Heavy leg swelling may be caused by over-exercise, atherosclerosis, lumbar spinal stenosis and so on. 1. Excessive exercise: Heavy leg swelling may be caused by excessive exercise, such as long distance running, cycling, playing ball games, etc., when the leg muscles are damaged after excessive exercise, thus causing heavy leg swelling. 2. Atherosclerosis: Heavy leg swelling may be caused by atherosclerosis which results in narrowing of the arteries in the lower limbs, resulting in ischemia of the muscles due to occlusion of the blood vessels, thus causing heavy leg swelling. 3. Lumbar spinal stenosis: Heavy leg swelling may be caused by long-term sitting posture incorrectly caused by lumbar spinal stenosis, lumbar spinal stenosis will compress the sciatic nerve innervating the lower limbs, thus causing heavy leg swelling. Heavy leg swelling may also be caused by lumbar disc herniation or muscle ischemia, it is recommended to go to the regular hospital for examination and treatment as prescribed by the doctor.