Body Composition and Cardiorespiratory Fitness Indicators in Prepubescent Boys and Girls

Abstract

Relations between frequently used indicators of cardiorespiratory fitness, sex and body composition were studied in a birth-cohort based sample of young prepubescent children (age range: 6.8 - 8.2 years). The Bruce treadmill test was used to assess submaximal heart rate, endurance time (ET), calculated total work (W_total) and maximal power output (P_max) in 100 children (50 boys, 50 girls). Body composition was determined by skinfold measurements. In 17 children, maximal oxygen consumption was measured. Percent body fat was negatively associated with ET and relative oxygen uptake (ml × min^-1 × kg^-1) and was positively related to submaximal heart rate at 6 minutes exercise (HR6). Fat-free mass was positively related to W_total, P_max and absolute oxygen uptake (ml × min^-1). Relative oxygen uptake (ml × min^-1 × kg^-1) was related to ET. Absolute oxygen uptake (ml × min^-1) was related to W_total and P_max. The observed differences in indicators of cardiorespiratory fitness between boys and girls were largely attributable to a difference in body composition. The results further demonstrate that when oxygen uptake measurement is not feasible, W_total or P_max (expressed per kilogram fat-free mass) seem to provide better indicators of aerobic power than endurance time.