Linked to this are the physiological aspects of performance. In the same way that a motor vehicle requires certain components to travel at 200 m.p.h. — a huge engine, fuel and aerodynamics — a cyclist requires certain physiological characteristics to produce the power output necessary to win the Tour de France. Those characteristics, which include a high maximal capacity to use oxygen and efficiency of converting metabolic energy into power, are identifiable and measurable.

It is possible to use these physiological characteristics to estimate the maximal sustainable power output for a cyclist. It requires some assumptions, but if they are consistent and made in favor of the cyclist, then they reveal that in the 1990s and 2000s, Tour performances routinely exceeded the predicted physiological capacity of humans. In contrast, 2010 and 2011 Tour riders have been beneath this ceiling on every climb of the race. The slowing in times thus brings physiology back in line with what are believed to be limits of performance.

Together, the climbing performances and physiological implications set up the compelling hypothesis that the Tour has returned to the days before 1989, when EPO became available. Until about a decade ago, athletes were able to use the drug with impunity, as there was no reliable test for it. Evidence has revealed that after the test was introduced, athletes simply adopted blood doping to achieve the same performance-enhancing effects.

Since 2008, however, the biological passport has made it increasingly difficult for athletes to use both of these techniques, and the result is that the proportion of suspicious blood samples has drastically fallen. Cyclists may still be doping, but their methods have been changed and then reduced to the point where they are using much smaller doses that have a concomitant effect on performance.

So if this year’s cyclists seem to be speeding over the French mountains at a slower pace, it could well be because they aren’t doping — or are doping less than past competitors have. Doping will always exist, as it does in every other sport, but cycling just might be restoring its credibility, one pedal stroke at a time.