The soreness of the concave area on both sides of the buttocks is mainly due to the strain of the gluteus maximus, gluteus medius, gluteus minimus and the posterior external rotators, such as the pear-shaped muscle, the upper and lower twin muscles, and the closed inner muscle, and is accompanied by cold, such as when lifting heavy objects or walking, which causes the muscle tissues on the posterior side of the buttocks to be in a state of tension and fatigue, and a strain will form after a long time, and this area As the area is susceptible to cold, local inflammation will accumulate and pain will be evident. In addition, the strain will produce more lactic acid, and the accumulation of lactic acid will lead to the feeling of soreness, and therefore the symptom of soreness will appear. There is also a case of hip arthritis, especially mild arthritis, where there is a small amount of joint fluid, and the inflammation stimulates the surrounding muscle tissue, which leads to muscle tissue tension and stimulation of peripheral circulation, which also leads to microvascular constriction, slowing down the local blood circulation and causing soreness.