC, horizontal distance from heel to COM at IC, horizontal distance from COP to COM at IC, angle between COP-COM- vertical projection of the COM, and percent of step length anterior to COM were calculated for all stance phases that displayed a VIP. Pearson’s correlation coefficients were used to assess the relationship between the kinetic and kinematic variables. Values are mean (SD). RFS – Rearfoot striker; NRFS – Non-rearfoot striker; BMI – Body mass index. RFS – Rearfoot striker; NRFS – Non-rearfoot striker; VIP – Vertical impact peak; AVLR – Average vertical loading rate; IVLR – Instantaneous vertical loading rate; COM – Centre of mass; COP – Centre of pressure. Negative values represent a negative correlation. * p < 0.05. Figure 2. The relationship between average vertical loading rate (AVLR) and horizontal distance from the heel to the centre of mass (COM) in rearfoot strikers. BW/s – Body weights/second. Figure 3. The relationship between average vertical loading rate (AVLR) and percent step length anterior to the centre of mass (COM) in non-rearfoot strikers. BW/s – Body weights/second. CONCLUSIONS Findings from this study suggest RFS and NRFS demonstrate moderate to strong, but opposing relationships between kinematic measures of overstriding and kinetic outcomes associated with RRI. Two potential measures of overstriding—horizontal distance from heel to COM and percent of step length anterior to COM—are associated with increased loading rates, but are dependent on classification of foot strike. Further investigation is warranted to determine whether these overstriding measures also result in increased injury incidence. Figure 1. Kinematic measures of overstriding REFERENCES ACKNOWLEDGEMENTS WEBSITE 1. Zadpoor AA et al. Clin Biomech 2011;26(1):23-28. 2. Bredeweg SW et al. J Sci Med Sport 2013;16(3):205-10. 3. Heiderscheit BC et al. Med Sci Sports Exerc 2011;43(2):296-302.