IT emerged on Wednesday that the 32-year-old Team Sky rider Chris Froome has been asked to explain why a urine sample he gave during the three-week La Vuelta race in Spain in September was found to contain twice the permitted concentration of salbutamol.

If Froome fails to provide a satisfactory answer, the UCI – the sport’s governing body – could proceed with an anti-doping rule violation case which could strip him of his Vuelta victory and result in him missing a large chunk of next season. Four-time Tour de France winner Froome said yesterday: “This is damaging. It’s come as a huge shock to me as well.

“At the same time I know within me that fundamentally I have followed the protocol, I have not overstepped any boundaries and I hope by the end of this process that will be clear to everyone and I’ll be exonerated of any wrongdoing.

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“As it stands, we’re doing everything we can to give the relevant authorities all the information we’ve got from the Vuelta.”

Recorded on September 7, the concentration of salbutamol in Froome’s sample was 2,000 nanograms per millilitre (ng/ml), double the World Anti-Doping Agency’s limit of 1,000 ng/ml.

When asked how the adverse finding could have come about, Froome added: “I think that’s exactly the question we’re facing now.

“I know the number of puffs of my inhaler that I use to treat my asthma. It’s a very common inhaler – it’s salbutamol – every asthmatic out there will know, this is a very common medication used to treat asthma.

“I’ve known exactly how many puffs I’ve taken at what times and there are records to show that. So we’ve been able to hand that over to the authorities and let’s go from there.

“Coming into the last week of La Vuelta I began to feel a lot more symptomatic – my asthma was playing up a lot more and that’s when the doctor advised me to increase the number of puffs – obviously staying well in the legal limit of the maximum allowed number of puffs you can take during the race.

“So we did increase it and that’s why we’re faced with this question of ‘I did stay within the limits but obviously the test results show a different reading’ so we’re trying to evaluate what has happened.”

SALBUTAMOL is a medication that helps to open up the medium and large airways in the lungs, and is a treatment for ailments such as asthma, chronic bronchitis and other breathing disorders. It is usually taken with an inhaler.

It was discovered by a team at the Allen and Hanburys laboratory in Hertfordshire in 1966, and three years later it was commercially launched as Ventolin.

After using the inhaler, salbutamol swiftly eases breathing. One use of the inhaler equates to about a five-hour benefit. It has very few side effects and is considered a safe and effective medication.

Salbutamol is banned by the World Anti-Doping Agency (WADA) when taken intravenously or in pill form – research suggests large doses administered like this can boost performance – but asthma sufferers can take up to 1,600 micrograms over 24 hours, without exceeding 800 micrograms every 12 hours. A typical dosage, or inhaler puff, is 100 micrograms.

Experts say Froome’s defence will hinge on his ability to prove there is a scientific reason for the spike in his salbutamol.

Professor Chris Cooper says Froome “would have to be really stupid” to try to cheat with the drug 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.

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,” explains Professor Cooper, who runs the University of Essex’s Centre for Sports and Exercise Science.

“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 says: “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.