Effects of Orthotic Insoles on Gait Biomechanics in Runners With Flatfoot Under Different Gait Loads

The purpose of this study was to quantify the biomechanical performance of the medial longitudinal arch (MLA) in the normal foot (NF), flatfoot (FF), and flatfoot with orthotic insoles (FF + insole) under different gait loads to identify their movement response strategies. Male runners with NF and flexible FF were instructed to walk and run using a rearfoot strike pattern. Subsequently, the FF group underwent the same test again while wearing orthotic insoles. The Qualisys capture system and Kistler force platform were synchronized to collect kinetic and kinematic data. A mixed-design two-way ANOVA and one-dimensional statistical parametric mapping (1-d SPM) were used to analyze the kinematics and kinetics of MLA and the kinematics of the first metatarsophalangeal joint (1st MTPJ) during the stance phase under different gait loads in the NF, FF, and FF + insole groups. Results showed that gait load and foot type had an interactive effect on MLA compression (p = 0.003). FF exhibited a smaller peak plantarflexion moment of the MLA during walking compared with NF (p = 0.001). The FF group exhibited a smaller dorsiflexion angle of the 1st MTPJ, with dorsiflexion initiating earlier. After wearing orthotic insoles, the kinematics of the MLA and the 1st MTPJ in the FF group shifted closer to those of the NF group, but the kinetics did not change. In conclusion, orthotic insoles modify the kinematics of the foot arch in flatfoot through physical support, but the kinetics remain unchanged compared with those observed without insoles. This indicates that after wearing orthotic insoles, flatfoot runners adjust their foot movement response strategy to maintain their habitual biomechanical pattern.