Isinbayeva back in form and bullish for Istanbul

Yelena Isinbayeva celebrates her winning vault in Stockholm last month (Reuters)

The pole-vaulter Yelena Isinbayeva and hurdler Liu Xiang are enjoying a return to form in Olympic year and head into this week's World Indoor Championships as favourites for their events but less familiar names are in contention for the sprints.

Russia's Isinbayeva was back to her formidable best with an indoor world record of 5.01 metres in Stockholm two weeks ago following a frustrating three years. That performance from the Olympic champion, whose struggles with form led her to take a break from the sport in 2010, has dampened expectation surrounding American Jenny Suhr, who until Isinbayeva's world mark had the leading clearance of 4.88m, and Britain's Holly Bleasdale (4.87m).

Such was Isinbayeva's confidence after her world record that when asked if anyone could challenge her this year, she simply said: "I think you can answer that question yourself." She will be seeking a fourth world indoor title, having last won it in 2008.

The Chinese hurdler Liu has struggled with injury since limping out of the 2008 Beijing Olympics with an Achilles problem but the 29-year-old is starting to come good again and set an Asian indoor 60m hurdles record of 7.41sec last month.

He will be deprived of a face-off with his rival Dayron Robles, however, after the 2010 champion pulled out on Monday with a back injury.

For the sprints, the 100m and 200m world record holder Usain Bolt is not competing indoors and fellow Jamaican Asafa Powell failed to make the team, such is the strength in depth of the country's sprinters. Instead it falls to Lerone Clarke and Nesta Carter, who both beat Powell in England last month and will attempt to become the first Jamaican to win the 60m title. Trell Kimmons of the United States, who heads the world list with 6.45sec, and the defending champion Dwain Chambers of Britain are also in the field.

In the women's event Tianna Madison has reinvented herself as a top-class 60m sprinter, having done little of note since winning the 2005 long jump outdoor world title. Madison is the fastest woman in the world this year with a best of 7.02sec.

"She kind of bounced around searching for herself. Trying to find the right situation. It took a while," said her coach, Rana Reider. "She understands there is work to do and she knows she can get a lot out of the sport and enjoy it for what it is instead of as a job."

Unbeaten in seven races, the 26-year-old's main challenge in Istanbul should be from Jamaica's defending champion, Veronica Campbell-Brown.

Ethiopia's 3,000m runner Meseret Defar is hoping to go one better and become the first woman to land a fifth successive individual world indoor title and match the achievement of Cuban long jumper Ivan Pedroso, who won five back-to-back from 1993.

Britain's 5,000m world champion Mo Farah will want a convincing display in the 3,000m as expectation grows leading into his home Olympics. He will be up against the man he beat in the World Championships in South Korea last year to take the 5,000m crown, 37-year-old American Bernard Lagat. The pair will have to contend with Kenyan duo Augustine Choge and Edwin Soi, who are the only men to have broken 7min 30sec this season.