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Background and Objective: The asymmetry index during walking can be used for clinical treatment. This study was done to determine the immediate and long-term effects of foot orthoses on asymmetry of ground reaction forces frequency spectrum in male children with flat foot during walking.
Methods: This clinical trial study was done on fifteen children with flat foot. Subjects were randomly divided into without foot orthoses, immediate and long term usage of foot orthoses groups. The kinematic and kinetic data during three without foot orthoses, immediate and long term use of foot orthoses conditions were recorded by the motion analysis and force platform systems, respectively.
Results: Asymmetry index of medio-lateral frequency spectrum component during walking without foot orthoses, immediate and long term use of orthoses in median frequency and band width were greater than 4 percent. There were not any significant differences in asymmetry index of ground reaction force frequency spectrum components, asymmetry index of essential harmony numbers, asymmetry index of essential harmony total powers, and asymmetry index of fundamental harmony number in vertical, anterior-posterior,  and medio-lateral axes between without foot orthoses, immediate and long term use of foot orthoses conditions. However, asymmetry index of essential harmony total power in medio-lateral axis during immediate use of foot orthoses tend to be reduced than that walking without foot orthoses. However, this difference was not significant.
Conclusion: Despite the high asymmetry index of the ground reaction force frequency spectrum in the medio-lateral component during walking without foot orthoses, immediate and long-term effects of foot orthoses in the median and bandwidth frequency variables, the acute or long term use of foot orthoses did not show any significant effect on improvement of asymmetry index of ground reaction force frequency spectrum components.