The relationship between arch height and intrinsic muscles/plantar fascial injury is controversial. Some authors suggest that height of the medial longitudinal arch does not affect function, while others claim it plays an important role in a wide range of injuries. In this paper, researchers from Japan measured cross-sectional area and stiffness of the extrinsic and intrinsic muscles of the feet and planter fascia while people with low or neutral arches loaded their feet at 10%, 50%, and 90% of body weight. The authors used ultrasound-based shear wave elastography to measure tendon strain. The authors noted the cross-sectional area peroneus brevis was larger in the flat-foot group under all loading conditions. Furthermore, mechanical stiffness of the flexor digitorum longus and abductor hallucis was higher in the flat-foot group than in the normal group and loaded 90% body weight. The authors conclude that “excessive stretching of the intrinsic foot muscles and planter fascia occurs in flat feet, and excessive contraction of the flexor digitorum longus may counteract the excessive lowering of the foot arch. Therefore, it is necessary to promote the contraction of the intrinsic foot musculature in feet with greater flexibility of the MLA during loading.” This research explains prior research showing that when foot strengthening exercises are given to people with flat feet versus neutral arches, the same exercises produced better outcomes when performed by people with flat feet (1). It also it explains why giving foot strengthening exercises to people with flat feet significantly improves balance and performance (2). It just makes sense, because people with low arches are unable to lock their midfoot during propulsion, they have to generate more muscle force to effectively push off. One study showed that low arched people generate 35% less force in the arch during propulsion (3), making them more dependent upon muscular stabilizing mechanisms. The bottom line is that to remain injury free, people with low arches need to keep their feet strong and flexible.

1. Sulowska I, Mika A, Oleksy Ł, Stolarczyk A. The influence of plantar short foot muscle exercises on the lower extremity muscle strength and power in proximal segments of the kinematic chain in long-distance runners. BioMed research international. 2019 Jan 2;2019.
2. Şahan TY, Arslan SA, Demirci C, Oktaş B, Sertel M. Comparison of short-term effects of virtual reality and short foot exercises in pes planus. The Foot. 2021 Jun 1;47:101778.
3. Hösl M, Böhm H, Multerer C, Döderlein L. Does excessive flatfoot deformity affect function? A comparison between symptomatic and asymptomatic flatfeet using the Oxford Foot Model. Gait & posture. 2014 Jan 1;39(1):23-8.