Physical activity and body mass index among US adolescents: youth risk behavior survey, 1999.
OBJECTIVE
To investigate associations of underweight and overweight with physical activity among high school students in the United States.


METHODS
A nationally representative sample of 15 349 US high school students participated in the 1999 Youth Risk Behavior Survey; 13 295 were included in these analyses. Five measures of physical activity were examined as dichotomous variables: (1) vigorous-intensity physical activity (>/=3 vs <3 sessions lasting at least 20 minutes each per week); (2) moderate-intensity physical activity (>/=5 vs <5 sessions lasting at least 30 minutes each per week); (3) strength training (>/=3 vs <3 sessions per week); (4) enrollment in physical education (yes or no); and (5) sports participation (yes or no). Using body mass indexes, students were categorized by percentiles as underweight (</=5th percentile), at risk for underweight (>5th to </=15th percentiles), normal weight (>15th to <85th percentiles), at risk for overweight (>/=85th to <95th percentiles), or overweight (>/=95th percentile). Potential associations between physical activity and body mass index were examined using logistic regression.


RESULTS
On several measures, adolescent boys who were underweight or overweight were less likely to be physically active than boys of normal weight (eg, odds ratio [OR], 0.23; 95% confidence interval [CI], 0.12-0.45; and OR, 0.75; 95% CI, 0.61-0.93; for boys who were underweight and overweight, respectively, for strength training). Adolescent girls who were overweight or at risk for overweight were less likely (OR, 0.62; 95% CI, 0.50-0.78; and OR, 0.63; 95% CI, 0.46-0.85; respectively) to be involved with sports than girls of normal weight; and girls who were underweight were less likely (OR, 0.44; 95% CI, 0.22-0.91) to be enrolled in physical education.


CONCLUSIONS
Weight status among high school students is correlated with selected physical activity behavior, especially among adolescent boys. Interventions to increase physical activity for high school students should target adolescents of all shapes and sizes, and may best be achieved by school policies requiring physical education or after-school sports.