Oxygen uptake kinetics in trained adolescent females.

UNLABELLED: Little evidence exists with regard to the effect that exercise training has upon oxygen uptake kinetics in adolescent females. PURPOSE: The aim of the study was to compare [Formula: see text] and muscle deoxygenation kinetics in a group of trained (Tr) and untrained (Utr) female adolescents. METHOD: Twelve trained (6.4 ± 0.9 years training, 10.3 ± 1.4 months per year training, 5.2 ± 2.0 h per week) adolescent female soccer players (age 14.6 ± 0.7 years) were compared to a group (n = 8) of recreationally active adolescent girls (age 15.1 ± 0.6 years) of similar maturity status. Subjects underwent two, 6-min exercise transitions at a workload equivalent to 80 % of lactate threshold from a 3-min baseline of 10 W. All subjects had a passive rest period of 1 h between each square-wave transition. Breath-by-breath oxygen uptake and muscle deoxygenation were measured throughout and were modelled via a mono-exponential decay with a delay relative to the start of exercise. RESULT: Peak [Formula: see text] was significantly (p < 0.05) greater in the Tr compared to the Utr (Tr: 43.2 ± 3.2 mL kg(-1 )min(-1) vs. Utr: 34.6 ± 4.0 mL kg(-1 )min(-1)). The [Formula: see text] time constant was significantly (p < 0.05) faster in the Tr compared to the Utr (Tr: 26.3 ± 6.9 s vs. Utr: 35.1 ± 11.5 s). There was no inter-group difference in the time constant for muscle deoxygenation kinetics (Tr: 8.5 ± 3.0 s vs. Utr: 12.4 ± 8.3 s); a large effect size, however, was demonstrated (-0.804). CONCLUSION: Exercise training and/or genetic self-selection results in faster kinetics in trained adolescent females. The faster [Formula: see text] kinetics seen in the trained group may result from enhanced muscle oxygen utilisation.

Cardiac strain during upright cycle ergometry in adolescent males.

Little evidence exists with regard to changes in cardiac strain that occur during submaximal exercise in young males. The aims of the study were to evaluate the changes that occur in longitudinal (L), radial (R), and endocardial circumferential (EC) strain during submaximal upright cycle ergometry and to examine the test-retest reproducibility of these measurements. Fourteen recreationally active, adolescent (age: 17.9 ± 0.7 years) males volunteered for the study. All subjects underwent an incremental (40 W) submaximal cycle ergometer test. L, R, and EC strain values were obtained using speckle tracking, from two-dimensional B-mode images of the left ventricle (LV) during rest and the initial stages of submaximal exercise (40 and 80 W). The average of 6 LV segments was used to determine both peak wall deformation (%) and the time to peak deformation (ms). There was a statistically (P < 0.05) significant increase from rest to submaximal exercise for peak deformation for L, R, and EC strain. There was a statistically significant (P < 0.05) decrease from rest to submaximal exercise for time to peak for L and R and EC strain and between submaximal workloads for time to peak for L strain and EC strain. Coefficients of variation demonstrated reproducibility for upright strain and strain rate measurements similar to published supine measurements. This study has demonstrated that changes in left ventricular wall deformation (L, R and EC strain) that occur during the transition from rest to submaximal exercise can be reliably measured and confirm that a healthy LV has a hyperdynamic response to exercise.

Time-of-day effect on cardiac responses to progressive exercise.

This study was designed to examine time-of-day effects on markers of cardiac functional capacity during a standard progressive cycle exercise test. Fourteen healthy, untrained young males (mean ± SD: 17.9 ± 0.7 yrs of age) performed identical maximal cycle tests in the morning (08:00-11:00 h) and late afternoon (16:00-19:00 h) in random order. Cardiac variables were measured at rest, submaximal exercise, and maximal exercise by standard echocardiographic techniques. No differences in morning and afternoon testing values at rest or during exercise were observed for oxygen uptake, heart rate, cardiac output, or markers of systolic and diastolic myocardial function. Values at peak exercise for Vo(2) at morning and afternoon testing were 3.20 ± 0.49 and 3.24 ± 0.55 L min(-1), respectively, for heart rate 190 ± 11 and 188 ± 15 bpm, and for cardiac output 19.5 ± 2.8 and 19.8 ± 3.5 L min(-1). Coefficients of variation for morning and afternoon values for these variables were similar to those previously published for test-retest reproducibility. This study failed to demonstrate evidence for significant time-of-day variation in Vo(2)max or cardiac function during standard progressive exercise testing in adolescent males.

Pulmonary oxygen uptake and muscle deoxygenation kinetics during recovery in trained and untrained male adolescents.

Previous studies have demonstrated faster pulmonary oxygen uptake (VO2) kinetics in the trained state during the transition to and from moderate-intensity exercise in adults. Whilst a similar effect of training status has previously been observed during the on-transition in adolescents, whether this is also observed during recovery from exercise is presently unknown. The aim of the present study was therefore to examine VO2 kinetics in trained and untrained male adolescents during recovery from moderate-intensity exercise. 15 trained (15 ± 0.8 years, VO2max 54.9 ± 6.4 mL kg(-1) min(-1)) and 8 untrained (15 ± 0.5 years, VO2max 44.0 ± 4.6 mL kg(-1) min(-1)) male adolescents performed two 6-min exercise off-transitions to 10 W from a preceding "baseline" of exercise at a workload equivalent to 80% lactate threshold; VO2 (breath-by-breath) and muscle deoxyhaemoglobin (near-infrared spectroscopy) were measured continuously. The time constant of the fundamental phase of VO2 off-kinetics was not different between trained and untrained (trained 27.8 ± 5.9 s vs. untrained 28.9 ± 7.6 s, P = 0.71). However, the time constant (trained 17.0 ± 7.5 s vs. untrained 32 ± 11 s, P < 0.01) and mean response time (trained 24.2 ± 9.2 s vs. untrained 34 ± 13 s, P = 0.05) of muscle deoxyhaemoglobin off-kinetics was faster in the trained subjects compared to the untrained subjects. VO2 kinetics was unaffected by training status; the faster muscle deoxyhaemoglobin kinetics in the trained subjects thus indicates slower blood flow kinetics during recovery from exercise compared to the untrained subjects.

Myocardial function and aerobic fitness in adolescent females.

A recent report indicated that variations in myocardial functional (systolic and diastolic) responses to exercise do not contribute to inter-individual differences in aerobic fitness (peak VO(2)) among young males. This study was designed to investigate the same question among adolescent females. Thirteen highly fit adolescent football (soccer) players (peak VO(2) 43.5 ± 3.4 ml kg(-1) min(-1)) and nine untrained girls (peak VO(2) 36.0 ± 5.1 ml kg(-1) min(-1)) matched for age underwent a progressive cycle exercise test to exhaustion. Cardiac variables were measured by standard echocardiographic techniques. Maximal stroke index was greater in the high-fit group (50 ± 5 vs. 41 ± 4 ml m(-2)), but no significant group differences were observed in maximal heart rate or arterial venous oxygen difference. Increases in markers of both systolic (ejection rate, tissue Doppler S') and diastolic (tissue Doppler E', mitral E velocity) myocardial functions at rest and during the acute bout of exercise were similar in the two groups. This study suggests that among healthy adolescent females, like young males, myocardial systolic and diastolic functional capacities do not contribute to inter-individual variability in physiologic aerobic fitness.

Sex influence on myocardial function with exercise in adolescents.

OBJECTIVES: Ventricular systolic functional response to exercise has been reported to be superior in adult men compared to women. This study explored myocardial responses to maximal upright progressive exercise in late pubertal males and females. METHODS: Doppler echocardiographic techniques were utilized to estimate myocardial function response to a bout of progressive cycle exercise. RESULTS: Systolic functional capacity, as indicated by ejection rate (12.5 +/- 2.8 and 13.1 +/- 1.0 [x10(-2)] ml s(-1) cm(-2) for boys and girls, respectively) and peak aortic velocity (208 +/- 45 and 196 +/- 12 cm s(-1), respectively) at maximal exercise, did not differ between the two groups. Similarly, peak values as well as increases in transmitral pressure gradient (mitral E flow velocity), ventricular relaxation (tissue Doppler imaging E'), and left ventricular filling pressure (E/E' ratio) as estimates of diastolic function were similar in males and females. CONCLUSIONS: This study failed to reveal qualitative or quantitative differences between adolescent boys and girls in ventricular systolic or diastolic functional responses to maximal cycle exercise.

Faster pulmonary oxygen uptake kinetics in trained versus untrained male adolescents.

UNLABELLED: 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. PURPOSE: The aim of the present study was to examine VO2 and muscle deoxygenation kinetics in trained and untrained male adolescents. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Myocardial performance during progressive exercise in athletic adolescent males.

PURPOSE: The extent that enhanced ventricular function contributes to superior aerobic fitness of trained athletes is unclear. This study compared cardiovascular responses to progressive cycle exercise in 12 adolescent soccer players and 10 untrained boys with assessment of ventricular inotropic 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.min, respectively. Maximal cardiac index and stroke index were greater in the athletes (11.10+/- 1.52 vs 9.02 +/- 2.05 L.min.m; 59 +/- 8 vs 46 +/- 10 mL.m). Athletes and nonathletes demonstrated similar maximal peak aortic velocity (231 +/- 20 and 208 +/- 45 cm.s, respectively) and ejection rate (13.3 +/- 1.0 and 12.5 +/- 2.8 mL.s.cm x 10, respectively). No significant group differences were observed in Emax (155 +/- 17 and 149 +/- 23 cm.s for athletes and nonathletes, respectively), adjusted E'max (5.9 +/- 1.2 and 5.8 +/- 1.2 cm.s.mm 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.