Image caption Children are advised to do at least an hour of vigorous activity every day 
 
 Many children cannot run as fast as their parents could when they were young, a study of global fitness says. 
 
 Experts say the work - being presented at the American Heart Association's annual meeting - suggests children's fitness levels may be declining. 
 
 Researchers analysed data spanning 46 years and involving more than 25 million children in 28 countries. 
 
 On average, children today run a mile 90 seconds slower than did their counterparts 30 years ago, they said. 
 
 If a young person is generally unfit now, then they are more likely to develop conditions like heart disease later in life Lead researcher Dr Grant Tomkinson , University of South Australia BBC - Health BMI calculator 
 
 Obesity 
 
 Across nations, cardiovascular endurance - gauged by how far children can run in a set time - has dwindled consistently by about 5% every decade, according to the findings. 
 
 The decline is seen in boys and girls and across all ages from nine to 17 years, and is linked to obesity, with some countries faring worse than others. 
 
 Lead researcher Dr Grant Tomkinson of the University of South Australia's School of Health Sciences said: "In fact, about 30% to 60% of the declines in endurance running performance can be explained by increases in fat mass." 
 
 The problem is largely one of Western countries, but some parts of Asia like South Korea, mainland China and Hong Kong are also seeing this phenomenon. 
 
 Dr Tomkinson said children needed to be inspired and encouraged to do more vigorous exercise. 
 
 If not, the public health consequences could be dire. 
 
 Huff and puff 
 
 "If a young person is generally unfit now, then they are more likely to develop conditions like heart disease later in life," said Dr Tomkinson. 
 
 To stay healthy, children and young people need to do at least an hour of physical activity - such as walking or cycling to school and running in the playground - every day. It can be done in small chunks rather than one session. 
 
 Prof Michael Gwitz of the American Heart Association said: "The type of exercise is really important." 
 
 He says exercise must be something that "makes you sweat" and is "sustained and dynamic" to promote cardiovascular fitness. 
 
 Simply going to the gym or belonging to a school sports team might not be enough, unless you are moving around a lot. 
 
 Christopher Allen of the British Heart Foundation, said: "It's well established that being physically inactive in childhood can have serious health implications later in life. 
 
 "Keeping active can reduce the risk of cardiovascular disease and the sooner kids start, the better. 
 
 "By encouraging children to get active, we can help protect their hearts as they grow up. Parents, schools and community groups can all help kids on their way to 60 minutes exercise a day." ||||| Today's kids can't keep up with their parents. An analysis of studies on millions of children around the world finds they don't run as fast or as far as their parents did when they were young. 
 
 FILE - In this May 13, 2007 file photo, boys participate in 100 meter race during two-day World Athletics Day meet in Bangalore, India. An analysis of studies on 250 million children around the world... (Associated Press) 
 
 On average, it takes children 90 seconds longer to run a mile than their counterparts did 30 years ago. Heart-related fitness has declined 5 percent per decade since 1975 for children ages 9 to 17. 
 
 The American Heart Association, whose conference featured the research on Tuesday, says it's the first to show that children's fitness has declined worldwide over the last three decades. 
 
 "It makes sense. We have kids that are less active than before," said Dr. Stephen Daniels, a University of Colorado pediatrician and spokesman for the heart association. 
 
 Health experts recommend that children 6 and older get 60 minutes of moderately vigorous activity accumulated over a day. Only one-third of American kids do now. 
 
 "Kids aren't getting enough opportunities to build up that activity over the course of the day," Daniels said. "Many schools, for economic reasons, don't have any physical education at all. Some rely on recess" to provide exercise. 
 
 Sam Kass, a White House chef and head of first lady Michelle Obama's Let's Move program, stressed the role of schools in a speech to the conference on Monday. 
 
 "We are currently facing the most sedentary generation of children in our history," Kass said. 
 
 The new study was led by Grant Tomkinson, an exercise physiologist at the University of South Australia. Researchers analyzed 50 studies on running fitness _ a key measure of cardiovascular health and endurance _ involving 25 million children ages 9 to 17 in 28 countries from 1964 to 2010. 
 
 The studies measured how far children could run in 5 to 15 minutes and how quickly they ran a certain distance, ranging from half a mile to two miles. Today's kids are about 15 percent less fit than their parents were, researchers concluded. 
 
 "The changes are very similar for boys and girls and also for various ages," but differed by geographic region, Tomkinson said. 
 
 The decline in fitness seems to be leveling off in Europe, Australia and New Zealand, and perhaps in the last few years in North America. However, it continues to fall in China, and Japan never had much falloff _ fitness has remained fairly consistent there. About 20 million of the 25 million children in the studies were from Asia. 
 
 In China, annual fitness test data show the country's students are getting slower and fatter over the past couple of decades. 
 
 Experts and educators blame an obsession with academic testing scores for China's competitive college admissions as well as a proliferation of indoor entertainment options like gaming and web surfing for the decline. 
 
 China's Education Ministry data show that in 2010 male college students ran 1,000 meters 14 to 15 seconds slower on average than male students who ran a decade earlier. Female students slowed by about 12 seconds in running 800 meters. 
 
 Tomkinson and Daniels said obesity likely plays a role, since it makes it harder to run or do any aerobic exercise. Too much time watching television and playing video games and unsafe neighborhoods with not enough options for outdoor play also may play a role, they said. 
 
 Other research discussed global declines in activity. 
 
 Fitness is "pretty poor in adults and even worse in young people," especially in the United States and eastern Europe, said Dr. Ulf Ekelund of the Norwegian School of Sport Sciences in Oslo, Norway. 
 
 World Health Organization numbers suggest that 80 percent of young people globally may not be getting enough exercise. 
 
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 Marilynn Marchione can be followed at http://twitter.com/MMarchioneAP
– Today's children are the most sedentary generation in history and they would be easily trounced in a race with younger versions of their parents, a new study finds. Researchers—who looked at data involving millions of children in 20 countries over more than 40 years—found that today's young people run a mile around 90 seconds slower than their counterparts did 30 years ago, reports the BBC. Children are, on average, 15% less fit than their parents were, and the decline is seen for both boys and girls and for all ages between 9 and 17, the AP notes. Fitness has been dropping by around 5% a decade, the study found, and while the decline is slowly leveling off in Europe and North America, fitness is still going downhill fast in China and other parts of east Asia. Researchers say obesity and sedentary lifestyles are probably playing the biggest role in the fall in fitness—and they warn that unfit young people will be unhealthier later in life. Experts recommend that children over 6 get at least an hour of moderately vigorous activity throughout the day, but the World Health Organization estimates as many as 80% of the world's young people aren't getting the necessary exercise.