A comparison of 15-year-olds across two generations, believed to be the first of its kind, has found a decline in adolescent physical fitness.
The findings were published today in the New Zealand Medical Journal.
The decline in fitness between generations has been accompanied by an increase in body weight, in keeping with global trends of increasing body weight among children and young people.
Fitness was measured on an exercise cycle among members of the Dunedin Multidisciplinary Health and Development Study when they were aged 15 in 1986-87.
The same fitness test was done on 343 of their 15-year-old children between 2007 and 2015.
The decline in fitness was particularly noticeable for girls, who weighed more and were less fit than their mothers had been at the same age.
The decline in fitness among boys was smaller, but they were also less fit than their fathers had been at age 15, once body weight was taken into account.
One of the researchers, Dr Helena McAnally, said while both girls and boys were less fit than their parents had been, the change was particularly noticeable for girls, whose fitness test scores were about 25% lower than their mothers' generation.
"It is well recognised that girls become less physically active earlier in adolescence, and this may be why their fitness levels were so much lower.
"We know fitness in adolescence tracks into adulthood and so these changes may have important long-term consequences for health and wellbeing," Dr McAnally said.
The research was led by Prof Bob Hancox, who explained that while trends of increasing levels of overweight and obesity among young people were well recognised, there had been little research on changes in fitness.
"Our study is unusual in that we have measured fitness using the same technique in two generations of New Zealanders.
"The findings support many people's perception that young people are less active and fit than their previous generations," Prof Hancox said.
The study measured fitness using a cycle test.
The cycle test measure used is less likely to be influenced by changes in body weight than running tests, because it does not require you to carry your weight while exercising.
Therefore, findings of reduced fitness in this research are not likely to be explained by increases in body weight.
The research was funded by the Health Research Council of New Zealand and supported by the department of preventive and social medicine.