Chris Froome needs scientific proof for his Salbutamol spike - experts

The 32-year-old rider has been asked to explain why a urine sample he gave during September's race in Spain contained twice the permitted concentration of the widely-used asthma drug.

If he fails to provide a satisfactory answer, cycling's governing body the UCI is likely to proceed with an anti-doping rule violation case which could strip him of his Vuelta victory and see him miss a large chunk of next season.

Speaking to Press Association Sport, Professor Chris Cooper said Froome "would have to be really stupid" to try to cheat with Salbutamol as it has no performance-enhancing effects when taken via an inhaler and he would have known he was being tested every day.

The Team Sky leader has made no secret of his use of Salbutamol throughout his career and he even notes it on his doping control forms.

Under World Anti-Doping Agency (WADA) rules, athletes with asthma can take up to 16 normal doses of the drug (100 micrograms) via an inhaler every 24 hours but no more than eight in a 12-hour window.

This translates to an allowed concentration of Salbutamol in a urine sample of 1,000 nanograms per millilitre. Froome was tested 21 times during La Vuelta but on September 7, after the 18th stage, his sample was double the permitted amount.

Mr Cooper, who runs the University of Essex's Centre for Sports and Exercise Science, said Froome and Team Sky are likely to have requested all of his other samples to find out if he was close to the limit on those days, too, as he has admitted that he upped his dosage, on his doctor's advice, to treat his worsening symptoms.

As everyone excretes and metabolises the drug in a slightly different way, Froome may be able to prove that the adverse finding is a result of his physiology and the unusual circumstances of riding a three-week bike race. To do this, he is likely to be tested in a laboratory.

"I'm sure Team Sky have been trying to do this already but it's not easy to replicate La Vuelta," explained Mr Cooper.

"Sure, you can replicate some of the variables - dehydration, for example - to get you in the ball park, but it's not going to be the same."

The University of Kent's Dr John Dickinson - who has tested numerous British Olympians for asthma, including Team Sky riders - agrees with Professor Cooper on Froome's likely approach.

Dr Dickinson said: "Some individuals may have a greater metabolism and excretion rate that may cause the Salbutamol concentration to be increased.

"The World Anti-Doping Agency are aware of this and they will ask any athlete with adverse levels to provide evidence to explain why."

As well as dehydration, it is possible that what Froome was eating that day may have played a part or if he was any other medication.

Dr Dickinson also agrees that the research on the possible benefits from inhaled Salbutamol are clear: it is not a performance-enhancing drug but it is performance-enabling for asthmatics.

There is, however, evidence to suggest that it does provide a competitive benefit if taken intravenously or in tablet form.