Gyms do little to improve the health of the nation and may even cause harm, according to a sports psychologist.
People may dash for the door after a bad gym experience
Braving the gym may be such an unpleasant experience that it puts people off altogether, according to Professor Stuart Biddle.
He said everyday exercises such as walking or climbing stairs could be a more sensible way to stay healthy.
And he said although past generations lacked gym facilities, they were leaner and fitter than people today.
Professor Biddle told the British Psychological Society's annual conference at Imperial College, London that gym-based exercise was often "hard work" which put people off.
"We've got to get the balance right between somehow benefiting from the effect of exercise without feeling unpleasant," he said.
Take a hike
"I think the gym is quite demanding for some people and I don't think that's the answer for the health of the average person in the street.
"We never had gyms in previous generations, who in some ways were leaner and fitter.
"We're not going to make that much difference to the health of society by being members of gyms."
He said that "incidental" activity was all-important and recommended leaving the car parked and walking for about half an hour a day.