Ten year secular declines in the cardiorespiratory fitness of affluent English children are largely independent of changes in body mass index.

Secular changes in body mass index (BMI) and cardiorespiratory fitness (20 m shuttle-run test performance) were assessed in 10-year-old children from an affluent area of England in 1998 (n = 303; 158 boys and 145 girls) and 2008 (n = 315; 158 boys and 157 girls). Girls' BMI did not change over the 10 year period. There was a significant increase in boys' BMI (p = 0.02). Cardiorespiratory fitness declined significantly (p<0.001) in both boys (7%) and girls (9%). This study shows a large and worrying decline in cardiorespiratory fitness in children from an affluent area of England.