Active Voice: Fitness, Fatness and Children
By Timothy Fairchild, Ph.D., FACSM, AEP and Niels Wedderkopp, M.D., Ph.D.
Timothy Fairchild, Ph.D., FACSM, AEP, is a senior lecturer and researcher in the School of Psychology and Exercise Science at Murdoch University, Perth, Australia. Dr. Fairchild’s research interest is in the management of weight and obesity-related disease through manipulation of diet and exercise. More recently, this interest has expanded into the pediatric population. He has been a member of ACSM since 2005 and is an accredited exercise physiologist with Exercise and Sports Science Australia (ESSA).
Niels Wedderkopp, M.D., Ph.D., is a professor in the faculty of health at the University of Southern Denmark in Odense. Dr. Wedderkopp’s research has primarily been focused on childhood health. He has published widely in the area of metabolic disease risks (obesity and physical activity), as well as on the side effects of sport and physical activity (injuries) in childhood and youth. Dr. Wedderkopp is a certified orthopedic surgeon and daily leader of a sport medicine clinic.
This commentary presents the authors’ views on the topic of a research article which they and professor Andrew Lloyd had published in the October 2016 issue of Medicine & Science in Sports & Exercise® (MSSE).
Through various information sources, we often are reminded about the increasing weight status and corresponding low levels of physical activity in children. However, the extent of these low physical activity levels is quite alarming, with global estimates showing children achieving only between 22 and 45 minutes of moderate-to-vigorous physical activity (MVPA) per day, which is considerably less than the recommended 60 minutes of daily MVPA. From a health perspective, we have learned from work conducted in adults that physical fitness levels appear to be a more important determinant of cardiovascular or metabolic disease risk than are physical activity levels. Unfortunately for our children, levels of cardiorespiratory fitness (CRF) appear to parallel the reduced physical activity patterns, with fitness trends indicating a decline of around 0.4 percent per year in children between the years 1980 and 2000. Furthermore, this time trend is likely to have extended beyond those years. This combination of low fitness and increasing weight status is clearly not an ideal health prognostic, but we were interested in exploring this relationship a little deeper.
Studies with large cohorts have traditionally adopted anthropometric measures such as BMI status, waist circumference or skinfold measures to assess weight status. While these findings have contributed greatly to our current understanding of the relationships between weight status, fitness and clinical biomarkers of disease in children, the exact role of adiposity (percentage body fat, i.e., %BF) in these relationships remain difficult to tease out. Several large data sets involving children have recently included measures of %BF using dual energy x-ray absorptiometry (DXA) as part of its testing battery. One such data set is the Childhood Health, Activity, and Motor Performance School Study Denmark (The CHAMPS-study DK) which incorporates both DXA and BMI measures along with a measure of aerobic fitness.
We, therefore, undertook a study in which we stratified children according to their BMI and %BF and then compared their levels of CRF across derived subgroups (September 2016 issue of MSSE). We were particularly interested in assessing the impact of BMI and %BF on levels of CRF. Our main finding from this first analysis was that both BMI and %BF were associated with CRF, but %BF impacted the CRF levels of 7-12-year-olds to a greater degree than did BMI. Specifically, children who were normal weight according to their BMI, but had excessive (=25 percent) body fat ran significantly less distance (lower aerobic fitness) than classmates who had a normal BMI without excessive %BF. The next question was whether an improvement in %BF or BMI could lead to an improvement in CRF. Of the original 641 children who were tested at baseline, 579 children returned for the follow-up running test, which was performed two years later. This second analysis revealed that children who improved either their BMI and/or %BF classification achieved CRF levels which were then comparable to children with normal BMI and %BF at both measurement time points.
From our perspective, a most surprising finding in our study was that a large proportion (~ seven percent) of children in this European cohort who were considered normal weight, but with excessive %BF, had significantly lower CRF than their normal weight counterparts without excessive %BF. An important, but currently elusive question is whether this translates to poorer clinical outcomes in adulthood. Finally, the authors would welcome more consistent and widespread assessment of fitness in school-aged children using robust measures of aerobic fitness.