In the absence of exercise at ordinary times, do some exercise beyond your physical load. In order to provide the energy you need for exercise, the muscle cells in your waist will do anaerobic breathing and release a lot of lactic acid, so you feel backache, and lactic acid will slowly decompose and recover in a few days. If you want to hurry, apply a hot towel and massage gently. The solution is to exercise regularly, improve vital capacity and ensure physical strength.