foot

Highly specialized structure that provides a rigid, weight-bearing base for the body during standing, and acts as a springboard for walking and running.

How the foot works The propulsive function of the foot depends on the arrangement of the bones into two longitudinal arches that act as shock absorbers; these arches flatten slightly when weight is put upon them and recoil when it is removed. In the standing position the weight of the body is mainly supported at the heel and the heads of the metatarsal bones, just behind the toes. On walking, the weight is first applied at the heel and then along the lateral border of the foot, medially across the metatarsal heads to the ball of the foot as the heel leaves the ground, and the big toe gives the final push-off. In running, the heel never touches the ground and the weight is applied only through the distal ends of the longitudinal arches, which recoil and reinforce the propulsive thrust delivered by flexing the medial toes. The arches of the foot are maintained by the shape of the interlocking bones, by muscle action, and by strong ligaments. If the ligaments become stretched and lax, part of the curvature will be lost, resulting in flat foot.

The foot is normally at right angles to the leg in the standing position. It can be drawn upwards (dorsiflexed) or lowered (plantar flexed) by movement at the ankle joint, and the sole of the foot may be turned inwards (inversion) or outwards (eversion); these movements involve the other bones of the foot swinging as a unit around the uppermost bone, the talus.