Comparisons between lower-extremity strengthening exercises and foot orthoses for improving medial longitudinal arch height in individuals with flexible flat foot: an 8-week randomised clinical trial

Objective Flexible flatfoot is a recognized risk factor for lower extremity injuries. This study aimed to compare changes in the medial longitudinal arch (MLA) between a strengthening exercise group (EG) and a foot orthoses group (FOG). Subjects and Methods Thirty-eight healthy participants with bilateral flexible flatfoot were randomly assigned to either the EG or the FOG (<i>n</i> = 19 per group). The EG performed exercises five days a week. The FOG wore foot orthoses for more than five hours daily. Measurements of navicular drop, arch height index (AHI), plantar pressure, static balance, dynamic balance, and lower extremity muscle strength were taken at baseline, four weeks, and eight weeks. Results Both groups significantly improved in most measures at four and eight weeks compared to baseline. At eight weeks, the EG demonstrated substantially greater improvements in navicular drop (<i>p</i> < 0.001, <i>d</i> = 1.542) and AHI (<i>p</i> < 0.001, <i>d</i> = -1.286) when compared to the FOG. The EG also exhibited significantly greater improvements than the FOG in static balance in the anteroposterior direction (<i>p</i> = 0.027, <i>d</i> = 0.517), dynamic balance in the medial (<i>p</i> = 0.049, <i>d</i> = -0.460) and lateral directions (<i>p</i> = 0.017, <i>d</i> = -0.562), as well as lower extremity muscle strength (<i>p</i> < 0.05, <i>d</i> = -0.755 and -1.109, <i>r</i> = 0.473). Conclusions Lower-extremity exercise proved more effective than foot orthoses in enhancing the MLA and improving balance in individuals with flexible flatfoot.