A new study suggests many immigrant children get even less vigorous exercise than kids born in the U.S.

The study -- said to be the biggest of its kind by far -- found almost 18 percent of foreign-born children with immigrant parents got no vigorous exercise on any days of the week. And 56 percent did not take part in organized sports.

By contrast, 11 percent of American-born children with American parents got no vigorous exercise, and 41 percent didn't participate in sports.

The researchers say the immigrant families surveyed were on the whole poorer than nonimmigrants, and lived in less safe neighborhoods. The researchers feel they likely had less time for exercise and sports, and worse access to places to engage in those activities.

But also, many immigrant parents place a high emphasis on reading, language lessons, studying and other inactive pursuits.

The study appears in Archives of Pediatrics and Adolescent Medicine.