British running star Mo Farah has refuted suspicions that his startling form is down to drugs, saying that it was solely hard work that got him atop the podiums at the London Olympics and Moscow worlds.
"I work hard at what I do," Farah told the Daily Telegraph from his altitude training base at the French Pyreanean town of Font-Romeu.
"If I didn't I wouldn't be up here in the mountains, spending more than six months a year away from my wife and kids. That's why it hurts."
Farah backed up his 5,000-10,000m double at the London Games with a similar feat at last month's world championships in the Russian capital to ensure his place among the top distance runners there have ever been.
But he has had to battle back against allegations that his streak to podium-topping form was down to doping.
"Look at my success, I didn't achieve it overnight. It has been the product of many years' struggle, and every year my times have shown gradual improvement," he told the Telegraph.
Farah even refutes claims that his times have improved exponentially since his move to the United States under coach Alberto Salazar.
"I was running sub-13 minutes for 5,000 when I was still coached by Alan Storey, and I won double gold at the Europeans in 2010," he maintained.
"Even if you compare my world-title run over 10,000 this summer to six years ago, I was still there at the bell in Osaka, too. It was only in the last 200 that I fell back to sixth."
Farah added: "All of this hurts, because deep down I know that I'm probably the most tested athlete in the world. I have to give up a one-hour slot every day, no matter where I am on the planet.
"I only wish that other countries had the same system. What we need, to get on top of this problem, is to apply the same rules worldwide. For my part, I know that Alberto is a great coach, and that for all my blood tests I work with Barry Fudge, the top physiologist at UK Athletics. I never go outside the system."
Farah's next outing will be against former winner Haile Gebrselassie and fellow Ethiopian Kenenisa Bekele in the half-marathon at Sunday's Great North Run.