Michelle Marder had maintained her petite, 110-pound frame for years by sweating through a rigorous hour of cardio on her stationary bike a few times a week.
Then she gave birth to her second child.
Breastfeeding helped her lose much of the 20 pounds she had packed on after Kyra (now 15 months old) was born, but her pre-pregnancy clothes hugged her body in an unfortunate new way, and she missed being active.
The 37-year-old Torontonian wanted to get back on the bike, but working out for an hour suddenly became an unobtainable luxury in a harried life that included an office job, child care and household chores.
Frustrated, Ms. Marder got in touch with a personal trainer - and found what she now considers to be the perfect solution: a four-minute workout.
Tabata, a type of high-intensity interval training that was originally developed for Japan's Olympic speed-skating team, is fast gaining popularity as a high-speed new-mom workout.
The Tabata method is used most widely by elite athletes.
But Tabata has recently taken off among women looking to get back into postpartum shape. Named after Izumi Tabata, a former researcher at Japan's National Institute of Fitness and Sports, the compressed workout has a simple format: Do an exercise (such as push-ups or jumping rope) for 20 seconds at full intensity, and then take a 10-second break. Repeat seven times, varying exercises, for a total workout of four minutes.
"After I started, my ass was killing me," says Ms. Marder.
The intense pain that coursed through her muscles was like nothing she had felt even after an hour of endurance training. But when the throbbing subsided after a few minutes, it was replaced with a different sensation. "You feel like you're working on your posture, and your whole body feels good," she says. "It's like coming out of a Pilates class."
Tabata training is effective, despite its brevity, because the body continues to burn calories at a high rate during the recovery period, says Martin Gibala, chair of the department of kinesiology at McMaster University in Hamilton.
In a study published last year in the Journal of Physiology, Prof. Gibala and his research team found that participants who did high-intensity interval training for just 1½ hours total each week enjoyed the same physical benefits as those who did 4½ hours of endurance training on a stationary bike. Both groups had similar levels of muscle development and lipid oxidation (which improves endurance and reduces the risk of developing obesity and diabetes).
"You can get away with less time and see many of the same adaptations we associate with endurance training," Prof. Gibala says.
He adds that Tabata can actually develop muscles in a way that isn't always possible with endurance training. "We have these very large, powerful muscle fibres, but there are some that don't get called upon in our daily lives even when we do moderate exercise. They respond and adapt during interval training," he says.
It took stay-at-home mom Amy Bonner only three months of high-intensity endurance training - including Tabata - to get rid of the last 10 pounds that had cushioned her 5-foot-2, 110-pound frame during pregnancy. But even after shedding her baby weight, the newly slimmed-down 29-year-old from Fort Bragg, N.C., says she won't ever go back to her tedious exercise routine of cardio three days a week and weightlifting two days.
"[Tabata]is so much more of an efficient workout, and you feel like you've worked your body so much harder than a regular workout - you see gains very quickly," she says. "It's easy to stay into it because your muscles start looking toned much quicker, and your body just takes on a new shape."
Though Prof. Gibala is quick to sing the praises of four-minute workouts, he says that all groups - including time-strapped moms - should still enjoy a traditional (and less painful) session of endurance training when they can. "I see a move to people demonizing traditional cardio and saying it's not good for anything. A varied approach is your best bet for fitness," he says.
Still, for the time-pressed, Tabata is appealing. Toronto trainer Jacqueline Gradish, a 37-year-old mom of two girls, extols the virtues of the quick system through Baby Bump Fitness - a program she developed for new moms frustrated by an excess of pounds on their bodies and a shortage of time on their hands. "It's definitely something that fits with your lifestyle" as a new mother, she says.
After Ms. Gradish's second child was born in March, 2008, she could wedge workouts only into the time when her children were taking a nap. Now, she's mastered a routine of warming up, doing eight Tabata intervals, showering and eating - all in under a half-half, while her baby sits in a high chair and her older child plays nearby.
Ms. Gradish says Tabata training can burn off baby weight months or even years after delivery - whenever a woman feels ready to start exercising again. But because Tabata is exhausting, she suggests easing into it with a lot of warm-ups for the first few sessions. "Focus on posture, core rehab and muscle balancing, and then make your workouts more progressive," she says.
Ms. Marder - trained by Ms. Gradish - says that the most punishing exercise she puts into her Tabata intervals is the front plank, where she's in the "up" portion of a push-up. She also alternates between push-ups, lunges and squats. She squeezes in training about three days a week, between dinner and bath time.
Her daughters usually join her in the basement for her workout. "When I'm doing push-ups, my four-year-old tries to come sit on my back," she says, laughing.
Despite the obvious physical results, Ms. Marder notes that the seemingly too-good-to-be-true Tabata method has been a hard sell to her colleagues, who have griped about their own flabby thighs and bellies. "They're kind of in the mindset that 'I have to run or use the stair climber,' " she says. "But why waste an hour and a half at the gym when you can feel even better at home in half an hour?"