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