Muscle soreness the day after fitness is a particularly common phenomenon, resulting in muscle soreness for two main reasons: one, after fitness leads to mild muscle damage, as muscle cells have mild damage, eventually after repair will lead to muscle hypertrophy, when the muscle damage will lead to soreness symptoms. Second, the fitness will lead to a large accumulation of lactic acid in the muscle, lactic acid accumulation stimulates the nerve will trigger soreness symptoms. If you want to make the soreness subside quickly, you should do proper muscle stretching for the sore parts, and you can do local hot compresses or microwave physical therapy to promote muscle repair and lactic acid discharge.