Footwear and Strike Pattern Associated with Altered Ankle Shear Forces During Running
Dr. Douglas Powell
INTRODUCTION: Evidence has suggested that many of the beneficial adaptations associated with barefoot running are mainly due to the requisite change from a rearfoot to forefoot strike pattern. However, little evidence exists to support this argument. The purpose of this study was to investigate the role of footwear and strike patterns on ankle shear forces, a potential mechanism of injury. It was hypothesized that a forefoot strike pattern would be associated with significantly greater ankle shear reaction forces.
METHODS: Twenty-four (12 M, 12 F) healthy young adults aged 18 to 30 years performed ten overground running trials at a self-selected pace in each of four conditions: barefoot forefoot (BFF), barefoot rearfoot (BRF), shod forefoot (SFF) and shod rearfoot (SRF). Running velocity was maintained (±5%) using an infrared timing gate. Three-dimensional kinematics and ground reaction forces were recorded simultaneously using an 8-camera motion capture system (240 Hz, Qualisys, Inc.) and force platform (960 Hz, AMTI, Inc.), respectively. Visual 3D was used to calculate ankle joint reaction forces. Custom oftware (MatLab, Mathworks, Inc.) was used to calculate peak anteroposterior ankle joint reaction forces (JRFs). A 2x2 (strike by shoe) repeated measures ANOVA was used to determine the effects of strike pattern and shoes on ankle JRFs. Alpha was set at p<0.05.
RESULTS: Mean anteroposterior JRFs (BFF: 258.6±70.2; BRF: 263.6±84.9; SFF: 270.4±62.8; SRF: 248.7±69.4) were not significantly different due to strike pattern (p=0.375) or shoes (p=0.698). However, a significant strike by shoe interaction was observed (p=0.005). In the forefoot strike pattern, the shod condition had greater ankle JRF than the barefoot condition. However, in the rearfoot strike pattern, the barefoot condition had greater ankle JRF than the shod condition.
DISCUSSION: These data suggest that anteroposterior ankle JRF is minimized when running the preferred condition (rearfoot-shod or forefoot-barefoot). These data may support the notion that proprioceptive feedback alters lower extremity biomechanics during running.
