Foot

Foot

The foot is an important element in human posture and gait.  As the last segment of the lower limb, it bears weight and provides a stable connection with the ground during standing, yet its flexible arch serves as a spring for walking, and running.

The foot is able to articulate at the ankle: placed flat on a walking surface, the foot remains rigid while the body rotates over it like an inverted pendulum during walking. The ankle is also able to tilt the foot left or right (invert and evert), allowing the foot to position solidly on a sloping or uneven surface. For example, a person walking horizontally along a hillside tilts the outside of the uphill foot slightly up and the outside of the downhill foot slightly down with each step, using the feet to improve balance. With each foot placed flat on the slanted surface, the body is positioned between them so that the gravitational force vector generally passes through the foot.

The foot dissipates and absorbs the shock of every step, reducing the impact forces on the knee and hip joints, spine, and other body parts. In addition, muscles and ligaments within the foot and ankle store energy from impact that is later transferred to improve running and gait efficiency.

The foot and ankle are also equipped with proprioceptive feedback sensors that track body position and provide information about weight distribution. This information is used make the constant small adjustments that make it possible for humans to stand upright. Exteroceptors like pressure and pain sensors inform the brain when the foot steps on something sharp that may damage it or when damage has already occurred so that appropriate action may be taken. Temperature sensors also provide important sensory feedback. 

There are medical conditions that can affect this sensory feedback. Peripheral neuropathy is a condition resulting from damage to the peripheral nerves that causes weakness, numbness, and pain in the hands and feet. Although there are many causes of peripheral neuropathy, the most common is diabetic neuropathy. People with diabetes mellitus have chronically high blood glucose levels that cause nerve damage.