So you think you're getting a good workout? Well, it could be that if you're convinced that what you're doing is making you fitter, you may actually be getting fitter — even if you're not really getting much of a workout.

It's like those drug trials — where half the people get the real drug the big drug company wants to eventually sell us and the other half get a dummy pill. Sometimes the folks on the placebo get the same benefits as the researchers expect from the people on the real medicine. It's called The Placebo Effect.

Turns out it may hold true for exercise as well.

A Harvard psychology professor and her student monitored a group of Boston hotel workers for four weeks. Half were told that their daily workload of cleaning 15 rooms a day was enough to keep them fit and healthy. The other half weren't given that message.

Dr. Helen J. Langer and Alia J. Crum checked back with the workers after the four weeks. They found that the group that had been told they were getting on-the-job exercise had lost an average of two pounds, lowered their blood pressure by 10 per cent, and had reduced their percentages of body fat, body mass index and the size of their waist in relation to their hips.

These are all signs of improved fitness.

The group that didn't get the message didn't see the benefits.

Crum and Langer say it's not clear whether telling the workers that they were getting enough exercise to keep them fit is what actually made them get fitter or whether the message helped them make other changes that resulted in fitness improvements.

What is clear, they wrote, is that health is "significantly affected by mindset."

The placebo effect has an evil twin. The nocebo effect. The term was coined in 1961 by researcher Walter Kennedy to describe a patient's negative expectation of a drug or course of treatment. He found that — in some patients — if they expected they would suffer a drug's predictable negative side effects, they would actually suffer them. If you set your mind to it, you help create the conditions for bad things to happen.

So if you believe there's no point in getting off the couch to try to increase your level of activity, there probably isn't.

It's like Yogi Berra said: "Ninety per cent of the game is half mental."