After sitting for a long time, if there is swelling and stiffness in the calves, it is mostly due to two reasons: first, poor venous reflux in the legs; second, pressure on the blood vessels of the legs. For example, there is venous thrombosis in the legs, varicose veins in the lower limbs or incomplete closure of the venous valves in the lower limbs. This condition will cause bruising and swelling in the legs after prolonged sitting, and will lead to muscle spasm after intermuscular vein stasis, resulting in stiffness of the muscles in the calf area. If the veins in the back of the leg are compressed after prolonged sitting, especially in the popliteal fossa, which is the back side of the knee joint. If squeezed, it is easy to cause compression of the blood vessels inside the popliteal fossa, which causes blood flow disorders and leads to significant bruising, edema and muscle stiffness in the calf area.