Weight limits designed to screen out unfit Army applicants are excluding some of the strongest candidates and will be relaxed, the MoD says.
It had been feared larger soldiers could not perform certain roles
Under previous regulations, men with a body mass index (BMI) of over 28 were barred from joining the military.
The threshold has been extended to 32 - two points above the World Health Organisation's definition of obesity.
An MoD spokesman said the decision was a reflection of "the fact that the BMI is not a perfect science".
BMI is calculated by squaring a person's height in metres and then dividing their weight in kilograms by the result.
It had been the case that world-class rugby players, such as England's Lawrence Dallaglio and New Zealand's Jonah Lomu, would be barred from entering the Army.
But under new, relaxed guidelines, a 6ft recruit could weigh almost 17 stone and still be admitted.
Meanwhile, the limits for women will remain the same at 28.
The weight test had been used because larger soldiers were often unable to take on certain roles.
For example, drivers' seats in tanks offer limited space.
But the notion that brute strength can be useful for tasks such as carrying artillery for extended periods and building bridges has prompted a re-think.
Despite the new approach, the MoD has insisted that there will not be any "lowering of standards" as a result of the rule change.
Army hopefuls must still pass physical fitness tests in which those aged under 30 will be obliged to complete 44 press-ups and 50 sit-ups in two minutes, before running a mile-and-a-half in 10 minutes 30 seconds.
"People like Lawrence Dallaglio are technically overweight," a MoD spokesman said.
"We are doing this because not all good applicants fit into the categories."
Recruitment has been a problem for the Army in recent years, which the government has attributed to high employment levels in the economy overall.
The shortage of applicants has also been due, in part, to the war in Iraq.