A Three-dimensional Gait Analysis of People with Flat Arched Feet on an Ascending Slope

[Purpose] The purpose of the study was to discover why people who have flat feet show a higher risk of damage to the musculoskeletal system than those who have normal feet. Furthermore, we examined the kinematic differences in the lower extremity between flat feet and normal feet in individuals on an ascending slope using three-dimensional gait 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. [Methods] A treadmill (AC5000M, SCIFIT, Berkshire, UK) was used to analyze the kinematic features during gait. These features were analyzed at slow, normal, and fast gait velocities on an ascending slope. Gait data were obtained using a 6-camera motion analysis system (Eagle system, Motion Analysis, Santa Rosa, CA, USA). [Results] Both groups showed significant differences in the sagittal, frontal, and transverse planes according to the speed changes. After comparing the lower extremity kinematics between those with flat feet and those with normal feet, significant differences were found with respect to hip adduction (frontal plane) in the stance phase and hip internal rotation (transverse plane) in the swing phase. [Conclusion] Due to hip adduction, the internal rotation angle of the lower extremity has a tendency to increase according to the increase in gait velocity on an ascending slope, and we can expect that the hip adductor muscles and internal rotator muscles in individuals with flat feet are used much more than would be the case for those with normal feet when they perform actions that require a lot of power, such as walking on an ascending slope and walking quickly.