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Brian W. Timmons

Despite significant advances in exercise immunology over the last two decades, our understanding of immune responses to exercise in children remains sparse. This review outlines and discusses commonly reported aspects of the immune response to exercise, with emphasis on child-adult differences. Compared with adults, children generally experience smaller perturbations to the immune system (e.g., NK cells and IL-6) in response to exercise of the same duration and intensity. Children also demonstrate a faster recovery of immune components (e.g., neutrophil and IL-6) after exercise. The health and clinical relevance of exercise-induced changes in a child’s immune system remain to be determined.

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Maple Liu and Brian W. Timmons

The adaptive effects of exercise-induced inflammation and reactive oxygen species production has been well studied in adults, but not in children. Characterizing the exercise responses in children compared with adults will start clarifying the transition from the child phenotype to that of an adult. Ten children aged 8–10 and 12 adults aged 19–21 performed 2 × 30-min bouts of continuous cycling, separated by a 6-min rest period, at a target work rate of 60% of their maximum aerobic capacity. Blood samples were collected pre- and immediately postexercise, and analyzed for neutrophil count, systemic oxidative and inflammatory markers, and intracellular neutrophil-derived reactive oxygen species. Although postexercise absolute neutrophils increased by approximately twofold in men (2.72 ± 0.49 × 109/L to 4.85 ± 2.05 × 109/L; p = .007), boys showed no such change (3.18 ± 0.67 × 109/L to 3.57 ± 0.73 × 109/L; p = .52). Contrary to these findings, boys did show an increase in overall intracellular neutrophil ROS production, whereas men did not. Boys also demonstrated higher overall protein carbonyl levels (0.07 nmol/mg vs 0.04 nmol/mg; boys vs men respectively), whereas men showed higher overall malondialdehyde (0.24 μM vs 0.67 μM; boys vs men respectively). The differences observed in the exercise-induced inflammatory and oxidative stress response may indicate growth-mediated adaptive responses to exercise during childhood development.

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Bhanu Sharma and Brian W. Timmons

The multidisciplinary field of pediatric traumatic brain injury (TBI) and exercise medicine is of growing importance. There is active study into the diagnostic and therapeutic potential of exercise in pediatric TBI as well as the effects of TBI on postinjury fitness. With the evidence-based growing, a literature review can help establish the state of the science and inform future research. Therefore, the authors performed a narrative review (based on a search of 6 health sciences databases) to summarize evidence on pediatric TBI and cardiorespiratory fitness, muscular fitness and neuromotor control, and obesity. To date, studies related to cardiorespiratory fitness have centered on exercise tolerance and readiness to return to play, and indicate that protracted rest may not facilitate symptom recovery; this suggests a role for exercise in concussion management. Furthermore, strength and gait may be impaired following pediatric brain injury, and interventions designed to train these impairments may lead to their improvement. Pediatric brain injury can also lead to changes in body composition (which may be related to poorer cognitive recovery), but additional research is required to better understand such associations. This narrative review of pediatric TBI and exercise medicine can serve as a reference for researchers and clinicians alike.

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Lisa Chu and Brian W. Timmons

Nutritional considerations for the overweight young athlete have not been thoroughly discussed in the scientific literature. With the high prevalence of childhood obesity, more children participating in sports are overweight or obese. This is particularly true for select sports, such as American football, where large size provides an added advantage. While sport participation should be encouraged because of the many benefits of physical activity, appropriate nutritional practices are vital for growth, and optimizing performance and health. The overweight young athlete may face certain challenges because of variable energy costs and nutrient requirements for growth and routine training, compared with nonoverweight athletes. Special attention should be given to adopting healthy lifestyle choices to prevent adverse health effects due to increased adiposity. In this review, we aim to discuss special nutritional considerations and highlight gaps in the literature concerning nutrition for overweight young athletes compared with their nonoverweight peers.

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Thanh Nguyen, Joyce Obeid and Brian W. Timmons

The purpose of this study was to determine the reliability of short-term power output, heart rate (HR) response during and after a treadmill test, and time to complete a 25-m dash in healthy preschool children. Thirty-two 3- to 5-year-old boys and girls completed two sessions approximately one week apart. Intraclass correlation coefficient (ICC) and coefficient of variation (CV) were calculated to evaluate reliability. Power output was found to be reliable with ICCs ranging from 0.83 to 0.93 and CVs from 8.1 to 9.7%. Time to complete the 25-m dash was highly reliable (ICC = 0.91, CV = 3.7%). Reliability for HR at submaximal exercise (ICC = 0.28, CV = 18.8%) and HR recovery (ICC = 0.42, CV = 14.0%) was not as strong. These findings should assist in determining appropriate fitness tests for preschoolers.

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Anthony D. Mahon and Brian W. Timmons

Exercise metabolism in children has traditionally been assessed using the respiratory exchange ratio (RER) to determine the contributions of fat and carbohydrate to the exercise energy demands. Although easily measured, RER measurements have limitations. Other methods to assess metabolism such as the obtainment of a muscle biopsy and the use of nuclear magnetic resonance spectroscopy carry ethical and feasibility concerns, respectively, which limit their use in studies involving children. Stable isotopes, used routinely in studies involving adults, can also be applied in studies involving children in an ethical and feasible manner. Two common stable isotopes used in metabolic studies involving children include carbon-13 (13C) and nitrogen-15 (15N). 13C-glucose can be used to study carbohydrate metabolism and 15N-glycine can be used to assess protein metabolism. This article reviews the use of 13C-glucose and 15N-glycine to study exercise metabolism in children, considers some of the associated ethical aspects, explains the general methodology involved in administering these isotopes and the resources required, and describes studies involving children utilizing these methods. Finally, suggestions for future research are provided to encourage further use of these techniques.

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Joyce Obeid, Maggie J. Larché and Brian W. Timmons

The Wingate Anaerobic Test (WAnT) can assess muscle function in youth with juvenile idiopathic arthritis (JIA). Our objective was to compare peak power (PP) and mean power (MP) when the WAnT is performed with a standard vs. an optimized braking force. Eight patients with JIA between the ages of 8 and 18 participated in two sessions. Optimal braking force was determined with a series of 15-s force-velocity tests performed against braking forces ranging from 3.5 to 8.5% of body weight. Participants then performed two randomized WAnTs against the standard (4.5%) and optimal braking forces. PP tended to be greater in the optimized vs. standard WAnT (12.5 ± 2.6 vs. 10.8 ± 1.0 W/kg, respectively; p =.07). No differences were observed for MP (standard: 6.2 ± 0.9 vs. optimized: 6.2 ± 1.1 W/kg; p = .9). Optimization of the WAnT tended to increase PP by 10–28% in youth with JIA.

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Kimberly Volterman, Daniel Moore, Joyce Obeid, Elizabeth A. Offord and Brian W. Timmons

Purpose:

In adults, rehydration after exercise in the heat can be enhanced with a protein-containing beverage; however, whether this applies to children remains unknown. This study examined the effect of milk protein intake on postexercise rehydration in children.

Method:

Fifteen children (10–12 years) performed three exercise trials in the heat (34.4 ± 0.2 °C, 47.9 ± 1.1% relative humidity). In a randomized, counterbalanced crossover design, participants consumed iso-caloric and electrolyte-matched beverages containing 0 g (CONT), 0.76 g (Lo-PRO) or 1.5 g (Hi-PRO) of milk protein/100 mL in a volume equal to 150% of their body mass (BM) loss during exercise. BM was then assessed over 4 h of recovery.

Results:

Fluid balance demonstrated a significant condition × time interaction (p = .012) throughout recovery; Hi-PRO was less negative than CONT at 2 hr (p = .01) and tended to be less negative at 3 h (p = .07). Compared with CONT, beverage retention was enhanced by Hi-PRO at 2 h (p < .05).

Conclusion:

A postexercise beverage containing milk protein can favorably affect fluid retention in children. Further research is needed to determine the optimal volume and composition of a rehydration beverage for complete restoration of fluid balance.

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Boguslaw Wilk, Nola Pender, Kim Volterman, Oded Bar-Or and Brian W. Timmons

The influence of puberty on sweating patterns of girls exercising in the heat is not known. Nine- to 17-year-old girls, representing 4 stages of breast development: T1 (n = 21); T2 (n = 22); T3 (n = 25); and T4 (n = 22), cycled for 20 min at 60% in 35 °C. The population density of heat activated sweat glands was higher in T1 vs T3 and T4 and in T2 vs T4. Sweat drop area was lower in T1 vs T3 and in T1 vs T4, T2 vs T4 and T3 vs T4. The proportion of skin covered by sweat was lower in T1 vs T4. Sweating patterns of girls exercising in the heat are influenced by pubertal stage.

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Leigh M. Vanderloo, Natascja A. Di Cristofaro, Nicole A. Proudfoot, Patricia Tucker and Brian W. Timmons

Young children’s activity and sedentary time were simultaneously measured via the Actical method (i.e., Actical accelerometer and specific cut-points) and the ActiGraph method (i.e., ActiGraph accelerometer and specific cut-points) at both 15-s and 60-s epochs to explore possible differences between these 2 measurement approaches. For 7 consecutive days, participants (n = 23) wore both the Actical and ActiGraph side-by-side on an elastic neoprene belt. Device-specific cut-points were applied. Paired sample t tests were conducted to determine the differences in participants’ daily average activity levels and sedentary time (min/h) measured by the 2 devices at 15-s and 60-s time sampling intervals. Bland-Altman plots were used to examine agreement between Actical and ActiGraph accelerometers. Regardless of epoch length, Actical accelerometers reported significantly higher rates of sedentary time (15 s: 42.7 min/h vs 33.5 min/h; 60 s: 39.4 min/h vs 27.1 min/h). ActiGraph accelerometers captured significantly higher rates of moderate-to-vigorous physical activity (15 s: 9.2 min/h vs 2.6 min/h; 60 s: 8.0 min/h vs 1.27 min/h) and total physical activity (15 s: 31.7 min/h vs 22.3 min/h; 60 s: = 39.4 min/h vs 25.2 min/h) in comparison with Actical accelerometers. These results highlight the present accelerometry-related issues with interpretation of datasets derived from different monitors.