1.Motion chain: Several links of the human body are connected in a certain order by means of joints, called the movement chain on the human body, the upper limb by the shoulder girdle, upper arm, elbow joint, forearm, wrist joint, hand, etc. to form the upper limb movement chain; the lower limb by the hip joint, thigh, knee joint, calf, ankle joint, foot, etc. to form the lower limb movement chain. 2.Open and closed chain movement: People usually regard one side of the upper and lower limbs as a long chain, each joint are the chain buckle. If the proximal end is fixed, the distal end is free that is open chain, then you can move a single joint or move a number of joints at the same time. Quadriceps chair training and biceps training with dumbbells are typical examples. Conversely, the distal end is closed, such as contact with the floor, wall or table, and the proximal end (torso) moves, which can be called a closed chain. The limb movements that can be done at this time can only be coordinated multi-joint activities. Such as squatting must be simultaneously active hip, knee and ankle joints, it is impossible to make a single joint activities; two upper limbs propped up on the ground for the push-up movement, can only be simultaneously active wrist, elbow, and shoulder joints, and it is not possible to move a single joint. Cycling training is also a typical example. In post-neurological rehabilitation, closed chain exercises are generally chosen to emphasize multi-joint synergy. However, if there is a single muscle that requires special emphasis for independent training, open chain exercises are chosen. Often the iliopsoas muscle is the weak link and may require open-chain movement training.3. Open-chain movement: refers to movements in which the proximal end of the limb is fixed while the distal joint moves, such as the swing phase during walking. The open chain movement is characterized by the specific range of motion of each joint chain, with the distal end having a greater range of motion than the proximal end and a faster speed than the proximal end. In the training of strengthening muscle strength, the training of muscle explosive power should choose open chain movement training. 4, closed chain movement: refers to the movement of the distal end of the limb fixed while the proximal joint activity, such as walking when the support phase. Closed chain actually converts the rotational movement of open chain into linear movement, so the movement does not increase the tangential force of the joint, which can increase the protective effect and is closer to functional rehabilitation. For certain disorders such as anterior cruciate ligament (ACL) reconstruction or laxity of the joint, it can provide an early, safe and effective means of rehabilitation. After understanding the difference between open and closed chain exercises, how can we apply them in physical training? Because open chain exercise can train a certain muscle in isolation, it is more suitable for beginners with weak muscle control ability; while closed chain exercise involves more muscles and joints, which naturally requires more muscle strength and nerve recruitment control for trainers. It is more suitable for intermediate and advanced level trainers with certain training experience. In open chain exercise, the distal limb or torso is free, that is, the distal limb (foot or hand) is free to move in space without bearing its own weight, which rarely exists in competitive sports, however, for professional athletes, closed chain exercise can be analogous to the real game, more functional, for example, basketball players need to enhance the strength of the quadriceps in order to improve bounce, barbell Squats are more effective than seated leg extensions, and basketball players will always jump from a standing position rather than a seated one, so closed chain exercises are the main choice of exercise for professional athletes. Through the above introduction, we can know that whether closed chain exercise or open chain exercise, they have their own characteristics and role, according to the characteristics of the exercise open chain exercise in the target and isolation training target muscle application more, while the closed chain exercise in the rehabilitation and functional training application more. But in the training of the choice of open chain or closed chain movement, or according to the level of the member and training purposes to choose the most suitable for his training movements.