Quantification of torsional stiffness in running footwear: proposed methodology

Abstract

There is evidence to suggest that certain extrinsic factors, such as footwear, may contribute to risk of running injury. Torsional shoe stiffness quantifies the resistance of a shoe to twisting about its long axis between the heel and toe box, and has been previously linked to changes in foot and ankle kinetics and kinematics during running and cutting motions. Despite the potential for torsional stiffness to influence gait and injury risk, torsional stiffness of running shoes is rarely reported in biomechanical research, and methods of quantifying shoe torsional stiffness are not currently standardised. The purpose of this study was to propose and validate a device for the quantification of torsional stiffness of a variety of types and sizes of running footwear. The device includes the measurement of shoe length. This provides required information for a more comprehensive calculation of torsional stiffness that represents the product of the area moment of inertia and the modulus of rigidity, both of which can be useful to characterise a particular type of shoe based on its shape and material properties. The results of inter-rater and intra-rater reliability analyses suggest that the device is useful for repeatable measurements of torsional stiffness in both the medial and lateral directions, as well as heel thickness.