New York (PTI): The physical activity among children in the United States declines sharply as they age leading to their becoming obese adults, researchers say. The study, published in the latest issue of Journal of American Medical Association, found that moderate-to-vigorous physical activities of children decreases by greater than

one-third as they aged from nine to 15. The researchers found that at the age of nine children are engaged in about three hours of moderate-to-vigorous physical activity per day on both weekdays and weekends. By the age of 15, the time was reduced to only 49 minutes per day during the week and 35 minutes on weekends, much less than the recommended time of 60 minutes per day. Moderate-to-vigorous physical activities has been defined as all types of physical activity, including walking.

The study was conducted by researchers at the University of California, San Diego School of Medicine; University of Arkansas; University of North Carolina at Greensboro; and RTI International. "While we all knew children and youth were moving less, the magnitude of the rate of decline calls for renewed action to increase activity levels in the population," said Philip R Nader, MD, professor emeritus, Department of Pediatrics, UC San Diego School of Medicine.

"Physical activity is a crucial part of the energy equation; declining physical activity will only complicate the obesity epidemic," the lead author said. The study measured the physical activity of more than 1,000 youths in ten cities, beginning in 2000, when the children were nine-year-old and ending in 2006, when they reached 15 years of the age.