Allyson Felix, who earned her first global400m title in the fastest time of the year so far, 49.26sec, told the post-race press conference that she was so exhausted afterward that she missed the start of the following men’s 200 final.

“I wasn’t in quite a good enough state to watch men’s 200,” said the US runner who has won three world titles of her own.“I just laid down on the ground, so I have to go back and watch it again. But I think I’ve seen it from 150 on. Usain is amazing and it was another great performance.”

Felix was one of four finalists who remained sprawled on the ground for several minutes after the race – among them also was defending champion Christine Ohuruogu, who remained on her knees, at one point pressing her forehead to the track, for some time after finishing last in 50.63.

“It’s very different running 400 and 200metres,” Felix said. “The 400 is more difficult because I don’t have this much experience so that was a big challenge for me. As for my strategy, I’m a sprinter and I had to take advantage of my speed, and then I just trusted my fitness coming home. That’s what I tried to do.”

Looking ahead to the possibility of the2016 Olympic program being changed to allow her to double over 200/400m, Felix said: “It would be great if we all have the opportunity to run 200 and400 meters in one event. For me, the choice depends on my fitness. The 200 will always be my favorite.”