Kinematic analysis of the lower extremities of subjects with flat feet at different gait speeds.

[Purpose] This study determined the difference between flat feet and normal feet of humans at different gait velocities using electromyography (EMG) and foot pressure analysis. [Subjects] This study was conducted on 30 adults having normal feet (N = 15) and flat feet (N = 15), all of whom were 21 to 30 years old and had no neurological history or gait problems. [Methods] A treadmill (AC5000M, SCIFIT, UK) was used to analyze kinematic features during gait. These features were analyzed at slow, normal, and fast gait velocities. A surface electromyogram (TeleMyo 2400T, Noraxon Co., USA) and a foot pressure analyzer (FSA, Vista Medical, Canada) were used to measure muscle activity changes and foot pressure, respectively. [Results] The activities of most muscles of the flat feet, except that of the rectus femoris, were significantly different from the muscle activities of the normal feet at different gait velocities. For example, there was a significant difference in the vastus medialis and abductor hallucis muscle. Likewise, flat feet and normal feet showed significant differences in pressures on the forefoot, midfoot, and medial area of the hindfoot at different gait velocities. Finally, comparison showed there were significant differences in pressures on the 2nd-3rd metatarsal area. [Conclusion] Because muscle activation has a tendency to increase with an increase in gait velocity, we hypothesized that the lower extremity with a flat foot requires more work to move due to the lack of a medial longitudinal arch, and consequently pressure was focused on the 2nd-3rd metatarsal area during the stance phase.