Exploring the Relationship between Adiposity and Fitness in Young Children

Purpose: High levels of cardiorespiratory fitness (CRF) may attenuate the association between the excessive adiposity and the risks of cardiovascular and metabolic disease. The purpose of this study was to stratify children according to their body mass index (BMI) and adiposity (body fat percentage [BF%]) and to compare levels of CRF across subgroups. Methods: This prospective cohort study comprises a cross-sectional and longitudinal analyses of data collected at baseline (n = 641) and 2 yr later (n = 579) on children (7.4-11.6 yr) attending public school in Denmark. Levels of CRF were measured using the Andersen test, whereas BF% was measured by dual-energy x-ray absorptiometry. Results: There were 560 children (87.4%) classified as normal weight according to BMI at baseline, of which 46 (7.4%) were identified as having excessive BF%. These children had significantly lower CRF (mean [95% confidence interval]: -63.1 m [-100.2 to -25.9]) than children with normal BMI and normal BF%, and the effect of BF% on CRF was significantly worse in boys than girls. Overweight children with high BF% had significantly lower prospective (2 yr) CRF levels (-34.4 m [-58.0 to -10.7]) than children with normal BMI and BF%. However, children who improved their BMI and/or BF% classification during the 2-yr period achieved CRF levels (8.9 m [-30.2 to 47.9]), which were comparable with children with normal BMI and BF% at both measurement time points. Conclusion: The CRF levels in children are affected by BMI and BF%, although BF% appears to play a greater role. This association between BF% and CRF is sex dependent, with CRF levels in boys being affected to a greater extent by BF%. Children identified as "normal weight'' by BMI but presenting with excessive BF% had significantly lower CRF than "normal weight'' children with low BF%.