Secular trends and distributional changes in health and fitness performance variables of 10-14-year-old children in New Zealand between 1991 and 2003.

BACKGROUND: New Zealand children's health and fitness performance is declining over time, but whether this change is because of deterioration in all children's health and fitness performance or can be attributed to just a certain portion of the population, is unknown.
OBJECTIVES: In this study, secular trends and distributional changes in health-related and performance-related fitness components among New Zealand primary school children aged 10 to 14 years between 1991 and 2003 were tracked.
METHODS: Health- and performance-related fitness parameters including height, weight, body mass index (BMI), flexibility, standing broad jump, 4 x 9-m agility run, abdominal curl-ups, and 550-m run were collected up to twice a year from 3306 children (10-14 years old) from a New Zealand school between 1991 and 2003.
RESULTS: Over the 12-year period, the boys' weight increased by 4.5 kg (95% CL 2.7 to 6.2, or 0.8% per year) and girls' by 3.9 kg (95% CL 2.0 to 5.9, or 0.7% per year). Mean BMI increased by 0.12 kg m(-2) (0.6%) and 0.11 kg m(-2) (0.5%) per year for boys and girls, respectively. Children's 550-m run performance declined by 1.5% and 1.7% per year for boys and girls, respectively. Little difference existed between children located in the highest performing and leanest percentiles in 1991 and 2003, but for children in the poorest performing and fattest percentiles, their results were substantially worse in 2003.
CONCLUSIONS: These results suggest that the deterioration in the health-related and performance-related fitness components of New Zealand 10-14-year-olds is not homogeneous but skewed towards those children who are the heaviest and perform worst in fitness tests. Previous research on health-related fitness parameters among children in New Zealand is limited but shows secular trends of increasing body mass1 2 in conjunction with deteriorating aerobic fitness performance, muscular endurance and explosive muscular power.3 Internationally, similar increases in body mass have been observed in children since the 1980s.1 4 5 Secular trends of deteriorating health-related fitness performance have also been reported among children around the world,1 5 6 with the most significant decreases observed in aerobic performance. However, trends in health-related variables reported as changes in mean body mass index (BMI) and mean aerobic fitness performance do not reveal possible changes in the distribution of BMI or aerobic performance within the population. Changes in such measures may come about because of a shift in the entire population under investigation or a change in a portion of the population. It is not clear whether New Zealand's entire childhood population is becoming heavier and less aerobically fit or whether only a portion of the children are becoming even heavier and more unfit, with the remaining children showing little secular change. The aim of this study was to track secular trends and distributional changes in body weight and physical fitness parameters among New Zealand primary school children aged 10 to 14 years.