A good run strengthens the muscles and bones, makes the heart more efficient, renews the spirit and improves overall body circulation. However, a good run also can be slightly damaging to the body. During a run, the legs endure incessant pounding as they strive to support your entire body weight. After a run, some people develop swelling in the legs. Although this condition is typically associated with injury, the causes of swollen legs after running are actually quite widespread.
Any injury to the bones, muscles, ligaments or tendons in the lower leg can lead to immediate swelling. While running, you easily can injure the bones, muscles, ligaments or tendons in the legs. Interestingly, many injuries can occur without your knowledge. A small crack in the bone or tear in the muscle will likely cause pain, but perhaps not enough pain to indicate a serious injury. Similarly, a tear or inflammation of the ligaments or tendons causes a mild amount of pain, but might simply be written off as normal aches and pains. Once an injury occurs, the body's inflammatory response draws excess fluids to the area of injury, causing swelling.
Chronic Venous Insufficiency
A variety of vascular conditions might cause swelling in the legs after running. Chronic venous insufficiency is a condition that occurs when damaged veins in the legs cannot sufficiently return blood to the heart. As a result, blood pools in the lower legs, causing the legs and ankles to swell. Although regular exercise can actually help the condition, running for too long causes additional blood to pool in the veins.
Although blood clots are unlikely to develop in regular runners, the occurrence of the blood clot will cause the legs to swell. A blood clot is a clump of hardened blood that partially blocks the veins in the log. These clots can be caused by a variety of factors, such as blood pooling, injury to the leg veins and previous long periods of inactivity. The blood clot prevents blood from moving out of the leg and causes swelling, redness and tenderness. Although running does not actually cause the blood clot, running with a clotted vein can be quite painful and dangerous.
As explained by the Mayo Clinic, gravity can cause fluids to accumulate and settle in the legs, especially during long periods of sitting or standing. Although running is not technically considered "standing," it does require your legs to support your entire body weight for an extended period of time. As you remain in this upright position, gravity pulls body fluids into the legs. As this fluid accumulates, it causes peripheral edema, or swelling. That said, fluid retention due to gravity is much more likely to cause swelling in the legs after a long-distance run, rather than a short run.
Although cholinergic urticaria does not actually cause the legs to swell, it does cause the legs to break out in a rash of small swollen bumps. If enough of these bumps develop, the legs begin to feel extremely swollen and itchy. As explained by the Health Hype website, cholinergic urticaria is an allergic reaction to a specific physical trigger. Common triggers include exercise, hot or cold temperatures, spicy foods and emotional stress. A visual inspection of the legs can help determine whether cholinergic urticaria is the cause of swollen legs after running. The skin on the legs will be covered in red, swollen and itchy bumps (hives).