Distance running places significant stress on the muscles at the rear of your legs -- the hamstrings, glutes and calves. The calf muscles are susceptible to soreness and injury from running, especially fast or up inclines. Numbness or the sensation of your calf falling asleep during running, however, is unusual and suggests a primary cause other than running itself. The reason for your calf numbness may be vascular or neurological, and may be the result of a chronic process or an acute condition.
Sensation in the Calves
Your calf muscles consist of the soleus, which is lower and connects to the Achilles tendon, and the gastrocnemius, which is higher than, as well as superficial to, the soleus. These muscles flex the foot at the ankle and provide driving power during the toe-off phase of your stride. Sensory and motor nerve fibers are supplied by the tibial nerve, a branch of the sciatic. Blood flows into the calf through the posterior tibial artery, a branch of the popliteal artery that arises from the large femoral artery above.
Peripheral Artery Disease
Problems with the blood supply to your calf muscles can cause various symptoms such as pain, tingling and numbness. These sensations tend to come on more frequently and with greater severity during exercise such as running because of the muscles' increased oxygen needs. The proximate cause is arteriosclerosis, or hardening of the arteries. Risk factors include high cholesterol, hypertension, diabetes and other forms of vascular disease. So if you want to keep active, remember that exercise alone isn't enough and that you need to look after other markers of health as well.
Sciatica
The sciatic is a large nerve with branches serving the skin and muscles in the back of your legs. It runs from the lumbosacral spine through the glutes in your butt and down the back of your thigh into your calf, giving off branches as it does. Sciatica refers not to a disease in its own right, but to pain felt as a result of pressure on the nerve at one of various common sites. It sometimes resolves on its own, while at other times, ice and physical therapy and even steroid injections are required to get you back to full speed.
Tibial Nerve Injury
While numbness in your calf after a run may occur as a result of a problem in a spinal nerve root or some other location above the calf itself, it can also happen due to direct damage to the tibial nerve. This condition, known as neuropathy, is most often brought on by a blow behind the knee or high in the calf, but it can also occur as a result of conditions such as diabetes that affect the entire nervous system. If the numbness does not resolve on its own or recurs frequently, especially when pain is also a symptom, seek medical treatment.
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