Running and walking are common ways to burn fat, firm up your legs and increase your aerobic endurance. However, they put a lot of stress on your legs. While knee problems and tendon or ligament pain resulting from overuse represent the most common running and walking maladies, muscle cramps can strike at any time and bring your exercise session to an immediate and painful halt.
Dehydration
Running or walking in warm weather can quickly lead to dehydration if you do not make a conscious effort to consume fluids at regular intervals to replace water losses in sweat. Dehydration has a host of deleterious effects on the body, and according to Dr. Cathy Fieseler of "Running Times" magazine, muscle cramps are among them. Be sure to be adequately hydrated before you head out the door; clear urine is a reliable sign that your tank is topped off. In addition, carry water or a sports drink with you if possible.
Electrolyte Disturbances
Low levels of potassium, magnesium and sodium -- minerals that are all excreted in sweat -- can lead to muscle cramps. The motor neurons supplying your muscles cause them to contract by firing electrochemical impulses that depend on given amounts of sodium and potassium crossing the nerve cell membrane in opposite directions. When there is a deficiency or imbalance in your electrolyte levels, your muscles can contract but may not be able to relax, causing a cramp. Maintain a proper diet and use sports drinks liberally on the go.
Circulatory Problems
According to the Mayo Clinic, circulatory problems that interrupt the blood supply to working muscles can lead to cramps. Arteriosclerosis, or hardening and narrowing of the arteries, is the most common cause of circulation-based cramping in the extremities. In many cases, you may experience symptoms only while walking or running, when your muscles' fuel and oxygen needs are far greater than when you are at rest. Modifying your diet is essential for treating arteriosclerosis, and if necessary, your doctor may prescribe a cholesterol-lowering or other medication.
Nerve Compression
A compression of the roots of the nerves supplying the legs at the level of the spine, a condition called spinal stenosis, can cause pain and cramping when you run, walk or even stand for an extended period. According to Dr. Richard P. Emmanuel of Southern California Orthopedic & Musculoskeletal Associates, these symptoms are typically reduced when you lean forward, offering clues to the diagnosis. Treatment includes rest, physical therapy, medications and, in severe cases, surgery.
