Dr Ross Tucker gives us the scientific low-down on what some of the more commonly used drugs some cyclists use are and how they work.
EPO, short for erythropoeitin, is a hormone that is normally produced by the kidneys. It then has its effect on the bone marrow, which produces more red blood cells. So the effect of injecting synthetic EPO is to increase the body's natural production of red blood cells.
Why would you want to do this? Well, the theory is that the red blood cells, which carry oxygen, are an important determinant of performance ability. That's because the oxygen is required by the muscles and the theory for fatigue during exercise is that if your muscles do not get sufficient oxygen, they rapidly fatigue. Connecting the dots, you get the logic that if you can increase the body's oxygen carrying capacity, you increase the ability to exercise before fatiguing.
And this is probably correct, but it might be a little over simplified. Why, for example, does EPO have it's greatest effects during endurance exercise like a Tour stage, where the cyclist is not really riding very close to their aerobic limit? In other words, if EPO was improving performance by increasing oxygen delivery to the muscle, then it would be most effective in the event where oxygen delivery is the potentially limiting factor. And when is oxygen potentially limiting?
During shorter, higher intensity exercise, like 1 500m running events, perhaps up to about 15 minutes of exercise. Longer than this, and oxygen supply is not really limiting. So anyone who's ever ridden for five hours will tell you that you never really hit that limit, because you don't exercise near your maximum level. So we believe that EPO must have some other effect in addition to the one it has on the blood and oxygen levels.
EPO use can be dangerous
Bottom line though - EPO works, and so that's why cyclists use it. The problem is that the more red blood cells you have, the thicker the blood becomes - and it becomes more viscous. Imagine adding flour to a mixture of milk and water when you are baking.
Eventually it gets so thick that it's difficult to mix. The heart has to do the 'mixing' for the blood and so if the red blood cell count is too high, then the heart has to work harder.
There was a spate of sudden deaths during the night in young, fit European cyclists about five years ago - these were all rumoured to be linked to EPO use, because the cyclist's hearts were just not able to pump the blood anymore.
I once saw the most chilling quote in a book - it spoke of how some cyclists would actually set their alarms to go off a few times a night, and they would then wake up, cycle for 10 minutes on the indoor rollers and then go back to bed.
The idea was that they would increase the heart rate and 'protect' the heart from having to pump too much per contraction. The quote was: "Cyclists would live to ride during the day, and then ride to stay alive at night".
EPO has now become much easier to detect, though there are of course still problems. However, I suspect that there are other, similar but undetectable drugs being used. Just because someone has not tested positive does not mean they are not using - some drugs are created specifically to ensure that they are not detectable. So I think there may well be drugs out there that will be discovered in maybe 10 years, but which are improving performance now.
The second drug we look at is the male sex hormone, testosterone. This was a super famous drug in the 1980's, when, together with similar anabolic drugs, it became widely used by sprinters and field athletes, particularly those from East Germany and other Eastern Bloc countries (where many of these synthetic hormones were created).
In general, anything ending in -one or -ol is an anabolic, used by athletes to increase muscle mass and promote recovery. Ben Johnson famously broke the 100 m world record in Seoul 1988, only to be stripped of the title and record for use of Stanozolol, an anabolic steroid.
More recently, testosterone hit the news after Floyd Landis tested positive after the 2006 Tour, specifically a stage where he heroically clawed back a huge deficit to claim the yellow jersey.
Testosterone, as we've said, is an anabolic agent, which increases muscle mass when used in conjunction with training. So why would a cyclist in the Tour de France wish to use it?
For one thing, cyclists need to be small, so that they can climb 10% gradients on mountain passes without having to haul too much mass up the climb. Secondly, testosterone is used best over long periods, in conjunction with training. It would have little effect when used once.
So either we have an anomaly, or perhaps cyclists are using it every day, but not being detected. It's important to remember that one is only picked up if the ratio of testosterone to another hormone, epitestosterone exceeds four, then they do further investigation. So it's possible to use both testosterone and epitestosterone in the right amounts and never be picked up by this screening process.
But we still haven't answered why a cyclist would use it? Some fascinating research from Spain has showed that during the course of the three-week tour, a cyclist's testosterone levels, together with other hormone levels, decrease progressively.
This decrease has been linked to an impairment in performance - the final time-trial in the Tour de France, for example, is always quite a bit slower than the first time-trial. So performance goes down over the course of the race, and so do the hormones.
The theory is that the stress of riding five or more hours every day puts the body into what is called a "catabolic" state - everything is breaking down. Now, in theory, the use of testosterone, which is "anabolic", prevents this and allows the cyclist to recover better. And so this is why it would be used - it prevents the normal decline in hormone levels and performance over the course of the race.
So that's an overview of two of the drugs that have been (and seem to be, and probably will be) used for cycling. Let's hope that the latest Tour is not affected by these or any other doping products, and that we can enjoy writing about the cyclists instead of the doctors.
(Dr Ross Tuckeralso blogs on www.sportsscientists.com)