The project was led by scientists at Edinburgh University.
The team assessed the activity levels and size of more than 4,000 Kennel Club registered Labrador Retrievers.
The study found that, on average, dogs were exercised for more than two hours each day.
Dogs that spent more time fetching, chasing and retrieving tended to weigh less, the team said.
Chocolate-coloured Labradors were found to weigh, on average, 1.4kg (3lb) more than yellow and black Labradors.
While exercise is important, other factors such as genetics appear to play a role in why some dogs gain more weight than others in early life, the team said.
Previous research suggests that, in the UK, Labrador Retrievers are the breed most likely to be overweight.
The dogs are fully grown after 18 months and are regarded as being near middle aged by the time they reach four.
Researchers said putting on nearly 1kg (2lb) every year after reaching maturity puts many at risk of obesity.
The findings are part of the Dogslife project, which seeks to gain a greater insight into links between the Labradors` lifestyles and their health and wellbeing.
Initial findings will help researchers carry out further studies into the links between dogs` body size, lifestyle and overall health.
The study, published in the journal Preventive Veterinary Medicine, was funded by the Kennel Club Charitable Trust, The Roslin Foundation and the Biotechnology and Biological Sciences Research Council.
Dr Dylan Clements, of the Royal (Dick) School of Veterinary Studies and The Roslin Institute, who led the study, said: "Dogslife is a ground-breaking study of canine health, which is made possible thanks to the incredible dedication of dog owners."
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