Sinking legs and feeling tired may be caused by long-term strain, varicose veins of the lower limbs, thromboembolic vasculitis and other reasons. 1. Long-term strain: Long-term or high-intensity use of the legs, such as standing for a long time, weight-bearing exercise, marathon, etc., resulting in swelling, congestion and exudation of the leg muscles, fascia, joint capsule and other tissues, resulting in pain, soreness, swelling, fatigue and other symptoms of the legs. 2. Varicose veins of lower limbs: congenital weakness of superficial vein wall, poor structure and function of venous valves cause obstruction of venous return in lower limbs, causing venous blood pooling in blood vessels and earthworm-like bulging. It can produce symptoms such as leg soreness, heavy fatigue, mild edema, calf muscle spasm, etc. Inflammation can have ulcers, bleeding and other manifestations. 3. Thromboembolic vasculitis: also known as “Buerger’s disease”, mainly in the distal limbs of the middle and small arteries and veins, is a chronic, segmental, periodic attacks of vascular inflammatory lesions. It is a chronic, segmental, cyclic vasculitis lesion with pain, lowered skin temperature of the affected limbs, soreness, fatigue, numbness, etc. Typical manifestations are intermittent claudication, with a long duration of the disease, which can be recurring. Sinking legs and feeling tired may also be caused by lumbar disc herniation and other diseases, it is recommended to consult a doctor for a clear diagnosis and targeted treatment under the guidance of the doctor.