The Relationship between Balance and Foot Pressure in Fatigue of the Plantar Intrinsic Foot Muscles of Adults with Flexible Flatfoot

Abstract

[Purpose] This research investigated whether fatigue of intrinsic muscles plays an important role in support of the medial longitudinal arch, affecting foot pressure and balance. [Subjects] The study subjects were 20 adults with flatfoot who did not exhibit musculoskeletal disorders, disease of the lower limbs, or lower back pain. [Methods] The subjects were instructed to perform 75 isotonic contractions of the intrinsic foot muscles, flexing the metatarsophalangeal joints through the full range of motion with an elastic band. This exercise was repeated until a drop in median frequency (MedF) of at least 10% was observed. Before and after exercise, balance and foot pressure were measured with the subject standing on one leg. [Results] After the exercise, the middle forefoot area and midfoot medial area showed a significant difference in foot pressure. In the middle forefoot area, the pressure increased from 21.83 ± 4.56 psi to 25.95 ± 2.92 psi. In the midfoot medial area, the pressure increased from 5.52 ± 1.97 psi to 12.75 ± 2.56 psi. Although the anterior/posterior index, medial/lateral index, and overall stability index of balance increased significant differences were not observed. [Conclusion] Increased pronation of the subtalar joint was seen in people with flatfoot after intrinsic muscle fatigue.