Why should I practice knee flexion after knee surgery? Patients who have undergone knee surgery, especially knee replacement surgery and ligament reconstruction surgery, are instructed by their surgeon to perform functional exercises with knee flexion after surgery. The exercises are often painful and painful, so why must the doctor advise the patient to flex the knee and reach a certain angle? The reason is that we need a certain angle of knee flexion in order to regain a healthy life and perform most of the functions of daily living. Generally speaking, the human body needs knee flexion mobility of 67° to walk normally, 83° to complete stair climbing, 90° to walk down stairs, 105° to stand from a seat, and 115° to rise from a couch. Therefore, a minimum of 110° of knee flexion is required to pass the majority of daily life after knee surgery.