Background: Flexible flatfoot is associated with altered plantar pressure distribution, but it is not clear how muscle fatigue affects plantar pressure characteristics in flexible flatfoot and normal foot.
Objective: To investigate the effects of calf muscles fatigue on plantar pressure variables in flexible flatfoot and normal foot.
Methods: Twenty-five people with flexible flatfoot and twenty-five people with normal foot were included. The unilateral heel-rise test was used to induce calf muscles fatigue. Plantar pressure variables were collected during preferred walking immediately before and after fatigue. The two-way mixed-design ANOVA was used to determine the main effect of fatigue and the interaction between foot posture and fatigue.
Results: Fatigue caused medialization of the contact area under the forefoot and the maximum force under the heel and forefoot (p< 0.05). When examining the differences in the effects of fatigue between groups, the contact area under the medial heel increased with fatigue in flexible flatfoot but decreased in normal foot; moreover, the contact area and maximum force under the midfoot and the maximum force under the third metatarsal decreased with fatigue in flexible flatfoot but increased in normal foot (p< 0.05).
Conclusions: Calf muscles fatigue caused medialization of the maximum force and contact area. Especially the midfoot was affected differently by fatigue in flexible flatfoot and normal foot.
Keywords: Pes planus; fatigue; foot biomechanics; heel rise; plantar pressure analysis.