I'm just reading Mark Cavendish's book Tour de Force about his record winning Tour de France last year, when he matched Eddy Merckx's sprint record of 34 stage wins. Cav was 35.
It is a must read for anyone interested in pro cycling, and really communicates the sheer brutality of the sport. He said that splits happen coming over the top of a climb. Lead riders go over the top pushing 400W, but get a bit of slipstreaming from the camera motorbike. The next group don't have that and have to push 440W. An individual doesn't get a group effect and has to push 480W - and, he says, that is why splits happen.
In a sprint, riders - including Cav - can push up to 2,000W for a number of seconds. After 4 or 5 hours in the saddle.
It is also perfectly clear he doesn't like Sagan one tiny bit.
Looking at the web, he's still competing age 36, will be doing the Tour of Britain, and probably another Tour de France to try and beat Merckx's sprint record.