When exercising, there is a “rattling” sound when you move your joints, which is also known as joint popping. Also, sometimes when walking or going up and down stairs, there is a sudden weakness in the knee joint and a feeling of wanting to kneel down, which is also known as the “weak leg” phenomenon. When these two conditions occur, many people are concerned about whether they have arthritis. Why does the knee joint pop under normal circumstances? There is a joint fluid that acts as a “lubricant” in the joints to prevent friction between the bones. This joint fluid is secreted by the synovial membrane and is constantly circulated and renewed during joint movement. For the average person, if there is a lack of movement and normal “squeezing”, the joint fluid in the joints will decrease, making the bones of the joints rub against each other and make a loud noise. Second, how to identify physiological and pathological joint popping joint popping? It can be divided into two categories: physiological and pathological, of which the characteristics of physiological joint popping are as follows: 1, only occurs when the joint is suddenly pulled or flexed; 2, the joint must have a certain period of rest before the popping; 3, the sound is crisp, single, not repeated; 4, not accompanied by pain or discomfort, and often a sense of relief after the popping. These four points are the key to identifying physiological joint popping and differentiating it from pathological joint popping. If the ringing does not meet any of the above points, then it is pathological ringing. Generally speaking, if there is only ringing, no redness or swelling, and no pain, this is a physiological ringing, which is normal and does not require special treatment. If the ringing is accompanied by painful symptoms, if it occurs in the knee joint, it is most likely osteoarthritis, which mostly occurs in the elderly. For people over 60 years of age, if the knee joint is rattling and painful with a little movement, arthritis is most likely; if the knee joint is rattling and accompanied by strangulation (stuck), it may be meniscal injury, synovial crepitus syndrome, synovial chondromatosis, etc.; if the joint is rattling and movement is limited, this may be joint adhesions. If the swelling of the joint does not go down after a fall, dislocation or fracture, and the limb does not move for a long time, joint adhesions are likely to occur, and the main clinical manifestations are impaired joint flexion and extension activities. Why does the phenomenon of “limp” occur? Generally speaking, there are several reasons for the “limp leg” phenomenon: 1. Insufficient strength of the quadriceps muscle, resulting in a “lack of power” in the knee extension device. 2, “synovial crease syndrome”, the crease in the knee joint movement embedded in the patellofemoral joint between the pain, and the “weak leg” 3, “chondromalacia patella”, degeneration of the patella When the knee joint flexes and extends, the patella slides in the femoral carriage, and the excessive pressure stimulates the degenerated cartilage surface to produce pain, resulting in a “soft retreat”. 4, “knee osteoarthritis”, we have talked about osteoarthritis is a chronic joint disease characterized by degeneration and destruction of articular cartilage and osteophytes. Extensive cartilage degeneration increases friction during joint movement, which in turn stimulates the degenerated cartilage, producing pain and “playing soft leg”. In summary, the lack of quadriceps strength is the kinetic cause of the “flaccid leg” phenomenon and can be eliminated through exercise. Then, it is especially important to systematically standardize the strength of the quadriceps muscle exercise. Four, quadriceps how to practice? 1, contraction exercises: supine position, a slightly thick towel roll under the knee; do knee extension, hold for 5 to 8 seconds, relax. 2, resistance exercises: sitting position, back straight; calf end tied a sandbag of about 1kg, do knee extension, hold for 5-8 seconds, relax. Exercise at 30 degrees, 60 degrees and 90 degrees respectively.