LONDON - With one final wave, Usain Bolt said goodbye to an adoring British crowd at the Olympic Stadium.The world’s greatest sprinter and his Jamaican 4x100 metres relay team mates had delivered the ultimate in athletics, a world record, and now it was time to move on.Jamaica’s summer will have given way to cooler times before he and coach Glen Mills sit down to discuss what course to follow.But this we know. These are transitional times for the only man to repeat as double Olympic champion in the 100 and 200 and twice add world records in the 4x100 at the Games.His push to be a "legend” has been achieved."Now I have to sit down and make another one (goal),” the 25-year-old told reporters. "I have done what I wanted to do.”"(The 2016 Rio de Janeiro Olympics) is a possibility, but it is going to be really hard because these young guys are coming up.”His coach would like him to take up the 400, Bolt said.Many had thought that event would be the Jamaican’s ticket to fame before he persuaded Mills to give him an opportunity to run his first serious 100 five years ago.Bolt has resisted the 400, even once suggesting he would show up at Rio in the long jump.Maybe he will mount an all-out effort to break the sprint records only he can seemingly touch at the 2013 world championships in Moscow, before deciding whether to step away or pursue less stressful campaigns at future world championships and the Rio Games.Sponsors and the sport he has massively enlightened for the past four years will want him on the track for as long as his health permits.His showmanship, antics and unworldly speed more than justify hefty contracts and massive ticket sales that push his annual income beyond $10 million, by far the most of any athletics performer.But how long will it last?Question marks hang over whether he will have the will to spend long hours training and sacrifice the partying he delights in for four more years and whether the 62-year-old Mills, the mastermind behind Bolt’s success, will continue to coach for as long as the world record holder wants to run.BACK PROBLEMSBolt also has endured chronic back problems in recent seasons. Could they worsen as his age progresses?The back troubles no doubt figured in a strained hamstring that slowed a less-than-fit Bolt in two losses to training partner Yohan Blake in the Jamaican Olympic trials.Even in his victorious 200 run in London, Bolt felt pain.A hard curve run "really put a lot of strain on my back,” he said. "I did not want to put too much stress on myself if something went wrong. So I really took it easy. At the end of the race I just slowed up.”Then there is age, that unconquerable factor that eventually catches up with the greatest of athletes."I would want to say great things,” Bolt said when asked about his plans for Rio, "but I will be 30 then, so I am not sure.”The reflective words contrasted greatly from the ‘I-am-the-greatest’ talk Bolt had delivered moments earlier.But only time will tell whether they portrayed Bolt’s line of thinking about the future or were just a tired athlete talking."Blake is going to be at his peak (in Rio) and he is going to do great things so we don’t know,” Bolt said."I told him two years before this ‘Yohan, this is not your time. This is my time. After the Olympics then it is your time ....Right now it is my time’.”What a time it has been.With Bolt on the track, world records have fallen three times each in the 100 and 4x100 relay and twice in the 200 and a sport mired in doping scandals has risen to the front page again simply because of his exploits.