The influence of gearing footwear on running biomechanics

The influence of nonlinear bending stiffness footwear, which alters the metatarsophalangeal (MTP) joint bending as a function of forefoot bending stiffness, has been postulated to improve athletic performance and reduce injury risk during many sports. As the shoe moves through greater amounts of bending, forefoot stiffness should increase nonlinearly, to shift the centre of pressure forward (improving performance), while restricting forefoot bending in regions where turf toe injury may result. Recently, materials which allow for stiffness modifications as a function of forefoot flexion angle have been developed; however, the efficacy of this technology is unknown. Therefore, the purpose of this project was to evaluate the influence of gearing technology (a variable bending stiffness shoe) on biomechanics during running and sprinting. Ten male recreational athletes performed running and sprinting in two footwear conditions consisting of an altered US 10 adidas 16.4 FXG cleat. The footwear was altered by placing carbon fibre insoles with variable (nonlinear stiffness) into the shoes creating two different conditions: Control (no insole) and the variable stiffness (varStiff) shoe (gearing insoles). Kinematic (joint angles) and kinetic (ground reaction force and 3D joint moments) data of the lower extremity were recorded during each movement. The results of the study indicate that the variable stiffness insoles did positively influence athlete lower extremity biomechanics. At the MTP joint, as running speed increased (and normal MTP bending range of motion increased), the variable stiffness insoles reduced the amount of MTP bending of the shoes and reduced the medial–lateral movement of the point of force application. Additionally, the variable stiffness insoles reduced key biomechanical injury risk variables, such as non-sagittal plane joint loading at the knee and ankle joint.