The process that causes "polio feet"—that cause them to turn blue and cold and become difficult to move when it’s only mildly cold outside—is the same process that causes other post-polio symptoms. The polio virus attacked the spinal cord and either destroyed or damaged the anterior horn cell motor neurons that transmit the message to move, that comes from the brain to a muscle. When those neurons were damaged, or especially when they died, they disintegrated and the muscle fibers that used to be "turned on" by those cells, no longer were.

There is another kind of motor neuron that was affected by the virus—the motor nerve that controls the muscle around your blood vessels. When these neurons died, there were no motor nerves to tell the blood vessels to contract; if the blood vessels cannot contract, blood pools, especially in the veins.

"Polio feet" happens when the blood that normally would be sent back to the center of the body (on its way back to the heart) pools in veins near the surface of the skin, especially in the extremities (feet, mostly). Because the veins cannot contract, the warm blood continues to radiate heat into the environment. The result is over-cooling of the body, especially the feet. The blue color is because of the bluish color of blood in veins. Difficulty in moving the feet occurs when the muscles and other tissue that lie below the skin start to cool, and become less elastic. They feel stiffer, and so are harder to move.

People who have had polio—and especially if they have "polio feet"— should dress as if it’s 20 degrees cooler than it actually is. Dressing in layers can help control your body temperature as well.

Adapted from "Post-Polio: You Can Live With It" by Richard L. Bruno, Ph.D.