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The GH-IGF-I Response to Typical Field Sports Practices in Adolescent Athletes: A Summary

Alon Eliakim, Dan M. Cooper, and Dan Nemet

The present study compares previous reports on the effect of “real-life” typical field individual (ie, cross-country running and wrestling—representing combat versus noncombat sports) and team sports (ie, volleyball and water polo—representing water and land team sports) training on GH and IGF-1, the main growth factors of the GH→IGF axis, in male and female late pubertal athletes. Cross-country running practice and volleyball practice in both males and females were associated with significant increases of circulating GH levels, while none of the practices led to a significant increase in IGF-I levels. The magnitude (percent change) of the GH response to the different practices was determined mainly by preexercise GH levels. There was no difference in the training-associated GH response between individual and team sports practices. The GH response to the different typical practices was not influenced by the practice-associated lactate change. Further studies are needed to better understand the effect of real-life typical training in prepubertal and adolescent athletes and their role in exercise adaptations.

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The Common Fund Initiative and Its Implication for Advancing Exercise and Physical Activity Research in Child Health

Dan M. Cooper and Shlomit Radom-Aizik

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Bridging the Gaps: The Promise of Omics Studies in Pediatric Exercise Research

Shlomit Radom-Aizik and Dan M. Cooper

In this review, we highlight promising new discoveries that may generate useful and clinically relevant insights into the mechanisms that link exercise with growth during critical periods of development. Growth in childhood and adolescence is unique among mammals and is a dynamic process regulated by an evolution of hormonal and inflammatory mediators, age-dependent progression of gene expression, and environmentally modulated epigenetic mechanisms. Many of these same processes likely affect molecular transducers of physical activity. How the molecular signaling associated with growth is synchronized with signaling associated with exercise is poorly understood. Recent advances in “omics”—namely genomics and epigenetics, metabolomics, and proteomics—now provide exciting approaches and tools that can be used for the first time to address this gap. A biologic definition of “healthy” exercise that links the metabolic transducers of physical activity with parallel processes that regulate growth will transform health policy and guidelines that promote optimal use of physical activity.

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The Relationships Between Leptin and Measures of Fitness and Fatness Are Dependent Upon Obesity Status in Youth

Peter A. Hosick, Robert G. McMurray, and Dan M. Cooper

The relationship between peak aerobic fitness (peakVO2) and plasma leptin was assessed in 25 normal (BMI < 85th %tile) and 25 overweight (BMI > 85th %tile) youth, ages 7–17 years. In the overall analysis peakVO2 was related to leptin when expressed in mL/kg/min (R 2 = .516, p < .0001), or as ml/kgFFM/min (R 2 = .127, p = .01). The relationships between peakVO2 and leptin were no longer significant when percent bodyfat was added to the models. In subanalyses by weight groups, peakVO2: leptin relationships were not evident for normal weight, but remained for overweight youth. In conclusion the relationship between aerobic fitness and leptin in youth is dependent upon weight status.

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Physical Activity, Fitness, and Physical Self-Concept in Adolescent Females

Genevieve Fridlund Dunton, Margaret Schneider, Dan J. Graham, and Dan M. Cooper

Cross-sectional research examined whether physical activity or physical fitness was more closely linked to physical self-concept in adolescent females ages 14 to 17 (N = 103, 63% Caucasian). Moderate physical activity and vigorous physical activity were measured through a 3-day physical activity recall. Physical fitness was assessed using highly accurate measures of peak oxygen consumption (via cycle ergometer) and percent body fat (via dual X-ray absorptiometer). The Physical Self-Description Questionnaire (PSDQ) assessed self-concept in 11 domains (e.g., health, endurance, appearance). Pearson’s correlations showed that vigorous physical activity was positively associated with scores on most of the PSDQ scales (p < .005). Peak oxygen consumption was positively related to all of the selfconcept domains (p < .001), and percent body fat was negatively related on most of the PSDQ scales (p < .005). Multiple-regression analyses found that physical fitness (i.e., peak oxygen consumption and percent body fat) was more closely related to physical self-concept than was physical activity. In addition to the possibility that genetically determined fitness levels may influence physical selfconcept, these findings suggest that programs designed to elevate self-perceptions may require physical activity levels sufficient to improve cardiovascular fitness and decrease body fat.

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Circulating T-Regulatory Cells, Exercise and the Elite Adolescent Swimmer

Lori D. Wilson, Frank P. Zaldivar, Christina D. Schwindt, Jessica Wang-Rodriguez, and Dan M. Cooper

Brief high intensity exercise induces peripheral leukocytosis possibly leading to a higher incidence of allergic symptoms in athletes undergoing excessive training. We studied the exercise-induced alternation of circulating Tregs and FoxP3+ Tregs due to acute intense swim exercise in elite swimmers (n = 22, 12 males, age = 15.4 yrs). Twelve had prior or current rhinitis or asthma and 10 had no current or prior allergy or asthma. Circulating Tregs increased significantly (p < .001) following exercise (pre = 133 ± 11.2, post = 196 ± 17.6) as did FoxP3+ cells (pre = 44, post = 64 cells/μl). Increases in Tregs and FoxP3+ Tregs occurred to the same extent in both groups of adolescent swimmers.

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Cardiopulmonary Exercise Testing in Children and Adolescents with High Body Mass Index

Dan M. Cooper, Szu-Yun Leu, Candice Taylor-Lucas, Kim Lu, Pietro Galassetti, and Shlomit Radom-Aizik

Consensus has yet to be achieved on whether obesity is inexorably tied to poor fitness. We tested the hypothesis that appropriate reference of cardiopulmonary exercise testing (CPET) variables to lean body mass (LBM) would eliminate differences in fitness between high-BMI (≥ 95th percentile, n = 72, 50% female) and normal-BMI (< 85th percentile, n = 142, 49% female), otherwise-healthy children and adolescents typically seen when referencing body weight. We measured body composition with dual x-ray absorptiometry (DXA) and CPET variables from cycle ergometry using both peak values and submaximal exercise slopes (peak VO2, ΔVO2/ΔHR, ΔWR/ΔHR, ΔVO2/ΔWR, and ΔVE/ΔVCO2). In contrast to our hypothesis, referencing to LBM tended to lessen, but did not eliminate, the differences (peak VO2 [p < .004] and ΔVO2/ΔHR [p < .02]) in males and females; ΔWR/ΔHR differed between the two groups in females (p = .041) but not males (p = .1). The mean percent predicted values for all CPET variables were below 100% in the high-BMI group. The pattern of CPET abnormalities suggested a pervasive impairment of O2 delivery in the high-BMI group (ΔVO2/ΔWR was in fact highest in normal-BMI males). Tailoring lifestyle interventions to the specific fitness capabilities of each child (personalized exercise medicine) may be one of the ways to stem what has been an intractable epidemic.

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Obesity, Asthma, and Exercise in Child and Adolescent Health

Kim D. Lu, Krikor Manoukian, Shlomit Radom-Aizik, Dan M. Cooper, and Stanley P. Galant

Obesity increases the risk of asthma throughout life but the underlying mechanisms linking these all too common threats to child health are poorly understood. Acute bouts of exercise, aerobic fitness, and levels of physical activity clearly play a role in the pathogenesis and/or management of both childhood obesity and asthma. Moreover, both obesity and physical inactivity are associated with asthma symptoms and response to therapy (a particularly challenging feature of obesity-related asthma). In this article, we review current understandings of the link between physical activity, aerobic fitness and the asthma-obesity link in children and adolescents (e.g., the impact of chronic low-grade inflammation, lung mechanics, and direct effects of metabolic health on the lung). Gaps in our knowledge regarding the physiological mechanisms linking asthma, obesity and exercise are often compounded by imprecise estimations of adiposity and challenges of assessing aerobic fitness in children. Addressing these gaps could lead to practical interventions and clinical approaches that could mitigate the profound health care crisis of the increasing comorbidity of asthma, physical inactivity, and obesity in children.

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Cerebral and Muscle Tissue Oxygenation During Incremental Cycling in Male Adolescents Measured by Time-Resolved Near-Infrared Spectroscopy

Goutham Ganesan, Szu-yun Leu, Albert Cerussi, Bruce Tromberg, Dan M. Cooper, and Pietro Galassetti

Near-infrared spectroscopy has long been used to measure tissue-specific O2 dynamics in exercise, but most published data have used continuous wave devices incapable of quantifying absolute Hemoglobin (Hb) concentrations. We used time-resolved near-infrared spectroscopy to study exercising muscle (Vastus Lateralis, VL) and prefrontal cortex (PFC) Hb oxygenation in 11 young males (15.3 ± 2.1 yrs) performing incremental cycling until exhaustion (peak VO2 = 42.7 ± 6.1 ml/min/kg, mean peak power = 181 ± 38 W). Time-resolved near-infrared spectroscopy measurements of reduced scattering (µs´) and absorption (µa) at three wavelengths (759, 796, and 833 nm) were used to calculate concentrations of oxyHb ([HbO2]), deoxy Hb ([HbR]), total Hb ([THb]), and O2 saturation (stO2). In PFC, significant increases were observed in both [HbO2] and [HbR] during intense exercise. PFC stO2% remained stable until 80% of total exercise time, then dropped (−2.95%, p = .0064). In VL, stO2% decreased until peak time (−6.8%, p = .01). Segmented linear regression identified thresholds for PFC [HbO2], [HbR], VL [THb]. There was a strong correlation between timing of second ventilatory threshold and decline in PFC [HbO2] (r = .84). These findings show that time-resolved near-infrared spectroscopy can be used to study physiological threshold phenomena in children during maximal exercise, providing insight into tissue specific hemodynamics and metabolism.

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Functional and Muscle Size Response to 5 Days of Treadmill Training in Young Rats

Alon Eliakim, Mark Y. Moromisato, David Y. Moromisato, and Dan M. Cooper

In this study, the hypothesis that improvements in functional and structural measures could be detected in the young, female rat with only 5 days of moderate treadmill training was tested. Eight-week-old female Sprague-Dawley rats were divided randomly into control (n = 10) and training groups (n = 11). Over the 5-day period, running duration and treadmill speed increased progressively. Maximal running time and gas exchange were measured on Day 6. In trained compared with control rats, maximal running time was 54% greater (p < .005), right hindlimb muscle was 16% heavier (p < .01), and end-exercise respiratory exchange ratio (RER) was 17% lower (p < .05). Substantial metabolic and structural adaptations occurred in young female rats after only 5 days of treadmill training. This protocol may be useful in discovering the initiating mechanisms of the training response in the young organism.