Hugh Pickens writes writes "Millions of Americans don’t engage in much exercise, if they complete any at all and asked why, a majority of respondents, in survey after survey, say, “I don’t have time.” Now Gretchen Reynolds reports that instead of wondering just how much exercise people really need in order to gain health and fitness, a group of scientists in Canada are turning that issue on its head and asking, how little exercise do we need to maintain fitness and the answer appears to be, a lot less than most of us think — provided we’re willing to work a bit. Most people have heard of intervals, or repeated, short, sharp bursts of strenuous activity, interspersed with rest periods. Almost all competitive athletes strategically employ a session or two of interval training every week to improve their speed and endurance. Researchers have developed a version of high-intensity interval training (HIIT) that involves one minute of strenuous effort, at about 90 percent of a person’s maximum heart rate (which most of us can estimate, very roughly, by subtracting our age from 220), followed by one minute of easy recovery. The effort and recovery are repeated 10 times, for a total of 20 minutes and the interval training is performed twice a week. Despite the small time commitment of this modified HIIT program, after several weeks of practicing it, both the unfit volunteers and the cardiac patients showed significant improvements in their health and fitness. "A growing body of evidence demonstrates that high-intensity interval training can serve as an effective alternate to traditional endurance-based training, inducing similar or even superior physiological adaptations in healthy individuals and diseased populations, at least when compared on a matched-work basis.""