06/03/2015 12:41 EDT | Updated 06/03/2016 05:59 EDT

Three weeks of pain at altitude camp in Flagstaff paid off for Canadian runners

By all appearances, Flagstaff is a postcard-perfect city nestled among the gorgeous mountains of northern Arizona.

But Canada's top distance runners know another side of the city that sits way up at 7,000 feet above sea level, with air so thin it leaves the lungs gasping and the legs screaming.

Training at altitude exacts a painful price, but it's already paid off this season for Canada's distance runners. Just two days after returning from a three-week national camp in Flagstaff, six Canadians ran the qualifying standard for the 2016 Rio Olympics.

One of them was Alex Genest, a steeplechaser from Lax-Aux-Sables, Que., who brought his wife and two young sons to Flagstaff. If they were hoping for family time, all he wanted to do between workouts was sleep.

"My wife was saying 'Let's go do this, let's do that.' And I'm saying 'No, I cannot do that,'" Genest said, laughing. "(The altitude) does hurt. The air is really dry. And then breathing is harder, you don't get as much oxygen. Even sleeping, sometimes you wake up and you're. . .gasp!. . . lacking oxygen. Even by the third week, when you're running well, oh my god, I still felt so tired."

Cam Levins of Black Creek, B.C., a bronze medallist at last summer's Commonwealth Games, shattered the Canadian 10,000-metre record last weekend, days after returning from training at 8,000 feet in Park City, Utah.

Altitude training, which has become an annual ritual that kicks off the outdoor track season, can be traced back at least to the 1968 Olympics in Mexico City. A large proportion of the distance medals in Mexico City — which is at 7,300 feet — were won by athletes living at higher elevations in countries like Kenya and Ethiopia.

Sport physiologist Trent Stellingwerff said it's like natural blood doping. At altitude, the body senses the lack of oxygen and releases the hormone erythropoietin (EPO), which in turn triggers the production of more red blood cells to aid in oxygen delivery to the muscles.

"It's natural and completely legal and anyone who goes up to altitude gets the same responses," said Stellingwerff, who oversaw the Flagstaff camp.

EPO more often makes headlines as a performance-enhancing drug — the use of synthetic EPO is banned by the World Anti-Doping Agency.

"Nothing we're doing is rocket science," said Stellingwerff, whose wife Hilary, an Olympian in the 1,500 metres, participated in the camp. "It's standard routine for most progressive sports countries in the world."

It's also routine for other endurance sports. Canadian swimmer Ryan Cochrane was in Flagstaff at the same time as the runners. He described it as a shock to the system.

"I remember the first year, I couldn't walk and talk at the same time, I could only walk. Or I couldn't walk and drink at the same time," the two-time Olympic medallist said with a laugh. "It's funny how slow we go, it takes a good five or six days to kind of be able to do anything."

Stellingwerff said he worked in Flagstaff with about half of Canada's rowing team before the London Olympics, and said altitude training is also common practice for speedskaters, cross-country skiers and cyclists. It's only been in the last few years that it's been systematically applied in track and field.

Clara Hughes, an Olympic medallist in both speedskating and cycling, spent most of her career living at altitude, Stellingwerff said.

"Their house in Utah is at 7,500 feet above Salt Lake City, way up in the mountains, so throughout her entire career she spent many months at altitude," Stellingwerff said.

Studies on altitude training, Stellingwerff said, show the boost in red cells last for about two to three weeks before they slowly return to normal. Some studies have shown a cumulative effect of training at altitude.

Matt Hughes (3,000 steeplechase), Jessica O'Connell (women's 5,000), Lanni Marchant (women's 10,000), and Jessica Furlan and Genevieve Lalonde (women's 3,000 steeplechase) were the other Canadians who ran the Olympic standard on the heels of Flagstaff.