Sex-Specific Longitudinal Modeling of Youth Peak Oxygen Uptake

A Prospective Study on Maximal Oxygen Uptake and Cardiovascular Functions in 12-Year-Old Endurance Athletes and Their Non-Endurance-Trained Peers

The maximal oxygen uptake (V̇O2max) is typically higher in endurance-trained adolescents than in non-endurance-trained peers. However, the specific mechanisms contributing to this remain unclear, as well as the impact of training during this developmental stage. This study aims to compare V̇O2max and cardiovascular functions between 12-year-old endurance athletes and non-endurance-trained over a 14-month period. Anthropometrics, V̇O2max, hemoglobin mass (Hbmass), blood volume (BV), and left-ventricular morphology were assessed four times over the 14 months in a group of young cross-country skiers (END, n = 42, age: 12.4 ± 0.5, girls: n = 27) and a group of controls (CON, n = 26, age: 12.3 ± 0.3, girls: n = 15). Throughout the 14-month follow-up, END did more weekly training than CON (7.0 ± 2.3 vs. 2.5 ± 2.4 h, p < 0.001), with only END conducting endurance training. END had ~18% higher V̇O2max relative to fat-free mass (FFM) than CON (p < 0.001). Stroke volume (SV) and left ventricular end-diastolic volume (LV EDV) relative to FFM were also higher for END than CON (p < 0.001 and 0.004), while no significant differences were found for Hbmass and BV. No significant interaction was seen for group and time for V̇O2max (p = 0.352-0.767) or any cardiovascular parameters (p = 0.131-0.956) in absolute measures or relative to FFM. In conclusion, the END group exhibited higher V̇O2max, LV EDV, and SV compared to the CON group, with no significant difference in BV and Hbmass. Despite substantial differences in training volume, the progression of these variables over the 14-month period was similar in both groups.

Mediative role of body mass index in cardiorespiratory fitness-associated vascular remodeling in youth

BACKGROUND

Data on fitness-associated arterial remodeling in children is limited. We assessed the relation between cardiorespiratory fitness (CRF) and intima-media thickness (IMT), diameter, IMT:diameter-ratio (IDR), and tensile stress of the common carotid artery (CCA) in 697 healthy German schoolchildren. Further, we explored how body mass index (BMI) may influence these associations.

METHODS

We measured the vascular parameters with a high-resolution ultrasound device. We determined CRF using the FITNESSGRAM® PACER test and calculated each child's allometrically scaled peak oxygen uptake capacity (VO2peak).

RESULTS

VO2peak, reflecting CRF, showed positive direct effects on IMT (girls: p < 0.001; boys: p = 0.02) and diameter in girls (p < 0.001). Considering BMI as a mediator, higher CRF was indirectly linked to decreases in IMT (girls: p = 0.04; boys: p = 0.02) and diameter (both p < 0.001), reflecting a competitive mediation. CRF indirectly mitigated the BMI-associated decrease in IDR (both p < 0.001) and increase in tensile stress (both p < 0.001) without affecting any of these parameters directly.

CONCLUSION

CRF appears to be linked to uniform arterial remodeling with balanced hemodynamics and to further alleviate BMI-associated, potentially adverse vascular alterations, highlighting its significant role in cardiovascular health in youth.

IMPACT

Data on CRF-associated arterial remodeling in youth is limited. Higher VO2peak, reflecting higher CRF, was positively associated with IMT in girls and boys and diameter in girls. These direct effects were counteracted by the indirect BMI-mediated effect of CRF on IMT and diameter, reflecting a competitive mediation. A higher CRF indirectly mitigated the BMI-associated decrease in IDR and increase in tensile stress without directly affecting any of these parameters. Our findings indicate homogenous remodeling and balanced hemodynamics with increasing CRF-and opposite effects with increasing BMI.

Effects of Small-Sided Soccer Games on Physical Fitness and Cardiometabolic Health Biomarkers in Untrained Children and Adolescents: A Systematic Review and Meta-Analysis

Objective: This systematic review and meta-analysis aimed to determine the benefits of an exercise intervention based on small-sided soccer games (SSSGs) on health-related physical fitness and cardiometabolic health in previously untrained children and adolescents. Methods: A systematic search on PubMed/MEDLINE, Web of Science, Scopus, Cochrane, and EBSCO databases was performed. Randomized or non-randomized controlled trials conducted in previously untrained children or adolescents (age < 18 years) that assessed the effect of SSSG-based intervention on health-related physical fitness and cardiometabolic risk biomarkers were included. Primary outcomes were cardiorespiratory fitness and waist circumference. Evidence was synthesized as the mean difference or standardized mean difference using a random-effects meta-analysis. The quality of evidence was assessed using ROB2 and ROBINS-I tools. Results: Sixteen studies (n = 2872 participants) were included in this meta-analysis. SSSGs significantly improved cardiorespiratory fitness (SMD, 0.12 [0.01; 0.23]) and showed a non-significant trend in decreased waist circumference (-7.49 cm [-15.03; 0.06]). Additionally, SSSGs significantly decreased systolic (MD, -3.85 mmHg [-5.75; -1.94]) and diastolic blood pressure (MD, -1.26 mmHg [-2.44; -0.08]) and triglycerides (-30.34 mg·dL-1 [-45.99; -14.69]). No effects on body composition or other cardiometabolic risk biomarkers were observed. After a sensitivity analysis, waist circumference and muscle strength were also shown to improve significantly following SSSGs. Comparisons between SSSG and other types of exercise interventions showed no differences in improved physical fitness or cardiometabolic risk. Conclusions: SSSG-based interventions effectively improve cardiorespiratory fitness, blood pressure, triglycerides, muscle strength, and waist circumference. There is less evidence of the effects of SSSGs on other health markers. Particular attention should be given to improving SSSG protocol reporting in future studies.

Physical Activity, Fitness, and Cardiovascular Disease Risk in Adolescent Childhood Cancer Survivors Compared to Controls: The Physical Activity in Childhood Cancer Survivors Study

Purpose: Childhood cancer survivors have increased risk of cardiac late effects that can be potentially mitigated by physical activity and fitness. We aimed to (1) compare cardiovascular disease (CVD) risk between survivors and controls, and (2) examine whether the associations of moderate-to-vigorous physical activity (MVPA), cardiorespiratory fitness (CRF), and musculoskeletal fitness (MSF) with CVD risk factors differed between survivors and controls. Methods: Within the Physical Activity in Childhood Cancer Survivors (PACCS) study, we assessed CVD risk factors (android fat mass, systolic blood pressure [SBP], total cholesterol/high-density lipoprotein [HDL]-cholesterol, and glycosylated hemoglobin) in 157 childhood cancer survivors and 113 age- and sex-matched controls aged 9-18 years. We used multivariable mixed linear regression models to compare CVD risk factors between survivors and controls, and assess associations of MVPA, CRF, and MSF with CVD risk factors. Results: Compared with controls, survivors had more android fat mass (861 vs. 648 g, p = 0.001) and lower SBP (114 vs. 118 mmHg, p = 0.002). MVPA, CRF, and MSF were associated with lower levels of android fat mass and total cholesterol/HDL-cholesterol, and higher SBP in survivors. Associations of MVPA, CRF, and MSF with CVD risk factors were similar in survivors and controls (Pinteraction > 0.05), except the associations of CRF and MSF with android fat mass, which were stronger in survivors than in controls (Pinteraction ≤ 0.001). Conclusion: Owing to higher levels of android fat mass and its stronger association with physical fitness in childhood cancer survivors compared with controls, survivors should get targeted interventions to increase fitness to reduce future risk of CVD.

Longitudinal development and tracking of cardiorespiratory fitness from childhood to adolescence

BACKGROUND

Cardiorespiratory fitness (CRF) is an important indicator of health in childhood and adolescence but longitudinal studies on the development and tracking of CRF from childhood to adolescence are scarce.

OBJECTIVES

The objectives of this study were (1) to assess longitudinal development and track CRF over 10 years from childhood to adolescence, and (2) to examine potential sex differences in the development and tracking of CRF during this period.

METHODS

Participants were Icelandic children born in 1999, measured at the age of 7 (n = 190, 106 girls), 9 (n = 163, 95 girls), 15 (n = 239, 134 girls), and 17 (n = 202, 119 girls). CRF was assessed with a maximal cycle ergometer test and expressed as maximal power output (Max W) and maximal power output relative to lean mass (W/kgLM). Multilevel regression models were used to study the longitudinal development of CRF, and tracking was assessed with Spearman's rank correlation, logistic regression, and the percentage of participants remaining in low, moderate, or high CRF categories between measurements.

RESULTS

Max W and W/kgLM increased for both boys and girls up to age 15. Max W plateaued for both boys and girls while W/kgLM plateaued for girls but declined for boys from age 15 to 17. Boys had higher Max W than girls from age 15 and higher W/kgLM from age 9. CRF tracked at low to moderate levels from childhood to adolescence and at high levels in adolescence, with higher values observed for boys than girls.

CONCLUSIONS

Age 15 was a critical time point in the development of CRF, with values starting to plateau for girls and decline for boys. The results support early intervention for improved CRF in later years, with interventions targeting all children, regardless of their CRF level.

Cardiorespiratory fitness and development of childhood cardiovascular risk: The EXAMIN YOUTH follow-up study

Background: Obesity- and hypertension-related cardiovascular (CV) risk has been shown to originate in childhood. Higher body mass index (BMI) and blood pressure (BP) have been associated with increased large artery stiffness and a lower microvascular arteriolar-to-venular diameter ratio (AVR) in children. This study aimed to investigate the association of cardiorespiratory fitness (CRF) with development of BMI, BP and vascular health during childhood. Methods: In our prospective cohort study, 1,171 children aged 6-8 years were screened for CRF, BMI, BP, retinal vessel diameters and pulse wave velocity using standardized protocols. Endurance capacity was assessed by 20 m shuttle run test. After 4 years, all parameters were assessed in 664 children using the same protocols. Results: Children with a higher CRF at baseline developed a significantly lower BMI (β [95% CI] -0.09 [-0.11 to -0.06] kg/m2, p < 0.001), a lower systolic BP (β [95% CI] -0.09 [-0.15 to -0.03] mmHg, p = 0.004) and a higher AVR (β [95% CI] 0.0004 [0.00004 to 0.0007] units, p = 0.027) after 4 years. The indirect association of CRF with development of retinal arteriolar diameters was mediated by changes in BMI. Conclusion: Our results identify CRF as a key modulator for the risk trajectories of BMI, BP and microvascular health in children. Obesity-related CV risk has been shown to track into adulthood, and achieving higher CRF levels in children may help counteract the development of CV risk and disease not only in pediatric populations, but may also help reduce the burden of CVD in adulthood. Registration: http://www.clinicaltrials.gov/ (NCT02853747).

Trajectories of cardiorespiratory fitness from childhood to adolescence: Findings from the QUALITY cohort

Estimate the shape and number of cardiorespiratory fitness (CRF) trajectories from childhood to adolescence; and verify whether CRF trajectory membership can be predicted by sex, biological maturation, body weight, body composition and physical activity (PA) in childhood. Data from QUALITY were used. Participants attended baseline (8-10 y old, n = 630) and follow-ups 2 years (n = 564) and 7 years (n = 359) after baseline. Group-based trajectory analysis for relative peak oxygen consumption (VO2peak, ml·kg-1·min-1) was performed. A multinomial logistic regression model was used to estimate the associations between baseline predictors and trajectory membership. Mean age of the 454 participants was 9.7 ± 0.9 years at baseline. Three distinct VO2peak trajectories were identified and all tended to decrease. They were labelled according to the starting point and slope. High-Decreasers were mostly boys, had lower body weight and fat-free mass index and higher PA levels at baseline (p < 0.05). Female sex and higher weight were associated with higher odds of being classified in the Low-Decreaser trajectory (OR = 74.03, 95%CI = 27.06-202.54; OR = 1.48, 95%CI = 1.36-1.60). Those with higher PA were less likely to be Low-Decreasers (OR = 0.96, 95%CI = 0.94-0.97). Sex, body weight and PA in childhood are important influencing factors of VO2peak (ml·kg-1·min-1) trajectories across adolescence.

Alterations in aerobic fitness and muscle deoxygenation during ramp incremental exercise in trained youth cyclists: a ~3-year longitudinal study

Alterations of aerobic fitness and muscle deoxygenation during a ramp incremental exercise test (GXT) were assessed on two occasions within a time-frame of 2.9 ± 0.1y in competitive youth cyclists. Nine cyclists (age, 14.5 ± 1.1y; peak oxygen uptake (V˙O_2peak), 62.6 ± 4.2 mL.min^-1.kg^-1) participated in this investigation. V˙O_2peak, the gas exchange threshold (GET) and the respiratory compensation point (RCP), as well as the muscle deoxygenation response pattern were determined during a GXT using open circuit spirometry and near-infrared spectroscopy, respectively. T-tests and Pearson's correlations were used to assess effects of time on the dependent variables and relationships between changes of parameter estimates of aerobic fitness and the muscle deoxygenation response, respectively. Workrate and metabolic rate at GET (33 ± 20 and 42 ± 23%) and RCP (36 ± 20 and 40 ± 22%), and V˙O_2peak (30 ± 18%) significantly increased throughout the study (P < 0.05). The muscle deoxygenation response showed a significant rightward shift from occasion one to two (P < 0.05). Alterations in the workrate/metabolic rate at RCP, and V˙O_2peak, were correlated with alterations of the muscle deoxygenation response (R = 0.71-0.89, P < 0.05). Together, this is thought to indicate a superior muscle perfusion within the tissue of interrogation at the same metabolic rate on occasion two vs. one, which partially contributed to the improved aerobic fitness in the cyclists herein.

Physiological Variables that Contribute to Aerobic Fitness in Boys During Early Adolescence in the Context of Basketball Training and the Maturity Level

The aim of this study was to assess physiological variables that contribute to aerobic fitness in respect to basketball training and the maturity level in adolescent boys. Our subjects were 28 basketball-trained and 22 control-group boys (average age: 11.83 ± 0.43 years). An incremental treadmill running test to exhaustion was performed twice with a 1-year interval between the sessions to determine the following peak aerobic fitness variables: oxygen uptake, stroke volume, cardiac output, minute ventilation, and others. Maturity offset was used to evaluate the maturity level. The basketball-trained group exhibited a higher peak ratio-scaled oxygen uptake (1st session: 50.55 ± 6.21 and 46.57 ± 5.68 ml/kg/min in basketball and control-group boys, respectively, p = 0.024; 2nd session: 54.50 ± 6.50 and 45.33 ± 5.99 ml/kg/min, respectively, p < 0.001) during both testing sessions. During the 2nd session, the basketball-trained group also showed a significantly higher peak arteriovenous oxygen difference (basketball-trained boys: 14.02 ± 2.17 ml/100 ml; control-group boys: 12.52 ± 2.49 ml/100 ml; p = 0.027) and peak minute ventilation (basketball-trained boys: 96.08 ± 21.71 l/min; control-group boys: 83.14 ± 17.85 l/min; p = 0.028). The maturity level among the basketball-trained boys was correlated with peak variables: oxygen uptake, stroke volume, cardiac output, and minute ventilation, but not with the ratio-scaled oxygen uptake. In conclusion, basketball training at a young age among boys improved aerobic fitness compared with sedentary boys. More mature basketball players were not superior to their less mature peers regarding aerobic fitness after adjusting for body dimensions.

Fitness, body composition, and metabolic risk scores in children and adolescents: the UP&DOWN study

We aimed to analyse the longitudinal association between physical fitness (PF) and body composition (BC) with a metabolic risk score (Met4) in children and adolescents and to elucidate whether the association between PF and Met4 differs when using relativized or absolute fitness variables. A total of 188 children (86 females) and 195 adolescents (97 females) were included. Cardiorespiratory fitness (CRF) was determined by the 20-m shuttle run test, and muscular fitness (MF) was determined by hand grip and standing long jump tests. Height and weight were measured, and the body mass index (Kg/m²) was calculated. Triceps and subscapular skinfolds were assessed to compute body fat percentage. Met4 was computed from systolic blood pressure, triglycerides, high-density lipoprotein cholesterol, and glucose levels. Relative CRF was longitudinally and negatively associated with Met4 in female children (β =  -0.031, p = 0.025), while absolute CRF was positively associated with Met4 in male children and adolescents (β = 0.000, p < 0.05). Relative upper and lower-body MF were longitudinally and negatively associated with Met4 in female adolescents (β =  -1.347, β =  -0.005, p < 0.05), while absolute lower-body MF was positively associated with Met4 in male children (β = 0.000, p = 0.019). BC was longitudinally and positively associated with Met4 in male children (β-ranging from 0.011 to 0.055, all p < 0.05) and male adolescents (β-ranging from 0.011 to 0.046, all p < 0.05).  Conclusion: BC is more strongly associated with Met4 than PF in children and adolescents. An optimal body weight status should be considered the main objective of health-promoting programs at childhood and adolescence. Furthermore, the way of expressing the fitness variables determines the direction of the association with Met4. What is Known: • Physical fitness is an important health indicator in children and adolescents, with great amount of previous evidence supporting the preventive role of maintaining optimal levels of both cardiorespiratory and muscular fitness for future cardiometabolic issues. What is New: • The way of reporting physical fitness variables can affect the associations between physical fitness features and cardiometabolic outcomes. Since body composition variables have a great impact on both physical fitness and cardiometabolic health, relativizing physical fitness performance by body composition could lead to erroneous conclusions.

Sex-Related Differences in Oxygen Consumption Recovery After High-Intensity Rowing Exercise During Childhood and Adolescence

PURPOSE

To determine sex-related differences in oxygen consumption (V˙O2) recovery after high-intensity exercise during childhood and adolescence.

METHODS

Forty-two boys and 35 girls (10-17 y) performed a 60-second all-out test on a rowing ergometer. Postexercise V˙O2 recovery was analyzed from (1) the V˙O2 recovery time constant obtained from a biexponential model (τ1V˙O2) and (2) excess postexercise oxygen consumption calculated over a period of 8 minutes (EPOC8) and until τ1V˙O2 was reached (EPOCτ1). Multiplicative allometric modeling was used to assess the concurrent effects of body mass or lean body mass, and age on EPOC8 and EPOCτ1.

RESULTS

EPOC8 increased significantly more in boys from the age of 14 years. However, the sex difference was no longer significant when EPOC8 was analyzed using an allometric model including body mass + age or lean body mass + age. In addition, despite a greater increase in EPOCτ1 in boys from the age of 14 years, τ1V˙O2 was not significantly different between sexes whatever age.

CONCLUSION

While age and lean body mass accounted for the sex-related differences of EPOC during childhood and adolescence, no significant effect of age and sex was observed on the V˙O2 recovery time constant after high-intensity exercise.

Increase in peak oxygen uptake and Andersen test performance in children from age six to ten: The Health Oriented Pedagogical Project (HOPP)

The increased prevalence of non-communicable disease risk factors among children because of lack of physical activity is concerning. The Health Oriented Pedagogical Project was set up to combine learning activities and physical activity, thus reducing sedentariness during school time. The current study aimed to measure and describe the longitudinal and cross-sectional development of oxygen uptake and running performance in children at ages six and ten. The validity of the Andersen Test in predicting V̇O2peak in these age groups was also evaluated. Eighty-six children (53 boys, 33 girls) with complete datasets at ages 6 and 10 years were included in the longitudinal study, while 192 children (106 boys, 86 girls) were included in the cross-sectional analysis because they missed data from 1 year. Oxygen uptake was measured using a metabolic analyser and maximal treadmill running, while the distance covered during the AT determined running performance. Body mass, height, and waist-to-height ratios were recorded. Multiple regression analysis was used to assess the association between oxygen uptake and running performance. The cross-sectional results did not differ from the longitudinal data for anthropometrical data, oxygen uptake and running performance. Height, body mass and waist-to-height ratio did not differ between the sexes at ages six or ten. Boys had significantly higher peak oxygen uptake than girls at 6 years of age, irrespective of how oxygen uptake was expressed. Allometric scaling of oxygen uptake revealed differences between sexes at both ages. Longitudinal running performance increased in both sexes from 6 to 10 years. Boys ran significantly longer only at age ten. The association between oxygen uptake and running performance varied according to how the oxygen uptake was expressed and with sex and age. Ten-year-old girls had the highest correlations in the longitudinal investigation, from r2 = 0.48 (fV̇O2peak) to 0.65 (rV̇O2peak) between AT and V̇O2peak. The AT was found to be as valid as the 20-m shuttle run test in estimating peak oxygen uptake, with a random measurement error of approximately 11% of mean values.

JA, Duque L, Chaves-Gomez S, Cristancho-Mejía E, Schmidt WFJ. Hemoglobin Mass, Blood Volume and VO2max of Trained and Untrained Children and Adolescents Living at Different Altitudes

Introduction: To a considerable extent, the magnitude of blood volume (BV) and hemoglobin mass (Hbmass) contribute to the maximum O2-uptake (VO2max), especially in endurance-trained athletes. However, the development of Hbmass and BV and their relationships with VO2max during childhood are unknown. The aim of the present cross-sectional study was to investigate Hbmass and BV and their relationships with VO2max in children and adolescents. In addition, the possible influence of endurance training and chronic hypoxia was evaluated.

Methods: A total of 475 differently trained children and adolescents (girls n = 217, boys n = 258; untrained n = 171, endurance trained n = 304) living at two different altitudes (∼1,000 m, n = 204, ∼2,600 m, n = 271) and 9–18 years old participated in the study. The stage of puberty was determined according to Tanner; Hbmass and BV were determined by CO rebreathing; and VO2max was determined by cycle ergometry and for runners on the treadmill.

Results: Before puberty, there was no association between training status and Hbmass or BV. During and after puberty, we found 7–10% higher values in the trained groups. Living at a moderate altitude had a uniformly positive effect of ∼7% on Hbmass in all groups and no effect on BV. The VO2max before, during and after puberty was strongly associated with training (pre/early puberty: boys +27%, girls +26%; mid puberty: +42% and +45%; late puberty: +43% and +47%) but not with altitude. The associated effects of training in the pre/early pubertal groups were independent of Hbmass and BV, while in the mid- and late pubertal groups, 25% of the training effect could be attributed to the elevated Hbmass.

Conclusions: The associated effects of training on Hbmass and BV, resulting in increased VO2max, can only be observed after the onset of puberty.

A Combined Analysis of Peak and Submaximal Exercise Parameters in Delineating Underlying Mechanisms of Sex Differences in Healthy Adolescents

Peak exercise parameters are considered the gold standard to quantify cardiac reserve in cardiopulmonary exercise testing (CPET). We studied whether submaximal parameters would add additional values in analyzing sex differences in CPET. We reviewed CPET of age-matched healthy male and female adolescents by cycle ergometer. Besides peak parameters, submaximal CPET parameters, including ventilatory anaerobic threshold (VAT), oxygen uptake efficiency slope (OUES), and submaximal slopes of Δoxygen consumption (ΔVO2)/Δwork rate (ΔWR), Δheart rate (ΔHR)/ΔWR, ΔVO2/ΔHR, and Δminute ventilation (ΔVE)/ΔCO2 production (ΔVCO2), were obtained. We studied 35 male and 40 female healthy adolescents. Peak VO2 (pVO2), peak oxygen pulse (pOP), and VAT were significantly lower in females than males (1.9 ± 0.4 vs. 2.5 ± 0.6 L/min; 10 ± 2.0 vs. 13.2 ± 3.5 ml/beat; 1.23 ± 0.3 vs. 1.52 ± 0.5 L/min, respectively, all p < 0.005). Females showed significantly lower pVO2, VAT, and OUES with the same body weight than males, implying higher skeletal muscle mass in males. When simultaneously examining ΔHR/ΔWR and pOP, females showed higher dependency on increases in HR than in stroke volume. Females demonstrated significantly lower pOP with the same levels of ΔVO2/ΔHR, suggesting more limited exercise persistence than males under an anaerobic condition at peak exercise. Oxygen uptake efficiency in relation to peak VE was significantly higher in males. There was no sex difference in either ΔVO2/ΔWR or ΔVE/ΔVCO2. Combinational assessment of peak and submaximal CPET parameters delineates the multiple mechanisms that contribute to the sex differences in exercise performance.

Association between Cardiopulmonary Capacity and Body Mass Composition in Children and Adolescents with High Body Weight: A Cross-Sectional Study

(1) Background: Excessive body weight is a global problem in the 21st century. Children and adolescents, in particular, are at risk. Recently, there has been an increasing interest in the relationship between aerobic capacity and body composition. Therefore, this study aimed to determine the association between the individual parameters of cardiopulmonary capacity obtained in cardiopulmonary exercise testing (CPET) and selected parameters of body mass composition in high-BMI children and children over the 85th percentile according to the WHO growth reference. (2) Materials and Method: The research included 100 children of school-age (7-15 years) with an excessive BMI, i.e., over the 85th percentile as per the WHO Growth Reference (BMI percentile 95.21 ± 4.65; Z-score BMI: 2.07 ± 0.94). The study consisted of three parts: anthropometric measurements, measurement of body mass composition using a body composition analyzer (TANITA MC-780 S MA) using the bioimpedance method, and a cardiopulmonary exercise test on a pediatric cycle ergometer (Corival Pediatric, Lode BV) using the Godfrey protocol; (3) Results: The correlation between BMI and fat mass (FM) was very high (rho = 0.83; p = 0.00) with moderate body fat percentage (BF%) (rho = 0.48; p = 0.00). There was a relevant correlation between the amount of fat-free mass in total body mass and cardiopulmonary capacity expressed as the absolute aerobic capacity (VO2peak) (rho = 0.55; p = 0.00). (4) Conclusions: In the case of children and youth with higher BMI, there was a correlation between the amount of fat-free mass in total body mass and cardiopulmonary capacity in terms of absolute aerobic capacity.

Cardiac Autonomic Modulation of Heart Rate Recovery in Children with Spina Bifida

We aimed to analyse cardiac autonomic control by assessing the post-exercise heart rate recovery (HRR) and physical fitness in children and adolescents with spina bifida (SB), compared to participants with typical development. A total of 124 participants, 42 with spina bifida (SB group) and 82 typical developmental controls (CO group) performed the arm cranking exercise test with a gas analysis system. HRR was determined at the first (HRR_1) and second (HRR_2) minute at recovery phase. Data are shown as [mean difference (95% CI)]. The SB group showed reduced HR reserve [14.5 (7.1-22.0) bmp, P<0.01], slower HRR_1 [12.4 (7.4-17.5) bpm, P<0.01] and HRR_2 [16.3 (10.6-21.9) bpm; P<0.01], lower VO2peak [VO2peak relative: 7.3 (4.2-10.3) mL·min-1·kg-1, P<0.01; VO2peak absolute: 0.42 (0.30-0.54) L·min-1, P<0.01], and lower O2 pulse [2.5 (1.8-3.2) mL·bpm, P<0.01] and ventilatory responses [13.5 (8.8-18.1) L·min-1, P<0.01] than the CO group. VE/VO2 was not different between groups [-2.82 (-5.77- -0.12); P=0.06], but the VE/VCO2 [-2.59 (-4.40-0.78); P<0.01] and the values of the anaerobic threshold corrected by body mass [-3.2 (-5.8- -0.6) mL·min-1·kg-1, P=0.01] were higher in the SB group than in the CO group. We concluded that children and adolescents with SB have reduced physical fitness and a slower HRR response after maximal effort.

Relationship between Anthropometric, Physical and Hormonal Parameters among Pre-Pubertal Handball Players

Background: The aims of our study were to investigate the changes in anthropometric and physical parameters and fasting hormonal levels among pre-pubertal female handball players (n = 14, age: 11.53 ± 0.58 yrs, height: 153.36 ± 5.12 cm, body mass: 43.59 ± 6.14 kg) in the pre-season period following 8 weeks of handball training, and to analyze the contribution of hormones, physical performance and anthropometric parameters. Methods: Prior to and immediately following the training period, several anthropometric, strength, and cardiorespiratory variables, including fasting hormonal concentrations (plasma cortisol, estradiol, testosterone and growth hormones) were measured. Athletes performed concurrent resistance and aerobic exercises, including game-based trainings during the 8-week training period. Results: Significant elevations were found in all strength parameters (maximal handgrip strength dominant (D): 16.40%, p < 0.01; non-dominant (ND): 25.15%, p < 0.05; maximal concentric (MVC) torque of quadriceps D: 13.82%, p < 0.05; ND: 12.61%, p < 0.05; MVC torque of hamstring D: 12.14%, p < 0.01; ND: 12.44%, p < 0.01), including plasma cortisol levels (C, 34.30%, p < 0.05) and peak respiratory quotient (5.24%, p < 0.05). Body composition and maximal oxygen uptake (VO_2max) remained unchanged. Percentage changes in thigh (r = 0.316, p < 0.05), hand (r = 0.361, p < 0.05), and hip circumference (r = 0.297, p < 0.05) correlated with C changes. Percentage changes in plasma growth hormone levels (GH) contributed to the magnitude of gains in handgrip strength (r = 0.553, p < 0.05). Percentage changes in maximal exercise pulmonary ventilation (MVE) correlated with elevated C (r = −0.592, p < 0.05). Discussion: Changes in anthropometric variables and fasting hormone levels (estradiol, testosterone and cortisol) were poor indicators of developing VO_2max and strength during pre-pubertal years. Physical adaptation may not be explained in consideration of the athletes’ hormonal or anthropometric characteristics. Conclusion: Gradually increased training volume followed by a summer break should be applied to youth handball, considering the anti-hypertrophic responses and the inhibitory effect of elevating C on pre-pubertal maturation.

Longitudinal changes in maximal oxygen uptake in adolescent girls and boys with different training backgrounds

The purpose of this study was to investigate the effects of high-volume endurance training on the development of maximal oxygen uptake (VO_2max ) in physically active boys and girls between the ages of 12 and 15 years, using a longitudinal design. The children participated in organized training in sports clubs for an average of 7-10 hours per week, with one group undertaking a high volume of endurance training (~7 hours per week; End boys, n = 23 and End girls, n = 17) and the other group having a primary focus on technical and tactical skill development, undertaking low volumes of endurance training (~1.6 hours per week; non-End boys, n = 29 and non-End girls, n = 9). VO_2max and anthropometrics were assessed at age 12, 13, and 15. At age 12, VO_2max was 58.9 (5.6), 65.5 (7.2), 56.5 (6.5), and 58.8 (7.9) mL·kg^-1 ·min^-1 in End girls, End boys, non-End girls, and non-End boys, respectively. Over the three years, there was no difference between the training groups in the development of VO_2max independent of scaling. In boys, VO_2max relative to body mass (BM) did not change from age 12 to 15, while VO_2max tended to decrease relative to fat-free mass (FFM). In girls, VO_2max relative to BM decreased slightly from age 12 to 15, with no changes over the years relative to FFM. The present longitudinal study suggests that in growing active children during puberty, high volumes of systematic endurance training do not have an additional effect on VO_2max compared with similar volume of training mainly aiming at developing motor skills.

Traditional and New Perspectives on Youth Cardiorespiratory Fitness

PURPOSE

This study aimed to review traditional and new perspectives in the interpretation of the development of youth cardiorespiratory fitness (CRF).

METHODS

We analyzed data from (i) the literature which for 80 yr has been traditionally based on interpretations of peak oxygen uptake (V˙O2) in ratio with body mass (BM) and (ii) recent multilevel allometric models founded on 994 (475 from girls) determinations of 10- to 16-yr-olds' peak V˙O2 with measures of age, maturity status, and morphological covariates (BM and fat-free mass), and from 10 to 13 yr, 110 peak V˙O2 determinations of maximum cardiovascular covariates (stroke volume, cardiac output, and arteriovenous oxygen difference).

RESULTS

The application of ratio scaling of physiological variables requires satisfying specific statistical assumptions that are seldom met. In direct conflict with the ratio-scaled data interpretation of CRF, multilevel allometric modeling shows that with BM controlled, peak V˙O2 increases with age but the effect is smaller in girls than boys. Maturity status exerts a positive effect on peak V˙O2, in addition to those of age and BM. Changes in maximum cardiovascular covariates contribute to explaining the development of CRF, but fat-free mass (as a surrogate for active muscle mass) is the most powerful single influence. With age, maturity status, morphological covariates, and maximum cardiovascular covariates controlled, there remains an unexplained ~4% to ~9% sex difference in peak V˙O2.

CONCLUSIONS

The traditional interpretation of peak V˙O2 in ratio with BM is fallacious and leads to spurious correlations with other health-related variables. Studies of the development of CRF require analyses of sex-specific, concurrent changes in age- and maturation-driven morphological and maximum cardiovascular covariates. Multilevel allometric modeling provides a rigorous, flexible, and sensitive method of data analysis.

Sex-related differences in accumulated O2 deficit incurred by high-intensity rowing exercise during childhood and adolescence

PURPOSE

The aims of the present study were to determine during childhood and adolescence (i) the effect of sex on non-oxidative energy production, quantified by the accumulated oxygen deficit (AOD), and (ii) the influence of AOD on high-intensity performance.

METHODS

Thirty-nine boys and 35 girls aged 10-17 years performed a 60 s all-out test on a rowing ergometer to determine AOD and mean power output (MPO). Multiplicative allometric modelling was used to assess the concurrent effects of lean body mass (LBM) and age on AOD.

RESULTS

AOD significantly increased with age in both sexes (p < 0.001) with boys exhibiting significantly higher AOD than girls from the age of 14 years (10-11.9 yr: 1.9 vs 1.9 L, 12-13.9 yr: 2.4 vs 2.7 L, 14-15.9 yr: 2.8 vs 4.6 L and 16-17.9 yr: 2.9 vs 5.2 L, in girls and boys respectively, p < 0.001). However, a sex difference was no longer significant when AOD was analysed using an allometric model including age and LBM (p = 0.885). Finally, significant correlations were found between AOD and MPO in boys and girls but with lower evidence in girls (r² = 0.41 vs. 0.89).

CONCLUSION

Non-oxidative energy production increased more extensively in boys than girls from the age of 14 years. Age and LBM accounted for the sexual differentiation of AOD during childhood and adolescence. In addition, AOD was found to be a determinant factor of high-intensity performance, more particularly in boys.

Comparison of Peak Oxygen Consumption During Exercise Testing Between Sexes Among Children and Adolescents in Taiwan

Objective: Studies among Western children have observed that the peak oxygen consumption (peak V ˙ O₂) of boys is higher than that of girls, and this difference increases as children progress through adolescence. However, the maturation process and social expectation toward Eastern boys and girls are much different from their Western counterparts. This study aimed to provide baseline information on cardiopulmonary fitness (CRF) of Taiwanese children and adolescents in relation to age and sex. We also evaluated the correlation between body mass and CRF and compared the CRF between non-obese and overweight/obese children. Methods: We conducted a retrospective study of children and adolescents aged 4-18 years in Taiwan. Participants were classified into four groups based on age (group 1, aged 4-6; group 2, aged 7-9; group 3, aged 10-13; and group 4, aged 14-18 years). All participants completed symptom-limited exercise test by treadmill and anthropometric measurements through bioelectrical impedance method. Results: In total, 897 (448 men, 449 women) participants were analyzed. Boys had higher peak V ˙ O₂ (all p < 0.01) and peak metabolic equivalent (MET, all p < 0.05) than girls in all the four groups. Age significantly (P < 0.001) correlated with peak V ˙ O₂ in all participants, boys, and girls, with coefficients of determination (R ²) of 0.9349, 0.9433, and 0.9085, respectively. The peak V ˙ O₂ (all p < 0.001) of all the groups and peak MET (all p < 0.05) of group 2-4 associated with BMI and FMI modestly to moderately. Non-obese children had higher peak MET in group 1 (p = 0.049) and group 2-4 (all p < 0.001) than overweight/obese children significantly. Conclusions: The difference in peak V ˙ O₂ and anthropometry-body composition between sexes was observed earlier in children in Taiwan than those in Western countries. Non-obese children had better CRF than overweight/obese children and the difference presented since preschool age.

Adiposity Mediates the Association of Objectively Measured Physical Activity with Cardiorespiratory Fitness in Children

Background: The relationship of physical activity (PA) to cardiorespiratory fitness (CRF) is well established in children. However, the extent to which adiposity affects this association remains unclear. Objective: The study aimed to explore whether the relationships of different PA intensities to CRF are explained by adiposity. Methods: Cross-sectional data were collected from 374 children (51.87% boys) aged 7-12 years. The time spent (min/day) in vigorous PA (VPA), moderate PA (MPA), light PA (LPA), and sedentary behavior was objectively measured using triaxial accelerometry. Height, weight, and waist circumference (WC) were objectively measured, from which the BMI was derived. The 20-meter shuttle run test was conducted to estimate maximal oxygen consumption [VO_2max, mL/(kg·min)]. Linear mixed models and mediation analysis with bootstrapping were used to analyze data. Results: VO_2max was positively associated with VPA [β = 0.143, 95% confidence interval (95% CI): 0.091 to 0.194], MPA (β = 0.051, 95% CI: 0.016 to 0.086), and moderate-to-vigorous PA (MVPA) (β = 0.052, 95% CI: 0.029 to 0.075), but not LPA or sedentary time. Both BMI and WC partially mediated the relationships of VPA and MVPA to VO_2max, with the percentage of the total effect mediated by adiposity ranging from 18.0% to 19.6%. Similar results were also observed among boys but not among girls. Conclusions: Only moderate or vigorous intensity of PA is favorably correlated with CRF in children. BMI and WC play a pivotal mediating role in these associations, especially in boys, suggesting that promoting higher intensity of PA might benefit children's CRF through reducing adiposity.

Association of Cardiorespiratory Fitness Levels During Youth With Health Risk Later in Life: A Systematic Review and Meta-analysis

IMPORTANCE

Although the associations between cardiorespiratory fitness (CRF) and health in adults are well understood, to date, no systematic review has quantitatively examined the association between CRF during youth and health parameters later in life.

OBJECTIVES

To examine the prospective association between CRF in childhood and adolescence and future health status and to assess whether changes in CRF are associated with future health status at least 1 year later.

DATA SOURCES

For this systematic review and meta-analysis, MEDLINE, Embase, and SPORTDiscus electronic databases were searched for relevant articles published from database inception to January 30, 2020.

STUDY SELECTION

The following inclusion criteria were used: CRF measured using a validated test and assessed at baseline and/or its change from baseline to the end of follow-up, healthy population with a mean age of 3 to 18 years at baseline, and prospective cohort design with a follow-up period of at least 1 year.

DATA EXTRACTION AND SYNTHESIS

Data were processed according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA). Random-effects models were used to estimate the pooled effect size.

MAIN OUTCOMES AND MEASURES

Anthropometric and adiposity measurements and cardiometabolic health parameters.

RESULTS

Fifty-five studies were included with a total of 37 563 youths (46% female). Weak-moderate associations were found between CRF at baseline and body mass index (r = -0.11; 95% CI, -0.18 to -0.04; I2 = 59.03), waist circumference (r = -0.29; 95% CI, -0.42 to -0.14; I2 = 69.42), skinfold thickness (r = -0.34; 95% CI, -0.41 to -0.26; I2 = 83.87), obesity (r = -0.15; 95% CI, -0.23 to -0.06; I2 = 86.75), total cholesterol level (r = -0.12; 95% CI, -0.19 to -0.05; I2 = 75.81), high-density lipoprotein cholesterol (HDL-C) level (r = 0.11; 95% CI, 0.05-0.18; I2 = 69.06), total cholesterol to HDL-C ratio (r = -0.19; 95% CI, -0.26 to -0.13; I2 = 67.07), triglyceride levels (r = -0.10; 95% CI, -0.18 to -0.02; I2 = 73.43), homeostasis model assessment for insulin resistance (r = -0.12; 95% CI, -0.18 to -0.06; I2 = 68.26), fasting insulin level (r = -0.07; 95% CI, -0.11 to -0.03; I2 = 0), and cardiometabolic risk (r = -0.18; 95% CI, -0.29 to -0.07; I2 = 90.61) at follow-up. Meta-regression analyses found that early associations in waist circumference (β = 0.014; 95% CI, 0.002-0.026), skinfold thickness (β = 0.006; 95% CI, 0.002-0.011), HDL-C level (β = -0.006; 95% CI, -0.011 to -0.001), triglyceride levels (β = 0.009; 95% CI, 0.004-0.014), and cardiometabolic risk (β = 0.007; 95% CI, 0.003-0.011) from baseline to follow-up dissipated over time. Weak-moderate associations were found between change in CRF and body mass index (r = -0.17; 95% CI, -0.24 to -0.11; I2 = 39.65), skinfold thickness (r = -0.36; 95% CI, -0.58 to -0.09; I2 = 96.84), obesity (r = -0.21; 95% CI, -0.35 to -0.06; I2 = 91.08), HDL-C level (r = 0.05; 95% CI, 0.02-0.08; I2 = 0), low-density lipoprotein cholesterol level (r = -0.06; 95% CI, -0.11 to -0.01; I2 = 58.94), and cardiometabolic risk (r = -0.08; 95% CI, -0.15 to -0.02; I2 = 69.53) later in life.

CONCLUSIONS AND RELEVANCE

This study suggests that early intervention and prevention strategies that target youth CRF may be associated with maintaining health parameters in later life.

The dose-response association between V̇O2peak and self-reported physical activity in children

BACKGROUND

Previous research into the association between aerobic fitness and physical activity in children is equivocal. However, previous research has always assumed that such an association was linear. This study sought to characterize the dose-response association between physical activity and aerobic fitness and to assess whether this association is linear or curvilinear and varies by sex, age and weight status.

METHODS

Physical activity (assess using the Physical Activity Questionnaire), aerobic fitness (20 m shuttle-run), BMI, screen-time and socio-demographic data were collected at ages 12, 14 and 16 years in (n = 1422) volunteers from 9 English schools. Multilevel-regression modelling was used to analyse the longitudinal data.

RESULTS

The analysis identified a significant inverted "u-shaped" association between VO₂max and PAQ. This relationship remained having controlling for the influences of sex, age and weight status. Daily screen time >4 hours and deprivation were also associated with being less fit (P < 0.01).

CONCLUSIONS

This longitudinal study suggests that the dose-response relationship between PA and aerobic fitness in children is curvilinear. The health benefits of PA are greater in less active children and that sedentary and less active children should be encouraged to engage in PA rather than more active children to increase existing levels of PA.

A Pilot Study of Cardiorespiratory Fitness, Adiposity, and Cardiometabolic Health in Youth With Overweight and Obesity

OBJECTIVE

To conduct a preliminary assessment of the relationships between cardiorespiratory fitness, adiposity, and cardiometabolic health using gold standard measures in diverse youth ranging from overweight to severe obesity.

METHODS

Twenty of 30 participants (mean [SD]; age 13.2 [1.8] y, 55% female, 45% African American) met the criteria for VO2peak during a graded cycle ergometer test to volitional fatigue. The body composition was measured by dual-energy X-ray absorptiometry (percentage of body fat, fat mass index, and fat-free mass) and magnetic resonance imaging (abdominal visceral and subcutaneous [SAT] adipose tissue). The VO2peak was expressed relative to fat-free mass. Fasting lipid levels, glycemic biomarkers, and vital signs were examined individually and used in a composite cardiometabolic risk score. Accelerometer-measured physical activity and sedentary time were included as covariates.

RESULTS

VO2peak was negatively associated with abdominal SAT (r = -.49, P < .05), but not visceral adipose tissue or markers of cardiometabolic health. The association between SAT and VO2peak was partly explained by habitual sedentary time.

CONCLUSIONS

We demonstrated a significant negative association between cardiorespiratory fitness and SAT in a diverse group of high-risk youth. The inclusion of rigorous, laboratory-based measures and youth with severe obesity extends the previous work in pediatric populations.

Multilevel allometric modelling of maximum cardiac output, maximum arteriovenous oxygen difference, and peak oxygen uptake in 11-13-year-olds

PURPOSES

To investigate longitudinally (1) the contribution of morphological covariates to explaining the development of maximum cardiac output ([Formula: see text] max) and maximum arteriovenous oxygen difference (a-vO2 diff max), (2) sex differences in [Formula: see text] max and a-vO2 diff max once age, maturity status, and morphological covariates have been controlled for, and, (3) the contribution of concurrent changes in morphological and cardiovascular covariates to explaining the sex-specific development of peak oxygen uptake ([Formula: see text]).

METHODS

Fifty-one (32 boys) 11-13-year-olds had their peak [Formula: see text], maximum heart rate (HR max), [Formula: see text] max, and a-vO2 diff max determined during treadmill running on three annual occasions. The data were analysed using multilevel allometric modelling.

RESULTS

There were no sex differences in HR max which was not significantly (p > 0.05) correlated with age, morphological variables, or peak [Formula: see text]. The best-fit models for [Formula: see text] max and a-vO2 diff max were with fat-free mass (FFM) as covariate with age, maturity status, and haemoglobin concentration not significant (p > 0.05). FFM was the dominant influence on the development of peak [Formula: see text]. With FFM controlled for, the introduction of either [Formula: see text] max or a-vO2 diff max to multilevel models of peak [Formula: see text] resulted in significant (p < 0.05) additional contributions to explaining the sex difference.

CONCLUSIONS

(1) With FFM controlled for, there were no sex differences in [Formula: see text] max or a-vO2 diff max, (2) FFM was the dominant influence on the development of peak [Formula: see text], and (3) with FFM and either [Formula: see text] max or a-vO2 diff max controlled for, there remained an unresolved sex difference of ~ 4% in peak [Formula: see text].

The 20 m shuttle run is not a valid test of cardiorespiratory fitness in boys aged 11-14 years

Objectives

The 20 m shuttle run test (20mSRT) is used to estimate cardiorespiratory fitness (CRF) through the prediction of peak oxygen uptake ( V ˙ O 2 ), but its validity as a measure of CRF during childhood and adolescence is questionable. This study examined the validity of the 20mSRT to predict peak V ˙ O 2 .

Methods

Peak V ˙ O 2 was measured during treadmill running. Log-linear regression was used to correct peak V ˙ O 2 for body mass and sum of skinfolds plus age. Boys completed the 20mSRT under standardised conditions. Maximum speed (km/h) was used with age to predict peak V ˙ O 2 using the equation developed by Léger et al. Validity was examined from linear regression methods and limits of agreement (LoA). Relationships between 20mSRT performance and allometrically adjusted peak V ˙ O 2 , and predicted per cent fat were examined.

Results

The sample comprised 76 boys aged 11-14 years. Predicted and measured mass-related peak V ˙ O 2 (mL/kg/min) shared common variance of 32%. LoA revealed that measured peak V ˙ O 2 ranged from 15% below to 25% above predicted peak V ˙ O 2 . There were no significant relationships (p>0.05) between predicted peak V ˙ O 2 and measured peak V ˙ O 2 adjusted for mass, age and skinfold thicknesses. Adjusted for body mass and age, peak V ˙ O 2 was not significantly related (p>0.05) to 20mSRT final speed but a weak, statistically significant (r=0.24, p<0.05) relationship was found with peak V ˙ O 2 adjusted for mass and fatness. Predicted per cent fat was negatively correlated with 20mSRT speed (r=-0.61, p<0.001).

Conclusions

The 20mSRT reflects fatness rather than CRF and has poor validity grounded in its flawed estimation and interpretation of peak V ˙ O 2 in mL/kg/min.

Multilevel allometric modelling of maximal stroke volume and peak oxygen uptake in 11-13-year-olds

PURPOSE

To investigate (1) whether maximal stroke volume (SVmax) occurs at submaximal exercise intensities, (2) sex differences in SVmax once fat-free mass (FFM) has been controlled for, and, (3) the contribution of concurrent changes in FFM and SVmax to the sex-specific development of peak oxygen uptake [Formula: see text].

METHODS

The peak [Formula: see text] s of 61 (34 boys) 11-12-year-olds were determined and their SV determined during treadmill running at 2.28 and 2.50 m s-1 using carbon dioxide rebreathing. The SVmax and peak [Formula: see text] of 51 (32 boys) students who volunteered to be tested treadmill running at 2.50 m s-1 on three annual occasions were investigated using multilevel allometric modelling. The models were founded on 111 (71 from boys) determinations of SVmax, FFM, and peak [Formula: see text].

RESULTS

Progressive increases in treadmill running speed resulted in significant (p < 0.01) increases in [Formula: see text], but SV levelled-off with nonsignificant (p > 0.05) changes within ~ 2-3%. In the multilevel models, SVmax increased proportionally to FFM0.72 and with FFM controlled for, there were no significant (p > 0.05) sex differences. Peak [Formula: see text] increased with FFM but after adjusting for FFM0.98, a significant (p < 0.05) sex difference in peak [Formula: see text] remained. Introducing SVmax to the multilevel model revealed a significant (p < 0.05), but small additional effect of SVmax on peak [Formula: see text].

CONCLUSIONS

Fat-free mass explained sex differences in SVmax, but with FFM controlled for, there was still a ~ 5% sex difference in peak [Formula: see text]. SVmax made a modest additional contribution to explain the development of peak [Formula: see text] but there remained an unresolved sex difference of ~ 4%.

Sex-Specific Longitudinal Modeling of Short-Term Power in 11- to 18-Year-Olds

Purpose

To investigate, longitudinally, short-term power output in relation to sex and concurrent changes in age, body mass, fat-free mass (FFM), and maturity status.

Methods

Multiplicative multilevel modeling which enables the effects of variables to be partitioned concurrently within an allometric framework was used to analyze the peak power (PP) and mean power (MP) of 388 11- to 18-yr-olds. Multilevel models were founded on 763 (405 from boys; 358 from girls) determinations of PP and MP from Wingate anaerobic tests, supported by anthropometric measures and maturity status.

Results

In both sexes, PP and MP were significantly (P < 0.001) correlated with age, body mass, and FFM. After controlling for body mass, initial models showed positive effects for age on PP and MP, with negative effects for sex and a sex by age interaction. Sex-specific models showed maturity status to have no additional effect on either PP or MP once age and body mass had been controlled for. Skinfold thicknesses in addition to body mass to provide a surrogate for FFM, yielded a significantly (P < 0.05) better statistical fit in all models compared with those based on either body mass or FFM estimated from youth-specific skinfold equations. Models founded on estimated FFM provided a significantly (P < 0.05) better fit than those based on body mass.

Conclusions

With body mass controlled for boys’ PP and MP are higher than those of girls and sex differences increase with age from 11 to 18 yr. A multilevel modeling approach has showed that in both sexes the most powerful influences on short-term power output are concurrent changes in age and FFM as reflected by the combination of body mass and skinfold thicknesses.

Youth cardiorespiratory fitness: evidence, myths and misconceptions

Rigorously determined peak oxygen uptake is internationally recognized as the criterion measure of youth cardiorespiratory fitness. The assessment and interpretation of children’s and adolescents’ peak oxygen uptake and the relationship of the measure with other health-related variables are well documented. There has been a recent resurgence of interest in the prediction of peak oxygen uptake from field performance tests in young people. However, coupled with ratio-scaling of data and the raising of clinical red flags, these practices risk clouding our understanding of youth cardiorespiratory fitness and its relationship with current and future health. We believe these methods have the potential to mislead clinical practice and misguide recommendations for the promotion of youth cardiovascular health. We discuss relevant scientific evidence and interpretations that have emerged from predicting youth cardiorespiratory fitness from performance test scores. We argue that children deserve to have health care founded on evidence-based science and not on myths and misconceptions.

Interpreting Youth Aerobic Fitness: Promoting Evidence-Based Discussion–A Response to Dotan (2019)

We welcome Raffy Dotan’s Letter to the Editor (14) as it gives us another opportunity to promote evidence-based discussion of the development of youth aerobic fitness. Readers of our contributions to the 2019 Special Issue of Pediatric Exercise Science (6,27,28) will recall that we concluded with, “The authors encourage all pediatric exercise scientists to engage with this discussion, to share ideas and methods, and be willing to explore alternatives. There are many issues to resolve and constructive, collaborative debate will speed our collective aim toward a better understanding of pediatric aerobic fitness in health and disease” (27, p. 256). Not the words of authors preaching a “gospel” with “evangelistic persistence” as Dotan (14) suggests, but of scientists genuinely seeking to stimulate evidence-based discussion of the development of youth aerobic fitness and its relationship with health and well-being.

Clarity and Confusion in the Development of Youth Aerobic Fitness

Peak oxygen uptake (V˙O2) is internationally recognized as the criterion measure of youth aerobic fitness, but flawed laboratory assessments and fallacious interpretations of peak V˙O2 in ratio with body mass have confused our understanding of the development of aerobic fitness. Moreover, the recent emergence of specious predictions of peak V˙O2 from performance tests and the promotion of spurious “clinical red flags” and cardiometabolic cut-points have confused our understanding of the relationship between youth aerobic fitness and health. Recent longitudinal studies of 10–18-year-olds using multilevel allometric modeling have empirically demonstrated that peak V˙O2 increases in accord with sex-specific, concurrent changes in age- and maturity status-driven morphological covariates with the timing and tempo of changes specific to individuals. During both cycle ergometry and treadmill running age- and maturity status- driven changes in fat free mass have been revealed as the most powerful morphological influences on the development of youth aerobic fitness. To bring some clarity to current confusion, this paper argues that future studies must be founded on rigorous assessment and interpretation of peak V˙O2 and ensure that they address the development of youth aerobic fitness and its relationship with present and future health in relation to appropriate sex-specific morphological covariates governed by individual biological clocks.

Development of 11- to 16-year-olds' short-term power output determined using both treadmill running and cycle ergometry

PURPOSE

To investigate the development of peak power output (PP) and mean power output (MP) during two different modes of exercise in relation to sex and concurrent changes in age, body mass, fat-free mass (FFM), maturity status and, in the case of MP, peak oxygen uptake ([Formula: see text]).

METHODS

PP and MP were determined cycling against a fixed braking force (Wingate anaerobic test) and running on a non-motorized treadmill. Peak [Formula: see text] was determined using cycle ergometry and treadmill running. 135 (63 girls) students initially aged 11-14 years were tested over 2 days on three annual occasions. The data were analysed using multiplicative allometric modelling which enables the effects of variables to be partitioned concurrently within an allometric framework. Multiplicative models were founded on 301 (138 from girls) determinations of PP and MP on each ergometer.

RESULTS

With body mass controlled for, both PP and MP increased with age but maturity status did not independently contribute to any of the multiplicative allometric models. Boys' PP and MP were significantly (p < 0.05) higher than girls' values on both ergometers. On both ergometers in both sexes, the most powerful morphological influence on PP and MP was FFM. Ergometer-specific peak [Formula: see text] had a significant (p < 0.05), additional effect in explaining the development of MP.

CONCLUSIONS

The development of short-term power output is sex specific but within sex multiplicative allometric models of running- and cycling-determined PP and MP were similar, suggesting that either mode of exercise can be used in future studies of short-term power output in youth.

Development of peak oxygen uptake from 11-16 years determined using both treadmill and cycle ergometry

PURPOSES

To investigate the development of peak oxygen uptake ([Formula: see text]) assessed on both a treadmill and a cycle ergometer in relation with sex and concurrent changes in age, body mass, fat-free mass (FFM), and maturity status and to evaluate currently proposed 'clinical red flags' or health-related cut-points for peak [Formula: see text].

METHODS

Multiplicative multilevel modelling, which enables the effects of variables to be partitioned concurrently within an allometric framework, was used to analyze the peak [Formula: see text]s of 138 (72 boys) students initially aged 11-14 years and tested on three annual occasions. Models were founded on 640 (340 from boys) determinations of peak [Formula: see text], supported by anthropometric measures and maturity status.

RESULTS

Mean peak [Formula: see text]s were 11-14% higher on a treadmill. The data did not meet the statistical assumptions underpinning ratio scaling of peak [Formula: see text] with body mass. With body mass appropriately controlled for boys' peak [Formula: see text]s were higher than girls' values and the difference increased with age. The development of peak [Formula: see text] was sex-specific, but within sex models were similar on both ergometers with FFM the dominant anthropometric factor.

CONCLUSIONS

Data should not be pooled for analysis but data from either ergometer can be used independently to interpret the development of peak [Formula: see text] in youth. On both ergometers and in both sexes, FFM is the most powerful morphological influence on the development of peak [Formula: see text]. 'Clinical red flags' or health-related cut-points proposed without consideration of exercise mode and founded on peak [Formula: see text] in ratio with body mass are fallacious.