For years, one of the few certainties at major international track meets was that Usain Bolt would outsprint everyone.
But at the world track and field championships, which open Saturday in Beijing, there is an exotic feeling of unpredictability: Bolt faces a real threat from the American Justin Gatlin.
Bolt first burst into stardom at the 2008 Olympics in the same stadium where this week’s championships will take place, winning the 100- and 200-meter double and setting world records in both. (He picked up a third gold in the relay.) The next year, at the world championships in Berlin, he broke both records, and the marks of 9.