Foot Joint Coupling Variability in Rearfoot and Forefoot Runners After an Exhaustive Run

Abstract

While most runners use a rearfoot strike (RFS), recent research suggests that midfoot or forefoot strike (FFS) running is more natural and reduces injuries. Joint coupling is believed to be an important factor in running related injuries. Further, according to the dynamical systems theory, increased joint coupling variability while running may prevent repetitive loading of tissues which may lead to overuse injury. PURPOSE: This study compared joint coupling variability of the foot in habitual RFS and FFS runners prior to and following an exhaustive run. METHODS: Fifteen FFS and 15 RFS runners performed a maximal 5 km treadmill run. Foot motion was assessed using a 7-segment foot model which identified 6 functional articulations (rearfoot, medial midfoot, lateral midfoot, medial forefoot, lateral forefoot, and 1st metatarsophalangeal). Motion capture data was collected for 10 s at the beginning and end of the run and 5 steps were processed for subsequent analysis. Vector coding methods were used to calculate 10 different joint couples. Standard deviations of the coupling angles were used to identify variability within the first 2 subphases of stance (0-20% and 21-50% stance). Mixed between-within subjects ANOVAs were used to compare differences between the foot strikes and pre and post run. RESULTS:Subphase 1: FFS group had increased variability over RFS group in 2 medial midfoot-forefoot couples (1.22° and 2.84° difference) while RFS group had increased coupling variability in 1 lateral midfoot-forefoot couple (0.94° difference). Subphase 2: RFS group had increased variability in 3 rearfoot-midfoot couplings over FFS group (3.43°, 3.66°, and 1.30° difference). Subphase 2 post run, both groups increased variability in rearfoot (0.68° difference pre to post run) and 3 rearfoot-midfoot couplings (0.77°, 0.65°, and 0.84° difference). An interaction occurred between group and pre-post run in the midfoot-forefoot where only RFS runners decreased variability over time (0.99°). CONCLUSION: FFS runners had greater variability in subphase 1, while RFS had greater variability in subphase 2 indicating that a FFS may provide better injury protection during the initial heel strike period. Increased variability post-run in subphase 2 suggests that overstressing tissues may be more critical to prevent during subphase 2.