Four-time Tour de France winner Chris Froome says his legacy will not be tainted after returning an "adverse" drugs test at the Vuelta a Espana.
The Team Sky rider, 32, had double the allowed level of legal asthma drug Salbutamol in his urine.
In an interview with the BBC in Mallorca, Froome said he "knows the rules" and there was "no wrongdoing".
"I understand this comes as a big shock to people," he said. "I certainly haven't broken any rules here."
Cycling's world governing body the UCI wants more details from the team but says Froome is not suspended.
The use of Salbutamol is permitted, without the need of a therapeutic use exemption (TUE), but only within certain doses.
Froome says he increased his dosage but it was within the legal limits, adding that he was "only too happy" to help the UCI "fill in the blanks".
Asked whether he felt his legacy was permanently tainted, Froome said: "No."
He added: "I can understand a lot of people's reactions, especially given the history of the sport. This is not a positive test.
"The sport is coming from a very dark background and I have tried to do everything through my career to show that the sport has turned around."
'I have done this for 10 years now'
Froome says he took his team doctor's advice to up his inhaler use after his asthma symptoms got worse during the Vuelta.
He became the first Briton to win the three-week race around Spain and it followed his Tour de France victory in July.
He was notified of the "adverse analytical finding" on 20 September 2017.
The urine test, taken on 7 September, showed levels of the drug, Salbutamol, which is commonly taken for asthma, were at 2,000 nanograms per millilitre (ng/ml).
That compares to the World Anti-Doping Agency's (Wada) threshold of 1,000 ng/ml.
"I have been a professional cyclist now, treating my symptoms and racing with asthma, for 10 years," said Froome.
"I know what those rules are, I know what those limits are and I have never been over those limits.
"I have got a very clear routine when I use my inhaler and how many times. I have given all that information to the UCI to help get to the bottom of it."
'I need to disguise my weaknesses'
Froome was named in leaked medical records by the Russian hackers Fancy Bears as one of the athletes to use TUEs during competition.
The documents claimed he was given the exemption for the asthma drug prednisolone in May 2013 and April 2014.
Earlier this year, the rider admitted he rejected a TUE for his asthma during his Tour de France win in 2015.
Froome said journalists could see he was struggling after stages during the Vuelta, but told them he was fine in order to "disguise any kind of weaknesses from his rivals".
"I am racing against guys who are looking for any kind of weakness," he added.
"I am not going to admit through a Grand Tour that 'yes. I am suffering with something', because the next day my rivals will come out absolutely swinging."
What now for Froome? - analysis
Dan Roan, BBC sports editorThe greatest cyclist in the world and arguably Britain's most successful current sports star now faces a fight to salvage his reputation.
Froome's domination and his use of medication to treat his asthma has meant he has been repeatedly been forced to insist he is clean, and infamously faced abuse from some roadside spectators during the 2015 Tour de France. He has also been a vocal critic of "abuse" of TUEs.
Some are surprised at Froome's announcement two weeks ago that he was riding next summer's Giro d'Italia when he knew that this situation could mean he may be banned. But others will remain confident he can satisfactorily explain the elevated levels of Salbutamol, and continue a career that has earned him a £4m-a-year contract with Team Sky. Certainly, there will be much at stake when the UCI rules.
This could also be yet another blow to Team Sky, too. A UK Anti-Doping investigation into a mystery delivery to former rider Sir Bradley Wiggins was damaging enough, but this could be much, much worse. Not just for Froome and his team, but for the whole of the sport too.
More controversy around Team Sky
Last week former UCI chief Brian Cookson said Team Sky should have its reputation "reinstated" following unproven doping allegations and questions over its use of TUEs.
"I don't think anyone should be surprised when a professional sports team pushes the rules right to the very limit," Cookson said.
In November, UK Anti-Doping completed its investigation into allegations of wrongdoing at Team Sky and British Cycling.
The 14-month inquiry was looking into claims a 'mystery' medical package delivered for Sir Bradley Wiggins at the Criterium du Dauphine in 2011.
Ukad said it had been "unable" to prove the package contained a banned substance.
Wiggins had sought TUEs to use banned anti-inflammatory drug triamcinoclone for allergies and respiratory issues before the 2011 Tour de France, his 2012 Tour win and the 2013 Giro d'Italia.
Wiggins, British Cycling and Team Sky always denied any wrongdoing.
Previous Salbutamol use in cycling?
The NHS say, Salbutamol is used to relieve symptoms of asthma such as coughing, wheezing and feeling breathless. It relaxes the muscles of the airways into the lungs which makes it easier to breathe.It comes in an inhaler, but can also be given as tablets, capsules or syrup and several studies have suggested there is no enhancement in performance for an athlete using it.
However, Wada introduced strict dosage regulations for 2017 for several asthma drugs - including Salbutamol - over concerns about the increase in use among athletes.
Italian rider Diego Ulissi got a nine-month ban in 2014 for having 1920ng/ml in his test results and countryman Alessandro Petacchi was banned for a year for a reading of 1320ng/ml in 2007.
But riders have also been able to successfully explain adverse analytic findings. Leonardo Piepoli avoided a ban in 2007.
Should Froome not be able to similarly successfully explain the anomaly, he could be stripped of his Vuelta title and may be unable to ride in May's Giro d'Italia - as he seeks to become just the third rider to win three successive Grand Tours - or defend his Tour de France title in July.
What happens to Froome next?
Dr Tom Bassindale, an anti-doping scientist at Sheffield Hallam University, now expects Froome to have laboratory tests to try to explain the abnormal result.
But he said he was surprised that such a common drug as Salbutamol had caused this issue.
"The regulations allow the athlete to go through a controlled experiment where he will replicate the dosage taken and try so show why his body might have a different physiological make-up which gave the result," he told BBC Sport.
"I wouldn't anticipate a few extra puffs on an inhaler would have any performance-enhancing effect. It can have similar effects to drinking coffee - your heart beats faster, it can give you a boost like caffeine."
Dr Bassindale said there are a number of reasons why the test result could have been so high - but the main explanation in athletes would be dehydration.
"When the body is dehydrated, it can increase the concentration of the drug in the system," he said.
"Hours out riding a bike through the mountains might have that effect. But, having said that, Froome has been a professional athlete for some time and hasn't had any issue like this before."
Why do so many elite athletes have asthma?
Analysis - Philippa Roxby, BBC health reporterTop athletes are more likely to have asthma than the general population.
This is down to the large volumes of air they breathe in through their mouths when exercising at high intensity over long periods of time.
When the air is cold and dry, this can trigger asthma-related symptoms such as wheezing, shortness of breath and tightness in the chest, also known as exercise-induced asthma. Cyclists are particularly at risk because of the high aerobic element of the sport. Air pollution getting into the airways out on the road can also be a trigger.
Research suggests that around 35-40% of British Olympic cyclists use an inhaler, compared with 21% of the Olympic team as a whole and 9% of the general population.
If asthma is already diagnosed in elite athletes, then intensive exercise can make it worse - but if it is properly treated, the condition should not prove a disadvantage.
BBC
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