The sudden appearance of soreness, swelling and pain on the left side of the waist is mainly due to two reasons: First, due to the waist to maintain a posture for too long, such as sedentary, standing, squatting and continuous bending state, which can easily lead to strain on the muscles of the waist. If the left side is exerted for a long time, the strain on the muscles of the lumbar area will easily cause symptoms of soreness, swelling and pain on the left side, which is due to local inflammation and metabolic products such as lactic acid, which stimulate the peripheral nerves and cause related symptoms. This is due to local inflammation and metabolic products such as lactic acid, which stimulate the peripheral nerves and cause symptoms.