CONTEXT Physical inactivity contributes to weight gain in adults, but whether this relationship is true for children of different ethnic groups is not well established.   
 OBJECTIVE To assess participation in vigorous activity and television watching habits and their relationship to body weight and fatness in US children.   
 DESIGN Nationally representative cross-sectional survey with an in-person interview and medical examination.   
 SETTING AND PARTICIPANTS Between 1988 and 1994, 4063 children aged 8 through 16 years were examined as part of the National Health and Nutrition Examination Survey III. Mexican Americans and non-Hispanic blacks were oversampled to produce reliable estimates for these groups.   
 MAIN OUTCOME MEASURES Episodes of weekly vigorous activity and daily hours of television watched, and their relationship to body mass index and body fatness.   
 RESULTS Eighty percent of US children reported performing 3 or more bouts of vigorous activity each week. This rate was lower in non-Hispanic black and Mexican American girls (69% and 73%, respectively). Twenty percent of US children participated in 2 or fewer bouts of vigorous activity perweek, and the rate was higher in girls (26%) than in boys (17%). Overall, 26% of US children watched 4 or more hours of television per day and 67% watched at least 2 hours per day. Non-Hispanic black children had the highest rates of watching 4 or more hours of television per day (42%). Boys and girls who watch 4 or more hours of television each day had greater body fat (P<.001) and had a greater body mass index (P<.001) than those who watched less than 2 hours per day.   
 CONCLUSIONS Many US children watch a great deal of television and are inadequately vigorously active. Vigorous activity levels are lowest among girls, non-Hispanic blacks, and Mexican Americans. Intervention strategies to promote lifelong physical activity among US children are needed to stem the adverse health consequences of inactivity.
True