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How To Prevent Blood Clots After Destination Races

It's true - flying right after a marathon does increase the risk of developing blood clots. Take these precautions to stay clot-free today!

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Reader Question: I like to do destination marathons, but I’ve heard hopping on a plane after a race can cause blood clots. Is this true? Should I stick to local races?


Answer: The short answer is yes—to your first question. Flying directly after running a marathon does increase your risk of developing blood clots. However, that doesn’t mean you should avoid far-away races completely. The best strategy is to be aware of the dangers and take steps to prevent them.

According to Dr. Brandon McMahon, hematologist at Northwestern Memorial Hospital, several factors increase a runner’s chances of developing a blood clot. “Because we often travel with our luggage at our feet, there is less room to move our legs during the  ight,” explains McMahon. He adds that dehydration and inflammation from the race, combined with the plane’s altitude changes, create a perfect storm for clot formation.

In fact, it’s quite common for athletes to develop blood clots. According to, 85 percent of air travel thrombosis victims are endurance athletes like marathoners. I know this all sounds scary, but the good news is that there are plenty of measures you can take to keep your legs healthy and clot-free. Next time you prepare for a destination race, use the following game plan:


-Schedule your flight home for more than 24 hours after the race.
-Book an aisle seat so you will have room to extend your legs.


-Walk for 10 minutes (don’t sit!) immediately after crossing the finish line.
-Take a cool bath to reduce inflammation.
-Eat small meals and sip fluids to replenish your energy and electrolytes.
-Avoid alcohol.


-Move on the plane! This is the most effective and important of all the strategies. Every 15 minutes, point and flex your feet 20 times. Get up each hour and walk in place, perform toe raises and leg extensions. You need to contract and release the calf muscles to increase blood flow to your lower legs and feet.
-Sit with your legs open, not crossed.
-Wear comfortable clothing to encourage movement and compression socks (if you have them) to reduce inflammation.
-Stow your bags in the overhead compartment to give your feet more room to move.

As always, the best tactic is to listen to your body. Last year, I developed a small but deep blood clot in my calf on a 10-hour flight home from Munich. I made a lot of mistakes. I was dehydrated, slept for hours, sat in the window seat with my legs crossed and didn’t move during the flight. I actually felt it mid-air and my gut told me it was a clot. The sensation resembled a Charlie Horse that hadn’t seized, and the dull pain stayed there for days.

I was treated with aspirin because the clot was small. But when I developed a second one later that fall on a four-hour flight from California, I visited a hematologist, and tests determined that I have two blood clotting disorders. I was fortunate neither clot broke off and traveled to my lungs.

Remember, be aware and move regularly. If a dull pain presents itself and persists, see a doctor immediately.

Know the Warning Signs

If you experience any of these symptoms, you could have a blood clot.

Signs and Symptoms

-Sensation of a muscle cramp that doesn’t let up

-Swelling in one leg

-Bruising or tenderness in lower leg or behind the knee

-Warm feeling in a particular area that may worsen when standing or walking


Jenny Hadfield is the co-author of Running for Mortals and Marathoning for Mortals. You can find more of her training programs, tips and running classes at