Arches of the foot

Load bearing curves in the tarsal and metatarsal bones of the feet

The arches of the foot, formed by the tarsal and metatarsal bones, strengthened by ligaments and tendons, allow the foot to support the weight of the body in the erect posture with the least weight. They are categorized as longitudinal and transverse arches.

The longitudinal arches of the foot can be divided into medial and lateral arches.

The medial arch is higher than the lateral longitudinal arch. It is made up by the calcaneus, the talus, the navicular, the three cuneiforms (medial, intermediate, and lateral), and the first, second, and third metatarsals.

Arched feet are generally more common in men, and studies have reported that women are more likely to have flat feet than men. Women who do have arched feet who experience pregnancy and may experience a flattening of their arched feet, as the surge of female sex hormones such as estrogen can cause the tendons in their feet to soften and relax, to the extent that their arched feet become flat. The anatomy and shape of a person's longitudinal and transverse arch can dictate the types of injuries to which that person is susceptible. The height of a person's arch is determined by the height of the navicular bone. Collapse of the longitudinal arches results in what is known as flat feet. A person with a low longitudinal arch, or flat feet will likely stand and walk with their feet in a pronated position, where the foot everts or rolls inward. This makes the person susceptible to heel pain, arch pain and plantar fasciitis. Flat footed people may also have more difficulty performing exercises that require supporting their weight on their toes. People who have high longitudinal arches or a cavus foot tend to walk and stand with their feet in a supinated position where the foot inverts or rolls outward. High arches can also cause plantar fasciitis as they cause the plantar fascia to be stretched away from the calcaneus or heel bone. Additionally, high or low arches can increase the risk of shin splints as the anterior tibialis must work harder to keep the foot from slapping the ground.

The non human apes (the gibbons, gorillas, orangutans, chimpanzees and bonobos) tend to walk on the lateral side of the foot, that is with an 'inverted' foot, which may reflect a basic adaptation to walking on branches. It is often held that their feet lack longitudinal arches, but footprints made by bipedally walking apes, which must directly or indirectly reflect the pressure they exert to support and propel themselves do suggest that they exert lower foot pressure under the medial part of their midfoot. However, human feet, and the human medial longitudinal arch, differ in that the anterior part of the foot is medially twisted on the posterior part of the foot, so that all the toes may contact the ground at the same time, and the twisting is so marked that the most medial toe, the big toe or hallux, (in some individuals the second toe) tends to exert the greatest propulsive force in walking and running. This gives the human foot an 'everted' or relatively outward facing appearance compared to that of other apes. The strong twisting of the anterior part of the human foot on the posterior part tends to increase the height of the medial longitudinal arch. However, there is now considerable evidence that shoe wearing also accentuates the height of the medial longitudinal arch and that the height of the medial longitudinal arch also differs very considerably between individuals and at different speeds. The presence of high arched feet in modern humans is a result of natural selection for long distance running. On the other hand, the primitive trait of arch less feet in our great ape relatives has been maintained because of selection for grasping tree branches as a part of their arboreal lifestyle. Divergence between ape feet and human feet began with the early human ancestor Ardipithecus ramidus, when strengthened plantar tissue evolved, which supported early terrestrial propulsion before evolving a true arch. However, the skeletal longitudinal arch structure itself did not begin to evolve until Australopithecus afarensis had evolved a relatively low longitudinal arch (compared to modern humans) and the first signs of a transverse arch accompanying it. and the roughly contemporaneous fossil footprint trail at Ileret, Kenya attributed to Homo erectus ergaster.