Other estimates suggest even higher numbers. A paper published in 2011 examined the prevalence of "blood doping", a catch-all term for ways to increase the capacity of blood to ferry oxygen to muscles. The researchers analysed samples from more than 2,700 athletes and concluded that 14% were probably guilty (though the tests fell short of explicit proof). That average concealed wide variations. Some countries had prevalence rates as high as 48%, though the researchers diplomatically refused to name the alleged offenders.
Another study, published in 2018, simply asked more than 2,000 athletes whether they were doping. The data were collected in 2011 at two big competitions—the World Championships in Athletics and the Pan-Arab Games. To encourage honest responses, the researchers used what is called the randomised-response technique. This guarantees individual answers will remain anonymous and untraceable. They concluded that 43.6% of the athletes surveyed had doped in the past year. Translated to Tokyo, that would imply around 4,800 drug-boosted competitors—roughly in line with Mr Chalmers' fears.
But all these estimates are just that: estimates. "My gut feeling, from having worked with many Olympic-level athletes, is that the randomised-response numbers are too high," says Yorck Olaf Schumacher, who helped develop the Athlete Biological Passport (ABP), a widely used anti-doping test that tracks blood readings, looking for suspicious changes. Some athletes may not have understood the question properly, he says, or may have confused legitimate dietary supplements with doping.
Athletes dope because drugs offer big advantages—potentially so big that undoped rivals have no hope of matching them. WADA, the rules of which bind many sports, maintains a list of hundreds of banned substances. They range from obscure chemicals with names like IGF-1 LR3 and AOD-9604 to insulin (to boost muscle size), amphetamines (for their stimulating effects) and even diuretics (used to mask the presence of other drugs). The clandestine nature of doping means that, for most drugs, there is little hard evidence for their effect on performance. Athletes are forced to rely instead on locker-room rumours and "street knowledge", says Chris Cooper, a sports scientist at the University of Essex, much of which will probably be exaggerated. But for some of the best-known drugs, science—and history—can give a sense of the advantages on offer.