The researchers emphasize that the new study, published in the latest issue of the journal Health Psychology, is correlational in nature and thus does not prove that perceptions of inactivity cause earlier death. However, other experimental research - such as Crum's 2007 study - does suggest a causal nature to the link between perceived amounts of exercise and health outcomes.

"So much effort, notably in public health campaigns, is geared toward motivating people to change their behavior: eat healthier, exercise more and stress less," Crum was quoted as saying in a news release. "But an important variable is being left out of the equation: people's mindsets about those healthy behaviors."

Zahrt and Crum offer possible explanations for mindsets and perceptions having such powerful effects on health. One is that perceptions can affect motivation, both positively and negatively. Those who are made aware of their healthy activity levels - like the hotel room attendants in Crum's 2007 study - can build on them and exercise more. Those who deem themselves unfit are more likely to remain inactive, fueling feelings of fear, stress or depression that negatively affect their health. And, there is established influence of placebo effects, where patients who think they are getting a treatment experience physiological changes without receiving actual treatment.

In the same way, people who believe they are getting good exercise may experience more physiological benefits from their exercise than those who believe they aren't getting enough exercise.

How can people use this finding? Many Americans think that vigorous exercise in a gym is the only way to attain a proper activity level, according to Zahrt and Crum. But being mindful of and feeling good about activities you do every day - like taking the stairs, walking or biking to work, or cleaning the house - could be an easy first step for everyone to benefit their health.

"In the pursuit of health and longevity," Crum said, "it is important to adopt not only healthy behaviors, but also healthy thoughts."