When a patient squats, the knee becomes sore because the knee joint is flexed during squatting, which increases the pressure in the knee joint, causing strain on the muscles around the knee joint, or on the meniscus and synovial membrane in the joint, resulting in soreness, tenderness, and pain in the knee. The patient’s knee may also become sore when squatting, causing the quadriceps muscles to contract under tension, which produces a large amount of inflammatory factors in the muscles. Patients with osteoarthritis of the knee joint and localized osteoporosis can experience this. Therefore, the patient should be instructed to minimize the squatting movement of the knee, to rest in bed, or to perform proper rehabilitation exercises in the knee area to reduce the occurrence of this phenomenon.