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Toolbox Special Edition! Hematocrit – Playing With Fire
Canadian Genevieve Jeanson’s explanation for her high hematocrit and removal from the start line at the Worlds in Hamilton was her use of altitude tents. Let’s take a briefer on just what hematocrit and altitude tents are all about…

Step Into Stephen’s Exercise Physiology Class

First off, let’s define hematocrit and the blood test that Jeanson failed. Blood can be broadly categorized as comprising liquid (mainly plasma) and solids (red blood cells that carry oxygen and white blood cells and platelets that ward off infections and help with clotting.

Hematocrit is the percentage of your blood that is composed of “solids.” UCI rules are that hematocrit must be 47% or under for women and 50% or under for men.

Why is a high hematocrit useful for endurance athletes? More red blood cells mean more haemoglobin, the molecule that carries oxygen. And nothing determines an endurance athlete’s ability more than the amount of oxygen that her body can deliver to the muscles. If you have more red blood cells and blood than your identical twin, you will be able to maintain a lower heart rate at any particular workload, and also be able to work at a higher workload before really having to tap into your anaerobic (without oxygen) metabolism, meaning less lactic acid buildup in your muscles.

Why is a high hematocrit dangerous? A greater fraction of solids in the blood means that the blood is thicker and more difficult to pump throughout the body. Think of putting super thick motor oil in your car and the strain that might put on your engine. Similarly, a high hematocrit puts a lot of strain on your heart and blood vessels, especially when it’s working hard in training or racing. This can lead to heart attacks or strokes.

The Blood Test and Its Fallout
The test that was administered to Jeanson and the Canadian team is performed on randomly selected teams the morning of a race or periodically throughout stage races. They are administered by the UCI staff, NOT by national teams or governing bodies. The blood test itself is very simple. A small blood sample is taken and then spun at high speeds in a centrifuge. This separates out the solids from the liquids, and the percentage is simply read off a scale. The blood test does not test for any banned substances, only hematocrit.

As the Canadian Cycling Association is very careful (and correct) in stating, a high hematocrit is NOT a positive test for doping. Therefore, I will restrict this article to other reasons for a high hematocrit. The immediate consequence for Jeanson was that her license was immediately suspended for 15 days for “health” reasons. She then had to submit to a full urinalysis for all possible banned substances. She will be retested in 15 days to see if her suspension will be lifted. Again, this is not a doping infraction.

Naturally High Hematocrits
Some individuals do have a naturally higher hematocrit than others. The UCI usually has a list of these individuals, and they are occasionally given allowance for a higher than normal value.

Dehydration will also naturally elevate your hematocrit. That’s because most of the initial sweat you produce comes from the plasma portion of your blood. So you still have the same amount of red blood cells, but less liquid portion and therefore less total amount of blood. Besides not drinking enough fluids, vomiting or diarrhea will also rapidly dehydrate you.

Altitude Tents
Another way to naturally elevate the amount of red blood cells in your body is to live at altitude. The lower amount of total air pressure, and therefore oxygen, in the air that you breathe at altitude results in the body compensating by producing more red blood cells. When you return to sea level, it takes about 3 weeks or so for your body to return to its normal levels of blood cells, so you have a temporary advantage in aerobic capacity.

It’s for this reason that Boulder, Colorado, at about 1500 m elevation, is such a mecca for cyclists and triathletes. Tony Rominger also spent a month or so in Colorado preparing for Le Tour each year during the early 1990s with this in mind. Since that time, a number of companies have come out with tents that can simulate the lower air pressures of high altitude. Therefore, rather than having to relocate and move to Boulder or elsewhere, athletes can sleep in these tents and get much of the same benefits in terms of increased red blood cells.

Keep in mind though that this increased red blood cell count will elevate your hematocrit, and this is where the ethical line gets really blurred. With these tents, you are “naturally” doing exactly what can be done pharmacologically and illegally with injecting erythropoietin. I’m not even going to try to wade in on the debate of whether this makes altitude tents ethical or legal.

Stay tuned for more as this story develops…

About Stephen:
Stephen Cheung is an Associate Professor of Kinesiology at Dalhousie University in Halifax, Nova Scotia, Canada, with a research specialty in the effects of thermal stress on human physiology and performance. He has been an avid roadie since beginning university in the mid-eighties, and still has non-indexed downtube shifters on his winter bike and wool jerseys hanging in his closet. He can be reached for advice or comments at


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