Foot: Anatomy and Physiology

The human foot is at once the most functional, the most intricate, and the most punished part of the anatomy. The intricate skeletal structure of the foot has been compared to the combined machinery and durability of a fine Swiss watch, a tool capable of propelling the body in any direction at high speed, while sustaining forces that are many times a person's body weight. As the structure that supports the body in every aspect of upright movement, the foot is exposed to constant physical stresses, some of which are exacerbated by conditions such as footwear and weather. As with many other components of the human anatomy that are functioning constantly, the foot is only noticed when it fails to function in its usual reliable fashion.

The foot has evolved over the hundreds of thousands of years of human physiological development into a mechanism that is both a complex machine and a foundation piece for the body. Including the bones of the ankle, the foot comprises 26 separate bones, many of which are relatively small and delicately fashioned. Over 100 muscles, tendons, and ligaments combine with the skeletal bones to create 33 separate joints in this flexible and dynamic structure. An intricate series of blood vessels and nerve pathways run within individual networks enclosed by foot tissues to support the cardiovascular and neurological demands of movement. The sophistication of the skeletal structure of the foot is underscored by the fact that the bones of the two human feet constitute almost 25% of all bones in the human body.

Where an irregularity or imbalance occurs in the structure of the foot, it will often cause other anatomical structures to be affected. For example, if a person tends to strike the ground forcefully on the front of the sole of the foot as opposed to the heel, greater degrees of force tend to radiate into the knee joint or hip.

The bone structure of the foot is divided into three parts: the forefoot, the midfoot, and the hind-foot. The forefoot is made up of the bones of the five toes, which are collectively known as the phalanges. The phalanges are connected to the other bones of the foot by a longer connecting bone, called the metatarsal, at joints created at the ball of the foot with each toe. The forefoot is capable of supporting one half of a person's body weight.

The midfoot is the portion of the foot that is designed to absorb the shock created by human movement. The midfoot is constructed of five tarsal bones, and it is supported by the plantar fascia, the ligament that is essential to the function of the arch of the foot. The plantar fascia extends along the entire length of the foot, attached at the calcaneus (the heel bone, the largest bone in the foot) to the forefoot. The hindfoot, including the ankle structure, is connected to the bones of the lower leg by the talus, the ankle bone. The joint created at the heel and the ankle is the subtalar joint, which permits the ankle to be completely rotated in clockwise and counterclockwise directions.

The 20 muscles that generate movement in the foot are as subtle and sophisticated in their structure as the companion foot skeletal bone. Along with the Achilles tendon, these muscles are responsible for the generation of the all types of movement by the foot. For example, the anterior tibial muscle permits the foot to move upwards, as is required to lift the forefoot off the ground. The posterior tibial is the muscle that supports the arch. The peroneal tibial muscle controls the movement on the outside of the ankle, such as the turning of the foot on its outside edge. Extensors are used to assist the ankle to raise the toes when the body is preparing to stride forward. Flexor muscles stabilize the toes on the ground, especially when the body is stationary and upright. The Achilles tendon, which connects the heel to the gastrocnemius and soleus, or calf muscles, is the largest and strongest tendon in the body. The Achilles is required to provide stability to the entire lower leg structure of the anatomy whenever the body runs or jumps.

The ligaments of the foot create joints with the ability to significantly flex the food and to bear great weight. The plantar fascia is the longest of the foot ligaments, acting as a cushioning device for the entire structure during movement. Each toe has small joints created by ligaments to provide flexibility for each of these appendages, independent of the rest of the structure.

Each movement of the foot is a synchronized series of musculoskeletal movements made in coordination with both the ankle and the lower leg. Every movement of the body that involves its propulsion, whether forward, backward, or upward, is made in an integrated way by these components. In sports where the foot is in a stationary position, it remains functional. An example of this state is rowing, where the primary emphasis of the athlete is on the delivery of the stroke of the oar in the water, and the foot is constantly flexing and assisting with the overall balance and stability of the body in the craft. In pursuits such as shooting and sailing, the stationary feet of the athlete contribute to the effective performance of other physical tasks by the athlete.

see also Achilles tendon rupture; Ankle anatomy and physiology; Lower leg anatomy.