Gretchen Reynolds in The New York Times:
For many of us, the most pressing question about exercise is: How little can I get away with? The answer, according to a sophisticated new study of interval training, may be very, very little. In this new experiment, in fact, 60 seconds of strenuous exertion proved to be as successful at improving health and fitness as three-quarters of an hour of moderate exercise. Let me repeat that finding: One minute of arduous exercise was comparable in its physiological effects to 45 minutes of gentler sweating. I have been writing for some time about the potential benefits of high-intensity interval training, a type of workout that consists of an extremely draining but brief burst of exercise — essentially, a sprint — followed by light exercise such as jogging or resting, then another sprint, more rest, and so on. Athletes rely on intervals to improve their speed and power, but generally as part of a broader, weekly training program that also includes prolonged, less-intense workouts, such as long runs.
But in the past few years, exercise scientists and many of the rest of us have become intrigued by the idea of exercising exclusively with intervals, ditching long workouts altogether. The allure of this approach is obvious. Interval sessions can be short, making them a boon for anyone who feels that he or she never has enough time to exercise. Previously, I have written about a number of different interval programs, involving anywhere from 10 minutes of exhausting intervals in a single session to seven minutes, six, four and even fewer. Each program had scientific backing. But because of time and funding constraints, most studies of interval training have had limits, such as not including a control group, being of short duration or studying only health or fitness results, not both.