The findings have called into question the army's policy of putting men and women through the same training regime.

A team from the Royal Hospital Haslar, Gosport, found that more female recruits suffered from stress fractures.

Since the Ministry of Defence introduced an equal opportunities policy in 1993, female recruits have been put through the same physically-demanding training schedule as men.

The researchers, writing in the British Medical Journal, observed a fourfold increase in patient referrals between 1994 and 1996.

This was in large part due to an increase in female patients with bone injuries, such as stress fractures, shin splints and covert fractures.

Bone scans

The researchers studied the bone scans of all recruits of an army training regiment who were referred with suspected trauma between April 1995 and March 1997.

During that time 4,222 recruits - 3,367 men and 855 women - carried out basic fitness training and were assessed at the regiment.

A total of 143 men and 121 women were referred with signs and symptoms of lower limb trauma.

The referral rate for men was therefore 4.2%, but for women it was 14.2%. In all, 71% of men and 77% of women who were referred were found to be suffering from an abnormality, mostly stress fractures and shin splints.

Dr Murdo Macleod, one of the study authors and a consultant in nuclear medicine, said: "The female skeleton is lighter than that of the male and the muscle is less bulky.

"Therefore, women are less efficient at counteracting periods of severe stress and strain such as those experienced during an endurance course."

Dr Macleod said female recruits experienced a particular problem with the small bones of the pelvis. He said women were less biomechanically suited to arduous activity than men.

"It is common sense that women are not as strong as men, and if you put them up against men they will suffer," he said.

"There is no reason why women cannot join regiments on the front line, but if they are recruited to join the infantry and you put them into a combat situation they are obviously going to let the side down because they are not strong enough."