USA Triathlon News Blogs Multisport Lab Triathlon Medical Co...

Triathlon Medical Corner: What You Need to Know About Blood Clots

By Dr. Robert Takla | April 28, 2020, 2 p.m. (ET)

blood clots triathletes

Athletes are perceived as healthy, active and mobile individuals. As triathletes, we do three activities - swim, bike and run.

Statistically, blood clots tend to occur with increased frequency in older, non-active, and less fit individuals. You wouldn't think of triathletes falling in this category. 

So how is it that some triathletes can get blood clots in their legs or lungs? And if you have a blood clot, can you train or race again?

The venous system is amazing in that it is able to remain in a fluid state to transport carbon dioxide from cells to the lungs while simultaneously being able to respond to a cut by activating proteins to form a clot, so we don’t bleed to death. This balance is tightly regulated. 

A blood clot occurs when the balance shifts and the proteins in the blood react inappropriately to create a clot without the veins being cut. When a clot occurs in one of the deep veins of the legs or the arms it is called a deep venous thrombosis (DVT). A clot in your lungs, called a pulmonary embolism (PE), can be dislodged from a DVT and transported to the lungs via the venous system or can develop spontaneously in the lungs. 

PEs are very serious and can be fatal. The incidence of PE/DVT depends on many risk factors, some that are modifiable, and some that we just have to accept such as genetic factors and increasing age. The mortality rate of a DVT/PE, collectively known as venous thromboembolism (VTE), is actually higher than that of HIV, car accidents, and breast cancer combined.

So what do we need to know?

We will describe some of the risk factors and highlight strategies to reduce your risk, recognize when to seek care, and discuss the latest treatment options. 

1. How can I prevent a VTE?
2. How can I recognize a VTE?
3. If I have one, how do I treat it?
4. If I have one, can I train and race again?

Let me start by answering the last question first. Yes, you can train and race with VTE. I have had two DVTs, and I still participate in triathlons and cycling events. Here is what you need to know.

A DVT often occurs in the setting of (1) injury, (2) immobility, and (3) in individuals prone to blood clotting more than normal (hypercoagulable). The more risk factors you have, the greater your risk of developing a VTE. If you develop a blood clot in your leg, it can embolize (dislodge and travel) to your lungs resulting in a pulmonary embolism.  

Training and racing keeps us mobile and decreases our risk for VTE. In fact, adaptation from endurance results in increased blood volume, so the blood flows easier unless we are dehydrated.  Unfortunately, at times we get injured which can increase our risks. Minor trauma is usually not significant, however in an individual who is otherwise predisposed, it may be sufficient to tip the balance and result in formation of a clot. 

Specific risk factors include:

  • Sport specific risk factors - trauma (injury and inflammation), increase in muscle size leading to popliteal entrapment.
  • Medical risk factors - being hospitalized, having hip or knee surgery, cancer, previous VTE ...and more
  • Age and Genetic predisposition - increased age, Several different blood protein deficiencies such as Factor V Leiden, Factor II mutation, Protein C/S deficiency, antiphospholipid syndrome, antithrombin deficiency...and more
  • Environmental/modifiable risk factors - Hydration status, immobilization with travel or recovery, oral contraceptives.

The key is to decrease your modifiable risks; stay mobile, stay well hydrated, and of course every triathlete loves their compression socks. 

Admittedly, it may be challenging to recognize if you have a blood clot. It is often misdiagnosed by the medical community.

As an athlete, you may presume you have pulled a muscle or have delayed onset muscle soreness. A few important key points are, if you notice one of your legs is swollen or red and/or more painful or larger than the other leg, you should see your physician.

A non-invasive simple ultrasound is the key test in determining if you have a blood clot in your leg. Your doctor may do a screening blood test first called a d-dimer but only if the risk of VTE is low.  A negative D-dimer in the right circumstance virtually eliminates the chance of a DVT. 

Similarly, if you suddenly become unexplainably short of breath, have rapid breathing, rapid heart rate, and/or feel faint especially in the setting with concern for a clot in your leg - you should seek medical attention right away to ensure you do not have a pulmonary embolism. You need to be vigilant because PEs can be missed by the physician because they don’t show up on x-ray.  If the clinical suspicion for a PE is high it is essential that the clinician obtain a special CT of the chest.

Treatment has come a long way. In the past, physicians used to prescribe an anti-coagulant (AKA- blood thinner) medication called warfarin or Coumadin. Warfarin was a huge problem because many different foods and medications can alter its effectiveness and thereby increase or decrease the amount of anti-coagulation which can result in a clot or a bleed (depending on which direction it is altered).  In addition, use of warfarin required frequent blood draws to determine if the level of anticoagulation was appropriate. 

Today, we have newer and safer shorter-acting options collectively known as DOACS, direct oral anticoagulants. You may have seen commercials on TV for Xarelto or Eliquis. Many professional athletes currently take these medications and continue to compete. Chris Bosh (NBA), Katie Hoff (Olympic swimmer), and Brian Vickers (NASCAR) have all taken Xarelto for DVT/PE.

These newer medications are much easier and generally safer to take than Coumadin. And within the last year a reversal agent for these medications now exists (Andexxa) which has further lowered the risk for athletes to participate in sports while anticoagulated. Fortunately, triathlon and cycling are not collision or contact sports (except that mass start at the swim sometimes). So, timing of your medication is important.

These newer medications act very quickly. They have peak concentrations in the blood within 2-4 hours after taking the pill, and they have a half-life of approximately 10-12 hours in individuals with good kidneys. They are mostly out of the system within 24-48 hours.

So one can reduce the risk of bleeding despite being anticoagulated by timing their DOAC strategically with their athletic event. I have completed numerous cycling and 70.3 and 140.6 triathlon events since 2013 while taking Xarelto.

Triathlon cycling does add an additional challenge to blood clots. Being in the aero position for a long time causes hip hyperflexion and can compresses the iliac vessels, which further decreases flow and may potentiate the development of DVT. And then, have you seen some of the calf muscles on these athletes? Hypertrophy of the gastrocnemius muscle may cause compression of popliteal vein), a condition called popliteal vein entrapment syndrome, which also results in decreased blood flow and predisposition to blood clot formation.

But triathlons are not for the weak of mind or body. Do not let these concerns stop you. We are much better equipped with knowledge, newer medications, and an active lifestyle.

Dr. Stephan Moll, division of Hematology-Oncology, at the University of North Carolina School of Medicine in Chapel Hill has an “Athletes and Blood Clot” program, where together with his sports medicine colleague, Dr. Josh Berkowitz, they see patients and develop individual plans for high level athletes. Based on information gained from personalized pharmacokinetic and pharmacodynamic studies they can personalize an anticoagulation plan specific for the athlete, particularly the one engaged in contact sports. By appropriately timing the dose of medication, they can allow athletes to participate when the concentration of the anticoagulant is minimal.   

Roland Varga is also a triathlete and advocate aiming to raise attention and education on blood clots. Though Roland himself has not had a clot, he has many close family and friends that are survivors and/or have the genetic predisposition. He runs a blog where he features more than 10 years of posts in which every month the personal story of blood clot survivor athlete is featured. These personal accounts cover a variety of issues focusing on how to these individuals were able to overcome the challenges of their very own blood clotting incident.

Find some inspiring stories here

If you see Roland, or one of the other athletes sporting a polka dot jersey, they may not have won king of the mountain, but they are raising awareness. His CLOT BUSTER efforts are associated with the National Blood Clot Alliance (NBCA)

We want to train and race. Even if you get a blood clot, you may still be able to return to the sport you enjoy. Newer medications make it safer and easier than ever. Minimizing your modifiable risk factors, recognizing when you may need to seek medical attention and if necessary, timing your anticoagulation strategically will allow you to remain active and enjoy cycling and triathlons for years to come.

If you have any personal questions you would like to send me, I will be happy to try and address. My contact information is

Robert Takla, MD, MBA

Medical director and Chair of Emergency Medicine

Ascension St John Detroit

email is

If you would like to reach Dr. Stephan Moll to make a clinic appointment, his contact is

Stephan Moll, MD

Professor of Medicine

University of North Carolina School of Medicine

Main Clinic: 984-974-2695; Main Clinic Fax: 984-974-2654

Triathlon Medical Corner Editor: Andrew Getzin, MD is the head team physician for USA triathlon.  He is a USAT level 1 coach, many year USAT age-group All-American and has qualified and competed in Kona.  He is a fellow of the American College of Sports Medicine.  Dr. Getzin is the medical director of Cayuga Medical Center Sports Medicine and Athletic Performance in Ithaca, NY, and the director of their shortness of breath in the athlete clinic,

Robert Takla, MD, MBA, FACEP is the Medical Director and Chair of Emergency Medicine for Ascension St John hospital in Detroit. He is a USA Triathlon and USA Cycling age-group athlete participating in numerous triathlons and cycling events. He is a fellow of the American College of Emergency Physicians and section member of Sports Medicine and lead physician and medical support for Stout multi-century ride across Michigan. Dr. Takla has a passion for the pursuit of physical, mental, and emotional health and fitness and helping others maximize their health and wellness goals


  • Rathburn S. Circulation 2009; 119(115)
  • Berkowitz J, Moll, S, American College of Cardiology Oct 19, 2016 expert analysis
  • Berkowitz J, Moll, S, Athletes and blood clots: individualized, intermittent anticoagulation management. Journal of Thrombosis and hemostasis, 15:1051-1054
  • Kean J et al – Deep vein thrombosis in a well-trained master cyclist, is it popliteal vein entrapment syndrome to blame? J Thromb Thrombolysis 2019, Feb; 47(2):310-304