The human foot has evolved from a flexible grasping organ to a relatively rigid weight bearing supportive system. Some claim that the evolution of the foot has been less than successful, or at least incomplete. For example, still present are the grasping muscles, which are of reduced importance.

The foot is composed of 33 joints and 26 bones, grouped as the seven tarsal bones (talus, calcaneus, navicular, cuboid, medial cuneiform, intermediate cuneiform, and lateral cuneiform); five metatarsal bones (arranged medial to lateral); and fourteen phalanges (three for each toe, except for the great toe, which only has two).

The bones of the foot articulate such that they form three structural arches that, along with an extremely complex system of ligaments, and to a lesser degree, of muscles, providing five layers of support. These arches, two longitudinal (medial and lateral) and one transverse, contributing to the strength, stability, mobility, and resilience of the foot. During weight bearing and other types of loading, the arches serve as shock absorbers, dissipating energy before it is transferred across the ankle joint and the shank.

The plantar fascia is found on the bottom of the foot. Running longitudinally, it is divided into central, lateral, and medial portions. It attaches posteriorly (back of) on the calcaneus and the anterior (front of) at the base of the first row of phalanges (toes).

Plantar Fasciitis is a common foot disorder in runners--although the cause remains unknown, anatomical abnormalities and overuse are suspected. The plantar fascia is presented as a truss, which is a rigid structure composed of elements fastened as to resist changes in its shape by preventing motion between its elements. Its purpose is to support a larger load or span a greater distance than the individual elements could by themselves. The plantar fascia serves as a mechanism by which the tarsal joints may be passively stabilized. As an individual performs heel raises or any activity requiring toe extension, the fascia becomes stretched and tightened because of the changes in orientation of its attachment at the toe area. This change then shortens at the base of the truss, from the heel to the ball of the foot. The result is tarsal and metatarsal stabilization and an increase of the height of the longitudinal arch.

Typically, a normal foot has a medium height longitudinal arch, which is an imprint of the foot not unlike a fingerprint, and a vertically oriented hindfoot, which is the angle that the achilles tendon makes from the vertical. A flat foot, or pes plantus, has a low arch or no arch and is often pronated. Pes cavus, or a highly arched foot, is supported mostly at the fore and hind foot.

The manner in which loads are distributed under the foot has been a focus of investigation for decades. In the normal weight-bearing stance, all of the metatarsal heads are in contact with the ground and together bear 50% of the load, the heel being responsible for the other 50%. The metatarsal of the great toe is responsible for twice the load of the other metatarsals.

Now that we have addressed the functions and anatomical make-up of the foot treatment for plantar fasciitis is done through specific exercises to strengthen the arch as well as the integrity of the ankle. Orthotics are given to people with flat feet to aid in the support of the arch and various Physical Therapy modalities such as ultrasound are administered to promote healthy tissue growth and healing after activity and exercises.