It remains the favourite defence of Lance Armstrong's dwindling band of defenders – he never failed a drug test.
Setting aside allegations that questionable results were brushed aside on several occasions, the question is still valid: How could someone cheat on the scale described by the U.S. Anti-Doping Agency (USADA) and not set off constant alarm bells in the testing program?
Although cycling maintains a far more strict testing protocol than many other sports, it is far from foolproof.
Bernard Kohl, the Austrian who placed third in the 2008 Tour de France before being stripped of the result for doping, admitted to having drugs in his system half the 200 times he was tested.
"I was caught, but 99 other times, I wasn't," he told The New York Times two years ago. "Riders think they can get away with doping because most of the time they do."
USADA admitted as much in the report outlining its evidence, saying that "the contention that an absence of positive drug tests is proof that a cyclist is clean does not bear serious scrutiny."
Here are seven ways an athlete can use performance-enhancing drugs (PEDs) and stay ahead of the testers:
DON'T TAKE THE TEST
The easiest way to prevent a positive result is to avoid being tested in the first place. In its report on Armstrong, USADA noted that his decision to focus his 1999 efforts entirely on the Tour de France gave him certain advantages in that respect.
"Intended or not, the plan had several aspects that would decrease the risk ... of doping," the report notes. "... By avoiding most of the early season races Armstrong would be avoiding most of the drug testing to which he could be subjected in the lead up to the Tour."
Out-of-competition testing eventually appeared but was easily ducked. In his memoir Racing Through the Dark , cyclist David Millar says racers were known to go to Italy or Spain to pick up PEDs and then "turn off [their] phone" so testers couldn't find them until the drugs cleared their system. In his own book, The Secret Race, former Armstrong teammate Tyler Hamilton said the "nightmare scenario" was to be surprised by a tester. Once in his apartment, he simply wouldn't answer the door if he had taken drugs recently.
"The testing agencies use what is known as a whereabouts program: You were supposed to inform them of your location at all times, and if you failed to do so, you could be penalized – given a strike," Hamilton writes. "Three strikes in an 18-month period was supposed to lead to a sanction, in theory – but that rule had never been tested in court."
USE A DRUG NO ONE CAN DETECT
Not all tests can be avoided – the winner and several other people are checked after each day of racing – but it took years before the most popular drug could be detected.
Erythropoietin, commonly known as EPO, is an anti-anemia drug that has been used widely in endurance sports. It boosts stamina by provoking the creation of red cells, raising their proportion within the blood. There was not a reliable test for EPO until 2001.
In the absence of an EPO test, it is now generally acknowledged that a free-for-all broke out in the top ranks of cycling. Danish racer Bjarne Riis, winner of the 1996 Tour de France, was nicknamed Mr. 60 Per Cent for the allegedly high red cell levels in his blood and years later admitted doping to win. Some people were taking so much EPO they thickened their blood to dangerous levels. A number of cyclists died in mysterious circumstances after the drug first appeared and there are stories of racers setting an alarm for the middle of the night, forcing them out of bed to do calisthenics that would raise their heart rate.
The Union Cycliste Internationale (UCI), which governs the sport worldwide, eventually determined that racers would not be allowed to compete if their hematocrit (red-cell count) was more than 50 per cent. This was billed as a health measure instead of a positive test. Anyone scoring above the threshold was suspended for two weeks.
DELAY, DELAY, DELAY
The problem, critics say, is that it is short work to get a cyclist back under the threshold. A quick transfusion, although against the rules, takes less than 30 minutes.
The report points to Armstrong's team constantly assessing and tweaking their hematocrit levels, boosting them with EPO and reducing them when necessary. In his book, Hamilton recalls his blood being spun in a portable centrifuge "the size of a toaster" to see what his level was and that other riders "talked about hematocrit all the time, as much as they talked about the weather or the road conditions."
According to the USADA report, former Armstrong teammate Jonathan Vaughters said in a sworn affidavit he was present when a drug tester was observed setting up nearby. He said a team doctor went to "retrieve a litre of saline which he put under his rain coat and smuggled right past the UCI tester and into Armstrong's bedroom. [The doctor] closed the bedroom door and administered the saline to Armstrong to lower his hematocrit, without alerting the UCI tester to their activities."
Vaughters explained that a simple strategy to outwit testers was to "have the guys with lower hematocrit be tested first." This way, the riders with higher hematocrit would have time to manipulate it downward by the time their turn came.
USADA says that "there were occasions when Armstrong did not immediately submit to testing."
With cyclists able to manipulate their system in short order, surprise testing was the only way to catch them.
But the USADA report shows how difficult that was.
The World Anti-Doping Agency (WADA) noticed that some cycling teams, which were not identified, kept a lookout at the 2010 Tour de France. People were watching the parking lot from hotel windows and a team member posted at the entrance "immediately used his mobile phone" when he saw the drug testing team, the report notes. It adds that prominent identification badges and race branding made the arrival of testers "at times so conspicuous as to provide advance notice to those about to be tested."
And the USADA report cites riders on Armstrong's team who say they seemed to be getting even more of an early warning.
In a sworn affidavit, former Armstrong teammate Dave Zabriskie said that team director Johan Bruyneel "always seemed to know when drug testers were coming at races. His warning that they're coming tomorrow came on more than one occasion."
Other times, the report alleges, the notice was shorter but still effective. Vaughters said that the team had an "outstanding early warning system" for drug tests.
"We typically seemed to have an hour's advance notice prior to tests," he said in his affidavit. "There was plenty of time in advance of tests to use saline to decrease our hematocrit level. There were at least three or four occasions during  where I and other riders used saline after receiving advance warning of a doping control."
BLOOD DOPING REAPPEARS
The appearance of an EPO test in 2001 prompted new approaches, including the reapperance of blood doping.
"From my conversations with Lance Armstrong and experiences with Lance and the team I am aware that Lance used blood transfusions from 2001 through 2005," former Armstrong teammate George Hincapie said in a sworn affidavit.
Blood doping, in which a racer's blood is withdrawn and then reinfused after his body has replaced the missing red cells, had largely been discarded as not as effective as EPO. But after 2001 its big advantage was that there was no test for it. Police raids in 2006 that turned up scores of blood bags in Madrid proved that the old method had come back in a big way.
Cyclists testifying in the Armstrong matter say blood doping was done in conjunction with "microdoses" of EPO, injected into the vein instead of under the skin. The dose size and method of injection meant that the drug was out of the system quickly, Hincapie said. In his book, Hamilton notes European laws that prevent surprise testing at night, leaving a big enough window of opportunity for careful PED use.
"This means you can take anything you like, as long as it leaves your system in nine hours or less," he wrote. "... One tester, a considerate older gentleman who lived an hour away in Barcelona, used to telephone the night before to make sure we were in town, so he didn't waste a trip."
Certain drugs that can help performance are allowed under a so-called therapeutic use exemption, essentially a doctor's approval that there is a legitimate need for it. Fair in theory, but easily abused according to riders.
In his book, Millar talks about the routine use of cortisone, which can "decrease pain and increase strength in the short term." One of his teammates was a notorious user and another later explained in his own book how to obtain a corticoid prescription by using salt to chafe the scrotum, raising a rash.
In 1999, a few days into his first winning Tour, Armstrong tested positive for corticosteroid. A team assistant named Emma O'Reilly told USADA she was giving Armstrong a massage while team officials concocted a cover story, backdating a prescription that was purportedly to treat a saddle sore.
"It was clear to me after the meeting that Lance's positive sample was not caused by the medical treatment of a saddle sore and that the only reason he obtained a prescription was to excuse his improper use of a banned substance," O'Reilly swore in her affidavit.
KEEP IT A SECRET
USADA calls Armstrong's doping a massive conspiracy. Although a shadow persisted through much of his career, fed by a number of leaks and allegations, deniability was maintained by the omertà of many of those cited in the report.
Armstrong's celebrity gave him an enormous presence in the sport, which has often deferred to the "patron," the biggest star of the day. He was famously aggressive with those who questioned his claims of clean riding. And many who could tell the truth had implicated themselves by cheating.
Vaughters, who admits using drugs, recalls a time in 1998 when he was with Armstrong in a hotel room. He said in his affidavit he saw the other rider give himself an injection in the stomach and say "words to the effect of, 'Now that you are doing EPO, too, you can't write a book about it.' From that point on, while I was on the U.S. Postal Service team, Lance was open with me about his use of EPO."
Former WADA head Dick Pound noted this week the difficulty many would have felt speaking up.
"Some who would have been willing to talk about Armstrong could not afford to defend against actual or threatened lawsuits," the Canadian told CNN. "Some needed the jobs they had, which would be at risk or disappear if Armstrong wanted that to happen. Others were not willing to risk the harassment and abuse that came from crossing him."