( CNN ) -- And that 's not such a good thing . Today 's kids are less fit than their parents were at the same age , according to new research presented at the American Heart Association 's Scientific Sessions , and that could mean health problems later on . The fact that younger kids are huffing and puffing more than their parents did at their age does n't just mean they are n't in shape . It 's also a red flag that they may more vulnerable to certain chronic diseases as adults . Researchers from the University of South Australia 's School of Health Sciences analyzed and compared 50 studies on children 's running fitness between the years 1964 and 2010 . The studies included about 25 million kids between the ages 9 and 17 in 28 different countries . The researchers recorded running times over a specific time frame -- typically about five to 15 minutes -- or over a certain distance -- a half mile to two miles . They found that over the 46 years , the cardiovascular endurance -- measured by the times it took to run the various distances -- among kids declined significantly . From 1970 to 2000 , U.S. children 's cardiovascular endurance fell about 6 % per decade , and among all countries , it fell about 5 % each decade . In other words , today , kids are 15 % less fit than their parents were , and in the mile run , kids are about a minute and a half slower than children were 30 years ago . TIME.com : Study : More active teens get higher test scores . The researchers say that cardiovascular fitness is one of the most important factors for good health , not just in childhood but in adulthood as well . `` If a young person is generally unfit now , then they are more likely to develop conditions like heart disease later in life , '' said lead study author Grant Tomkinson in a statement . Currently , the Centers for Disease Control recommends that children get at least an hour of daily activity that involves the entire body , such as running , biking or swimming . Not only does the exercise benefit the body , but research shows that kids who are more physically active tend to do better in school too . This story was initially published on TIME.com . Are you fitter than your fifth grader ? Yes , you probably are . & copy 2012 TIME , Inc. TIME is a registered trademark of Time Inc. Used with permission .
Kids today are less fit than their parents were at the same age , research shows . That could put them at risk for chronic diseases as adults . The CDC recommends kids get an hour of exercise involving the entire body .