Can your perception of your exercise habits change your weight? Harvard psychologist Ellen Langer performed an experiment with hotel maids. She found that the maids didn’t consider what they did as exercise, although their daily work activity exceeded recommendations. Half the maids were told their activity levels met the surgeon general's definition of an active lifestyle. One month later, the group that had the information was found to have lower weight, lower blood pressure, and smaller waists! However, there was no indication of changes in the group’s overall activity.
Essentially, what Langer is talking about is a placebo effect. She says that if you believe you are exercising, your body may respond as if it is. It's the same as if you believe you are getting medication when you are actually getting a sugar pill — your body can sometimes respond as if a placebo is actually working.
http://www.npr.org/templates/story/story.php?storyId=17792517 -via Reddit