``We're looking at the effect thongs have on children's foot development,'' he said.

``A lot of parents put them on children for convenience, for fashion or because they are concerned about hot feet.''

The research will involve the application of 42 reflective markers to the feet of children aged 8 to 13, who will walk, run, jog, sidestep and balance in thongs while cameras and motion sensors record the movements.

Mr Chard said this was technology similar to that used to create the character Gollum in The Lord of the Rings and was accurate to within 0.5millimetres.

``We're trying to identify very accurately what happens when children wear thongs.''

He said this was important because children are typically born with flat feet and develop arches as they grow. The key time for this is before the ages of 6 and 10.

Mr Chard said it was rare for a clinician to endorse thongs because of widespread professional opinion that they are bad for feet but that it would be useful to assess the actual impact of the footwear on development.

``Children with flat feet fatigue more quickly and function with more pathological knee and ankle movements.

``This can affect how the joint works, how long the joint lasts and what injuries develop in later life.

``Some people argue they have to claw their toes to hold on to the thong, others extend their toes. The main thing is that compensations occur. You have to walk differently when you wear thongs.''

Mr Chard will give free foot and leg assessments this Saturday, January30, at The Athlete's Foot, shop GR136, Rouse Hill Town Centre, from 9am to 2pm.

The assessments are the Australian Podiatry Association's initiative to make podiatrists more accessible to the public.

``I'm happy to discuss questions about feet and legs and if they have an ache or a pain what treatment may be available,'' Mr Chard said.

Details: People with children aged 8 to 13 interested in taking part in Angus Chard's research can email info@footandlegpain.com.