In my recent post on le Tour de France, I predicted an average speed of 41.741 kph (25.936 mph) for the winner this summer based on regression analysis of the winning speeds over all 99 previous races. If you hadn't heard yet, Chris Froome won the yellow jersey this year with an average speed of 40.545 kph (25.193 mph), which is below the 95% confidence interval of my prediction. Although I can't say this with any statistical significance yet, it seems that speeds have slowed since 2005. In fact, average speeds over the last seven races have been below what the model predicts. Why would a trend that has been rather consistent over the last 110 years apparently reverse? Well, this is precisely what one would predict if the racers had suddenly gotten clean. There have been a number of reasons to expect average speeds for professional bicycle races to increase steadily, including technological (e.g. carbon fiber) and biomedical (e.g. better designed training and recovery regimens) advances. Bridging tech and medicine are the so-called doping strategies employed by riders like Lance Armstrong. If we agree that the human body--even a body belonging to a genetically gifted professional athlete--has limits, then extraordinary means like doping simply stretch those biological limits a wee bit. When abandoned, the bodies tend back toward their ordinary constraints. I'll be keeping an eye on these trends for the next few years.