Research has shown that 1 in 30 passengers on a long-haul flight are at risk of Deep Vein Thrombosis (DVT). The use of Lifesystems graduated compression flight socks can improve circulation, relieving discomfort & helping to prevent circulatory problems such as Deep Vein Thrombosis (DVT). Your ankle has little muscle in it & requires more stimulus than your calf to speed up circulation. The knee length socks provide graduated compression to stimulate blood flow.