08/08/2012 04:00 EDT | Updated 10/07/2012 05:12 EDT

Canada's Olympic synchronized swim duo perform lung-busting routines in London

To experience the same oxygen deprivation as a synchronized swimmer, Marie-Pier Boudreau-Gagnon suggests the following exercise.

Get on an exercise bike and start pedalling like mad. Get your heart rate up to 180 to 190 beats per minute.

Now hold your breath and pedal at the same time. After 15 seconds, take just two breaths.

Keep pedalling hard and hold your breath for another 15 seconds.

When you take your next two breaths, smile your most brilliant smile.

Repeat that sequence for three and a half minutes, if you can.

"I think it's a good exercise for people who want to know how hard synchro is," says Boudreau-Gagnon, a member of Canada's Olympic team.

Even when her body is screaming for oxygen, which it is at the end of her Olympic routines, Boudreau-Gagnon has to make her moves look effortless while moving in sync with duet partner Elise Marcotte to score top marks with the judges.

The 29-year-old from Riviere-du-Loup, Que., estimates she and Marcotte, from L'Ancienne-Lorette, Que., spend half their free duet program underwater.

"The Jester is a really hard program where we hold our breath for a long time," Boudreau-Gagnon says. "For me and Elise, it took two months before we were able to do it (from start to finish).

"It's the hardest routine I've ever swum, the Jester, but I think it's the coolest one too. We are not breathing a lot. We are doing a lot of figures in the water. We are just going in and out (of the water) non-stop at the end, which makes it really hard.''

The longest they go without a gulp of air during the program is about 25 seconds, during which time they're in constant motion.

They're kicking their legs in an egg-beater motion to push their torsos out of the water, sculling furiously with their arms while upside down to get their hips above the water line or hoisting each other clear of the water.

"Our heartbeat is really, really high," says Marcotte. "It's around 180 to 200. Holding our breath at the same time that is hard."

It takes hours of pool and dryland training to get their bodies to adapt to those physical and respiratory demands. They run stairs in the gym. They swim laps underwater or swim hard on the surface without taking a breath.

Simply rehearsing their routines over and over again pushes their hearts and lungs to the maximum.

"It's really, really hard so we need to repeat it a lot to get the cardio we need to finish it really well," Marcotte says.

The pair finished fourth in the duet event Tuesday. They will compete in the team competition starting Thursday.