NYT here; original study here:
"The men exercising half as much, however, seemed to grow energized and inspired. Their motion sensors show that, compared with the men in the other two groups, they were active in the time apart from exercise. “It looks like they were taking the stairs now, not the elevators, and just moving around more,” Mr. Rosenkilde says. “It was little things, but they add up.”
The overall message, he says, is that the shorter exercise sessions seem to have allowed the men “to burn calories without wanting to replace them so much.” The hourlong sessions were more draining and prompted a stronger and largely unconscious desire to replenish the lost energy stores.
Of course, the study involved only young men, whose metabolisms and weight-loss motivations may be quite different from those of other groups, including women.
The study also was short-term, and the results might shift over the course of, say, a year of continued exercise, Mr. Rosenkilde says. The men working out for 60 minutes were, after all, packing on some muscle, while the 30-minute exercisers were not. That extra muscle offset some of the vigorous exercisers’ weight loss in the short term — they sloughed off fat but added muscle, decreasing their net loss — but over the longer term it could amp up their metabolism, aiding in weight control."