Veronique Billat, who established a laboratory near Paris which studies sports physiology, said that notion was unfair to a great many riders who trained intelligently.

She said even though Rasmussen went faster than seven-times winner Lance Armstrong on one of the climbs during the race (Plateau de Beille), it does not necessarily mean he had resorted to doping.

"When a professional cyclist arrives at the bottom of a hill, he has often not put in a lot of effort beforehand. It's a little bit like a hiker who walks for several hours and then, at the end, sprints to catch a bus," she said.

"During an effort of five hours, the riders are prepared to ride at heart rates of 110/120 beats per minute (low effort) with their team-mates but at the end of a race they put in a maximum effort.