You heard about the interval workouts that helped your friend lose her baby weight before she finished maternity leave and the high-intensity DVDs that promised to tone you "in just 60 days." Now even university researchers are publishing papers that sound like infomercials, claiming that you can get fit in just two weeks, using an approach called HIIT.

HIIT (high intensity interval training) involves short, challenging bursts of activity with rests in between. It's not new: Hard sprints are familiar to athletes and jocks. What's notable is that this type of workout, which can be done in 20 or 30 minutes, has been adapted for adults of most ability levels and that it's been compared in the lab with the traditional, I'm-getting-serious-about-fitness workouts of 45 to 60 minutes of cardio 4 to 5 times a week, with impressive results.

Multiple studies led by exercise physiologist Martin Gibala, PhD, the chair of the department of kinesiology at McMaster University in Hamilton, Ontario, have found that HIIT workouts can provide the same cardiovascular and muscular benefits in half to one-third the time as those endurance workouts, in—yes, he says it's true—two weeks. A separate study from Ontario's University of Guelph showed that a total of seven hours of HIIT over two weeks raised women's fat-burning power, compared with 12 hours of medium-speed sessions.

Next: Here's what you need to know
As a reminder, always consult your doctor for medical advice and treatment before starting any program.


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