Patient Education Blog

Athletes and Blood Clots

Many people think of blood clots as a problem occurring in elderly people, but not in young and apparently healthy individuals. While it is true that clots occur more commonly in the elderly and in non-athletic overweight individuals, they can, nevertheless, happen in young, normal weight, and athletic people.

How Commonly do Blood Clots Occur in Athletes?

No studies have determined whether athletes are at increased, the same, or lower risk for developing DVT and PE than non-athletes of same age.

Why do Athletes Clot

There are several mechanisms whereby an athlete may become at “higher risk” for development of a clot. For example, blood clots can occur when:

  1. there is a disparity between the two systems that balance the clotting process in our blood; either (A) too much activity of the proteins and blood platelets that form clots (the procoagulant system), or (B) too little activity of the system that dissolves blood clots as they form (the fibrinolytic system);
  2. there is trauma to the blood vessel wall, as may occur after a bone fracture or in thoracic outlet obstruction (see discussion below);
  3. blood return from the extremities to the heart is impaired, such as when sitting with bent legs in cramped positions for a prolonged period of time;
  4. the blood is “thicker” than usual, as occurs when an athlete is dehydrated, using the drug erythropoietin (EPO), or has received excessive blood transfusions (blood doping).

Unfortunately, there are few studies investigating the influence that physical training has on blood clot formation and dissolution.  So, the exact net effect of training on this equilibrium is unknown. It is known, for example, that blood levels of the clotting protein “factor VIII” increase with exercise and that the elevation persists during recovery. Theoretically, this could lead to an increased risk of blood clots in athletes. However, data also indicate that the fibrinolytic system that dissolves blood clots is overactive in people who exercise.  With this overactivity present, the athlete would be protected from having a blood clot. Yet, the net effect of these changes in the athlete is not known. A detailed scientific discussion of the coagulation issues relevant to exercise and training can be found in a medical review publication [ref 1]. However, the conclusions are sparse and vague, because of a lack of data and conflicting results from different studies.

Risk Factors for DVT and PE in the Athlete

  1. General risk factors: The athlete is at risk for DVT and PE for the same reasons as non-athletes. Risk factors, with particular focus on the athlete, are listed in Table 2. Risk factors for the athlete. A few unique risk factors for DVTs that play a role mostly in the young and the athlete are:
  2. Thoracic Outlet Obstruction
    In some individuals an extra (cervical) rib or excess muscle or tendon tissue compresses the big vein in the upper chest (subclavian vein) that drains the blood from the arm (see image 1 – red area reflects clot, i.e. DVT in the subclavian vein).  This compression typically gets worse when the arm is lifted up. This obstruction, often combined with repeated trauma to the vein (due to throwing activities or gymnastics maneuvers), may cause a DVT to form in this area, extending into the arm veins. This is termed “effort thrombosis” or “thoracic outlet obstruction/syndrome.” If the DVT resolves, such as after clot buster treatment, resection of the extra rib or the excess tissue may be indicated to increase space in the thoracic outlet.

    Image 1. Effort Thrombosis (aka thoracic outlet syndrome). Graphic design: Jeff Harrison, Wilmington, NC. Copyright: Stephan Moll

  3. May-Thurner Syndrome (read a detailed discussion here) This is a common congenital anatomic variation that predisposes to DVT in the left leg, because the main left pelvic vein is compressed by the overlying main right pelvic artery. This increases the risk of clot formation at the site of this narrowing in the left pelvis with extension of clot down into the left leg.

  4. Congenital Absence or Malformation of the Vena Cava
    Congenital abnormalities of the anatomy of the big vein in the abdomen (vena cava) or pelvic veins can be a cause of DVT in young people. The abnormal anatomy probably leads to disturbed blood flow and an increased risk of clotting.

Misdiagnosis of DVT and PE

If an athlete develops symptoms of DVT (deep vein thrombosis) or PE (pulmonary embolism) (Table 1. Symptoms), the diagnosis may be delayed or missed because the athlete is typically young and healthy. And blood clots in young and healthy people are uncommon. In addition, the athlete is considered to be particularly healthy. Symptoms may, therefore, be misinterpreted as something less serious: in the case of leg DVT as “muscle tear”, “Charley horse”, “twisted ankle”, or “shin splints”; and in the case of PE as a “pulled muscle”, “costochondritis”, “bronchitis”, a “touch of pneumonia”, or “new onset of asthma”. Of course, such misdiagnosis occurs in non-athletes as well.

Treatment of DVT and PE

Treatment decisions for people affected with blood clots must always be individualized. Such individual treatment regime is particularly true for young, apparently healthy individuals, such as athletes. In the case of unexplained DVT, testing for an inherited or acquired clotting disorder (thrombophilia) may be appropriate. When first diagnosed with the DVT, clot buster medication (fibrinolytic therapy) can be considered to quickly dissolve the clot. However, clot buster treatment has not been systematically studied to determine whether it really decreases the risk for long-term damage to the leg and arm veins, i.e. the postthrombotic syndrome. A clinical trial, the ATTRACT trial, is presently ongoing (details here). A major question for any patient with DVT or PE is how long “blood thinners” (typically warfarin or Xarelto) should be given. This decision needs to take all risk factors that caused the clot into consideration, as well as all the implication for the person to be on a “blood thinner”. It can be a very difficult decision, particularly since a number of sports, particularly the very competitive ones, cannot be continued as long as the person is on the “blood thinner”.


Athlete-Specific Challenges and Questions

Often, an active individual – be it an athlete or one who remains physically fit through routine training and exercise – is suddenly thrown of his/her path by the clotting incident.  Questions, lot of questions, are poised to the health care professional.  Sometimes, those questions are never asked, as the affected individual remains perplexed by what may or may not be his/her limitations. Here are a few of questions with general responses that an athlete may find helpful.

  1. Can I continue my sport while on blood thinners?
    A solid medical assessment should be made whether the person who has had a blood clot can come off “blood thinners” (typically warfarin or Xarelto) or should remain on them. Being on a blood thinner increases the risk of bleeding. Therefore, contact sports and sports with a risk for serious injury, such as football, hockey, basketball, soccer, gymnastics, alpine skiing, or boxing should not be pursued by a person on blood thinners. However, athletes such as runners, bicyclists or triathletes may be able to continue their sport, but they should adapt their activities to avoid trauma that might put them at risk for bleeding (i.e from such things as bicycle crashes). Xarelto has the advantage over warfarin of (a) being out of the system quicker once the drug is stopped (within 1 1/2 to 2 days  for Xarelto versus approximately 5 days with warfarin), and (b) being fully active again three hours after intake (warfarin takes 5 days after restart to reach its full blood thinning effect. This quick on-and-off of Xarelto allows the consideration of stopping Xarelto for athletic performances that put a person at risk for bleeding, and restarting soon afterwards, if no significant trauma occured. This can be listed as one of the reasons that makes Xarelto a more attractive blood thinner for some athletes than warfarin. Other individual blood thinning treatment plans can also be designed, such as (a) a decrease in warfarin dose a few days prior to athletic events that might put the person at less risk for bleeding, (b) stopping “blood thinner” during the athletic season and accepting a higher risk for blood clots during that time, but restarting the “blood thinner” during the off season. Finally, an athlete may decide to switch from a high risk bleeding competitive sport to one with a lower risk. Obviously, these are all very individual treatment decisions that should be thoroughly discussed between the patient’s personal physician, a thrombosis specialist, the patient, and the team physician (if the patient is participating in a team sport).
  2. How soon after a DVT or PE can I go back to training?
    Patients with a DVT may have significant extremity swelling and pain which may improve only slowly over weeks and months. Some residual symptoms may persist long-term. This is termed “postthrombotic syndrome”. It appears that being highly active one month after a DVT is not detrimental; it may, actually be beneficial and lead to less symptoms of postthrombotic syndrome [ref 2]. This can be used as an argument to encourage individuals to return to physical activity relatively soon after a DVT. No official guidelines exist as to when and how quickly an athlete might return to exercising. Each patient will need an individualized exercise plan (an example is described in reference 3). It seems appropriate to refrain from any athletic activities for the first 10-14 after an acute DVT or PE until the clot is more attached to the blood vessel wall and the risk of having the clot break loose (causing a PE) has decreased. To lessen deconditioning during this period of relative inactivity, the athlete may do some strength training – arm and trunk exercises in the case of a leg DVT, leg and trunk exercises in the case of an arm DVT. The athlete may then increase activity between week 2 and 4 and return to pre-clot activity levels by week 4.
  3. Psychosocial Implications
    Athletes need to appreciate that significant deconditioning can occur after a DVT or PE. Depression can also set in after such a life-changing event. This is not surprising, given that athletes often view themselves as healthy and, from a health point of view, invincible, and now suddenly realize that they are vulnerable, sick, and sometimes even disabled. Patient support structures, including connecting with other athletes who have faced DVTs and PEs may be helpful in this situation. Also, antidepressants are sometimes indicated in this situation.


How to minimize the risk for clots

Measures that the athlete (and non-athlete) should take to minimize the risk for DVT or PE are listed in Table 3. How to prevent clots. For the athlete, the most important ones may be to (a) avoid dehydration, and (b) take breaks when traveling long distances.



  1. El-Sayed MS et al: Exercise and training effects on blood haemostasis in health and disease: an update. Sports Med 2004;34(3):181-200.
  2. Shrier I, Kahn SR: Effect of physical activity after recent deep venous thrombosis: a cohort study. Medicine and Science in Sports and Exercise 2005;37: 630-634.
  3. Roberts WO, Christie DM: Return to training and competition after deep venous calf thrombosis. Medicine and Science in Sports and Exercise 1992;24:2-5.


Authors: This blog was written by Dr. Stephan Moll. Input was also provided by Dr. William Roberts and Dr. Edward Libby.


Disclosure: I have consulted for Janssen.

Last updated: March 16th, 2013

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9 Responses to “Athletes and Blood Clots”

  1. Renee says:

    What do you think of ressection of the first rib (not an extra rib) versus physical therapy for TOS related DVTs in a swimmer?

    • Stephan Moll says:

      Arm DVT – risk factors, diagnosis, management – will be discussed in detail in a future blog entry. Here in short: There are 2 potential reasons to consider “thoracic outlet surgery” (resection of the first rib): (1) if a patient has persistent, marked symtpoms of postthrombotic sydnrome of the arm, i.e. marked swelling or pain – that’s a failry solid reason. (2) Another reason, much less solid, is that one could contemplate the surgery to potentially decrease the risk of a recurrent (2nd clot), if there is impingement on the subclavian vein from the surrounding structures. However, there are no good clinical trials that have investigted whether such surgery truly decreases the risk of recurrent DVT. Thus, one should think hard whether this surgery is really warranted. If it is done, then it should be done in a very experienced center. It is very rare that I send a patient with arm DVT to have this surgery done.

      Reference: Kucher N. Deep Vein Thrombosis of the Upper Extremities. N Engl J Med 2011;364:861-869.

  2. Kim says:

    Does anyone know how blood thinners (Lovenox in particular) can effect an athlete’s performance? Such as VO2 max levels and efficiency of exercise compared to someone not on blood thinners?

    • Stephan Moll says:

      Blood thinners have no known effect on athletic performance with respect to VO2 max. Of course, blood thinners do potentially restrict activity in contact, collision types of activity as the risk of internal bleeding is increased.

  3. kerrie johnson says:

    Im running the london marathon in april 2012, i have thrombophilia but im not on any blood thinners, do i need to take blood thinners before i race or after i race. As im not sure if running the 23 miles would make me get a blood clot . Is there anything special i should do?

    • Stephan Moll says:

      a) “Do I need to take blood thinners before I race or after I race?” This is a data free zone, i.e. there are a number of unknowns. It is not known whether the risk for clots is increased with (a) racing (marathon running, for example), (b) dehydration. In addition, I do not know the details of this person’s medical history. However, very likely I would NOT recommend any blood thinners before or after a race, but just the usual precautions: (a) avoid dehydration, (b) when travelling to and from the event, long distance by care and train or plane, take breaks every so often to strecth the legs.

      b) “Is there anything special I should do?”. Discussed above. Plus: Consider purchasing one of our unique Clot Connect athletes’ running shirts and wearing it (as an awareness campaign or fundraiser) during the London marathon.

  4. Duncan Broatch says:

    Hello, I’m wondering if you have any suggestions regarding my “dilemma”! I am a healthy, athletic 57 year old male on Pradaxa since October due to a “small” stroke and occasional afib heartbeats.
    The dilemma is that my lifestyle has been disrupted to the point of mild depression because, with suggestions from family and Doctor, I am not able to participate in the contact-type sports that I have always enjoyed: off road motorcycling, mountain biking and skiing. Of course the fear is that I may crash then die from uncontrollable internal bleeding.
    On Wednesday I see my Cardiologist (first appointment since being prescribed Pradaxa last October) and I’m preparing information and questions to present. I have read all related subjects on this site – lots of good info. Should I consider switching to Xarelto since it may be easier to reverse? Any other suggestions? Thanks.

    • Stephan Moll says:

      Xarelto is not easier to reverse than Pradaxa. With both drugs we do not have a reversal agent, a reversal strategy, nor any published data (other than suggestions) on the management of patients who had major bleeding on these drugs. All the data available stem from animal data (mice bleeding model; rat tail bleeding tests), ex vivo test tube mixing studies, or a human volunteer study. Thus, I would view Xarelto and Pradaxa regarding our lack of knowledge how to deal with bleeding similarly.