Mick Doohan, a nearly marathon-distance runner before his severe ankle injury, told us, "The idea is to be as fast at the end of the race as you are at the beginning. Some guys are really quick for two or three laps, but then go backward. You know their bikes are still good, so the problem's got to be them." Being physically fit improves your ability to concentrate for long periods. Get in shape and you'll not only ride longer, you'll make fewer mistakes and find you're more able to see and process visual information.