In his admission to Oprah Winfrey last week that he had taken performance-enhancing drugs, cycling legend Lance Armstrong argued that it was not possible to win the Tour de France seven times in a row without doping. Indeed, since 1995, all but two of the winners of the race have been implicated in doping controversies. Among the questions this depressing fact raises is: Why is doping so effective in cycling?
To appreciate how hard the competitors work during a multi-stage cycling race, you have to understand an exercise physiology concept known as VO2 max. Also known as maximal oxygen uptake, VO2 max represents your ability to transport and utilize oxygen during periods of high exertion.
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Doctors measure VO2 max by putting a patient on an exercise apparatus — usually a treadmill or stationary bike — and raising the intensity of exercise every two or three minutes until the subject can no longer sustain the activity. VO2 max is typically expressed in milliliters of oxygen used per kilogram of body weight per hour of activity.
The average person has a VO2 max of around 45. Professional athletes in sports such as soccer and hockey usually register in the 50s or low 60s. Elite endurance athletes typically have high VO2 max values because they’re able to absorb the large amount of oxygen needed to sustain them over hours of hard work. The numbers for cyclists are particularly high. Armstrong’s VO2 max is 85. Miguel Indurain, who ruled the cycling world before the ascendance of Armstrong, was rumored to have a VO2 max of 95, although people who worked with him say it was more like 78.
Since the 1990s, participants in the Tour de France have worn heart rate monitors, enabling researchers to examine their level of exertion (which can then be expressed as a percentage of the VO2 max). Over the long, flat stages, the monitors suggest that riders hover between 50 and 70 percent of their VO2 max. That may sound like a light workout, but keep in mind that when a Tour de France rider is “resting” at 60 percent of his maximum capacity, he’s working about as hard as an average person at full exertion.
The time trials and mountain stages are entirely different. The long time trials last more than an hour, during which the cyclists remain above 90 percent of VO2 max. (As a crude comparison, for the average person that would be like sprinting for an entire hour.) In the mountains, thinning oxygen supply becomes an issue as riders traverse terrain above 8,000 feet, all the while staying in the vicinity of 90 percent of full exertion. Researchers have identified pulmonary edema — an accumulation of fluid in the lungs caused by the effort to supply enough oxygen to the body — in Tour riders after mountain stages.
Studies have also shown that, during the course of a multi-stage race, professional riders experience a steady decrease in levels of testosterone and cortisol as the body struggles to rebuild itself after each day. This decline seems to be unique to cycling, as professional marathon runners have to train hard for six months before experiencing the kind of hormonal deficit that cyclists suffer in three weeks.