Experts say some children are fit and fat and BMI may be misleading

Scientists have questioned UK and U.S. guidelines on children's physical activity levels and say they need revising.

The researchers from the Peninsula Medical School in Plymouth in the UK based their findings on a study which monitored the long term health of a group of children born between 1995 and 1996.

The children, 113 boys and 99 girls from 54 different schools, were all 5 years old when the study started and were part of the 'EarlyBird study'.

Their weekly physical activity levels were measured using a tiny device called an accelerometer, worn around the waist.

Changes in weight and predictive health indicators, such as insulin resistance, blood fat and cholesterol levels, and blood pressure were measured annually between the ages of 5 and 8.

These health indicators together can help predict the risk of developing cardiovascular disease and diabetes.

Both the UK and U.S. guidelines recommend that children are moderately physically active for at least an hour every day, to avoid obesity and its attendant health risks and they measure body mass index (BMI) to monitor impact.

The results showed a wide range of physical activity among the children with some spending as little as 10 minutes a day at the recommended intensity while others were spending over 90 minutes a day and only around 42% of boys and 11% of girls met the 60 minute guideline.

There was however no difference in BMI change between those who did and did not meet the guidelines - however both sexes who met the guidelines showed progressive improvement in their predictive health indicators, while those who did not showed a progressive deterioration.

The researchers suggest that the measure used to gauge impact may simply be too crude, and that applying the same guideline to both sexes may not be appropriate.

While it is recognised that it is important for children to take regular exercise, experts say using a child's BMI as a measure of the success of exercise targets may be misleading.

Some experts say it is possible for an individual child to be "fat and fit", provided they are sufficiently active and they suggest that blood tests might be the only way to measure exercise benefits.

They say children who do more exercise clearly benefit, but experts have little to offer on how to encourage the 60% of boys and 90% of girls who do not meet the deadline to do more.

The study is published in the Archives of Disease in Childhood.