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American children become less active as they age, according to a report in The Journal of the American Medical Association.

Nine-year-old children usually exercise a couple of hours each day. However, when a child reaches adolescence, he or she becomes more sedentary.

Inactivity can cause many health problems later in life, such as heart disease and obesity.

Words

to age: to get older.
adolescence: (usually) a person’s teenage years.
sedentary: inactive, sitting down a lot.
obesity: the state of being very fat.