Distributional changes in the performance of Australian children on tests of cardiorespiratory endurance

There is accumulating evidence of worldwide declines in cardiorespiratory endurance (CRE) among children. To date, few studies have focused on trends in distributional characteristics of CRE performance. This study analyzed 1985 and 1997 samples of Australian children on the 1.6 km run/walk test, using a variety of descriptive and inferential statistics to compare distributions of average running speed among 10- to 11-year-olds. The analysis was conducted on 965 boys and 935 girls from 1985, and 661 boys and 553 girls from 1997. Among boys there was a significant increase in the coefficient of variation of average completion times, with a marked decrease in negative skew. This was largely attributable to the largest declines occurring in the middle percentiles, with relatively smaller declines at low (<5th) and high (>90th) percentiles. The bulk of the scores have shifted towards the left side of the distribution, reducing the skew. Among girls the distributional trends were different; there was little change in 'scatter' and skew of test scores, with declines in performance being relatively uniform across the distribution. These findings contrast with previous reports of greater declines among the lowest ranked performers on CRE tests. The observed declines in all percentiles other than the lowest and highest ranked boys suggest that mechanisms for declining fitness are widespread throughout the population and may reflect changes in environmental barriers and enablers of regular physical activity among Australian youth.