Ic and relaxation properties by Doppler ultrasound techniques. Methods: Resting cardiac dimensions were measured by M-mode echocardiography. Stroke volume was estimated by the Doppler technique, and systolic function by peak aortic flow velocity and ejection flow rate. Diastolic transmitral pressure gradient was assessed by pulse wave peak E-wave velocity, ventricular relaxation properties by tissue Doppler imaging (E′ velocity, adjusted for ventricular size), and ventricular filling pressure by E/E′ ratio. Results: Size-adjusted cardiac dimensions were significantly greater in the athletes. Peak V˙O2 values for the athletes and nonathletes were 57.4 ± 4.8 and 44.4 ± 6.6 mL·kg−1·min−1, respectively. Maximal cardiac index and stroke index were greater in the athletes (11.10± 1.52 vs 9.02 ± 2.05 L·min−1·m−2; 59 ± 8 vs 46 ± 10 mL·m−2). Athletes and nonathletes demonstrated similar maximal peak aortic velocity (231 ± 20 and 208 ± 45 cm·s−1, respectively) and ejection rate (13.3 ± 1.0 and 12.5 ± 2.8 mL·s−1·cm−2 × 10−2, respectively). No significant group differences were observed in Emax (155 ± 17 and 149 ± 23 cm·s−1 for athletes and nonathletes, respectively), adjusted E′max (5.9 ± 1.2 and 5.8 ± 1.2 cm·s−1·mm−1 for athletes and nonathletes, respectively), and E/E′max (265 ± 40 and 262 ± 56 for athletes and nonathletes, respectively). Conclusions: This study revealed no differences between young trained athletes and nonathletes in myocardial functional responses to progressive exercise, implying that greater aerobic fitness in these athletes reflected volume expansion of the cardiovascular system without contribution of enhanced systolic or diastolic ventricular function. Such findings should be considered limited to the context of young athletes with limited duration of athletic training....

Exercise training results in a speeding of pulmonary oxygen uptake (VO2) kinetics at the onset of exercise in adults; however, only limited research has been conducted with children and adolescents. The aim of the present study was to examine VO2 and muscle deoxygenation kinetics in trained and untrained male adolescents. Sixteen trained (15 +/- 0.8 yr, VO2peak = 54.7 +/- 6.2 mL x kg-1 x min-1, self-assessed Tanner stage range 2-4) and nine untrained (15 +/- 0.6 yr, VO2peak = 43.1 +/- 5.2 mL x kg-1 x min-1, Tanner stage range 2-4) male adolescents performed two 6-min exercise transitions from a 3-min baseline of 10 W to a workload equivalent to 80% lactate threshold separated by a minimum of 1 h of passive rest. Oxygen uptake (breath-by-breath) and muscle deoxygenation (deoxyhemoglobin signal from near-infrared spectroscopy) were measured continuously throughout baseline and exercise transition. The time constant of the fundamental phase of VO2 kinetics was significantly faster in trained versus untrained subjects (trained: 22.3 +/- 7.2 s vs untrained: 29.8 +/- 8.4 s, P = 0.03). In contrast, neither the time constant (trained: 9.7 +/- 2.9 s vs untrained: 10.1 +/- 3.4 s, P = 0.78) nor the mean response time (trained: 17.4 +/- 2.5 s vs untrained: 18.3 +/- 2.3 s, P = 0.39) of muscle deoxygenation kinetics differed with training status. The present data suggest that exercise training results in faster VO2 kinetics in male adolescents, although inherent capabilities cannot be ruled out. Because muscle deoxygenation kinetics were unchanged, it is likely that faster VO2 kinetics were due to adaptations to both the cardiovascular system and the peripheral musculature.

Physical activity and psychological well-being contribute to positive lifestyle and well-being in youngsters who have Type 1 diabetes. The aims of this study were to objectively assess the physical activity levels of children with Type 1 diabetes, and investigate associations between physical activity levels, psychological well-being and HbA_1c. Thirty-six children, mean age 12.8 years, participated in the investigation. Physical activity was assessed using heart rate monitoring over four days. Children further completed the Diabetes Quality of Life for Youths Questionnaire, the Physical Self-Perception Profile for Children and the Self-Efficacy for Diabetes Scale. Routine outpatient HbA_1c measurements were recorded. There were no significant associations between psychological well-being and physical activity, or HbA_1c and physical activity, thus suggesting physical activity does not directly relate to psychological well-being in children with Type 1 diabetes. It may be that the effect of physical activity differs from that in children without Type 1 diabetes because of the place of physical activity within diabetes management and the need to balance this with insulin dosage and dietary intake to maintain blood glucose levels.

No studies to date have evaluated the relationship between exercise and microvascular function in youth with type 1 diabetes mellitus (T1DM). Twenty-nine complication free children and adolescents with T1DM were assessed for skin microvascular reactivity, aerobic fitness (VO2_peak) and physical activity. VO2_peak but not physical activity was significantly and independently associated with maximal hyperemia of the skin microcirculation (p < .01). No significant associations were found between venoarte-riolar reflex (VAR) vasoconstriction and VO2_peak or physical activity. Aerobic fitness may be an important indicator or mediator of effective microvascular endothelial function in youth with T1DM.