“Sedentary lifestyles are making children less fit - even among those who are not obese,” the BBC has reported.
This story is based on a scientific study testing the BMI and fitness of 10-year-olds from Essex in 1998 and again in 2008. The study found a decrease in fitness in girls and boys over this period, despite little change in the children’s BMI. The researchers suggest that heart and lung fitness should be assessed alongside BMI when monitoring the wellbeing of children.
However, the study did not look at what diet or lifestyle changes in the last decade may lie behind these changes. Also, it only looked at children from one affluent area of Essex, so the results may not represent children from other areas or poorer backgrounds. While this particular study did not look at the general population, other recent studies have: overall, these suggest a decline in the fitness of children that may need intervention.
Where did the story come from?
This research was carried out by Dr G Sandercock and colleagues at the University of Essex. The study was funded by Sport Chelmsford. The study was published in Archives of Disease in Childhood, a peer-reviewed medical journal.
The press accurately covered the science of this short report. However, the newspapers generally focused on potential causes of the decline in fitness although this study did not collect any lifestyle data on the participants and did not directly address this question.
What kind of research was this?
This was a repeated cross-sectional study comparing the average body mass index and cardiorespiratory fitness levels of 10-year-olds from Chelmsford, Essex in 1998 and in 2008.
Although obesity has shown to be increasing in children in the UK, the researchers suggest that BMI measurements may have remained stable in affluent areas. To test this theory, they looked for any changes in the BMI and cardiorespiratory fitness of this demographic group over time. Chelmsford was selected as a location for this research because of it is in the top 20% of most affluent areas in the UK, as defined through its low score on an index of multiple deprivation.
What did the research involve?
The researchers recruited 10-year-olds from six schools in Chelmsford: 158 boys and 145 girls in 1998, and 158 boys and 157 girls in 2008. The researchers measured the height and weight of the children and calculated their body mass index (BMI).
The researchers then recorded the children’s performance in a “shuttle-run test”, also known as a bleep test. This required children to run 20 metres between two points (“shuttles”) before a bleep was sounded. As the test continued, the frequency of the bleeps increased, requiring the children to run faster. The children stopped when they could no longer keep up with the pace of the bleeps.
The researchers looked for differences in the BMI and shuttle-run score from 1998 and 2008, analysing data on boys and girls separately.
What were the basic results?
There was an increase in the average BMI of the boys from 17.6 to 18.3 from 1998 to 2008. However, the girls’ average BMIs remained roughly the same: 18.6 in 1998 and 18.4 in 2008.
Both sexes performed worse in the shuttle run test in 2008 than in 1998. The boys ran an average (median) of 60 shuttles in 1998 and 40 in 2008. The girls ran an average (median) of 46 shuttles in 1998 and 29 in 2008.
The researchers calculated that between 1998 and 2008 there had been an annual decrease in cardiorespiratory fitness of 0.8% in both girls and boys. The researchers reported that, based on results from other studies from countries across the world, they would expect an annual rate of decline of 0.4%.
How did the researchers interpret the results?
The researchers say their results suggest that:
- the mean BMI of girls from affluent areas of England may not be changing significantly,
- the mean BMI of boys from affluent areas may be increasing, but at a slower rate than in more deprived areas,
- the decline in cardiorespiratory fitness in English 10-year-olds is greater than would be predicted from global data, and
- the decline in cardiovascular fitness appears largely independent of changes in BMI, at least in girls.
This study suggests a decline in the cardiorespiratory fitness of English 10-year-olds from 1998 to 2008. This decline in fitness appears to be independent to changes in BMI, and may be greater than in other nations.
One shortcoming of this research is that the study did not collect any information about the children’s personal characteristics or lifestyles, therefore it cannot identify potential causes for the changes seen. Also, the researchers focused on Chelmsford as an example of an affluent area, but did not have a comparison group of children from a less affluent area. This means it is not possible to say whether the reported trends are associated with affluence or how closely this trend mirrors the country as a whole.
Furthermore, the study was very small and collected data from only two years. Therefore the calculation of the average rate of annual decline in cardiorespiratory fitness is a rough estimate.
Overall, this study is in keeping with other studies that have shown a decrease in cardiorespiratory fitness in children in the general population, and provides another reason why initiatives to increase fitness in children should be encouraged.