Background and aim: The purpose of this study was to compare immediate and long-term effects of foot orthoses on co-contraction ratio of leg muscles among individuals with pes planus during stance phase of walking.
Materials and methods: Forty- five male students were categorized based on foot structure into neutral, experimental pes planus, or control pes planus groups (15 subjects per group). Electromyographic activity was recorded from the tibialis anterior and the peroneus longus of all subjects while walking barefoot as pretest measures. Experimental  pes planus group also walked under two conditions including wearing the shoe only and wearing the shoe with foot orthosis. Subjects in experimental  pes planus group were required to wear foot orthoses  for 6 months. All groups were assessed in a 6 months follow-up period. Co-contraction ratio of leg muscles among groups during stance phase of walking were compared using analysis of variance (α=0.05).
Results: Co-contraction ratio were significantly different in stance subphases between both supinated foot groups and neutral group.The leg muscles co-contraction ratio changed immediatly and 6 months after foot orthoses use.
Conclusion: According to these results, we concluded that leg muscles co-contraction ratio could  provide useful index to explain motion controlling characteristics of the foot. Use of foot orthoses, also by changing in muscular activity alter co-contraction ratios.