Children are the most naturally physically active human beings; reduced physical activity is a cardinal sign of childhood disease, and exercise testing provides mechanistic insights into health and disease that are often hidden when the child is at rest. The physical inactivity epidemic is leading to increased disease risk in children and, eventually, in adults in unprecedented ways. Cardiopulmonary exercise testing (CPET) biomarkers are used to assess disease severity, progress, and response to therapy across an expanding range of childhood diseases and conditions. There is mounting data that fitness in children tracks across the life span and may prove to be an early, modifiable indicator of cardiovascular disease risk later in life. Despite these factors, CPET has failed to fulfill its promise in child health research and clinical practice. A major barrier to more accurate and effective clinical use of CPET in children is that data analytics and testing protocols have failed to keep pace with enabling technologies and computing capacity. As a consequence, biomarkers of fitness and physical activity have yet to be widely incorporated into translational research and clinical practice in child health. In this review, the author re-examines some of the long-held assumptions that mold CPET in children. In particular, the author suggests that current testing strategies that rely predominantly on maximal exercise may, inadvertently, obfuscate novel and clinically useful insights that can be gleaned from more comprehensive data analytics. New pathways to discovery may emanate from the simple recognition that the physiological journey that human beings undertake in response to the challenge of exercise may be far more important than the elusive destination of maximal or peak effort.
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.
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.
Dan M. Cooper and Shlomit Radom-Aizik
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.
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.
Margaret Schneider, Genevieve F. Dunton, Stan Bassin, Dan J. Graham, Alon Eliakim, and Dan M. Cooper
Many female adolescents participate in insufficient physical activity to maintain cardiovascular fitness and promote optimal bone growth. This study evaluates the impact of a school-based intervention on fitness, activity, and bone among adolescent females.
Subjects were assigned to an intervention (n = 63) or comparison (n = 59) group, and underwent assessments of cardiovascular fitness (VO2peak), physical activity, body composition, bone mineral density (BMD), bone mineral content (BMC), and serum markers of bone turnover at baseline and at the end of each of two school semesters.
The intervention increased physical activity, VO2peak, and BMC for the thoracic spine (P values < 0.05). Bone turnover markers were not affected. In longitudinal analyses of the combined groups, improvements in cardiovascular fitness predicted increased bone formation (P < 0.01) and bone resorption (P < 0.05).
A school-based intervention for adolescent females effectively increased physical activity, cardiovascular fitness, and thoracic spine BMC.
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.
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.
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.