After a knee injury, activity restriction measures are often taken due to local swelling, pain, and instability. However, prolonged braking often brings about complications such as joint stiffness, muscle atrophy, and traumatic arthritis. According to the specific injury, functional exercise under the guidance of a doctor can gradually improve the function of the knee joint and effectively avoid complications. 1, quadriceps isometric contraction exercises The quadriceps is a muscle group in the front of the thigh, which has an important role in knee extension and stability. Isometric contraction means that only the muscles are tense and the joint is not active. Quadriceps isometric exercises are the most commonly used muscle strength exercises for knee injuries and early post-surgery, to maintain muscle tone and maintain or increase muscle strength. How to do it: Tense the thigh muscles with as much force as possible for 5 seconds and then relax to count 1 time. Do 50-100 times per hour, and strive to reach 1000 times per day. For best results, do isometric contraction exercises for the quadriceps muscles of both legs at the same time. After completing static quadriceps isometric contraction exercises, you can start straight leg raise anti-gravity contraction exercises to further strengthen the quadriceps muscles. After a knee injury, activity restriction measures are often taken due to local swelling, pain, and instability. However, prolonged braking often brings about complications such as joint stiffness, muscle atrophy, and traumatic arthritis. According to the specific injury, functional exercise under the guidance of a doctor can gradually improve the function of the knee joint and effectively avoid complications. Wang Fang, Department of Orthopedics, Shanghai First People’s Hospital, Shanghai, China Quadriceps isometric contraction exercises Quadriceps is a muscle group in the front of the thigh that plays an important role in knee extension and stability. Isometric contraction means that only the muscle is tensed and the joint is not moving. Quadriceps isometric exercises are the most commonly used muscle strength exercises for knee injuries and early post-surgery, to maintain muscle tone and maintain or increase muscle strength. How to do it: Tense the thigh muscles with as much force as possible for 5 seconds and then relax to count 1 time. Do 50-100 times per hour, and strive to reach 1000 times per day. For best results, do isometric contraction exercises for the quadriceps muscles of both legs at the same time. After completing the static quadriceps isometric contraction exercises, you can start the straight leg raise anti-gravity contraction exercises to further strengthen the quadriceps muscle strength. 2, knee flexion and extension exercises Early start knee flexion and extension exercises are very important to avoid intra-articular adhesions and restore knee mobility. Specific methods: Knee extension exercises (leg compression exercises): lying down, heel on a cushion of about 750px, their own or others hands on the distal end of the thigh, evenly and continuously press hard to the back of the knee joint when there is a pulling sensation and pain to maintain 3min, alternating between the two legs, 5 times a day. Exercises for knee flexion (bedside leg drop): sit on a high enough stool or bedside with the healthy leg under the affected leg and hook the ankle of the affected leg with the foot underneath, that is, hold the affected leg with the healthy leg. The muscles of the affected leg are completely relaxed and the weight of the whole leg is put on the healthy leg. Then, slowly lower the leg with the strength of the healthy leg, the lower the leg, the greater the angle of knee flexion of the affected leg. After feeling significant pain, stop and hold still for 1-2 minutes as the tissues adapt and the pain may disappear or decrease, then lower the leg again. This method is suitable for flexion exercises within 0-90°. 3, resistance quadriceps exercise In the knee mobility improvement, quadriceps muscle strength until a certain degree of recovery, you can start resistance quadriceps exercise, squatting exercises are the most common method, followed by walking, jumping, etc. to further strengthen the quadriceps muscle strength. The specific method: try to squat, while the heel does not leave the ground, adhere to 5-10 seconds and then slowly stand up.