Maurice Greene, increasingly troubled by injury, is looking suddenly fallible. Marion Jones is absent and the form of her partner Tim Montgomery has dipped precipitously since he broke the world 100 metres record last September.
These and a host of other variables make the men's and women's 100 finals at the Paris world championships starting on Saturday the most unpredictable races yet in the event's 20-year history.
Paris, candidate city for the 2012 Olympics, has been enthusiastically publicising the ninth edition of the championships to be staged at the imposing Stade de France, venue for the 1998 World Cup final.
So too has the International Association of Athletics Federations (IAAF), the sport's governing body which is fighting to keep the central sport of the Olympic Games in the public eye.
The IAAF has been promoting the biennial championships as a general changing of the guard in the year before the Athens Games.
"Wise, or should that be brave, is the person who tries to predict the names of the eight athletes who will line up for the men's final on 25 August in Paris, let alone try to name the medallists," said an article on the world governing body's official website.
"Everyone has beaten everyone. Everyone has lost to everyone."
VULNERABLE CHAMPIONS
Three times champion Greene has been afflicted with tendinitis since clocking 9.94 seconds early in the northern hemisphere season. He still possesses the speed, mental strength and determination to win Monday night's title but there must be real doubts over his ability to survive four rounds in two days.
Montgomery does not look a realistic medal shot, let alone a title contender after cutting short his European season, and with U.S. champion Bernard Williams losing consistently in Europe, Britain's European champion Dwain Chambers could emulate compatriot Linford Christie who won the title 10 years ago in Stuttgart.
Triple Olympic champion Jones misses the championships after giving birth to her son, giving the new American champion Kelli White a real chance of seizing the 200-400 double.
Other recent champions besides Greene are looking vulnerable. Defending 1,500 metres champion Hicham El Guerrouj, who is also entered for the 5,000, pulled out of the London grand prix this month because of a back injury. Olympic 10,000 champion Haile Gebrselassie has been beaten twice over the 5,000 this season and, at the age of 30, he is increasingly susceptible to injury.
Two women who swept all before them on the track last season are in shape to win their first global titles this month. Turkey's Sureyya Ayhan won each of her four 1,500 metres races from the front last year, including a stunning victory in the European championships final in a time four seconds faster than her own national record.
Mexican Ana Guevara was similarly dominant in the 400, winning each of her 12 races including the World Cup in Madrid.
In the field events, the women's pole vault contains defending champion Stacy Dragila and the new world record holder Yelena Isinbayeva, who cleared 4.82 metres in Gateshead, England, last month. Isinbayeva is one of three Russian women to set world records this year.
The weather has been cool in Paris this week after the recent heat wave which has gripped Europe and persuaded the Ethiopian track team to change their training camp to a warmer location. Hotter conditions are forecast for the opening weekend of the championships.
