The effects of a low-dose physical activity intervention on physical activity and body mass index in severely obese adolescents

: Background While severe obesity in childhood poses the greatest long-term health risks, access to treatment is a common barrier. The present pilot study examined the effect of a 7-week low-dose physical activity (PA) intervention on PA and body mass index (BMI) in severe obese adolescents delivered via telephone and mail. Methods Adolescents (n = 64) receiving care from a pediatric obesity medical clinic were randomized to a control (n = 30) or intervention (n = 34) group. Height and weight were measured and BMI z-scores were calculated. PA was assessed by a pedometer. All measurements were completed pre- and post-intervention. The intervention group received weekly newsletters and telephone calls discussing various PA topics based on motivational interviewing for 7 weeks. The control group received no contact. A series of 2 × 2 (group by time) repeated measures analysis of covariances (ANCOVAs) adjusting for length of time between visits were performed to examine the effect of the intervention on PA and BMI z-scores. Results The majority of adolescents were severely obese (77%, BMI: > 99th percentile). Intention-to-treat analysis revealed intervention effects were not observed for either pedometer steps or BMI z-score (p > 0.05). Among those with complete data, adolescents who successfully changed their BMI z-score had larger BMI z-score changes than those who did not change their BMI z-score (p = 0.0001). This improvement was due to something other than PA as the change in BMI z-score was similar among those who did and did not successfully increase PA levels (p > 0.05). Conclusions More intensive, comprehensive, and longer-term treatment is needed in this high risk population.