Effect of Insoles on Plantar Fascia Tension During Running in Individuals with Flatfoot

Background: Plantar fasciitis is a common condition likely caused by abnormal foot alignment, such as flatfoot. Insoles are commonly used to treat flatfoot, and systematic reviews have shown that insoles improve pain; however, the underlying mechanism is unclear. This study aimed to investigate the effects of insoles on plantar fascial tension during running in individuals with flatfoot. Methods: The participants were 14 individuals with flatfoot. The task involved running under two conditions: with and without insoles. Insoles that absorbed the shock and supported the medial longitudinal arch were used. The foot marker trajectories and ground reaction forces were measured during running sessions. The plantar fascia tension was estimated based on the ground reaction force, moment arm of the ground reaction force, and that of plantar fascia. Statistical parametric mapping was used to compare the plantar fascia tension during the stance phase between the two conditions. Results: When running with and without insoles, the peak plantar fascial tension was observed at midstance. Planar fascial tension was significantly lower with insoles over a wider range during the stance phase than that without insoles (p < 0.05). Conclusions: This study provided evidence that insoles can reduce plantar pain while running. This result may be useful for reducing pain in individuals with flatfoot and preventing the onset of plantar fasciitis.