Overweight children as young as 9 years old are already participating in less PA than normal weight youth. Although PA declined from childhood to adolescence, overweight girls with normalized weight status, had less of a decline in MPA or VPA than normal weight girls who became overweight. The data highlight the complexity of the interrelationship between physical activity and weight gain or loss. These data suggest that habitual physical activity levels, especially in girls, may have a role in adolescents attaining a healthy weight status.

The magnitude of the ICC varied by the outcome of interest, and factors such as age, gender, and ethnicity also influenced the magnitude of the ICC. The presence of ICCs should be assumed when using cluster designs, and ICCs should be considered when conducting sample size calculations for such studies.

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