Jed Jacobsohn for The New York Times  Usain Bolt, center, on his way to victory in the 200-meter sprint on Thursday.  LONDON — After finishing a double-double that no Olympian before him had finished, where does Usain Bolt run from here?  First, let’s hear from him what he will not be doing.  “No to the 400 meters, no!” Bolt said. “Please do not ask any more questions about the 400 meters.”  Now for what Bolt just might be doing: Putting his — to understate the case — world-class speed to use in another sport altogether. He has been half-joking about a Manchester United tryout for years.  “I made a goal to become a legend,” he said. “Now I need to sit down and find something that’s going to really motivate me to come out and do great things. Yeah, I have fans I want to show I’m the best still, but if I can’t, find something that will motivate me — maybe football.”  It is an alluring, if far-fetched, prospect: Bolt on the wing, chasing down a through ball. (Imagine the goal celebrations and the yellow cards that could follow.)  Star Olympic sprinters have made the transition to other sports before. Bob Hayes won the 100-meter dash in 1964 and then became an All-Pro wide receiver with the Dallas Cowboys. Renaldo Nehemiah, once the world’s fastest 110-meter hurdler, also went on to play wide receiver in the N.F.L.  But transitions only rarely end in glory for the world’s greatest athletes: Consider Michael Jordan’s minor league efforts in baseball between periods ruling the world on the basketball court.  No, the most likely prospect is that after this Olympic double-double in the 100 and 200 — winning both titles in 2008 and 2012 — which could still turn into a double-triple if the Jamaicans win the 4x100 relay on Saturday, Bolt will cruise through the end of the track season, live the good life in Jamaica for a time and ultimately decide that the best place to run from here is back to the track.  Too bad he does not like the 400, because that would seem to be just the right new frontier, with the 19-year-old Grenadian Kirani James breaking 44 seconds in his victory in London, and with LaShawn Merritt of the United States still a major factor.  There is also still the prospect of the long jump, which has been a traditional complement to a sprinter’s arsenal. Jesse Owens won the 100, 200 and long jump at the 1936 Games in Berlin. Carl Lewis won five gold medals in the sprints and four consecutive golds in the long jump from 1984 to 1996.  Bolt’s longtime coach, Glen Mills, is not a jump coach. He coaches the sprints and would be much more inclined to help Bolt move up on a serious basis to the 400. Trying the long jump also seems unlikely in light of Bolt’s continuing concerns about his back, which has troubled him this season and troubled him again, according to Bolt, coming out of the curve Thursday night.  He has scoliosis, as photos of him shirtless make abundantly clear, and the pounding that goes with long jumping could pose a risk of further injury.  Bolt still sounds intrigued, but the 400 remains the more likely new direction if there is a new direction. So what of a triple-double in Rio in 2016?  “I think it’s going to be a hard mission,” Bolt, who will turn 26 on Aug. 21, said Thursday. He then gestured to his 22-year-old Jamaican compatriots Yohan Blake and Warren Weir. Blake won the silver in the 100 and 200 in London. Weir, a former hurdler, won the bronze in the 200.  “Both these guys are running extremely well right now, and I think I’ve had my time,” Bolt said. “In life anything is possible, but for me it’s going to be a hard reach.”  The talented younger runners will have an exceedingly tough act to follow. Bolt is, without doubt, the greatest sprinter in history, able to produce his best under the greatest pressure, although Michael Johnson, the American who dominated the 200 and 400 in the 1990s, could have a superior case to make for enduring greatness.  “Let Usain Bolt be free of injury; let him keep his motivation, which I think will be the case,” Jacques Rogge, the International Olympic Committee president, said this week. “Let him participate in three, four Games, and he can be a legend.”
So, Usain Bolt has established that he is definitely the fastest man on earth. Well, now what does he do?