Objective: To examine the relationship between physical activity, TV watching, and weight in U.S. youth ages 14 to 18 years.
Research methods and procedures: Data from a nationally representative sample of 15,143 U.S. high-school students participating in the 1999 Centers for Disease Control and Prevention (CDC) Youth Risk Behavior Survey were examined. Prevalence rates of participation in moderate physical activity (MPA), vigorous physical activity (VPA), and television watching (TV) were determined. The association between MPA, VPA, TV and the body mass index (BMI) and overweight status (BMI > or =85th percentile of age- and sex-specific CDC/National Center for Health Statistics reference values) were examined by analysis of covariance and logistic regression.
Results: Overall, 45% reported participating in MPA > or =3 d/wk, 65% reported participating in VPA > or =3 d/wk, and 25% reported watching TV > or =4 h/school day. Boys reporting six to seven bouts of MPA had a significantly lower BMI compared with boys reporting three to five or less than two. The mean BMI differed significantly between the lowest and highest levels of MPA groups in girls. The mean BMI was significantly lower in the highest VPA group compared with the other two groups in both sexes. There was a significant graded response for BMI across all levels of TV. Decreased levels of MPA and 3 to 4 days of VPA were significantly associated with an increased risk of overweight in boys when compared with those engaging in 6 to 7 d/wk (odds ratio = 1.26 to 1.37). A graded response existed between TV and overweight in both sexes. Boys and girls were approximately 20% to 25% less likely to be classified as overweight if they reported 2 to 3 hours of TV per day and approximately 40% less likely to be classified as overweight if they reported < or =1 hour of TV per day compared with those who watched > or =4 hours of TV. In general, youth who engaged in less physical activity watched more TV per week.
Discussion: Increased levels of physical activity are associated with a lower BMI and less TV watching. However, the relationship between TV watching and weight status is more pronounced.