Location: Children's Nutrition Research CenterTitle: Prospective BMI category change associated with cardiovascular fitness change) Author
Submitted to: Medicine and Science in Sports and Exercise
Publication Type: Peer reviewed journal
Publication Acceptance Date: 8/21/2012
Publication Date: 2/1/2013
Citation: Baranowski, T., Chen, T., Mendoza, J.A., O'Connor, T., Baranowksi, J., Jago, R. 2013. Prospective BMI category change associated with cardiovascular fitness change. Medicine and Science in Sports and Exercise. 45(2):294-298. Interpretive Summary: Although higher cardiovascular fitness (CVF) has been associated with lower body mass index (BMI), few longitudinal studies have assessed the relationship of changes in BMI with changes in CVF. In a large sample of mostly lower income ethnic minority middle school students, change in BMI category from early 6th to late 8th grades was tested with change in CVF, baseline CVF, and baseline BMI. Baseline BMI was very highly predictive of change in BMI, suggesting that elevated BMI values in 6th grade were a deterrent to losing weight. Change in CVF was only weakly related to change in BMI, suggesting that CVF-enhancing interventions (e.g., physical activities) should be introduced earlier than 6th grade, before the inhibiting effect of prevalent high BMI.
Technical Abstract: The relationship of change in body mass index (BMI) percentile score group (from 6th to 8th grade) with change in cardiovascular fitness (CVF), baseline BMI z-score and CVF was tested. 3,998 (92%) children in the HEALTHY trial provided complete data at the beginning of 6th and end of 8th grades. Height and weight were assessed according to standardized protocol. CVF was measured using the 20-meter shuttle run. Changes in BMI percentile were categorized into five groups: increased a BMI category, stayed obese, stayed overweight, stayed healthy weight, and decreased a BMI category. Data were analyzed separately by gender, controlling for race, parental education, change in pubertal stage, and baseline BMI z-score, and CVF. Youth (males and females) who lowered their BMI group or remained in the healthy or overweight groups had significantly larger increases in CVF, than the stayed obese or increased a BMI category groups. But these relationships accounted for a small percentage of variance (i.e., weak relationship). Staying obese was associated with the highest baseline BMI z-score, with the second highest among those who decreased a BMI category. BMI category change accounted for the most variance in baseline BMI z-score. Changes in BMI categories were substantially more strongly related to 6th grade values of BMI z-score than to CVF changes. Since pre-existing adiposity may inhibit adiposity change, changes in CVF and adiposity should be attempted prior to middle school.