Four workouts a week may be better than six

The women working out six times a week, though, reacted very differently. "They complained to us that working out six times a week took too much time," Dr. Hunter says. They did not report feeling fatigued or physically droopy. Their bodies were not producing excessive levels of cytokines, sending invisible messages to the body to slow down.

Rather, they felt pressed for time and reacted, it seems, by making choices like driving instead of walking and impatiently avoiding the stairs.

Despite the cautionary note, those who insist on working out six times per week need not feel discouraged. As long as you consciously monitor your activity level, the findings suggest, you won't necessarily and unconsciously wind up moving less over all.

But the more fundamental finding of this study, Dr. Hunter says, is that "less may be more," a message that most likely resonates with far more of us. The women exercising four times a week "had the greatest overall increase in energy expenditure," he says. But those working out only twice a week "weren't far behind."

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