Kenya's former Olympic and world 1500m champion Asbel Kiprop has vowed to fight on to clear his name after being handed a four-year suspension on Saturday for using the banned blood-booster EPO.
The 29-year-old failed an out of competition test in November 2017 and was provisionally suspended in 2018.
On Saturday, the Athletics Integrity Unit (AIU) upheld that ban, concluding that the case had been "convincingly made out" despite an "a la carte menu of reasons why the charges should be dismissed" from Kiprop's representative.
After the verdict, Kiprop continued to maintain his innocence.
"The decision is not only a blow to me, but it is not good for the sport of athletics," Kiprop told AFP.
"I have been insisting that I did not dope," he said. "I will continue to maintain my innocence, even if this decision now means I will not be eligible to run again for the next four years.
"It's sad that the world will believe that I am guilty of taking the performance-enhancing drugs and yet I have been at the forefront of fighting doping in the sport."
The AIU said in its statement that Kiprop had "at various times and various formats...proposed a number of possible explanations" for the positive test.
It went on to state that at the hearing his representative, Katwa Kigen, presented an "a la carte menu of reasons why the charges should be dismissed."
Among these, the AIU said, were that the "EPO was naturally produced due to intense exercise at altitude," that it was produced by medication, that the test, or the analysis, was badly conducted or that the sample was spiked.
His ban is backdated to last February.
The AIU statement added that while Kigen presented his arguments with "tenacity and charm" the International Association of Athletics Federations (IAAF) representative Ross Wenzel had argued that "none of the various reasons proposed...when subject to strict scrutiny had any plausibility."
The three-man panel agreed.
It concluded that high altitude could not explain the presence of EPO in the test and that Kiprop had produced no evidence to support the other possible explanations.
Kiprop accepts the long ban virtually puts an end to a long and illustrious athletics career, but he can still appeal to the Court of Arbitration for Sport.
He originally came second in the 1500m final at the 2008 Beijing Olympics but was upgraded when Rashid Ramzi tested positive for a performance-enhancing drug and was stripped of the gold medal.
A total of 138 Kenyan athletes have tested positive in anti-doping campaigns since 2004.
In 2016, Kenya were placed on the list of countries under IAAF surveillance.
And it was only after the adoption of a new anti-doping law just before the Rio 2016 Olympics that the country was removed from the list of "non-compliant" WADA nations.
Asbel Kiprop won the third of his 1500 metre world titles in Beijing in 2015