This time my flight was preceded by a very strenuous walk 36 hours before. I figured I'd get in my exercise before a full day of travel. But I overdid it. I underestimated the irregularity of the 2000 foot downhill trail from the summit. It was so strenuous that I had quadriceps pain that limited a normal gait. But I figured I'd have the next 2 days to recover and then get back to my biking. 36 hours after the flight I developed unilateral calf pain from a DVT.

Doing a little research, I found this was a high risk combination - extreme exercise followed by a long (> 4 hour) flight/car trip. If you are a triathlete or run marathons you should take note. I'm not sure about century+ bike rides but that probably adds a little risk as well.

Strenuous exercise increase both the clot forming as well as the blood clot "busting" (fibrinolytic) arms of the blood coagulation system. They are normally in balance and remain balance as exercise ramps up. BUT then the clot "busting" side returns to a normal level of activity more quickly than the clot forming side, and this imbalance puts you in a "hypercoaguable" state for a few days. Add a long period of sitting and DVT risk goes up.

This study of blood parameters that reflect both the clotting and busting pathways post marathon and demonstrates the imbalance - the physiologic background.

And this paper (with references) pulls it all together.

How can you minimize your risk if you are traveling after a major event such as an ironman or marathon?

1. If possible, delay the travel for a few days. But this is not realistic for those of us who have other responsibilities back home.
2. Get up and walk around every hour - or stop if you are in the car.
3. Keep hydrated.
4. And perhaps most importantly, take an aspirin before getting in the car or on the plane.

This article which reviewed the literature on DVT formation post orthopedic surgery (which is a much greater DVT risk than flying) demonstrated aspirin to be as effective as a preventative measure as using coumadin and other blood "thinning" medications.