A Comparison of Muscle Activities in the Lower Extremity between Flat and Normal Feet during One-leg Standing

[Purpose] This study examined the differences in muscle activation between flat andnormal feet in the one-leg standing position which delivers the greatest load to the lowerextremity. [Subjects] This study was conducted with 23 adults, 12 with normal feet and 12with flat feet, with ages ranging from 21 to 30 years old, who had no neurological historyor gait problems. [Methods] The leg used for one leg standing was the dominant leg of thesubjects. The experimenter instructed the subjects to raise the non-dominant leg withtheir eyes open, and the subjects maintained a posture with the non-dominant leg''s kneeflexed at 90° and the hip joint flexed at 45° for six seconds. In the position of one-legstanding, a horizontal rod was set at the height of the waist line of the subjects wholightly placed two fingers of each hand on the rod to prevent inclination of the trunk toone side. Measurements were taken three times and the maximum value was used. A surfaceelectromyogram (TeleMyo 2400T, Noraxon Co., USA) was used to measure muscle activities.[Results] We compared muscle activities between flat and normal foot, and the results showa significant difference between normal and flat feet in the muscle activity of theabductor hallucis muscle. [Conclusion] The subjects with flat feet had relatively loweractivation of the abductor hallucis muscle than those with normal feet during one legstanding. We infer from this that the abductor hallucis muscle of flat foot doesn''t workas well as a dynamic stabilizer, compared to a normal foot, during one leg standing.Key words: Flat foot, Electromyography, One-leg standing