Just a year earlier he had been diagnosed with blood clot on the brain. Doctors put him in a coma to save his life, and it was unclear if he would ever run again.
But while convalescing, he stumbled across news of the first Afghan woman to run a marathon. Inspired, he made a promise to himself.
"I said... if I get better and I can run again, and I can run marathons again, I will come to Afghanistan and run that marathon to support those women that are free to run and are helping to change things," he told AFP.
He was one of a handful of foreigners taking part in the second edition of the ancient city's marathon in the country's central highlands: a loop that starts and ends at the base of the world famous Buddha caves.
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The route, at an altitude of almost 3,000 metres,passes dusty villages and is set against a backdrop of dusky-pink cliffs; sheep and donkeys amble freely across the landscape.
Bamiyan is a rare oasis of tranquility, which has largely been spared the wrenching conflict that afflicts the rest of the country.
The marathon, where both sexes compete together in public, has become a symbol of freedom for Afghan women.
For Kubra and others like her -- 15 women took part in total including six from Afghanistan -- just the act of running in public is controversial, widely seen as a subversive act.
Parnell says he advised her to set aside her nerves about taking part and focus on the road ahead, ten minutes at a time.
And while it was not his first race after recovering -- he competed in Calgary in May -- it is one he won't forget.
"My best memory is holding hands with Kubra as we ran across the line at 6 hours 52 minutes," the 60-year-old recalls.
Parnell, known in Canada as the 'Marathon Man', sees the sport as a form of meditation and admits he struggles when he's unable to run.
"One of the hardest times was after I was diagosed with the clot. I had double vision and had to sit on my sofa. It was five months before I could start running again," he explains.
It hasn't always been his passion, the retired mining engineer came to the sport late in life.
Parnell says: "When I started in 2002 it certainly filled a gap that was left after the death of my wife, Wendy, due to cancer. If I hadn't found running maybe I would have turned to something less healthy like alcohol or drugs."
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Instead he channelled his energy into sporting challenges, running renowned marathons around the world before taking on more gruelling endeavours such as the Canadian Death Race (125 kilometres) and the Lost Souls (160 kilometres).
He is also in the Guinness World Record books after taking part in the longest games of netball (61 hours), lacrosse (24 hours) and five-a-side soccer (42 hours).
His antics are all in aid of charity. After a trip through Africa, he began working with NGO Right to Play, which aims to improve the lives of children through sport.
"A football match in Sudan, a ping-pong game in Ethiopia, in five minutes you're surrounded by 100 smiling kids. I realised sport could be important for them," he explains.
In 2010, he ran 250 marathons -- covering some 10,000 kilometres (2,600 miles) -- in a year, and raising $185,000 for charity.
Parnell sees it as everyone's responsibility to do what they can to help those less fortunate.
"I believe that in life you don't have to do a lot but you must do something," he explains.
"You must make a difference in the lives of the children or in the lives of other people. Do something to make a difference."
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