On Thursday nights (work permitting!) we try to make it to Central Park for our weekly running class with New York Road Runners. It’s intense and often reminds me of high school track—lots of drills and exercises, always pushing us to our max.

Each week is a surprise—sprints? hills? half-mile intervals? Each week we push ourselves further than we would have on our own. Each week we run until we feel like we can’t go anymore, and then we run a little more.

I’m always dead last in this class (not an exaggeration), but I never regret going. Through the pain and heaving breathing, I know I’m getting a little stronger and a little faster. I know my heart is becoming more efficient at pumping oxygen through my body, and that my body is making new veins and clearing the clots in the old.

But what I hadn’t realized until recently is that although running is saving my life, long-distance running can also increases your odds of blood clots.

When most people think of deep vein thrombosis (DVT or blood clots), they picture the elderly or overweight. It’s hard to imagine the young or active getting sick or suddenly dying.

But what about tennis star Serena Williams (29 years)? Hockey player Adam McQuaid (26 years)? Professional golfer Joey Sindelair (51 years)? They all had blood clots and pulmonary embolisms and are lucky to be alive today.

Blood clots can happen to anyone. That’s why it’s important to know the risk factors and warning signs so you can avoid a clot yourself.

In fact, the English National Football Team takes this issue so seriously that for the last two World Cup games, the players have been fitted with compression stockings for their flights.

What many people don’t realize is that runners and other endurance athletes (and not just professionals!) are particularly prone to getting DVT. Although they combat some of the risk factors by being active and in generally good health, according to AirHealth.org, 85% of air travel DVT victims are athletic, endurance athletes like marathoners. 83% of athlete victims on planes are under 60 years.

So why is this? Endurance runners and athletes have their own set of risk factors in addition to those that apply generally.*

1. Dehydration. Prolonged periods of exercise can lead to dehydration, which leads to thicker blood. When your blood is thicker, it is more likely to clot. Caffeine and alcohol are also diuretics that can in turn thicken your blood.
   
2. Lower Heart Rate. A lower heart rate means your blood is moving through your body at a slower rate. When your blood moves slowly, it is more likely to clot.
   
3. Soreness and Injury. When your body experiences trauma, it may begin to form a clot at the site. Additionally, if you break a bone or strain a muscle, you may be required to wear a brace or a cast—these limit your mobility, and increase your chance of clotting.
4. Travel. Many athletes travel for games and races. If you travel long distances and are immobile in a car or plane, your blood can pool in your legs and form a clot.
5. Physical Abnormalities. There are also some physiological abnormalities that compress one of the deep veins and with repeated trauma/use, can eventually lead to a DVT. See more about Thoracic Outlet Obstruction for DVT in the arm, or May-Thurner Syndrome for DVT in the left leg. 

So what can you do?

Stay HYDRATED. 

Stay ACTIVE. 

Wear COMPRESSION STOCKINGS on planes.

LISTEN to your body. If something feels off, see your physician.

*There are other risk factors that may apply, but there have not been enough studies to determine their significance and/or correlation.