Star German swimmer Paul Biedermann is confident he can defend his crowns in the men's 200m and 400m freestyle events at the 14th FINA World Championships.

"I have high expectations of myself. I want to prove myself again. I want to definitely defend my world titles," said 24-year-old Biedermann, who claimed two gold medals at the last World Championships two years ago in Rome.

"I know it's really hard. I know there are so many fast guys in the world who also want to be world champions. But I will try to do my best."

Competing in 200m and 400m freestyle again, Biedermann faces tough challenges from the likes of US superstar Michael Phelps, South Korea's Park Tae-hwan, seven-time medalist at the 2010 Short Course World Championships, Ryan Lochte of the US, as well as China's rising star, Sun Yang.

"There are many more competitors. It just pushed me more in training," Biedermann told China Daily after a training session in Shanghai on Tuesday.

"I think it will be really tough, even to make the finals," he said.

"I felt well in the training camps. I'm getting excited about the competition pool now."

As a defending champion of two world titles, Biedermann has noticed there are also high expectations on him from his countrymen.

"I notice it. I really want to prove myself and show my best side," he said.

Biedermann won't be facing the challenge alone as he will have the company of teammate and girlfriend, Britta Steffen, the reigning world champion in the women's 50m and 100m freestyle.

"We feel pretty well. We are looking forward to the competition. I think we both have big-competition experience," he said. "We take the pressure together and handle it. For me, it's great that we are both here."

But the German is not sure he will break his own world records in the two events.

"For the moment, I don't think I can beat any of my world records. I think they are just too far away," he said.