The Royal College of General Practitioners has called for tax relief on sports activities in order to raise fitness levels among the population.
Spokesman Graham Archard said that the costs of formal exercise were sometimes prohibitive, especially for families with young children.
"If you have a young family and you want to take your children swimming, the costs could be absolutely astronomical," he told Sky News.
"If you were able to reduce some of the financial burdens of sport, we think that there will be an enormous increase in the amount of exercise being taken."
Dr Archard accepted that many informal forms of exercise, such as walking or jogging, were free.
But he stressed the importance of encouraging children to take up "a whole selection of activities so that they do develop a new lifestyle to keep themselves healthy".
"What we are asking for at the Royal College of General Practitioners is recognition of the fact that we need to be exercising throughout life, not just when we are overweight," he said, adding that this would save the NHS a huge amount of money in the long-run.
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