Ever since the “first marathon” 2500 years ago in ancient Greece when Pheidippides completed his run to Athens and then died upon arrival, we worry about the chance of a catastrophic health event during intense competitions like marathons, triathlons and distance cycling. The most common cause of death during a race is unrecognized coronary artery disease, but there are also cases of thromboembolic incidents that can be fatal.
One study looked to answer the question of what happens to our blood coagulation system before and after a big race. So they analyzed the blood of 68 previously healthy males with no history of coagulopathy pre and post marathon, triathalon, and cycling, and demonstrated that whole blood coagulation is increased during heavy endurance sports.
They also saw that marathon runners have elevated platelet aggregation post race indicating that marathon runners might be at higher risk for thromboembolic incidents in otherwise healthy athletes compared to triathletes or cyclists.1 There are many published cases of athletes diagnosed with a deep venous thrombosis (DVT) or blood clot in the leg. One study reported a female triathlete who was diagnosed with DVT and pulmonary embolism after competing in a Half Ironman triathlon 4. The patient completed a triathlon and experienced symptoms of left lower extremity swelling and pain, accompanied thereafter by dyspnea and lightheadedness upon exertion the next day after driving five hours in her car. She was not properly diagnosed and treated until she visited the emergency department three weeks after the triathlon.
There are a few speculations as to why athletes might tend to form blood clots post race. Endurance athlete's experience repetitive microtrauma, vascular endothelial damage dehydration and a period of immobility directly post race.3 Platelets are activated and most adherent to white blood cells 30 minutes post exercise. As the athletes cools down there is a massive amount of inflammation that the body experiences from the trauma of a long run. Ensuring the athlete stays adequately hydrated and continues to move, the risk for a blood clot formation is low. But should an athlete immediately head to the airport and sit on a plane or drive in a car for many hours, a clot may form in the legs and spell trouble.2
Whole Blood CoagulatIon and Platelet activation in the Athlete: a Comparison. Marathon,Triathalon and Long DistanCE Cycling: Hanke1, a. staib1, K. görlinger2, M. Perrey1, d. dirkmann2, P. Kienbaum. Klinik für anästhesiologie, universitätsklinikum düsseldorf, germany,
Platelet Activation Through Triathlon Competition in Ultra-Endurance Trained Athletes: Impact of Thrombin and Plasmin Generation and Catecholamine Release. M. Möckel1 , N. V. Ulrich2 , G. Heller3 Jr. , L. Röcker4 , R. Hansen5 , H. Riess1 , H. Patscheke6 , T. Störk7 , U. Frei1 , A. Ruff
Ali MS, Kutty MS, Corea JR. Deep vein thrombosis in a jogger. Am J Sports Med 1984; 12(2):169.