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Mind over Muscle: Placebo boosts health benefits of exercise

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12:20pm, January 24, 2007
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The physical rewards of exercise derive not just from muscular exertion but, to a surprising extent, from a person's mind-set about exercise, a new report suggests.

Alia J. Crum and Ellen J. Langer, psychologists at Harvard University, made this provocative discovery when they studied 84 women who clean rooms at seven Boston-area hotels. It's a physically taxing job. Each woman scours a hotel room for 20 to 30 minutes, cleaning an average of 15 rooms daily.

For at least a month, women who had heard a brief presentation that explained how their work qualifies as good exercise displayed more weight loss, larger blood pressure declines, and other health advantages compared with peers given no such information, Crum and Langer say.

This finding suggests that exercise enhances physical health, at least in part, via the placebo effect—that is, as a consequence of an individual's beliefs and expectations. "If our mind-sets control our psychological and physical reactions and we can control our mind-sets, then we can have direct control over our health," Langer says.

The new study appears in the February Psychological Science.

Crum and Langer recruited the women, officially known as room attendants, at franchise, condominium-type, and luxury hotels. All room attendants in any hotel either did or didn't receive the work-exercise presentation.

Participants ranged in age from 18 to 55, and most were Hispanic.

A total of 44 women attended a presentation, in Spanish and English, in which Crum and Langer showed that many of the activities that the attendants engaged in while cleaning hotel rooms satisfy the surgeon general's recommendations for an active lifestyle.

Handouts and posters in the attendants' lounge areas offered daily reminders of how much exercise participants were getting.

Four weeks after the presentation, women in both groups reported no change in how much they exercised outside of work. Hotel managers confirmed that room attendants' workloads remained constant.

However, the exercise-informed women perceived themselves to be getting markedly more exercise than they had indicated before the presentation. Members of that group lost an average of 2 pounds, lowered their blood pressure by almost 10 percent, and displayed drops in body-fat percentage, body mass index, and waist-to-hip ratio. Given the study's short length, the researchers call the observed changes "small but meaningful."

Participants who weren't offered the presentation didn't show such changes in perception of their activity or in health measures.

"These data are compelling and surprising," remarks psychologist Irving Kirsch of the University of Hull in England. Kirsch has studied placebo effects of substances such as antidepressant drugs and caffeine.

Presentations to room attendants may have increased their optimism or raised expectations about the benefits of their work activities, but it's unclear how such mental adjustments would lead to health changes, Kirsch says.

To test whether women behave differently after the presentation, Crum is planning a longer investigation that will monitor physical activity using accelerometers and daily logs.

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