LOS ANGELES (AFP) - Michael Phelps returns to China, scene of his astonishing Beijing Olympic swimming triumphs, seeking to kick-start another Olympic campaign at the 2011 world championships in Shanghai. With the 2012 London Games looming, Phelps and his American team-mates will get a chance to test themselves against the world's best, aiming to stay top of the medals table in this pre-Olympic year. For all his achievements, Phelps heads to Shanghai with questions swirling. If not exactly floundering, the 14-time Olympic gold medallist has appeared at least to be drifting after a series of rare defeats. Invincible in the 200m butterfly for nine years, he lost three times in the 200m butterfly in this year's USA Swimming Grand Prix Series twice to China's Wu Peng and once to Aussie Nick D'Arcy. However, after falling to D'Arcy in Santa Clara in June, Phelps was talking less about the deficiencies in his training and more about his confidence following high altitude workouts in Colorado, saying he was "in a lot better place mentally" than he had been earlier in the season. Phelps's latest tune-up saw him notch two victories at the Canada Cup earlier this month, including a 100m butterfly victory that put him top of the world rankings in that event. Phelps could swim up to seven events in Shanghai, and his performance there will help him and coach Bob Bowman plot his London programme. He could be lured to the 200m freestyle by the chance to regain the world title he lost to Germany's Paul Biedermann in Rome two years ago, while in the 200m individual medley Phelps is the top performer to date in 2011. Overall, America's men do not figure prominently in this year's world rankings, but that could be misleading because of the lack of a world championships selection meeting. The US team, including 25 Olympians, was selected based on performances at the 2010 national championships and Pan Pacific Swimming Championships, leaving swimmers free to pursue their training schedules with an eye to peaking in Shanghai without worrying about trials. Ryan Lochte, whose stellar 2010 included six Pan Pacs gold medals and a short course world championships campaign that saw him set the first world record since high-tech bodysuits were banned, has had a relatively quiet season, even battling a strained knee at one point.