Another week, another scandal, this time for distance running, with some of its biggest names implicated in a doping controversy that further undermines the credibility of track and field athletics. The big revelation came from investigative journalists in the US and the UK, who produced a damning report on Alberto Salazar and the Nike Oregon Project.Among other things, it alleges that athletes in his distance-running programme have been using banned testosterone since they were 16, and were regularly given banned substances by Salazar, who played fast and loose with his athletes' medical products. This included cutting pages out of a paperback thriller to wrap pills to send to Europe for an athlete to take before racing.Among these athletes is Galen Rupp, who won the silver medal in the 10000m at the London Olympics. He is the biggest name implicated in the report, but much of the focus and reaction has centred on his training partner,Mo Farah, who was the Olympic champion at 5000m and 10000m and is one of the sport's biggest drawcards.His involvement in illegal and unethical practices is unknown. David Epstein, one of the journalists on the report, has said that no incriminating evidence came up for Farah, but people are understandably asking whether it is believable that lower-level athletes in an ambitious, well-controlled programme were doping, but not the best athlete?I have known about these allegations for many years. The margin of the improvements achieved by athletes in the programme, combined with their relative and rapidly achieved dominance (three Olympic medals produced outside of Africa is extra-ordinary), were always going to attract some scepticism, and the regular emergence of reports of unethical and illegal practices slowly built a foundation for mistrust.The allegations, now formalised with the on-record testimony of insiders, were therefore hardly surprising, but are depressing nevertheless.Only two weeks ago I wrote about the mistrust of athletics at the opposite end of the running spectrum, where Justin Gatlin dominates the short sprints. Now distance running is implicated too.Some of what Salazar is alleged to have done is not illegal - corticosteroids and thyroid hormone are not banned all the time, and can be used with or without a medical prescription, something I'd say is a substantial loophole that authorities need to close. Certainly, their use is unethical and highly questionable, and the use of testosterone is illegal however you view it.But what this episode shows is that the distinction between black and white is not nearly as clear as we would like it to be.One of the problems is that the programme is exceptionally well-funded by Nike, and was known (to the point of mild ridicule) for some of the gadgets it used to find every possible advantage. With his underwater treadmills and nasal strips and masks to combat pollen allergies, Salazar gained a reputation as a "tinkerer" or innovator who was also ruthlessly ambitious.Given the pursuit of every tiny advantage, it is not difficult to conceive that medical products, which offer more than a tiny advantage, would feature in their thinking, and allegedly their actions.When we demand performance in a world where 0.5% is the difference between a gold medal and finishing fourth, then tie significant financial rewards to these achievements, is it any wonder that people will push the limits, then break them?Perhaps most depressingly, there's no easy way to prevent mistrust becoming scepticism or outright cynicism.This is best illustrated by the somewhat naive quote of Richard Kilty, the world indoor 60m champion, before yesterday's Diamond League event in Birmingham. Discussing Gatlin and the latest doping allegations, he said he hoped for "some great performances this weekend, which will try to blow away the shadow that programme has caused".Unfortunately, the greater the performances, the larger that shadow becomes. Doping is an area where on-field and off-field controversy and corruption cannot be separated. Faster means less trust, slower means less appeal. That's a catch-22 no sport would want, but athletics has it, and there is no end in sight...