Hidden danger: DVT in endurance athletes

Have you heard of DVT? Well, if you haven't you are not alone. As a bike rider, you should be aware of DVT.

A survey released at the American Public Health Association conference in Washington, D.C. showed that 74% of Americans have never heard of DVT. [Clinical Advisor, June 2004, page 53]

It is an acronym for Deep Venous Thrombosis. It is sometimes referred to as "deep vein thrombosis" and occurs when a blood clot forms in the veins of the extremities, usually in the lower leg or thigh.

Some people are familiar with the potential for DVT to occur during or after a long airplane flight. This has been referred to "Economy Class Syndrome."

Did you know that 85% of air travel thrombosis victims are athletic, usually endurance athletes? [www.airhealth.org/athletes.html, July 11, 2004]

DVT can kill you.

If not treated, DVT can lead to pulmonary embolism or stroke caused by blood clots moving from the legs to the heart or the brain. Both conditions can lead to death.

DVT affects about 2 million Americans a year. Failure to correctly diagnose blood clot formation causes up to 100,000 deaths a year. [Clinical Advisor, June 2004, page 53]

Contributing factors

What are some of the factors that can contribute to DVT? DVT is a concern when one undergoes an operation or suffers a trauma, like a fall in a bike race, where blood clots may form.

Today, hospitals pay particular attention to patients that will be sedentary for a period of time. Being sedentary leads to blood pooling in the lower extremities and can lead to blood clots forming. This is the same problem exhibited during long plane flights.

The tendency to clot more readily than others can be inherited, and is not reduced by being physically fit.

Hydration level is a factor in DVT. As dehydration occurs, the blood thickens. Thick blood moves slower through the veins.

Everyone knows that when you are on your bike and you dehydrate, you are done. Even professional athletes become dehydrated, look at the face of Lance Armstrong at the end of the 2003 Tour De France Stage 13 time trial.

It is easy to become dehydrated; we have all done it. Cold weather can increase the risk of DVT due to constriction of the veins in the extremities. [Gallerani, Boari, de Toma, Salmi, & Manfredini, "Seasonal Variation in the Occurrence of Deep Vein Thrombosis", University of Ferrara, Italy]

Anything that causes a constriction in the legs (tight clothes or folded leg position, for example) can lead to DVT. Women who are pregnant or on birth-control medicine are at a higher risk for DVT.

DVT and athletes

So what does this have to do with riding a bicycle? Bicycle riders typically are in good shape, watch what they eat, and take care of themselves. They are not generally overweight. If they have been riding for some time and cover 300 miles or more a month at a good pace, their resting heart rate is generally lower than the norm for their age.

Lower resting heart rate means slower blood flow throughout the body. This is especially true for those riders who participate in endurance events such as century rides, time trials, and other competitive events.

Slower blood flow -- sound familiar?

I ride between 400 and 600 miles a month, mostly back and forth to work with some additional long rides on weekends. I am 58. I am 6'3" and weigh 250 pounds. My blood pressure is normal. My maximum heart rate is 185 bpm. My resting heart rate is 48 bpm.

I usually try to maintain my average heart rate at or above 75% of my maximum heart rate. My schedule includes a rest day every third day. I monitor my heart rate, speed, cadence, and power every ride. I feel great -- or at least I did until late April of this year.

In late April I noticed that my left calf muscle felt crampy and tight. I also noticed that my left lower leg was a little swollen when compared to the right leg. The swelling always went down after an hour.

I assumed that since I ride hard and it was early in the season that I must have just overdone it and strained something. I did more stretches during warm-ups and cool-downs. I didn't push as hard during my rides.

However, the swelling continued to occur after every ride. In May I mentioned the swelling to my Doctor during my yearly physical. He sent me for an ultrasound of my left leg. The diagnosis was DVT.

I had never heard of DVT or blood clots in the legs and was astonished. I was immediately taken off my bike and placed on blood-thinning medicine. After three weeks I am back on my bike, but am still taking a blood thinner. It will take some time for the clot to dissolve.

DVT is not something that goes away quickly after taking a few pills. It can become a chronic disabling condition. You need to minimize your risk factors for DVT as much as possible.

Minimizing risk

You have no control over heredity and age, but hydration and sitting in one position for long periods of time without moving your legs are controllable factors.

You also need to be aware of other contributing factors like low resting heart rate, medicine you take that may affect your blood's capability to clot, and any trauma that may cause blood clots to form.

An athlete does not have to fly to be susceptible to DVT. The physical constraints imposed during an air flight can be present in everyday life, but not recognized.

I work in an office sitting at a computer for long periods. I used to sit with my legs folded back under my chair. Now I ensure that I do not cross my legs or fold them under me.

I thought that I drank enough water, but I also drank lots of coffee. Coffee is not water. Now I drink lots of water and very little coffee.

You can't control your genetic makeup, but you can ensure that you stay hydrated and periodically move around and stretch to prevent blood pooling.

You can pay close attention for the symptoms of DVT, which may include pain similar to a cramp in one leg, sudden swelling in one leg, enlargement of superficial veins, or reddish-blue discoloration of the skin in the affected leg.

If you have symptoms like these, you should contact your doctor right away. If you experience shortness of breath, sharp chest pains, rapid pulse, sweating, cough with bloody sputum, a feeling of apprehension, or fainting, you may have a pulmonary embolism. You should seek medical help immediately.

Be aware of what your body is telling you. I recommend that after reading this article if you want to learn more about DVT go to www.airhealth.org.

Do not think that because you are fit that DVT can't happen to you. It can. As a bike rider, you are more likely to be hit with DVT than the average couch potato.


Tom Isbell is a 59-year-old mechanical engineer living in Port Orchard, Wash. He is an avid bike rider who rides over 4,000 miles a year. He enjoys backpacking and mountain climbing. He has climbed a number of the volcanoes in the Cascades Mountain Range, including Mt. Rainier (when he was 50), Mt. Adams, and Mt. Hood. He completed the Seattle to Portland bike race when he was 55. When he retires this year he plans to devote more time to bicycle advocacy issues in Washington State, ride his bike more, and volunteer to help with trail maintenance in Olympic National Park.


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