As a runner, you expect the occasional aches and pains like muscle soreness and blisters. But a foot that goes numb when you're running is a strange sensation. You are undoubtedly used to the feeling of your foot "falling asleep" when you sit cross-legged on the floor too long. But when that numbness and tingling develops while you're running, you may be alarmed. Fear not: Foot numbness while running is not uncommon, and most of the time, it's easily remedied.
Causes of Foot Numbness
Foot numbness is most often caused by a compressed nerve. The nerves that cause sensation in your foot and ankle can get trapped between bones or soft tissue. Because the nerve is compressed, it's unable to send the correct signals to your brain from your skin and soft tissue. Nerve compression can make your foot feel like it's on "pins and needles," or it can make your foot completely lose sensation. The feeling sometimes makes you want to take off your shoe and rub your foot. It's usually localized to one part of your foot, often your toes; occasionally, your entire foot may feel numb.
Causes of Nerve Compression
Nerves in the foot can become compressed for many reasons, including:
Poorly fitting shoes. Shoes that are too tight, which don't have enough room in the toe box, or are laced too tight can cause the nerves in the foot to become compressed. Thick socks may be another culprit.
Trauma. An injury that causes the tissue in the foot to swell, or causes direct damage to a nerve, can lead to foot numbness. Increasing your running mileage suddenly can cause trauma to your feet; likewise, improper running form may cause damage that in turn can lead to foot numbness.
Foot structure. If your feet are flat, or if the sole of your foot is overly flexible, you are more likely to compress the nerves of your foot when you run.
Scar tissue. Occasionally, a nerve that is repeatedly compressed becomes thickened and develops scar tissue. This is called a neuroma; the most common neuroma is between the second and third base of the toes, and is called a Morton's neuroma.
Foot numbness, especially heel and base of the foot numbness, may also be caused by compression of the sciatic nerve, a large nerve that runs from the spine down the back of the leg. This nerve may be compressed by a herniated/slipped disk, or by muscles that overlie the nerve.
There are steps that you can take to prevent or alleviate your foot numbness: Buy larger shoes, and make sure that there's adequate room in the toe box at the front so that you can wiggle your toes freely. Buy shoes with a stiffer sole; shoes with a pliable sole can cause swelling and trauma to the ball of your foot, where the nerves to the toes pass through the bones. Don't lace your shoes as tightly. Loosen the laces on your shoes to relieve any pressure points on your foot. Try wearing thinner socks, which take up less room in your shoe. Pay attention to your running form. Avoid "slapping" or "pounding" your feet on the ground as you run. Don't suddenly increase the duration or distance of your run. This may lead to trauma.
If these steps don't alleviate your foot numbness, a trip to a foot and ankle specialist, orthopedic surgeon or sports medicine doctor may be in order. The specialist will ask about your medical history, to rule out any diseases that may be causing your foot numbness. He may obtain X-rays and examine your foot to try to identify the source of the nerve compression. He may prescribe special shoe inserts, anti-inflammatory medications, or special exercises. Occasionally, more severe cases of foot numbness, including numbness caused by a neuroma, may need treatment with injections to the nerve, or with surgery.
Although foot numbness while running is uncomfortable, it is often easily remedied by relieving pressure on the compressed nerves. Simple remedies such as buying larger shoes, lacing your shoes less snugly, paying attention to your running form and making increases in running time or distance gradually may be enough to keep foot numbness from occurring. If self-help fails, a physician may try other treatments to relieve the discomfort.