The effect of flat foot on lower limb muscles activity pattern and plantar pressure characteristics during walking

The effect of abnormal foot structure on dynamic function in lower extremity, particularly among children and adolescents has yet received little attention. The purpose of this study was to determine the electromyographic (EMG) activation patterns of selected lower limb muscles and plantar pressure characteristics during gait in teenage boys with normal and flat foot deformity.

Twelve subjects with flat foot and twelve with normal foot defined by arch index method participated in this study. Surface electromyographic activity of selected lower limb muscles for tibialis anterior, peroneus longus, soleus, medial and lateral gastrocnemius were recorded. Plantar pressure characteristics were measured at their self-selected walking speed along a 10 m walkway. Independent t-test was used for statistical analyses.

EMG of medial and lateral gastrocnemius muscles were significantly greater in individuals with normal foot compared with flat foot group during loading response phase (P = 0.001) While medial gastrocnemius showed a decreased activation in terminal stance phase (P = 0.048). Peak pressure under foot regions including hallux and other toes, head of 2nd and 3th metatarsals and medial part of heel was greater in pes planus group. Center of pressure displacement was different between two groups during loading response, mid stance, and stance phase (P = 0.011, P = 0.015, and P = 0.050, respectively).

Abnormal foot posture could change the lower limb muscle activity and plantar pressure parameters during gait. The results of this study suggest that further studies can focus on the effects of foot abnormality on dynamic function in lower extremity to understand the underlying mechanisms and also set the suitable treatment manner.