This is called delayed muscle soreness, and the exact reason cannot be given in sports medicine, but there are many hypotheses, such as accumulation of metabolites, local inflammation, slight injury of muscle structure and so on. Although we don't know the specific cause of the problem, we can be sure that it is usually caused by an overload training, which generally lasts for 3~7 days and reaches the peak of pain in 48 ~72 hours. So your symptoms are typical. Delayed muscle soreness can be effectively avoided through reasonable training arrangement, long-term persistence in training, full warm-up and comprehensive relaxation. If you have pain after training, you can use nutrition supplement, hot and cold water bath, massage, traction, myofascial relaxation, etc., but its effect is not easy to measure. First of all, eating (protein) and sleeping (8 hours) should ensure the gradual pace of squatting for two days, which should not be a big problem. If you want to help you recover, wash your thighs with cold water (ice water) or apply cold compress after squatting. Don't take a hot bath right away. You can wash it alternately the next day. As we all know, squat is the trump card for practicing thighs. Squat is an action that requires great lung capacity and a strong heart. The standard of squat is to keep the back straight, the hip joint is lower than the knee joint, and the knee joint should not exceed the toes. Incorrect technical movements can damage the knee joint. Weight-bearing squat, also known as full weight-bearing squat, is one of the most complicated movements in bodybuilding, and it is also an action of strength lifting competition. "Squat with load" has a strong stimulation to the whole lower limbs and trunk, and can exercise quadriceps femoris (rectus femoris, midthigh, lateral thigh and medial thigh), gluteus maximus, biceps femoris, semitendinosus and semimembranous muscle, and also has a strong effect on erector spinae, piriformis, adductor, gluteus medius, gluteus minimus and calf muscle. In addition, "weight-bearing squat" has a positive impact on a series of physiological and biochemical reactions such as cardiopulmonary function, nerve regulation and hormone secretion, so practicing "weight-bearing squat" is a compulsory course for professional athletes and amateur bodybuilders.