Running is a good way to work out the cardiovascular system and the muscles of the leg, but it is also very hard on your joints and bones. Each time your foot strikes the ground while walking, it puts pressure equivalent to 1.5 times your body weight on your legs. Running increases this pressure significantly. Over time, that can cause damage to the bones, muscles, tendons and ligaments, especially if you have ill-fitting footwear or weak joints.
Some lumps on your lower leg after exercise can be treated with self-care measures, but there is a risk the lump could be cancerous. Consult your doctor for a diagnosis.
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Read more: Knots & Pain in Lower Leg
Shin Splint Lump
Medial tibial stress syndrome, more commonly known as a shin splint, is characterized by pain on the tibia — the bone on the inner part of the lower leg below the knee. Lumps caused by shin splints are felt along the inside of the tibia, and there may be associated swelling of the leg.
The pain from shin splints often goes away once you start to run, but returns when you finish running. Shin splints occur most frequently in runners that run on an uphill or downhill grade and those that stop and start a lot or wear ill-fitting or worn-out shoes.
Muscle Hernia in Lower Leg
Muscle hernias in the lower leg are caused by a weakness of the fascia — the tissue that forms a sheath around the muscles and nerves. If the fascia is weak or defective, the muscles of the leg push through, forming a lump.
The lump is not always painful, but it can be if the pressure exerted on the hernia is made worse by exercise. Lumps formed by muscle hernias usually occur on the outside of the lower leg.
Other Causes of Shin Lumps
A lump on the lower leg after exercise can develop for a variety of other reasons, and running may simply make them more noticeable or exacerbate the lumps. Trauma to the leg can cause swelling or a bump, as can an infection.
Inflammatory diseases, such as rheumatoid arthritis and lupus can produce lumps, particularly around the knee. There is also the chance it could be a tumor of some kind, which in rare cases can be cancerous.
Treatment for Leg Conditions
Shin splints can be treated by resting the leg and applying ice when the lump initially forms, then heat after it is reduced. Wearing shoes with arch supports or adding arch supports to an older shoe can help reduce the shock on the joints when running.
Stretch your legs before and after running and wear a shin splint or calf brace to support you after you return to running. A physical therapist can also provide an individualized treatment plan for you if you have this condition.
Muscle hernias, if not painful, should not cause a problem when running, but it's best to consult a doctor to be sure. All other possible causes will need to be diagnosed by a doctor. Even if the lump is not painful, there is the possibility it could be malignant, or cancerous.