Bumpy ride for favorite Sun

A row involving China's swimming superstar Sun Yang, an air hostess and his coach has given the Chinese a turbulent run-up to the world championships in Barcelona.

The swimming section of the world aquatic championships starts on Sunday with Sun spearheading China's bid to dethrone the US's supremacy at the top of the medals table.

Sun, 21, led his country to its best-ever Olympic performance in London last year, snaring two gold medals and smashing his own 1,500m freestyle world record as China finished with five titles.

Along with teen phenom Ye Shiwen, beset by doping innuendo as she claimed two individual medley golds, China cemented its new position as the world's No 2 two team behind the US.

But a falling-out between Sun and his coach over his love affair with a stewardess has rocked the Asian swimming power as it prepares for Barcelona.

Sun, the tall distance specialist from Zhejiang, rejected coach Zhu Zhigen's demand that he stop seeing his new girlfriend and concentrate on his swimming instead.

Despite a public show of reconciliation with Zhu, Sun has been training in Hong Kong under former Chinese head coach Zhang Yadong.

"Athletes want to get good results, and to do this you need systematic and scientific training without outside interference," Sun said on his official microblog.

"I was not able to do this in the past for various reasons, and have been making up ground through my own efforts.

"With the world championships approaching, I want to eliminate outside interference and prepare well, to give me added strength."

Sun became the leading light of Chinese swimming when he tore up Grant Hackett's 10-year-old 1,500m record at the 2011 Shanghai world championships - a mark he lowered again at the Olympics.

Sun also claimed the 800m world title in Shanghai. In Barcelona he will compete in the 400m, 800m and 1,500m freestyle.

"Sun Yang only had two events registered. We are concerned that he is not able to perform well as he has lacked systematic training the past six months," Chinese swimming's deputy head Shang Xiutang told Chinese media.

"We are even not so sure about these two events now."

While attention will focus on Sun, 17-year-old Ye will also be in the spotlight as she tries to defend her 200m individual medley world title and again deflect the speculation that accompanied her feats in London.

Ye, then 16, raised eyebrows when she obliterated the 400m medley world record with a sensational freestyle lap, timing faster over the final leg than men's winner Ryan Lochte a few races earlier.

"I was very depressed and angry after London but everything is fine now," she told Britain's Independent last month.

"It is a long journey. Different people have their different views but I will just keep on going," she said.

Meanwhile, Asia's other swimming nations have also faced problems.

South Korea heads to Spain without its most high-profile performer and only reigning world champion, Park Tae-hwan.

Park, whose 400m freestyle gold at Beijing 2008 was South Korea's first ever Olympic swim medal, was at the center of controversy in London when he was disqualified from his title defense over a false start, before being reinstated and eventually finishing second.

But the "Marine Boy" has since lost his key sponsor, which reportedly judged the 23-year-old as past his peak, and has been at odds with Korean officials, who refused to give him prize money for his two silver medals in London.

Park, who has appeared on a home shopping channel to fund his training, skipped South Korea's trials and will not defend his 400m world title, with China and Japan leading Asian hopes in the pool.

Japan's "Frog King" Kosuke Kitajima, 30, returns to the city where he set 100m and 200m breaststroke records at the 2003 worlds.

Akihiro Yamaguchi arrives as the reigning men's 200m breaststroke world record-holder, while backstroker Ryosuke Irie hopes to improve on his bronze and silver medals in London.

Fellow Japanese Kosuke Hagino, 18, and Aya Terakawa, 28, also have Olympic pedigree after winning bronze medals in London in the men's 400m individual medley and women's 100m backstroke respectively.