Objectively Measured Aerobic Fitness is Not Related to Vascular Health Outcomes and Cardiovascular Disease Risk In 9-10 Year Old Children.

The purpose of the study was to examine whether a higher aerobic fitness in 9-10 year old children is related to superior macro and microvascular health and cardiovascular disease (CVD) risk. Ninety-six 9-10 year olds (53 boys) completed the study. Body composition was assessed from air displacement plethysmography and magnetic resonance imaging. Peak oxygen uptake (V̇O2) was assessed from a ramp-incremental cycling exercise test. Macrovascular outcomes were assessed from pulse wave analysis and pulse wave velocity (PWV) using applanation tonometry. Microvascular function was assessed from the functional microvascular reserve and skin erythrocyte flux after iontophoretic application of skin vasodilators. Assessment of CVD risk was assessed via body mass index, total body fat percentage and visceral adipose tissue, glucose, triglyceride, total cholesterol, HDL cholesterol and LDL cholesterol, while insulin resistance was calculated using Homeostatic model assessment. Aerobic fitness groups (higher vs lower) were calculated from V̇O2 peak scaled for body mass (mL·kg-0.61·min-1) and fat free mass (mL·FFM-1·min-1). Children with a higher V̇O2 peak scaled for body mass had a greater carotid to ankle PWV compared to those with lower aerobic fitness (mean ± SD: 6.08 ± 0.47 vs. 5.87 ± 0.43 m·s-1; p = 0.039), although this became non-significant when scaled for FFM (p = 0.56). No other mean differences in vascular or CVD risk health markers were present between higher and lower groups of aerobic fitness when scaled for body mass or FFM. Conclusion: Directly assessed aerobic fitness is not related to macro and microvascular health outcomes or CVD risk markers in 9-10 year olds.

Aerobic Function and Muscle Deoxygenation Dynamics during Ramp Exercise in Children.

PURPOSE: This study aimed to characterize changes in deoxyhemoglobin ([HHb]) response dynamics in boys and girls during ramp incremental exercise to investigate whether the reduced peak oxygen uptake (peak V˙O2) in girls is associated with poorer matching of muscle O2 delivery to muscle O2 utilization, as evidenced by a more rapid increase in [HHb]. METHODS: Fifty-two children (31 boys, 9.9 ± 0.6 yr, 1.38 ± 0.07 m, 31.70 ± 5.78 kg) completed ramp incremental exercise on a cycle ergometer during which pulmonary gas exchange and muscle oxygenation parameters were measured. RESULTS: When muscle [HHb] was expressed against absolute work rate and V˙O2, girls had an earlier change in [HHb], as evidenced by the lower c/d parameter (girls, 54 ± 20 W, vs boys, 67 ± 19 W, P = 0.023; girls, 0.82 ± 0.28 L·min(-1), vs boys, 0.95 ± 0.19 L·min(-1), P = 0.055) and plateau (girls, 85 ± 12 W, vs boys, 99 ± 18 W, P = 0.031; girls, 1.02 ± 0.25 L·min(-1), vs boys, 1.22 ± 0.28 L·min(-1), P = 0.014). However, when expressed against relative work rate or V˙O2, there were no sex differences in ([HHb]) response dynamics (all P > 0.20). Significant correlations were observed between absolute and fat-free mass normalized peak V˙O2 and the HHb c/d and plateau parameters when expressed against absolute work rate or V˙O2. Furthermore, when entered into a multiple regression model, the [HHb] plateau against absolute V˙O2 contributed 12% of the variance in peak V˙O2 after adjusting for fat-free mass, gas exchange threshold, and body fatness (model R2 = 0.81, P < 0.001). CONCLUSIONS: The sex difference in peak V˙O2 in 9- to 10-yr-old children is, in part, related to sex-specific changes in muscle O2 extraction dynamics during incremental exercise.

Reliability of peak VO(2) and maximal cardiac output assessed using thoracic bioimpedance in children.

The purpose of this study was to evaluate the reliability of a thoracic electrical bioimpedance based device (PhysioFlow) for the determination of cardiac output and stroke volume during exercise at peak oxygen uptake (peak VO(2) in children. The reliability of peak VO(2) is also reported. Eleven boys and nine girls aged 10-11 years completed a cycle ergometer test to voluntary exhaustion on three occasions each 1 week apart. Peak VO(2) was determined and cardiac output and stroke volume at peak VO(2) were measured using a thoracic bioelectrical impedance device (PhysioFlow). The reliability of peak VO(2) cardiac output and stroke volume were determined initially from pairwise comparisons and subsequently across all three trials analysed together through calculation of typical error and intraclass correlation. The pairwise comparisons revealed no consistent bias across tests for all three measures and there was no evidence of non-uniform errors (heteroscedasticity). When three trials were analysed together typical error expressed as a coefficient of variation was 4.1% for peak VO(2) 9.3% for cardiac output and 9.3% for stroke volume. Results analysed by sex revealed no consistent differences. The PhysioFlow method allows non-invasive, beat-to-beat determination of cardiac output and stroke volume which is feasible for measurements during maximal exercise in children. The reliability of the PhysioFlow falls between that demonstrated for Doppler echocardiography (5%) and CO(2) rebreathing (12%) at maximal exercise but combines the significant advantages of portability, lower expense and requires less technical expertise to obtain reliable results.