The immediate effect of foot insole on electromyography activity and co-contraction of leg muscles in individuals with flat feet

Introduction: The human foot is a strong mechanical structure that can affect function of the feet. The aim of this study was to determine the immediate effect of foot insole on myoelectric activity and co-contraction of lower leg muscles in individuals with flatfeet in comparison with healthy subjects. Materials and Methods: Thirty university male students participated in this study. Subjects were divided into two groups of flatfeet and control. Surface electromyography was used to record muscular activity of tibialis anterior, peroneus longus, medial gastrocnemius and soleus muscles. All subjects walked barefoot along a 15m walkway for three trials. Participants with flatfoot also walked on the walkway while wearing shoes with foot insole. Results: Findings of this study showed that individuals with flatfoot have more co-contraction ratio in midstance (P < 0.05) and propulsion (P < 0.05) sub-phases. The use of foot insole increased co-contraction ratio at heel contact sub-phase (P = 0.009), while co-contraction ratio decreased at midstance sub-phase (P = 0.015). Conclusion: Results of this study demonstrated using of foot orthotics could reduce the extra muscular activity. According to the effect of foot orthotics on co-contraction ratio at heel contact sub-phase, it could be concluded that excessive motion of rear foot has a non muscular source. Keywords: Foot orthotics, Co-contraction, Walking, Flat foot