Using BMI for kids' fitness questioned
Children who exercise daily have better health
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Monday, 30, Jun 2008 10:45
Using body mass index (BMI) to monitor the impact of physical activity in children may not be the best method, a new study claims.
Researchers studying five-year-olds and the UK's recommended physical activity levels found that there was no difference in BMI change between those who did and did not meet the guidelines.
The team at the Peninsula Medical School, Plymouth, assessed 113 boys and 99 girls from 54 different schools.
The children were part of the EarlyBird study, which is tracking the long-term health of 307 children born between 1995 and 1996.
Weekly physical activity levels were measured using a tiny device worn around the waist and 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 five and eight.
Guidelines in the UK recommend that children are moderately physically active for at least an hour every day in a bid to prevent obesity and its related health risks.
The study, published in the journal Archives of Disease in Childhood, found that less than half the boys and just one in eight girls met the guideline.
There was no difference in BMI change between those who did and did not meet the guideline.
But both boys and girls who met the guideline showed progressive improvement in their predictive health indicators, while those who did not showed worsening health.
The researchers argue therefore that their findings suggest BMI may be "too blunt" a measure to gauge the impact of activity levels.
"As BMI combines both lean mass and fat mass, it may be an inappropriate outcome measure for assessing changes in physical activity as any decrease in fat mass may have been off-set by an increase in lean mass," they add.
Other problems with physical activity guidelines uncovered by the study include the difference in exercise undertaken by girls and boys.
"Girls undertake systematically less physical activity than boys, and it is unclear whether the guideline should be lowered for girls to allow for what may be a biological difference, or particular encouragement given to girls to do more," the researchers argue.
"Whichever, and notwithstanding the lower levels, the metabolic benefits of physical activity are as strong in girls as they are in boys."
The study concludes that researchers need to understand why some children undertake more physical activity than others to extend the positive health benefits of exercise to less active children.