By Julien Pretot
PARIS (Reuters) - British cyclist Chris Froome said on Friday that tests he took after winning the Tour de France proved that he does not use performance-enhancing drugs, although at least one rival coach said they would not silence the doubters.
The tests were carried out at the GlaxoSmithKline Human Performance Lab in London in August, a few weeks after the Tour, and the results he released suggest that a huge weight loss could help explain his rapid rise from 2007, when at 22 he was a rough diamond at best, to Tour champion in 2013 and 2015.
During this year's race, Froome was accused of doping by former riders, reporters and fans of a race that has been beset by doping scandals for almost 20 years, and had to strip seven-times winner Lance Armstrong of his titles. Some fans even threw urine at Froome, who has always vigorously denied doping.
"The figures make one thing very clear to me, if I ever needed any reminder," Froome said in a statement. "Natural ability is only one piece of the puzzle of what it takes to win an event like the Tour de France. I have always prided myself on my work ethic, dedication and perseverance."
Frederic Grappe, performance director at the French team FDJ who helped France's Thibaut Pinot finish third in the 2014 Tour, told Reuters that the best way to assess Froome's performance would be to release his power output data over the years.
"The tests are a step in the right direction but it's not accurate enough," Grappe said.
There was one indicator, however, that suggested Froome is not a donkey turned into a racehorse: the "VO2 max", which is the maximum rate of oxygen consumption. The higher the reading, the fitter the athlete.
"One thing is sure, his VO2 max suggests he has the engine to achieve what he's achieved," said Grappe.
Froome's VO2 max was measured at 84.6 ml/kg/min, equivalent to 88.2 when adjusted to his Tour de France weight.
"It is possible that it is even higher because, very often, the numbers we have from outdoor tests are higher than the ones conducted in labs," Grappe explained.
"NOT ENOUGH DATA"
But the Frenchman said more data might have helped to silence the doubters: "For instance, we don't have the gross efficiency, which is key in determining the profile of a rider."
The Journal of Science and Cycling defines gross efficiency as the "ratio of work generated to the total metabolic energy cost".
Another much debated figure during the 2015 Tour was Froome's power - the rate at which he can expend energy - and power-to-weight ratio.
All teams use power meters to assess performance, and some experts say this data can show that a rider is cheating. Froome calls them "clowns", however, and his Sky team's manager Dave Brailsford says it is "pseudo-science".
Antoine Vayer, a former coach at the Festina team, which was at the heart of the Tour's 1998 doping scandal, believes it is possible to determine the maximum power that can be achieved without doping.
Froome's tests show that he can produce 419 Watts for "20-40 minutes", which, for Vayer, puts him in the 'suspicious' zone.
"This figure means little because we don't know whether it's the power he produced for 20 or 40 minutes. And you usually lose one Watt per minute after 20 minutes," said Grappe, who believes a power passport for all riders would help detect doping, just like the blood passport already in use.
"If your power meter is well calibrated, you have landmarks," Grappe said during the 2015 Tour. "The guy who has a well-established profile and beats his record by 10 per cent ... you know something is wrong."
Team Sky's Brailsford dismissed the doubts.
"There's been a growing move for transparency, and that's what we're trying to embrace," he told Sky Sports News. "We want to take a role in this to show you can win the biggest bike races clean."
(Additional reporting by Steve Tongue; Editing by Kevin Liffey)