Scientists have long known the placebo effect can be incredibly powerful: Fake pills can ease pain as much as real medication, and rubbing fake poison ivy on people can cause actual rashes. (There was a terrific story in the New York Times magazine last spring about the placebo effect.)

But now a new study poses an even trippier idea: That merely imagining that you got a workout can give you the same effects as a real-life one. A group of researchers led by Harvard’s Ellen Langer recently performing an interesting experiment. As a press release describes it:

The researchers studied 84 female housekeepers from seven hotels. Women in 4 hotels were told that their regular work was enough exercise to meet the requirements for a healthy, active lifestyle, whereas the women in the other three hotels were told nothing. To determine if the placebo effect plays a role in the benefits of exercise, the researchers investigated whether subjects’ mind-set (in this case, their perceived levels of exercise) could inhibit or enhance the health benefits of exercise independent of any actual exercise.

Four weeks later, the researchers returned to assess any changes in the women’s health. They found that the women in the informed group had lost an average of 2 pounds, lowered their blood pressure by almost 10 percent, and were significantly healthier as measured by body-fat percentage, body mass index, and waist-to-hip ratio. These changes were significantly higher than those reported in the control group and were especially remarkable given the time period of only four weeks.

That’s just lovely! Even your weight loss can be affected by your mindset. The full paper is here online if you want to read it. I can just imagine the hilarious ways this study will get twisted out of proportion in the popular press. Someone’s probably going to start an “imaginary gym”, and charge people $100 a month merely to tell them that they’ve had workouts.