By Grace Chua

HEAVY schoolbags do not just give children backaches. They actually change the way children walk, a Republic Polytechnic study has found.

In it, 17 primary school boys were put on a treadmill while bearing low-slung backpacks weighing 20 per cent of their body weight.

They took shorter, quicker steps to keep their balance on the moving treadmill than when they were carrying nothing. They also leaned forward while on the move.

While the changes in gait reduce the impact on children's limbs, they are not enough to ward off problems to their posture or their joints and ligaments, said Dr Michael Koh, a biomechanist and director of the polytechnic's School of Sports, Health and Leisure.

These problems can result in back and shoulder pain.

The study, published this month in the journal Gait and Posture, was done by Dr Koh and Mr Tarkeshwar Singh, who is now pursuing a PhD programme in kinesiology, the science of human movement.

The issue of heavy schoolbags, a bane of parents and children, has been raised in Parliament a few times. Many primary schools have come around to the idea of providing pupils with lockers.

But the number of children with back and shoulder pain has not come down by much, lamented Dr Kevin Lim, an orthopaedic consultant at KK Women's and Children's Hospital. He treats five to 10 children a week for such pain.

He said that, ideally, schoolbags should weigh in at 10 per cent of a child's body weight, and no more than 20 per cent.

Republic Polytechnic's Dr Koh said his four sons' experience with their backpacks inspired the study on the effect of hefty schoolbags on children's gait.

He said of his youngest son, who is in Primary 1 and weighs 18kg: 'It doesn't take much to tip him over.'

The study has given him the basis for a larger study, involving full-body laser scans of 300 children for an overview of their growth patterns, and to collect detailed data on 30 children, both boys and girls.

He also wants to design a backpack for Asian children's smaller frames, since most bags in the market are made with bigger Western children in mind, he said.

The ideal backpack would be lighter and smaller so children cannot overstuff them, and have straps set close together to fit their narrower shoulders. The straps should be tightened so the load is on the child's upper back, and the straps should be on both shoulders, he said.

Primary school teacher Catherine Yeo, 64, who has taught since the 1960s, said she encourages her pupils to leave their textbooks in their lockers and to carry to school only what they need.

Besides textbooks, the children here lug water bottles, coloured pencils and bulky pencil cases, she noted.

'Previously, there were no lockers but haversacks were made of lighter material and the kids survived,' she said.

This article was first published in The Straits Times on January 05, 2009.