An investigation into the physical abilities of Scottish Fire and Rescue Service (SFRS) staff found fewer crew members in the area, which covers Glasgow, passed the tests than anywhere else in Britain.
The probe, based on data compiled before the merger of brigades into the new service, found one in 10 firefighters failed to reach the recommended fitness levels in the past year across Britain as a whole.
Results in Scotland were worse than the UK average, with around 2890 firefighters of 24,272 failing the tests. In Strathclyde, of 652 tested, there were 435 "unfit" firefighters, of whom 111 were "seriously unfit".
The SFRS has now launched a review of working practices, but said it could not explain why Scotland's figures were worse than the rest of the UK.
The results come as the Fire Brigades Union prepares for industrial action over changes to pension rules, which will raise retirement age to 60.
The Chief Fire Officers Association is expected to produce a nationwide fitness standard next year, but currently the majority of fire services measure the "maximum rate of oxygen uptake" (VO2 max). This assesses the maximum vlume of oxygen a firefighter's body uses while exercising, in proportion to body weight.
The generally accepted standard is 42ml of oxygen per kilogram per minute. It does not test a firefighter's physical strength, which some services test separately. Below this level, a firefighter is likely to be told to improve their fitness.
Freedom of Information requests were submitted to 52 fire services asking how many firefighters had failed tests between May 2012 and April 2013. Of these, 36 provided figures, which have not previously been compiled and published.
Around 665 firefighters failed to reach a lower standard (35ml of oxygen/kg/min), below which a Government-sponsored review published in December 2012 said someone was at risk "of sudden death particularly while undergoing high levels of physical exertion".
Professor Kevin Sykes, who advises UK fire services on fitness, said it was well established being in good physical condition minimised the risk to health and unfit firemen could be forced to retire earlier. He said: "Firefighters are asked to carry additional weight, which can have a dramatic effect on their ability to perform arduous physical work, particularly for the less fit."
But the Department for Communities and Local Government said a recent review found there was no reason every firefighter who stays physically fit could not work until 60.
A spokesman said: "That report also found the majority of firefighters who lose fitness can improve their fitness within a few months. Where this happens, their fire service will ensure they get the necessary support."