This Sunday, in one of the biggest nights of the sporting calendar, the BBC’s sports personality of the year is decided. Apart from the shortage of women, the other striking feature of the 12-strong shortlist is that only one of the contenders favoured by bookies – the boxer Anthony Joshua – comes to the contest free of the small nagging questions about their fitness to be heroes. The latest to be questioned is the four-times Tour de France champion Chris Froome, who faces further inquiries over an “adverse analytical finding”. The Guardian revealed on Wednesday that questions had been raised by a test carried out in early September when Britain’s best cyclist was on his way to victory in La Vuelta, the Spanish race that, in an almost unprecedented feat, he won only a few weeks after winning the Tour de France. The test suggests he exceeded the permitted levels of the asthma drug salbutamol, which as an asthmatic he can take in strictly controlled amounts. He protests that he stuck to the advice of his doctors, and Team Sky is confident that further testing on the speed with which his body absorbs the drug will exonerate him – as, last month, Bradley Wiggins, a former Team Sky member, was cleared of “jiffygate” doping allegations.

Of the other leading contenders, the distance runner and icon of the London Olympics Mo Farah has now split from the controversial coach Alberto Salazar, strongly denying that it was connected with allegations of misuse of prescription drugs. Lewis Hamilton is a tax exile – as indeed is Chris Froome. They are all rich far beyond the dreams of Sunday night’s voters: Anthony Joshua, the boy from Watford, is tipped to be the first boxing billionaire. Their trouble is that they compete in a world of eye-watering rewards, where marginal advantage is the alchemy they all seek. It would be hard to design a better system to incentivise the use of performance-enhancing drugs.

Worldwide, sporting authorities always appear just off the pace: playing catch-up, duped afresh by each novel drug, or new use of a familiar one. The incentive to cheat always looks stronger than the disincentive, despite the onerous nature of the drug-testing regime, with its obligation on athletes to report their movements months in advance and the intrusive nature of testing. On some estimates, only 1% of tests returns a positive result; yet some cyclists have claimed that 90% of their rivals dope. An anonymised survey of competitors in the World Athletics Championships in 2011 found 30% of respondents admitted to having used illegal drugs in the year before the competition, but just 0.5% failed tests.

Against this onslaught of cheating, the main anti-doping agency, Wada, has a budget of a mere $30m a year, less than the annual earnings of a couple of top athletes. The Russians, smarting from the exposure of their state-sponsored doping programme – which led to the exclusion of more than a hundred of their athletes from last year’s Rio Olympics and now a further ban from next year’s winter games in South Korea – will be watching closely. The claim from Thomas Bach, the president of the IOC, that the latest sanctions on Russia would be a catalyst for a more effective anti-doping system, stretches credulity. But the yearning for athletes who appear to transcend human limits is as old as the Games of classical times. And so is trying to cheat.