Cardiovascular fitness in prepubescent children

Assessing cardiovascular (CV) fitness in children is important for monitoring the health status of this population and for evaluating different interventions in prevention and treatment of obesity. Since the prevalence of children who are overweight or obese has tripled since the determination of the 20mSRT regression equation, the validity of the equation to predict V02max per kg body mass (BM) could be in question. Purpose. To compare CV fitness derived from a running test, the 20mSRT, and a cycle test (body mass independent exercise), while normalizing maximal oxygen uptake (V0 2) to various body composition parameters (body mass (BM), fat free mass (FFM), and skin fold corrected leg girth (SFLG) in prepubescent children across different body composition levels. Method. Seventy-seven subjects (mean age 9.95+/-0.8 yrs) performed a 20mSRT to predict maximal oxygen uptake (V02max) relative to BM and a subset of fifty-seven also performed a cycle test to measure maximal oxygen uptake (V02max ), using indirect calorimetry. To determine absolute V0 2max and V02max normalized to body composition parameters (BM, FFM and SFLG) for the 20mSRT a back calculation method was performed. Subjects were classified into the three categories using (BF) using body fat; non-overweight (≤20%), overweight (20.1-25.0%) and obese (>25.0%), and body composition was also examined on a continuum. Physical activity was assessed using pedometers (daily step counts, mean over 7 days). Results. The 20mSRT and the cycle test were significantly correlated (p<0.05) independent of V02 expression. Using the categorical data for body composition V02 per BM was significantly different (p>0.05) between all body composition categories for the cycle test except V02 per FFM, which was not significantly different between body composition categories. However an inverse relationship between %BF and V02max per FFM was observed. When examined using continuous data significant negative correlations were observed between %BF and V02 per FFM and V02 per BM on the cycle (r=-0.298, r=-0.662, p< 0.01). Conclusion. The CV fitness of children decreases with increasing adiposity regardless of the method of expression, (BM, FFM) on the cycle test. The 20mSRT provides a moderately high level of agreement with the CV fitness derived from cycle testing, which is body weight independent. This allows the 20mSRT to be used as a test of CV fitness.