Soreness and swelling of the waist and legs may be due to the following reasons: 1. It may be caused by the accumulation of lactic acid in the body after doing strenuous exercise, resulting in swelling and pain in the muscles of the waist and legs, and the symptoms will disappear after resting for 2-3 days. 2. It may be caused by the third lumbar transverse process syndrome, which is due to the inflammation of the transverse process of the third lumbar vertebrae, leading to soreness and pain in the muscles in the waist, or affecting the L3 nerve root. 3. The L3 nerve root leads to soreness and pain in the front lateral or medial thigh muscles.3. It may be caused by a herniated lumbar disc, which in addition to lumbar discomfort can also cause nerve pulling pain or soreness and numbness in the buttocks, thighs or calves.