If you’re sitting still for more than four hours, it’s possible for blood clots to form in your legs. Serious clots are rare, but can be life threatening, so it's recommended that anybody who takes long flights (or car rides) over four hours should know how to reduce their risk.
What’s the problem?
Your heart pumps blood through your body, but then the action of your muscles is partly responsible for squeezing that blood back toward the heart. Normally, that’s no problem — as we walk around, or even fidget in our seats, the blood keep moving.
But if your muscles are still for hours on end—for example, you spend a flight sleeping with your legs crossed, blood flow can be reduced enough that a clot forms in the veins that are deep inside your leg muscles. This is known as a deep vein thrombosis. The clot may dissolve on its own over time, but if not, it can potentially break loose and cause a pulmonary embolism (a dangerous condition involving blood clots in the lungs).
Before you fly
If you’re at risk for developing blood clots, check with a doctor before a long flight. Risk factors include:
If you’ve had a clot before
Hormone replacement therapy, or estrogen-containing birth control pills
Recent surgery, injury, or having a body part immobilised (for example, if your leg is in a cast)
If you’ve been pregnant in the last 3 months
Varicose veins, obesity, and being over 40
Many of these things are very normal and, like we said, clots are rare. But if you have several risk factors, or if you’re just worried about the situation, talk to your doctor. Some people who are at risk of clots may need to be on blood thinners. But unless you’re at very high risk, you’ll likely just get a recommendation to wear compression stockings and/or to keep moving during the flight.
How to keep moving
Get up and walk around. Hey, it’s a long flight, so even if you’re in the middle seat your seatmates are going to expect you to need the bathroom at some point, so it’s definitely ok to get up. Walk up and down the aisle, and do some calf raises by standing on your tiptoes and lowering back down.
In your seat, take a break every now and then to stretch or move your body, including your legs. (The calves are an especially common place for clots to form.) Flex and extend your ankles, and try hugging your knee to your chest if space allows. Here’s a 10-minute aeroplane seat workout — on a long flight, set a reminder on your phone to do it every few hours.
Know the signs of a blood clot
During the flight and for the next few days, don’t ignore any calf pain, especially if it’s accompanied by redness or swelling. If you also develop a cough or shortness of breath, get checked out right away.