Justin Gatlin has insisted that he is confident of getting even better after his disappointment at the World Championships last month.

After months of build-up to the meet in Beijing, Usain Bolt held off the challenge from his American rival to win gold in both the 100m and 200m.

Gatlin has recorded personal bests over both distances this year, and he believes that the improvement will continue as the top two sprinters turn their focus to next summer's Olympics.

"The margin between us is getting smaller and smaller," the 33-year-old, who has faced criticism after returning from two drug suspensions in his career, told reporters.

"In 2014 I was in consistent 9.8 shape and this year I've been pretty much consistently in 9.7 shape. Next season I hope to do even better. It's just about growth and being there on the day to perform.

"It's not for me to say what you can and can't do at a particular age. I don't think I'm going to hit a limit like 'Uh! I'm 34 I can't learn anything anymore - I can't focus on being a better athlete'."

Gatlin returns to action at the Diamond League meeting in Brussels on Friday.