Imagine straddling an iron chin-up bar, the entire weight of your body centered on that delicate zone between your legs known as the perineum, for an hour. That's what happens whenever you go for a bike ride. Eventually, the area starts to tingle with pain or the first stages of numbness. If you're a guy, the tubes and nerves that fuel erection get squeezed and damaged, leading to predictably disappointing results in the bedroom. If you're a woman—well, let's just say sex is the last thing on your mind after a long day in the saddle. While some physicians believe that cycling causes…