Heavy leg swelling may be caused by prolonged strenuous exercise, lower extremity venous thrombosis and lower extremity phlebitis. 1. Long-term strenuous exercise: when the human body in daily life, long-term strenuous exercise, leg muscles continue to contract repeatedly, resulting in a large number of lactic acid and metabolites accumulated in the muscle tissues, which in turn cause leg swelling and heavy situation. 2. Lower extremity venous thrombosis: factors such as high coagulation of blood or damage to the venous wall vascular tissues make the lower extremity thrombus form, which leads to poor blood circulation in the legs and causes leg swelling and heaviness. 3. Phlebitis of the lower limbs: If the position of the leg is hit by external force, the inner wall of the local blood vessel is seriously stimulated, which is not detected in time and makes the wall of the blood vessel become inflamed. Under the stimulating effect of inflammation, it can cause swelling and heaviness of legs. It is recommended to go to the regular hospital for a comprehensive examination to understand the cause of leg swelling and then carry out the corresponding treatment.