There are many reasons for hamstring pain at the bend of the leg when squatting, and the common causes are hamstring injury, popliteal cyst, lumbar disc herniation and so on. 1. Hamstring injury: overstretching of the hamstring muscle, such as dancing, hurdles, squatting and other activities combining hip and knee flexion and extension, overstretching of the hamstring muscle, triggering strains. Acute hamstring strains with hamstring strain are usually accompanied by pain in the posterior thigh. 2. Popliteal cyst: trauma, wear and tear causes increased fluid and pressure in the knee joint, joint fluid enters the popliteal fossa to form a cyst, and pain and swelling in the posterior aspect of the knee joint occurs. Due to the compression of the cyst, the symptom of hamstring pain when squatting occurs. 3. Lumbar disc herniation: when the lumbar disc herniation compresses the nerves of the legs, the symptoms of the lower limbs will appear, manifested as numbness, swelling and pain in the lower limbs, sensation fading or pain in the lower limbs, such as walking difficulties, which is similar to the tendon pain. The tendon pain in the bend of the leg when squatting may also have other causes, such as knee arthritis, it is recommended to go to the hospital in a timely manner, improve the examination to clarify the cause of the disease, and then give targeted treatment or treatment.