Allan Taylor, of Kensington Park, with his sons Lukaz Solding, 7, and Mereki Solding, 10,, both of whom cycle to school. Picture: Stephen Laffer Source: News Limited

A University of South Australia study also found the number of children exercising during recess and lunch has dropped significantly.

Researchers have warned that children will opt for sedentary activities if given the choice. They say part of the solution to the "alarming" trend is for adults to organise structured exercise and make it fun.

UniSA researchers compared a random sample of 300 school students aged 9-13 years in 1985 with this year.

They found two-thirds of current students never cycled or walked to school, compared with one-third in 1985.

Cycling to school has almost vanished, down from two in every five students in 1985, to only one in 20 this year.

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Study co-author, Associate Professor James Dollman, blamed the "alarming" findings on society's exaggerated fears of crime and overcautious attitude to road safety.

"There is certainly a pervading perception among parents of the risks (walking and cycling to school) but that is not borne out by objective crime statistics,'' he said.

"Cycling has almost disappeared, and there are not even many schools encouraging it with bike parking any more.''

Associate Professor Dollman said the results of the study, presented to a Melbourne conference this month, measured how much children exercised en route to and from school, during recess and lunch, and in physical education and school sport.

The number of students who participated in no physical education increased from 12.8 per cent to 16.5 per cent between 1985 and 2013.

This and the big drop in school sport participation, from 60.1 per cent to 46.5 per cent, could be partly explained by changing definitions, the introduction of newer style sports and the way PE was taught, Associate Professor Dollman said.

But the loss of "active transport" to school and also a reduction in exercise during recess and lunch breaks was "unequivocal", he said.

The number of children cycling to school has halved in a generation. Source: The Advertiser

He said the education system should address the fact that many children were now shunning exercise during their school lunch breaks.

Kensington Park father Allan Taylor said his sons Mereki, 10, and Lukaz Solding, 7, had never encountered any problems cycling to school.

"Mereki has been cycling to school for a couple of years, and he started by following his mum cycling on the footpath,'' he explained.

"I watched him and saw he was up to it so he can cycle on his own (three blocks) now.''

In 1985, 12.8 per cent of students did no exercise during their lunch break, 26 per cent did low-intensity exercise and 59 did vigorous exercise.

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But by 2013, the numbers of sedentary students had increased to 15.8 per cent, those engaging in low-intensity exercise fell to 15.4 per cent and vigorous exercise dropped to 45 per cent.

"This is a clear example of where if kids are given the choice, they appear to be opting for more sedentary alternatives,'' Associate Professor Dollman said.

"I think that is alarming and I think that reflects a trend along with the active transport decline.''

Associate Professor Dollman said children responded better when adults organised exercise activities which could be achieved at school during lunch breaks.

Australian Medical Association SA branch president Dr Patricia Montanaro said doctors were concerned about the trends which were emerging in such studies.

"The AMA view is that it is very important for children to be physically active and studies like this highlight that it is something we need to keep reminding people of,'' she said.

"Physical activity is vital for health and it is up to everyone to be encouraging that within the family, within the school, within social settings, within the broader community and at the government level," she said.

"It is very easy to become less active, and it is a natural tendency, so what studies like this show is that there has to be a clear and conscious decision to participate.

"Exercise can still be made fun, it can be structured by adults to make it fun."

Dr Montanaro said in terms of children who were discouraged from walking or cycling to school because of safety reasons, risks needed to be balanced.

"We need to balance risks and while there may be risks involved in activity, The risks in being too cautious may outweigh other risks, and often it should be about risk minimisation and making sensible choices,'' she said. "The pendulum can swing too far and we can be too cautious.''