Young female garda recruits are the most likely to fail the fitness and physical capacity tests that are in place for entry to the force.
A detailed breakdown of success rates according to age and gender has been released for the first time by An Garda Siochana following a Freedom of Information (FOI) request.
It shows wide variations in success rates, with more than 60pc of women under the age of 21 failing their fitness test last year.
That compared with a failure rate of just 11.3pc among men between the ages of 31 and 35.
The stringency of the testing system has been a source of concern for the Garda Representative Association (GRA), which last year sought a review after saying the system was "excessively harsh".
Those concerns have been disputed by Garda Headquarters according to correspondence, which was also obtained under FOI.
In a letter to the GRA, the force's chief administrative officer Joseph Nugent said it was "somewhat surprised" about questions over the necessity of passing the fitness test.
"Notwithstanding that it is correct to say that some members have failed the test, the vast majority of probationers do pass the test," Mr Nugent wrote.
"The standard required is well known and has not changed and all those entering the organisation are made aware of their requirement to achieve the necessary fitness level."
New garda recruits currently have to pass two separate tests - a fitness test and a physical competency test.
The fitness test involves a progressive shuttle run, a sit-up test and a press-up test, with targets tailored to age and gender.
Candidates must also complete a physical competency test which involves an obstacle-style course of sprinting, climbing, carrying, jumping and lifting.
Last year, failure rates in the fitness test were higher than in the physical competency test, according to official figures.
The failure rate in the fitness test among women under 21 was 61.9pc; under 26 it was 43.6pc; under 31, 24.8pc; and under 36, 31.9pc.
A single female candidate, who was aged 36 or older, also took the test and failed.
Rates of success were significantly higher for men but, among males, older candidates were also more likely to pass their fitness test.
The failure rate for men under 21 was 24.7pc; under 26, 19.1pc; under 31 it was 18.4pc; and under 36, 11.3pc. Three candidates aged over 35 also took the test, just one failing.
For the physical competency test, males had a very high rate of success.
Of 73 men under 21 tested, 91.8pc passed. The success rate rose to 96.4pc for under 26s, 98.6pc for under 31s and 98.3pc for those under 36.
For male candidates above that age, there were just two tests with both successful.
Female candidates had much more difficulty with the physical competency test, according to the figures.
Among women under 21, the failure rate was 39.6pc. For those 25 or under, it dropped to 28.8pc.
For candidates between 26 and 35, the rate of success was around 23.5pc.
The official figures also recorded 277 "no shows" out of 1,612 total tests.
Internal correspondence also shows how the Garda Representative Association first raised concerns about the issue in a letter to the Garda Commissioner in December 2018.