On a blustery Saturday morning, I am about to climb Alpe d’Huez near Grenoble. I have waited years for the chance. For followers of the Tour de France, this is hallowed asphalt – a mountainous ribbon of road where mortals have pedalled into legend. The race I have entered finishes at the summit. My thighs already crackle with heat when the going gets steep. After 21 hairpin bends, eight miles and a final sprint against a Dane called Arne, I cross the line in 44th place. As I slump over my handlebars, my beard dispensing sweat like a full sponge, I receive a text message: “Can you come and do this nappy?” I get off my bike, turn off my iPad and hobble downstairs. Perhaps Arne is doing the same. The next morning, I am transported to New York, where I take part in a spinning class alongside hundreds of other masochists. Robin Arzón, the instructor, leads a brutal interval class of sprints separated by “active recovery”. Each pedal stroke is matched to the beat of the music. As Britney Spears tells me, “You better work, bitch,” Arzón spits one of her catchphrases: “I don’t babysit on this bike… you…