Courts across the world are grappling about whether to allow data from Fitbits and other devices as evidence, especially in personal injury claims.

The devices, often in conjunction with smartphone apps, monitor activity, heart rates, sleep and kilojoules consumed.

In the Canadian city of Calgary, one law firm is set to use data from a fitbit to prove their client, a young woman, is significantly less active than she was five years ago because of a personal injury.

Maurice Blackburn principal lawyer Geraldine Collins said she was not aware of such devices being used as evidence in an Australian court but added it was an "interesting idea".

"It's one of various tools that may be used but it's not going to replace other evidence," she said.

The problem with introducing such devices into the court system was that such data would need to be verified.

"It's problematic in that regard," Ms Collins said. "How does the court know the person in question actually wore the device? Also, these items are very subjective – they show how long someone has walked but not the impact that had on them."

The Calgary case could possibly be a world-first: McLeod Law is representing a young womanwho claims she is significantly less active because of an accident she was involved in four years ago.

Her lawyer Simon Muller said  his client's device would back up her claims and avoid having to solely rely on "clinical interpretation" by doctors.

"Now we're looking at longer periods of time though the course of a day, and we have hard data," he said. "We're expecting the results to show that her activity level is less and compromised as a result of her injury."

Slater and Gordon senior associate of medical law, Nick Mann, said it was likely insurance companies would be eager gain access to data, which would be used to discredit claims, thus making it easier to avoid paying out dubious claims.

That potential raises privacy issues, Mr Mann said, especially if insurance companies filed subpoenas to gain access to people's exercise regimes.

"I have no doubt they'd be eager to use this. A device that measures your blood pressure – they'd be very keen to access that data. That's a concern, but I don't think they could force someone to wear one."