Some athletes have genetic advantages and others arrange for chemical ones. And a certain amount may have both, according to a recent Mail Online article by Nick Harris which says that some competitors have natural masking agents that allow them to dope at will. The opening:

“Eight of the most explosively gifted sprinters in the world are settling into their blocks on the start line of the 100m final at a major championship. The tension is almost unbearable; the rewards for success are huge.

To the spectators in the stadium and millions of fans watching on TV around the world, it is a spectacle without equal in sport.

But what very few of them will even suspect is that it is statistically likely that at least one of those runners will have a genetic make-up allowing him to take performance-enhancing steroids for his entire career — and never fail a drug test.

Science fiction? Far from it.

Now imagine the starting blocks of a swimming final at a significant international event in Asia — the 2014 Asian Games in Incheon, South Korea, for example.

It is quite feasible that half of the athletes about to dive into the water — perhaps as many as six out of eight depending on whether they are Chinese, Japanese, Korean or from another background — also have bodies that naturally allow them to take drugs but not get caught.

Astonishing though it sounds, significant numbers of sportsmen and women are born to dope, and get away with it. The proportion ranges from around one in 10 of those with European ancestry to one in five with African heritage, and up to a staggering two-thirds of people in some Asian countries, notably Korea.

These shocking statistics, largely unknown to followers of sport, go part of the way to explaining the vast difference between the numbers of elite athletes who are taking banned performance-enhancing drugs and the numbers being caught.”