Police were today warning gym members to be on their guard after a spate of thefts in the city centre.
At least six gym users have had personal items - worth thousands of pounds - stolen in the last three weeks.
Thefts from gyms in the city centre have increased by more than 20% in the past year, the Evening Times can reveal.
Personal possessions, including wallets, purses, watches, mobile phones, and laptops, were stolen from locker rooms.
Police said it is not yet clear if the crimes are linked.
The warning comes after the Evening Times reported how one gym user was devastated to find his belongings - including his wedding ring - had been stolen from his locker.
The 26-year-old said he believed suspects looked over his shoulder and watched him enter a four-digit code on a padlock which he used to secure his locker.
In total, he had around £1600 worth of personal items stolen, including a mobile phone, a watch and his wedding ring, at the 24-hour Pure Gym on Bath Street.
Thieves also took £270 in cash from his bank account using his bank card.
As he tried to work out how they could know his bank PIN number, he realised he used the same number for his gym locker.
He said: "It's my wedding ring that I'm most gutted about losing.
"I only got married in summer last year."
Between January and December 2012, there were 17 reported thefts from city gyms. That increased to 21 thefts in 2013.
Police urged gym users to keep their personal belongings safe - and always use a padlock to secure their locker.
Chief Inspector Alan Porte, area commander for the city centre, said: "I would ask people to consider the security of their property when using any sports facility.
"If using a pin code lock, always change it from a default setting to one of your own."