Exploring the relationship between adiposity and fitness in young children

Abstract

Objective: High levels of cardiorespiratory fitness (CRF) may attenuate the association between excessive adiposity and the risks of cardiovascular and metabolic disease. The purpose of this study was to stratify children according to their BMI and adiposity (body fat percentage, BF%) and compare levels of CRF across subgroups. Methods: This prospective cohort study comprises a cross-sectional and longitudinal analyses of data collected at baseline and two years later on children (7.4-11.6 y) attending public school in Denmark. Levels of CRF were measured using the Andersen test, while BF% was measured by dual-energy x-ray absorptiometry (DXA). Results: Of the 87.5% (n=1091) of children classified as being normal weight according to BMI, 9.5% (n=114) were identified as having excessive BF%. These children had significantly lower CRF (mean [95% Confidence Interval]: -45.6m [-67.0, -24.3]) than children with normal BMI and normal BF%. The detrimental effect of BF% on CRF was significantly worse in boys than girls (-37.4m [-67.4, -7.3]). Overweight children with high BF%, had significantly lower prospective (2 years) CRF levels (-34.4m [-58.0, -10.7]) than children with normal BMI and BF%. However, children who improved their BMI and/or BF% classification over the two year period, achieved CRF levels (8.9m [-30.2, 47.9]) which were comparable to children with normal BMI and BF% at both measurement time points. Conclusion: A large proportion of children identified as being „normal weight‟ according to BMI present with excessive BF%. These children have low levels of CRF, a known risk factor for cardiovascular and metabolic disease; and this association between BF% and CRF appears to be sex-dependent, with CRF levels in boys being impacted to a greater extent by BF%.