Influence of age and pubertal status on substrate utilization during exercise with and without carbohydrate intake in healthy boys

Enhancing Performance in Young Athletes: A Systematic Review of Acute Supplementation Effects

BACKGROUND/OBJECTIVES

The increasing popularity of acute supplementation among young athletes is concerning, given the limited scientific evidence to guide recommendations specific to this group. Therefore, the aim of this systematic review was to synthesize the available scientific evidence on the acute effects of supplementation in young athletes to understand the impact on physical and cognitive performance.

METHODS

Following pre-registration on INPLASY (INPLASY202310017) and according to the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, systematic searches of three electronic databases (Web of Science, PubMed, and Scopus) were conducted by independent researchers from inception until July 2024. Only original studies in English that examined the acute effects of supplementation on young athletes' physical and/or cognitive performance, specifically when taken on the same day as exercise (before or during), were included. The risk of bias was individually assessed for each study using the revised Cochrane risk of bias tool for randomized trials (RoB 2.0).

RESULTS

A total of 16 studies were included in the review. A range of ages, participants, sports, and methodological approaches were involved in the studies included in the current review. The studies mainly used carbohydrates, beetroot juice, and sodium citrate, with carbohydrates being the most used acute supplementation. Carbohydrate supplementation enhanced endurance capacity and increased blood glucose, but mixed results were found for anaerobic performance. Mixed results were found for beetroot juice, with one study finding increases in power production. One study used sodium citrate supplementation, with improvements in technical performance observed.

CONCLUSIONS

Since this review identified only three substances meeting our eligibility criteria, further research is needed to confirm the acute effects of supplements in young athletes and to better understand their benefits and limitations. Carbohydrate supplementation shows strong evidence for enhancing endurance performance, particularly during prolonged activities, while sodium citrate appears to support the preservation of skill performance. In contrast, the effects of beetroot juice are less consistent. Additional research is required to confirm the acute effects of supplements like beetroot juice in young athletes.

Sleep, Nutrition, and Injury Risk in Adolescent Athletes: A Narrative Review

This narrative review explores the impact of sleep and nutrition on injury risk in adolescent athletes. Sleep is viewed as essential to the recuperation process and is distinguished as an active participant in recovery through its involvement in growth, repair, regeneration, and immunity. Furthermore, the literature has shown that the sleep of athletes impacts elements of athletic performance including both physical and cognitive performance, recovery, injury risk, and mental well-being. For sleep to have a restorative effect on the body, it must meet an individual's sleep needs whilst also lasting for an adequate duration and being of adequate quality, which is age-dependent. The literature has suggested that athletes have increased sleep needs compared to those of the general population and thus the standard recommendations may not be sufficient for athletic populations. Therefore, a more individualised approach accounting for overall sleep health may be more appropriate for addressing sleep needs in individuals including athletes. The literature has demonstrated that adolescent athletes achieve, on average, ~6.3 h of sleep, demonstrating a discrepancy between sleep recommendations (8-10 h) and actual sleep achieved. Sleep-wake cycles undergo development during adolescence whereby adaptation occurs in sleep regulation during this phase. These adaptations increase sleep pressure tolerance and are driven by the maturation of physiological, psychological, and cognitive functioning along with delays in circadian rhythmicity, thus creating an environment for inadequate sleep during adolescence. As such, the adolescent period is a phase of rapid growth and maturation that presents multiple challenges to both sleep and nutrition; consequently, this places a significant burden on an adolescent athletes' ability to recover, thus increasing the likelihood of injury. Therefore, this article aims to provide a comprehensive review of the available literature on the importance of sleep and nutrition interactions in injury risk in adolescent athletes. Furthermore, it provides foundations for informing further investigations exploring the relation of sleep and nutrition interactions to recovery during adolescence.

Enhancing cardiometabolic health through physical activity and breakfast manipulations in children and adolescents: good for humans, good for the planet

The human health benefits of cardiometabolic disease prevention can be accompanied by planetary co-benefits. Focusing efforts towards young people, including children and adolescents, is conducive to disease prevention. In the context of cardiometabolic disease prevention, this review paper critically summarises the available literature on the acute cardiometabolic responses to physical activity and breakfast manipulations among young people. Given the seriousness of global climate change, which will disproportionally affect our younger generations, this review paper offers new insights into the inherent interactions between child-adolescent behaviour and cardiometabolic health from an environmental sustainability perspective to aid climate change mitigation efforts, including exploring future research avenues. A growing evidence base suggests acute moderate- to high-intensity exercise bouts can attenuate postprandial plasma glucose, insulin and triacylglycerol concentrations for up to 24-48 h in young people. Whether accumulating physical activity throughout the day with short, frequent bouts promotes cardiometabolic risk marker attenuations is unclear. Breakfast consumption may enhance free-living physical activity and reduce glycaemic responses to subsequent meals for a possible additive impact. If repeated habitually, attenuations in these cardiometabolic risk factors would be conducive to disease prevention, reducing the greenhouse gas emissions associated with disease diagnosis and treatment. To progress current understanding with high public health and planetary relevance, research among samples of 'at risk' young people that span cellular-level responses to ecologically valid settings and address human and planetary health co-benefits is needed. Indeed, certain physical activity opportunities, such as active travel to school, offer important direct co-benefits to humans and planetary health.

Acute Cardiometabolic and Exercise Responses to Breakfast Omission Versus Breakfast Consumption in Adolescent Girls: A Randomised Crossover Trial

Girls often begin to skip breakfast during adolescence. This study compared the acute effect of breakfast omission versus consumption on cardiometabolic risk markers and perceived appetite and mood during rest and/or exercise in adolescent girls classified as habitual breakfast consumers. Girls (aged 13.2 ± 0.7 years) completed two 5.5 h conditions in a randomised crossover design: breakfast omission (BO) and standardised breakfast consumption (BC). A standardised lunch was provided at 3 h. Incremental cycling exercise was performed at 5 h. Blood and expired gas samples were taken at regular intervals. Whilst pre-lunch plasma glucose, insulin, and Metabolic Load Index incremental area under the curve (IAUC) were significantly lower in BO versus BC, post-lunch differences were reversed and larger in magnitude. Peak plasma glucose and insulin were significantly higher in BO versus BC. Pre-lunch perceived fullness and hunger were significantly lower and higher, respectively, in BO versus BC. Perceived energy and concentration were lower, and tiredness was higher, in BO versus BC. Exercise peak fat oxidation and Fatmax were unaffected. The lower physical activity enjoyment in BO versus BC approached significance. To conclude, acutely omitting breakfast adversely affects cardiometabolic risk markers and exercise enjoyment among adolescent girls who habitually consume breakfast.

Breakfast Consumption Suppresses Appetite but Does Not Increase Daily Energy Intake or Physical Activity Energy Expenditure When Compared with Breakfast Omission in Adolescent Girls Who Habitually Skip Breakfast: A 7-Day Randomised Crossover Trial

With concerns that adolescent girls often skip breakfast, this study compared the effects of breakfast consumption versus breakfast omission on free-living physical activity (PA) energy expenditure (PAEE) and dietary intakes among adolescent girls classified as habitual breakfast skippers. The participants went through two 7-day conditions in a trial with a crossover design: daily standardised breakfast consumption (energy content: 25% of resting metabolic rate) before 09:00 (BC) and daily breakfast omission (no energy-providing nutrients consumed) until 10:30 (BO). Free-living PAEE, dietary intakes, and perceived appetite, tiredness, and energy levels were assessed. Analyses were linear mixed models. Breakfast manipulation did not affect PAEE or PA duration. Daily fibre intake was higher (p = 0.005; d = 1.31), daily protein intake tended to be higher (p = 0.092; d = 0.54), post-10:30 carbohydrate intake tended to be lower (p = 0.096; d = 0.41), and pre-10:30 hunger and fullness were lower and higher, respectively (p ≤ 0.065; d = 0.33-1.01), in BC versus BO. No other between-condition differences were found. Breakfast-skipping adolescent girls do not compensate for an imbalance in energy intake caused by breakfast consumption versus omission through subsequent changes in PAEE but may increase their carbohydrate intakes later in the day to partially compensate for breakfast omission. Furthermore, breakfast can make substantial contributions to daily fibre intake among adolescent girls.

Sports Dietitians Australia Position Statement: Nutrition for Exercise in Hot Environments

It is the position of Sports Dietitians Australia (SDA) that exercise in hot and/or humid environments, or with significant clothing and/or equipment that prevents body heat loss (i.e., exertional heat stress), provides significant challenges to an athlete's nutritional status, health, and performance. Exertional heat stress, especially when prolonged, can perturb thermoregulatory, cardiovascular, and gastrointestinal systems. Heat acclimation or acclimatization provides beneficial adaptations and should be undertaken where possible. Athletes should aim to begin exercise euhydrated. Furthermore, preexercise hyperhydration may be desirable in some scenarios and can be achieved through acute sodium or glycerol loading protocols. The assessment of fluid balance during exercise, together with gastrointestinal tolerance to fluid intake, and the appropriateness of thirst responses provide valuable information to inform fluid replacement strategies that should be integrated with event fuel requirements. Such strategies should also consider fluid availability and opportunities to drink, to prevent significant under- or overconsumption during exercise. Postexercise beverage choices can be influenced by the required timeframe for return to euhydration and co-ingestion of meals and snacks. Ingested beverage temperature can influence core temperature, with cold/icy beverages of potential use before and during exertional heat stress, while use of menthol can alter thermal sensation. Practical challenges in supporting athletes in teams and traveling for competition require careful planning. Finally, specific athletic population groups have unique nutritional needs in the context of exertional heat stress (i.e., youth, endurance/ultra-endurance athletes, and para-sport athletes), and specific adjustments to nutrition strategies should be made for these population groups.

Carbohydrate Drink Use During 30 Minutes of Variable-Intensity Exercise Has No Effect on Exercise Performance in Premenarchal Girls

PURPOSE

This study examined the physiological, perceptual, and performance effects of a 6% carbohydrate (CHO) drink during variable-intensity exercise (VIE) and a postexercise test in premenarchal girls.

METHODS

A total of 10 girls (10.4 [0.7] y) participated in the study. VO2peak was assessed, and the girls were familiarized with VIE and performance during the first visit. The trial order (CHO and placebo) was randomly assigned for subsequent visits. The drinks were given before VIE bouts and 1-minute performance (9 mL/kg total). Two 15-minute bouts of VIE were completed (10 repeated sequences of 20%, 55%, and 95% power at VO2peak and maximal sprints) before a 1-minute performance sprint.

RESULTS

The mean power, peak power, heart rate (HR), %HRpeak, and rating of perceived exertion during VIE did not differ between trials. However, the peak power decreased, and the rating of perceived exertion increased from the first to the second bout. During the 1-minute performance, there were no differences between the trial (CHO vs placebo) for HR (190 [9] vs 189 [9] bpm), %HRpeak (97.0% [3.2%] vs 96.6% [3.0%]), rating of perceived exertion (7.8 [2.3] vs 8.1 [1.9]), peak power (238 [70] vs 235 [60] W), fatigue index (54.7% [10.0%] vs 55.9% [12.8%]), or total work (9.4 [2.6] vs 9.4 [2.1] kJ).

CONCLUSION

CHO supplementation did not alter physiological, perceptual, or performance responses during 30 minutes of VIE or postexercise sprint performance in premenarchal girls.

Metabolic Flexibility during Exercise in Children with Obesity and Matched Controls

BACKGROUND

Impaired metabolic flexibility (MetFlex) could contribute to ectopic fat accumulation and pathological conditions, such as type 2 diabetes. MetFlex refers to the ability to adapt substrate oxidation to availability. To the best of our knowledge, no studies have examined MetFlex under exercise conditions in children with obesity (OB) compared with a control group (CON) without obesity. Therefore, the primary objective was to compare MetFlex during exercise in children with OB compared with CON matched for chronological age, sex, and biological maturation. A better understanding of MetFlex could help elucidate its role in the pathogenesis of childhood obesity and insulin resistance.

METHODS

Children with obesity and without obesity age 8 to 17 yr attended two visits, which included anthropometric measurements, blood work (OB group only), a maximal aerobic fitness (V˙O2max) test, and MetFlex test with a C-enriched carbohydrate (1.75 g per kg of body mass, up to 75 g) ingested before 60 min of exercise at 45% V˙O2max. Breath measurements were collected to calculate exogenous CHO (CHOexo) oxidative efficiency as a measure of MetFlex.

RESULTS

CHOexo oxidative efficiency (CHOexo oxidized/CHO ingested × 100) during exercise was significantly lower in OB (17.3% ± 4.0%) compared with CON (22.6% ± 4.7%, P < 0.001). CHOexo contributed less to total energy expenditure during exercise in OB compared with CON (P < 0.001), whereas the contribution of endogenous CHO (P = 0.19) and total fat was not significantly different (P = 0.91).

CONCLUSIONS

The ability to oxidize oral CHO, an indicator of MetFlex, was 23.5% lower in children with obesity compared with controls, independent of age, sex, and pubertal effects. Thus, obesity at a young age could be associated with reduced MetFlex and future comorbidities.

UEFA expert group statement on nutrition in elite football. Current evidence to inform practical recommendations and guide future research

Football is a global game which is constantly evolving, showing substantial increases in physical and technical demands. Nutrition plays a valuable integrated role in optimising performance of elite players during training and match-play, and maintaining their overall health throughout the season. An evidence-based approach to nutrition emphasising, a 'food first' philosophy (ie, food over supplements), is fundamental to ensure effective player support. This requires relevant scientific evidence to be applied according to the constraints of what is practical and feasible in the football setting. The science underpinning sports nutrition is evolving fast, and practitioners must be alert to new developments. In response to these developments, the Union of European Football Associations (UEFA) has gathered experts in applied sports nutrition research as well as practitioners working with elite football clubs and national associations/federations to issue an expert statement on a range of topics relevant to elite football nutrition: (1) match day nutrition, (2) training day nutrition, (3) body composition, (4) stressful environments and travel, (5) cultural diversity and dietary considerations, (6) dietary supplements, (7) rehabilitation, (8) referees and (9) junior high-level players. The expert group provide a narrative synthesis of the scientific background relating to these topics based on their knowledge and experience of the scientific research literature, as well as practical experience of applying knowledge within an elite sports setting. Our intention is to provide readers with content to help drive their own practical recommendations. In addition, to provide guidance to applied researchers where to focus future efforts.

Endogenous versus exogenous carbohydrate oxidation measured by stable isotopes in pre-pubescent children plus 13C abundances in foods consumed three days prior

PURPOSE

The purposes of the present study were to (a) examine resting metabolism, substrate utilization, and endogenous versus exogenous carbohydrate (CHO) oxidation before and after 30-g rapidly-digesting carbohydrate (RDC) ingestion using indirect calorimetry and breath test analysis of stable isotope concentrations in pre-pubescent children and (b) report the 13C abundances in foods consumed for three days prior.

METHODS

Nineteen children (n = 10 boys, n = 9 girls) at Tanner stage I or II participated (mean age ± 95% CI = 9.84 ± 0.77 y) in this study. Food was administered to the children for three days preceding their scheduled breath tests. Breath tests and indirect calorimetry were performed after an 8-h fast before and 60 min following consumption of a 30-g simple RDC drink consisting of maltodextrin and sucrose. Open circuit spirometry and indirect calorimetry monitored resting metabolism and CHO oxidation. Separate breath samples were taken every 15 min. Samples of all foods and breath samples were analyzed for 13C and 12C abundances with a stable-isotope mass spectrometer.

RESULTS

13C in expired breath samples were -23.81 ± 1.64‰ at baseline and increased every 15 min after consumption of the CHO drink (p < 0.001-0.009). Cumulative total, endogenous, and exogenous CHO utilization increased during the post-prandial period (p < 0.001). Endogenous CHO oxidation was consistently greater than exogenous CHO oxidation (p < 0.001-0.002).Blood glucose was elevated from baseline at 30- and 60-min post-prandial (p < 0.001). Insulin did not change over time (p = 0.184).

CONCLUSIONS

The foods provided during the 3-day controlled diet effectively minimized 13C variation prior to metabolic testing. The 13C abundances of foods reported herein should serve as practical recommendations to reduce 13C intake before breath tests. While endogenous CHO oxidation remained greater in proportion to exogenous CHO oxidation, these findings suggest that even a relatively small amount of RDC can increase exogenous CHO oxidation and blood glucose in normal-weight children. To further examine shifts in endogenous versus exogenous CHO utilization, we recommend that future studies take steps to minimize 13C variation before breath tests and examine changes in substrate metabolism at rest and during exercise in normal weight and overweight pre-pubescent children.

CLINICAL TRIAL REGISTRATION NUMBER

NCT03185884.

Contributions of Fat and Carbohydrate Metabolism to Glucose Homeostasis in Childhood Change With Age and Puberty: A 12-Years Cohort Study (EARLYBIRD 77)

Puberty-a period when susceptibility to the onset of Type 2 diabetes (T2D) increases-is marked with profound physiological and metabolic changes. In the EarlyBird cohort, children who developed impaired fasting glycemia in adolescence already exhibited higher fasting blood glucose at 5 years of age, independent of their body mass index (BMI), suggesting that pubertal factors may modify existing predisposition. Understanding how the physiological changes during childhood influence glucose homeostasis and how the central energy metabolism may help deciphering the mechanisms that underlie the risk of developing T2D in children and adults. We investigated these associations by analyzing glycemic variations with molecular markers of central energy metabolism, substrate oxidation status and pubertal stages in the EarlyBird cohort. The EarlyBird study is a non-interventional, prospective cohort study, that recruited 307 healthy UK children at age 5, and followed them annually throughout childhood for 12 years. Longitudinal data on blood biochemistry, respiratory exchange ratio, and anthropometry, available from 150 children were integrated with fasting glycemia. The gradual rise in blood glucose during childhood associates with age-dependent changes in molecular processes and substrate oxidation status, namely (i) greater pre-pubertal fat utilization, ketogenesis, and fatty acid oxidation, and (ii) greater pubertal carbohydrate oxidation and glycolytic metabolism (Cori and Cahill Cycles) associated with different amino acid exchanges between muscle and other tissues (proline, glutamine, alanine). Since children's metabolic and nutritional requirements evolve during childhood, this study has potential clinical implications for the development of nutritional strategies for disease prevention in children.

TNF blockade contributes to restore lipid oxidation during exercise in children with juvenile idiopathic arthritis

BACKGROUND

Children with juvenile idiopathic arthritis (JIA) have impaired physical abilities. TNF-α plays a crucial role in this pathogenesis, but it is also involved in the use of lipids and muscle health. Objective of this study was to explore substrate oxidation and impact of TNF blockade on energy metabolism in children with JIA as compared to healthy children.

METHODS

Fifteen non-TNF-blockaded and 15 TNF-blockaded children with JIA and 15 healthy controls were matched by sex, age, and Tanner stage. Participants completed a submaximal incremental exercise test on ergocycle to determine fat and carbohydrate oxidation rates by indirect calorimetry.

RESULTS

The maximal fat oxidation rate during exercise was lower in JIA children untreated by TNF blockade (134.3 ± 45.2 mg.min- 1) when compared to the controls (225.3 ± 92.9 mg.min- 1, p = 0.007); but was higher in JIA children under TNF blockade (163.2 ± 59.0 mg.min- 1, p = 0.31) when compared to JIA children untreated by TNF blockade. At the same relative exercise intensities, there was no difference in carbohydrate oxidation rate between three groups.

CONCLUSIONS

Lipid metabolism during exercise was found to be impaired in children with JIA. However, TNF treatment seems to improve the fat oxidation rate in this population.

TRIAL REGISTRATION

In ClinicalTrials.gov, reference number NCT02977416 , registered on 30 November 2016.

Carbohydrate consumption and variable-intensity exercise responses in boys and men

PURPOSE

The effect of carbohydrate (CHO) supplementation on physiological and perceptual responses to steady-state exercise has been studied in children. However, little is known about these responses to variable-intensity exercise (VIE) and how these responses might differ from adults. This study examined the physiological and perceptual effects of CHO on VIE in boys and men.

METHODS

Eight boys (11.1 ± 0.9 years) and 11 men (23.8 ± 2.1 years) consumed CHO or a placebo (PL) beverage before and throughout VIE (three 12-min cycling bouts with intensity varying every 20-30 s between 25, 50, 75, and 125% peak work rate). Pulmonary gas exchange was assessed during the second 12-min bout. RPE was assessed twice per bout.

RESULTS

In CHO, blood glucose increased and then decreased more from pre-exercise to 12 min and was higher in this trial at the end of exercise in men versus boys. In boys, blood glucose in CHO was higher at 24 and 36 min of exercise than in PL. RER during the CHO trial was higher in both groups; the other physiological responses were unaffected by CHO. All RPE measures (whole body, legs and chest) increased over time, but were not different between groups or trials.

CONCLUSION

Blood glucose patterns during VIE were differentially affected by CHO in boys and men, but most physiological and perceptual responses to VIE were unaffected by CHO in either group. Knowledge of the underlying mechanisms of glucose regulation and effects on physical performance during this type of exercise in children is warranted.

Burn Injury May Have Age-Dependent Effects on Strength and Aerobic Exercise Capacity in Males

Whether burn injury affects boys and men differently is currently unknown. To test the hypothesis that burned boys have lower exercise capacity and exercise training-induced responses compared with burned men, 40 young boys (12 ± 4 years, 149 ± 20 cm, 46 ± 18 kg) were matched to 35 adult men (33 ± 9 years, 174 ± 10 cm, 84 ± 16 kg) based on extent of burn injury (total body surface area burned, boys 46 ± 14% vs men 47 ± 30, P = .85) and length of hospital stay (boys 33 ± 23 vs men 41 ± 32 days, P = .23). Strength (peak torque) and cardiorespiratory fitness (peak VO2) were normalized to kg of lean body mass for group comparisons. Each group was also compared with normative age-sex matched values at discharge and after an aerobic and resistance exercise training (RET) program. A two-way factorial analysis of covariance assessed interaction and main effects of group and time. We found that boys and men showed similar pre-RET to post-RET increases in total lean (~4%) and fat (7%) mass (each P ≤ .008). Both groups had lower age-sex matched norm values at discharge for peak torque (boys 36%; men 51% of normative values) and peak VO2 (boys: 44; men: 59%; each P ≤ .0001). Boys strength were 13-15 per cent lower than men at discharge and after RET (main effect for group, P < .0001). Cardiorespiratory fitness improved to a greater extent in men (19%) compared with boys (10%) after the RET (group × time interaction, P = .011). These results show that at discharge and after RET, burn injury may have age-dependent effects and should be considered when evaluating efficacy and progress of the exercise program.

Validity and reliability of a novel metabolic flexibility test in children with obesity

Existing methods for diagnosing diabetes and for identifying risk of diabetes development are completed under resting conditions and based on adult data. Studying additional methods to identify metabolic risk in children is warranted. Our objective was to examine the validity and reliability of a metabolic flexibility (MetFlex) test for screening glycemia and insulin resistance (IR) in children. We hypothesized higher MetFlex during exercise would be correlated with lower fasting glucose and homeostasis model assessment of insulin resistance (HOMA-IR) and higher whole body insulin sensitivity index (WBISI) and insulin secretion-sensitivity index-2 (ISSI-2). Thirty-four children with obesity (14 boys, 20 girls) attended two visits. At visit 1, an oral glucose tolerance test (OGTT) was followed by anthropometric and aerobic fitness (V̇o_2max) assessments. Insulin and glucose during the OGTT were used to calculate HOMA-IR, WBISI, and ISSI-2. At visit 2, a ¹³C-enriched carbohydrate drink was ingested before 60 min of exercise at 45% V̇o_2max. Breath measurements were collected to calculate area under the curve exogenous carbohydrate to measure MetFlex. Pearson's r correlation showed no significant association between MetFlex during exercise with fasting glucose ( r = -0.288, P = 0.110). MetFlex was associated with log-HOMA-IR ( r = -0.597, P = 0.024), log-WBISI ( r = 0.575, P = 0.051), and log-ISSI-2 ( r = 0.605, P = 0.037) in boys but not girls. When repeated ( n = 18), MetFlex was deemed a reliable test (intraclass correlation coefficient = 0.692). MetFlex during exercise was negatively associated with IR and β-cell function in boys. Further research is required to explore clinical utility of the MetFlex test and explain the lack of association in girls. NEW & NOTEWORTHY This study is the first to investigate the validity and reliability of a novel noninvasive metabolic flexibility (MetFlex) test for identifying insulin resistance in children with obesity. MetFlex was measured during exercise using [¹³C]glucose stable isotope methodology. Findings showed that MetFlex was negatively associated with insulin resistance in boys but not in girls with obesity. Future work is required to investigate these sex differences. MetFlex test results were deemed reliable when repeated on a separate day.

Effect of 7 days of exercise on exogenous carbohydrate oxidation and insulin resistance in children with obesity

The capacity to match carbohydrate (CHO) oxidation with CHO availability (deemed metabolic flexibility (MetFlex)) may be important for type 2 diabetes prevention. In adults, impaired MetFlex is associated with insulin resistance (IR), which can be improved with as little as 7 days of exercise. Whether this occurs similarly in children is unknown. We hypothesized that 7 consecutive days of exercise would improve MetFlex and IR in children with obesity. Twelve children (8 boys, 4 girls) completed 2 study visits before (PRE) and 2 study visits after (POST) exercise training. At visit 1, fasting blood was collected, and anthropometry and maximal oxygen uptake were assessed. At visit 2, a ¹³C-enriched CHO drink was ingested before exercise (3 × 20 min) at ∼59% maximal oxygen uptake. Exogenous CHO oxidative efficiency, used as a surrogate measurement of MetFlex, was calculated from breath samples. During training, participants alternated between continuous and high-intensity interval cycling sessions at home under supervision. In spite of good training adherence, there was no improvement in MetFlex (PRE: 20.7% ± 1.8%, POST: 18.9% ± 4.9%, p = 0.22) or homeostasis model assessment of insulin resistance (PRE: 8.7 ± 4.6, POST: 8.1 ± 6.0, p = 0.51). Future research should investigate exercise volume, sex, and pubertal effects on the early responsiveness of MetFlex to exercise therapy.

Physical Activity Duration but Not Energy Expenditure Differs between Daily and Intermittent Breakfast Consumption in Adolescent Girls: A Randomized Crossover Trial

Background

It is not known whether breakfast frequency affects physical activity (PA) in children or adolescents.

Objective

This study examined the effect of daily compared with intermittent breakfast consumption on estimated PA energy expenditure (PAEE) in adolescent girls.

Methods

Under a randomized crossover design, 27 girls [mean ± SD age: 12.4 ± 0.5 y, body mass index (in kg/m2): 19.3 ± 3.0] completed two 7-d conditions. A standardized breakfast (∼1674 kJ) was consumed every day before 0900 in the daily breakfast consumption (DBC) condition. The standardized breakfast was consumed on only 3 d before 0900 in the intermittent breakfast consumption (IBC) condition, alternating with breakfast omission on the remaining 4 d (i.e., only water consumed before 1030). Combined heart rate accelerometry was used to estimate PAEE throughout each condition. Statistical analyses were completed by using condition × time of day repeated-measures ANOVA. The primary outcome was PAEE and the secondary outcome was time spent in PA.

Results

Daily estimated PAEE from sedentary or light-, moderate-, or vigorous-intensity PA and total PAEE were not significantly different between the conditions. The condition × time of day interaction for sedentary time (P = 0.05) indicated that the girls spent an additional 11.5 min/d being sedentary in the IBC condition compared with the DBC condition from 1530 to bedtime (P = 0.04). Light PA was 19.8 min/d longer in the DBC condition than in the IBC condition (P = 0.05), which was accumulated from waking to 1030 (P = 0.04) and from 1530 to bedtime (P = 0.03). There were no significant differences in time spent in moderate PA or vigorous PA between the conditions.

Conclusions

Adolescent girls spent more time in light PA before 1030 and after school and spent less time sedentary after school when a standardized breakfast was consumed daily than when consumed intermittently across 7 d. However, breakfast manipulation did not affect estimated daily PAEE. This trial was registered at www.isrctn.com as ISRCTN74579070.

Hip region muscular dystrophy and emergence of motor deficits in dysferlin-deficient Bla/J mice

The identification of a dysferlin‐deficient animal model that accurately displays both the physiological and behavior aspects of human dysferlinopathy is critical for the evaluation of potential therapeutics. Disease progression in dysferlin‐deficient mice is relatively mild, compared to the debilitating human disease which manifests in impairment of particular motor functions. Since there are no other known models of dysferlinopathy in other species, locomotor proficiency and muscular anatomy through MRI (both lower leg and hip region) were evaluated in dysferlin‐deficient B6.A‐Dysf^prmd/GeneJ (Bla/J) mice to define disease parameters for therapeutic assessment. Despite the early and progressive gluteal muscle dystrophy and significant fatty acid accumulation, the emergence of significant motor function deficits was apparent at approximately 1 year of age for standard motor challenges including the rotarod, a marble bury test, grip strength, and swimming speed. Earlier observations of decreased performance for Bla/J mice were evident during extended monitoring of overall exploration and rearing activity. Comprehensive treadmill gait analyses of the Bla/J model indicated significant differences in paw placement angles and stance in relation to speed and platform slope. At 18 months of age, there was no significant difference in the life expectancy of Bla/J mice compared to wild type. Consistent with progressive volume loss and fatty acid accumulation in the hip region observed by MRI, mass measurement of individual muscles confirmed gluteal and psoas muscles were the only muscles demonstrating a significant decrease in muscle mass, which is analogous to hip‐girdle weakness observed in human dysferlin‐deficient patients. Collectively, this longitudinal analysis identifies consistent disease parameters that can be indicators of efficacy in studies developing treatments for human dysferlin deficiency.

Structure-Based Designed Nano-Dysferlin Significantly Improves Dysferlinopathy in BLA/J Mice

Dysferlinopathy is an autosomal recessive muscular dystrophy characterized by the progressive loss of motility that is caused by mutations throughout the DYSF gene. There are currently no approved therapies that ameliorate or reverse dysferlinopathy. Gene delivery using adeno-associated vectors (AAVs) is a leading therapeutic strategy for genetic diseases; however, the large size of dysferlin cDNA (6.2 kB) precludes packaging into a single AAV capsid. Therefore, using 3D structural modeling and hypothesizing dysferlin C2 domain redundancy, a 30% smaller, dysferlin-like molecule amenable to single AAV vector packaging was engineered (termed Nano-Dysferlin). The intracellular distribution of Nano-Dysferlin was similar to wild-type dysferlin and neither demonstrated toxicity when overexpressed in dysferlin-deficient patient myoblasts. Intramuscular injection of AAV-Nano-Dysferlin in young dysferlin-deficient mice significantly improved muscle integrity and decreased muscle turnover 3 weeks after treatment, as determined by Evans blue dye uptake and central nucleated fibers, respectively. Systemically administered AAV-Nano-Dysferlin to young adult dysferlin-deficient mice restored motor function and improved muscle integrity nearly 8 months after a single injection. These preclinical data are the first report of a smaller dysferlin variant tailored for AAV single particle delivery that restores motor function and, therefore, represents an attractive candidate for the treatment of dysferlinopathy.

Energy substrate utilization with and without exogenous carbohydrate intake in boys and men exercising in the heat

Little is known about energy yield during exercise in the heat in boys compared with men. To investigate substrate utilization with and without exogenous carbohydrate (CHOexo) intake, seven boys [11.2 ± 0.2 (SE) yr] and nine men (24.0 ± 1.1 yr) cycled (4 × 20-min bouts) at a fixed metabolic heat production ( Ḣ p) per unit body mass (6 W/kg) in a climate chamber (38°C and 50% relative humidity), on two occasions. Participants consumed a 13C-enriched 8% CHO beverage (CARB) or placebo beverage (CONT) in a double-blinded, counterbalanced manner. Substrate utilization was calculated for the last 60 min of exercise. CHOexo oxidation rate (2.0 ± 0.3 vs. 2.5 ± 0.2 mg·kg fat-free mass−1·min−1, P = 0.02) and CHOexo oxidation efficiency (12.8 ± 0.6 vs. 16.0 ± 0.9%, P = 0.01) were lower in boys compared with men exercising in the heat. Total carbohydrate (CHOtotal), endogenous CHO (CHOendo), and total fat (Fattotal) remained stable in boys and men ( P > 0.05) during CARB, whereas CHOtotal oxidation rate decreased ( P < 0.001) and Fattotal oxidation rate increased over time similarly in boys and men during CONT ( P < 0.001). The relative contribution of CHOexo to total energy yield increased over time in both groups ( P < 0.001). In conclusion, endogenous substrate metabolism and the relative contribution of fuels to total energy yield were not different between groups. The ingestion of a CHO beverage during exercise in the heat may be as beneficial for boys as men to spare endogenous substrate.

No difference in exogenous carbohydrate oxidation during exercise in children with and without impaired glucose tolerance

The capacity to match carbohydrate (CHO) utilization with availability is impaired in insulin-resistant, obese adults at rest. Understanding exogenous carbohydrate (CHOexo) oxidation during exercise and its association to insulin resistance (IR) is important, especially in children at risk for type 2 diabetes. Our objective was to examine the oxidative efficiency of CHOexo during exercise in obese children with normal glucose tolerance (NGT) or impaired glucose tolerance (IGT). Children attended two visits and were identified as NGT (n = 22) or IGT (n = 12) based on 2-h oral glucose tolerance test (OGTT) glucose levels of <7.8 mmol/l or ≥7.8 mmol/l, respectively. Anthropometry, body composition, and aerobic fitness (V̇o2max) were assessed. Insulin and glucose at baseline, 30, 60, 90, and 120 min during the OGTT were used to calculate measures of insulin sensitivity. On a separate day, a (13)C-enriched CHO drink was ingested before exercise (3 × 20 min bouts) at 45% V̇o2max Breath measurements were collected to calculate CHOexo oxidative efficiency. CHOexo oxidative efficiency during exercise was similar in IGT (17.0 ± 3.6%) compared with NGT (17.1 ± 4.4%) (P = 0.90) despite lower whole body insulin sensitivity in IGT at rest (P = 0.02). Area under the curve for insulin (AUCins) measured at rest during the OGTT was greater in IGT compared with NGT (P = 0.04). The ability of skeletal muscle to utilize CHOexo was not impaired during exercise in children with IGT.

Nutritional Considerations for Performance in Young Athletes

Nutrition is an integral component to any athletes training and performance program. In adults the balance between energy intake and energy demands is crucial in training, recovery, and performance. In young athletes the demands for training and performance remain but should be a secondary focus behind the demands associated with maintaining the proper growth and maturation. Research interventions imposing significant physiological loads and diet manipulation are limited in youth due to the ethical considerations related to potential negative impacts on the growth and maturation processes associated with younger individuals. This necessary limitation results in practitioners providing nutritional guidance to young athletes to rely on exercise nutrition recommendations intended for adults. While many of the recommendations can appropriately be repurposed for the younger athlete attention needs to be taken towards the differences in metabolic needs and physiological differences.

Muscle metabolism changes with age and maturation: How do they relate to youth sport performance?

AIM

To provide an evidence-based review of muscle metabolism changes with sex-, age- and maturation with reference to the development of youth sport performance.

METHODS

A narrative review of data from both invasive and non-invasive studies, from 1970 to 2015, founded on personal databases supported with computer searches of PubMed and Google Scholar.

RESULTS

Youth sport performance is underpinned by sex-, age- and maturation-related changes in muscle metabolism. Investigations of muscle size, structure and metabolism; substrate utilisation; pulmonary oxygen uptake kinetics; muscle phosphocreatine kinetics; peak anaerobic and aerobic performance; and fatigue resistance; determined using a range of conventional and emerging techniques present a consistent picture. Age-related changes have been consistently documented but specific and independent maturation-related effects on muscle metabolism during exercise have proved elusive to establish. Children are better equipped for exercise supported primarily by oxidative metabolism than by anaerobic metabolism. Sexual dimorphism is apparent in several physiological variables underpinning youth sport performance. As young people mature there is a progressive but asynchronous transition into an adult metabolic profile.

CONCLUSIONS

The application of recent developments in technology to the laboratory study of the exercising child and adolescent has both supplemented existing knowledge and provided novel insights into developmental exercise physiology. A sound foundation of laboratory-based knowledge has been established but the lack of rigorously designed child-specific and sport-specific testing environments has clouded the interpretation of the data in real life situations. The primary challenge remains the translation of laboratory research into the optimisation of youth sports participation and performance.

High cycling cadence reduces carbohydrate oxidation at given low intensity metabolic rate

Cycling cadence (RPM)-related differences in blood lactate concentration (BLC) increase with increasing exercise intensity, whilst corresponding divergences in oxygen uptake (V.O₂) and carbon dioxide production (V.CO₂) decrease. Aim of the present study was to test whether a higher RPM reduces the fraction (%) of the V.O₂ used for carbohydrate oxidation (relCHO) at a given BLC. Eight males (23.9 ± 1.6 yrs; 177 ± 3 cm; 70.3 ± 3.4 kg) performed incremental load tests at 50 and 100 RPM. BLC, V.O₂ and V.CO₂ were measured. At respiratory exchange ratios (RER) < 1, relCHO were calculated and the constant determining 50 % relCHO (k_CHO) was approximated as a function of the BLC. At submaximal workload V.O₂, V.CO₂, and relCHO were lower (all p < 0.002; η² > 0.209) at 50 than at 100 RPM. No differences were observed in V.O₂peak (3.96 ± 0.22 vs. 4.00 ± 0.25 l · min⁻¹) and RER_peak (1.18 ± 0.02 vs. 1.15 ± 0.02). BLC was lower (p < 0.001; η² = 0.680) at 50 than at 100 RPM irrespective of cycling intensity. At 50 RPM, kCHO (4.2 ± 1.4 (mmol · l⁻¹)³) was lower (p = 0.043; η² = 0.466) than at 100 RPM (5.9 ± 1.9 (mmol · l⁻¹)³). This difference in k_CHO reflects a reduced CHO oxidation at a given BLC at 100 than at 50 RPM. At a low exercise intensity, a higher cycling cadence can substantially reduce the reliance on CHO at a given metabolic rate and/or BLC.

Effect of fat- and carbohydrate-rich diets on metabolism and running performance in trained adolescent boys

OBJECTIVES

A randomized crossover trial was designed to analyze the impact of a short-term, isoenergetic fat-rich or carbohydrate (CHO)-rich diet on substrate oxidation rates during submaximal exercise and on performance in a 10,000-m running time trial in trained, mid- to late-pubertal boys.

METHODS

An incremental test was performed to determine the peak oxygen uptake (VO2peak). After 2 days on a fat-rich (24.2% ± 0.8% CHO, 60.4% ± 0.3% fat, and 15.5% ± 1.0% protein), CHO-rich (69.3% ± 1.2% CHO, 15.9% ± 2.1% fat, and 15.1% ± 1.1% protein), or habitual (56.1% ± 7.0% CHO, 27.5% ± 4.9% fat, and 16.5% ± 4.0% protein) diet, 19 trained adolescent boys (15.2 ± 1.5 years) performed a 10-minute constant run at 65% VO2peak to determine the respiratory exchange ratio (RER) during exercise and 10,000-m running on an outdoor track.

RESULTS

During the constant run, the RER and CHO contribution to energy expenditure were lower, and fat contribution higher, in the fat-rich diet than in the CHO-rich diet (P < 0.05), but the results were not different from those of the habitual diet. Performance in the 10,000-m run after consuming CHO- and fat-rich diets was similar to performance after a habitual diet (50.0 ± 7.0, 51.9 ± 8.3, and 50.9 ± 7.4 minutes, respectively), but consuming a CHO-rich diet enhanced performance compared with that after a fat-rich diet (P = 0.03).

CONCLUSIONS

These findings indicate that a CHO-rich diet provides additional benefits to 10,000-m running performance in trained adolescent boys compared with a fat-rich diet.

Reduced fat oxidation rates during submaximal exercise in adolescents with Crohn's disease

BACKGROUND

Children with Crohn's disease (CD) suffer from malnutrition. Understanding substrate utilization during exercise may help patients with CD sustain a healthy active lifestyle without compromising nutrition. The aim of this study was to determine whether substrate utilization and bioavailability during exercise are altered in children with CD compared with controls.

METHODS

Seven children with CD (mean age ± SD: 15.2 ± 2.3 yr) and 7 controls (14.4 ± 2.3 yr) were matched by sex and biological age. Participants completed 60 minutes of cycling at an intensity equivalent to 50% of their peak mechanical power. Rates of total fat and carbohydrate (CHO) oxidation, the amount of fat and CHO oxidized, and the contribution of fat and CHO to total energy expenditure were calculated from expired gases collected during exercise. Blood was collected before, during, and at the end of exercise and analyzed for insulin, free fatty acids, and glucose.

RESULTS

Whole-body fat oxidation rate (expressed in mg · kg(-1) of body weight per min) during exercise was lower in children with CD (5.8 ± 1.0) compared with controls (8.0 ± 2.2, P < 0.05). Children with CD relied significantly more on CHO, with approximately 10% greater contribution toward total energy expenditure (P < 0.05) than controls. There were no differences in plasma insulin, free fatty acids, or glucose between the groups.

CONCLUSIONS

Fat metabolism during exercise seems to be impaired in children with CD. A greater reliance on CHO is required to meet the energy demands of submaximal exercise.

Carbohydrate supplementation and prolonged intermittent high-intensity exercise in adolescents: research findings, ethical issues and suggestions for the future

In the last decade, research has begun to investigate the efficacy of carbohydrate supplementation for improving aspects of physical capacity and skill performance during sport-specific exercise in adolescent team games players. This research remains in its infancy, and further study would be beneficial considering the large youth population actively involved in team games. Literature on the influence of carbohydrate supplementation on skill performance is scarce, limited to shooting accuracy in adolescent basketball players and conflicting in its findings. Between-study differences in the exercise protocol, volume of fluid and carbohydrate consumed, use of prior fatiguing exercise and timing of skill tests may contribute to the different findings. Conversely, initial data supports carbohydrate supplementation in solution and gel form for improving intermittent endurance running capacity following soccer-specific shuttle running. These studies produced reliable data, but were subject to limitations including lack of quantification of the metabolic response of participants, limited generalization of data due to narrow participant age and maturation ranges, use of males and females within the same sample and non-standardized pre-exercise nutritional status between participants. There is a lack of consensus regarding the influence of frequently consuming carbohydrate-containing products on tooth enamel erosion and the development of obesity or being overweight in adolescent athletes and non-athletes. These discrepancies mean that the initiation or exacerbation of health issues due to frequent consumption of carbohydrate-containing products by adolescents cannot be conclusively refuted. Coupled with the knowledge that consuming a natural, high-carbohydrate diet -3-8 hours before exercise can significantly alter substrate use and improve exercise performance in adults, a moral and ethical concern is raised regarding the direction of future research in order to further knowledge while safeguarding the health and well-being of young participants. It could be deemed unethical to continue study into carbohydrate supplementation while ignoring the potential health concerns and the possibility of generating similar performance enhancements using natural dietary interventions. Therefore, future work should investigate the influence of pre-exercise dietary intake on the prolonged intermittent, high-intensity exercise performance of adolescents. This would enable quantification of whether pre-exercise nutrition can modulate exercise performance and, if so, the optimum dietary composition to achieve this. Research could then combine this knowledge with ingestion of carbohydrate-containing products during exercise to facilitate ethical and healthy nutritional guidelines for enhancing the exercise performance of adolescents. This article addresses the available evidence regarding carbohydrate supplementation and prolonged intermittent, high-intensity exercise in adolescent team games players. It discusses the potential health concerns associated with the frequent use of carbohydrate-containing products by adolescents and how this affects the research ethics of the field, and considers directions for future work.

Fluid Balance and Dehydration in the Young Athlete

Many young athletes train and compete under conditions that put their body fluid balance at risk, and hypohydration is usually the major concern. Another less frequent condition is hyperhydration that—if accompanied by other risk factors—may cause hyponatremia. Water and electrolyte losses during physical activities occur primarily from sweat. Such losses have been identified mostly in active (but nonathletic) young populations under laboratory settings. Studies have been trying to estimate fluid losses in the athletic population under field conditions, taking into account the sport modality and environmental conditions. Besides these external conditions, young athletes adopt different drinking attitudes, which may depend on knowledge, education, and the opportunities to drink during the break periods as well as fluid availability. Focusing on the young athlete, this review will discuss water and sodium losses from sweat, the effects of hypohydration on performance, and fluid intake attitudes within and during practices and competitions. Some considerations related to the methods of identifying hydration status and guidelines are also given, with the understanding that they should be individually adapted for the athlete and activity. The young athlete, parents, coaches, and athletic/health professionals should be aware of such information to prevent fluid imbalances and the consequent hazardous effects on performance and health.

Carbohydrate ingestion during team games exercise: current knowledge and areas for future investigation

There is a growing body of research on the influence of ingesting carbohydrate-electrolyte solutions immediately prior to and during prolonged intermittent, high-intensity exercise (team games exercise) designed to replicate field-based team games. This review presents the current body of knowledge in this area, and identifies avenues of further research. Almost all early work supported the ingestion of carbohydrate-electrolyte solutions during prolonged intermittent exercise, but was subject to methodological limitations. A key concern was the use of exercise protocols characterized by prolonged periods at the same exercise intensity, the lack of maximal- or high-intensity work components and long periods of seated recovery, which failed to replicate the activity pattern or physiological demand of team games exercise. The advent of protocols specifically designed to replicate the demands of field-based team games enabled a more externally valid assessment of the influence of carbohydrate ingestion during this form of exercise. Once again, the research overwhelmingly supports carbohydrate ingestion immediately prior to and during team games exercise for improving time to exhaustion during intermittent running. While the external validity of exhaustive exercise at fixed prescribed intensities as an assessment of exercise capacity during team games may appear questionable, these assessments should perhaps not be viewed as exhaustive exercise tests per se, but as indicators of the ability to maintain high-intensity exercise, which is a recognized marker of performance and fatigue during field-based team games. Possible mechanisms of exercise capacity enhancement include sparing of muscle glycogen, glycogen resynthesis during low-intensity exercise periods and attenuated effort perception during exercise. Most research fails to show improvements in sprint performance during team games exercise with carbohydrate ingestion, perhaps due to the lack of influence of carbohydrate on sprint performance when endogenous muscle glycogen concentration remains above a critical threshold of ∼200  mmol/kg dry weight. Despite the increasing number of publications in this area, few studies have attempted to drive the research base forward by investigating potential modulators of carbohydrate efficacy during team games exercise, preventing the formulation of optimal carbohydrate intake guidelines. Potential modulators may be different from those during prolonged steady-state exercise due to the constantly changing exercise intensity and frequency, duration and intensity of rest intervals, potential for team games exercise to slow the rate of gastric emptying and the restricted access to carbohydrate-electrolyte solutions during many team games. This review highlights fluid volume, carbohydrate concentration, carbohydrate composition and solution osmolality; the glycaemic index of pre-exercise meals; fluid and carbohydrate ingestion patterns; fluid temperature; carbohydrate mouthwashes; carbohydrate supplementation in different ambient temperatures; and investigation of all of these areas in different subject populations as important avenues for future research to enable a more comprehensive understanding of carbohydrate ingestion during team games exercise.

Carbohydrate gel ingestion significantly improves the intermittent endurance capacity, but not sprint performance, of adolescent team games players during a simulated team games protocol

The aim of this study was to investigate the influence of ingesting a carbohydrate (CHO) gel on the intermittent endurance capacity and sprint performance of adolescent team games players. Eleven participants [mean age 13.5 ± 0.7 years, height 1.72 ± 0.08 m, body mass (BM) 62.1 ± 9.4 kg] performed two trials separated by 3-7 days. In each trial, they completed four 15 min periods of part A of the Loughborough Intermittent Shuttle Test (LIST), followed by an intermittent run to exhaustion (part B). In the 5 min pre-exercise, participants consumed 0.818 mL kg(-1) BM of a CHO or a non-CHO placebo gel, and a further 0.327 mL kg(-1) BM every 15 min during part A of the LIST (38.0 ± 5.5 g CHO h(-1) in the CHO trial). Intermittent endurance capacity was increased by 21.1% during part B when the CHO gel was ingested (4.6 ± 2.0 vs. 3.8 ± 2.4 min, P < 0.05, r = 0.67), with distance covered in part B significantly greater in the CHO trial (787 ± 319 vs. 669 ± 424 m, P < 0.05, r = 0.57). Gel ingestion did not significantly influence mean 15 m sprint time (P = 0.34), peak sprint time (P = 0.81), or heart rate (P = 0.66). Ingestion of a CHO gel significantly increases the intermittent endurance capacity of adolescent team games players during a simulated team games protocol.

Beverage carbohydrate concentration influences the intermittent endurance capacity of adolescent team games players during prolonged intermittent running

This study investigated the influence of consuming a 2, 6, and 10% carbohydrate-electrolyte (CHO-E) solution on the intermittent endurance capacity and sprint performance of adolescent team games players. Seven participants (five males and two females; mean age 13.3 ± 0.5 years, height 1.71 ± 0.05 m, body mass (BM) 62.0 ± 6.3 kg) performed three trials separated by 3-7 days. In each trial, they completed four 15-min periods of part A of the Loughborough Intermittent Shuttle Test (LIST) followed by an intermittent run to exhaustion (part B). Participants consumed 5 ml kg(-1) BM of the solution during the 5-min pre-exercise period, and a further 2 ml kg(-1) BM every 15 min during part A of the LIST. Intermittent endurance capacity increased by 34% with ingestion of the 6% CHO-E solution compared with the 10% solution (5.5 ± 0.8 vs. 4.1 ± 1.5 min, P < 0.05), equating to a distance of 931 ± 172 versus 706 ± 272 m (P < 0.05). There was no significant difference between the 2% (4.8 ± 1.2 min) and 6% (P = 0.10) or the 2 and 10% solutions (P = 0.09). Carbohydrate concentration did not significantly influence mean 15-m sprint time (P = 0.38). These results suggest that the carbohydrate concentration of an ingested solution influences the intermittent endurance capacity of adolescent team games players with a 6% solution significantly more effective than a 10% solution.

Metabolic flexibility and obesity in children and youth

The concept of metabolic flexibility describes the ability of skeletal muscle to switch between the oxidation of lipid as a fuel during fasting periods to the oxidation of carbohydrate during insulin stimulated period. Alterations in energy metabolism in adults with obesity, insulin resistance and/or type 2 diabetes induce a state of impaired metabolic flexibility, or metabolic inflexibility. Despite the increase in the prevalence of type 2 diabetes in obese children and youth, less is known about the factors involved in the development of metabolic inflexibility in the paediatric population. Metabolic flexibility is conditioned by nutrient partitioning in response to feeding, substrate mobilization and delivery to skeletal muscle during fasting or exercising condition, and skeletal muscle oxidative capacity. Our aim in this review was to identify among these factors those making obese children at risk of metabolic inflexibility. The development of ectopic rather than peripheral fat storage appears to be a factor strongly linked with a reduced metabolic flexibility. Tissue growth and maturation are determinants of impaired energy metabolism later in life but also as a promising way to reverse metabolic inflexibility given the plasticity of many tissues in youth. Finally, we have attempted to identify perspectives for future investigations of metabolic flexibility in obese children that will improve our understanding of the genesis of metabolic diseases associated with obesity.

Carbohydrate intake reduces fat oxidation during exercise in obese boys

The recent surge in childhood obesity has renewed interest in studying exercise as a therapeutic means of metabolizing fat. However, carbohydrate (CHO) intake attenuates whole body fat oxidation during exercise in healthy children and may suppress fat metabolism in obese youth. To determine the impact of CHO intake on substrate utilization during submaximal exercise in obese boys, seven obese boys (mean age: 11.4 ± 1.0 year; % body fat: 35.8 ± 3.9%) performed 60 min of exercise at an intensity that approximated maximal fat oxidation. A CHO drink (CARB) or a placebo drink (CONT) was consumed in a double-blinded, counterbalanced manner. Rates of total fat, total CHO, and exogenous CHO (CHO(exo)) oxidation were calculated for the last 20 min of exercise. During CONT, fat oxidation rate was 3.9 ± 2.4 mg × kg fat-free mass (FFM)(-1 )× min(-1), representing 43.1 ± 22.9% of total energy expenditure (EE). During CARB, fat oxidation was lowered (p = 0.02) to 1.7 ± 0.6 mg × kg FFM(-1 )× min(-1), contributing to 19.8 ± 4.9% EE. Total CHO oxidation rate was 17.2 ± 3.1 mg × kg FFM(-1 )× min(-1) and 13.2 ± 6.1 mg × kg FFM(-1) × min(-1) during CARB and CONT, respectively (p = 0.06). In CARB, CHO(exo) oxidation contributed to 23.3 ± 4.2% of total EE. CHO intake markedly suppresses fat oxidation during exercise in obese boys.

Ingesting a 6% carbohydrate-electrolyte solution improves endurance capacity, but not sprint performance, during intermittent, high-intensity shuttle running in adolescent team games players aged 12-14 years

The main aim of this study was to investigate the influence of consuming a 6% carbohydrate-electrolyte (CHO-E) solution on the intermittent, high-intensity endurance performance and capacity of adolescent team games players. Fifteen participants (mean age 12.7 +/- 0.8 years) performed two trials separated by 3-7 days. In each trial, they completed 60 min of exercise composed of four 15-min periods of part A of the Loughborough Intermittent Shuttle Test, followed by an intermittent run to exhaustion (part B). In a double-blind, randomised, counterbalanced fashion participants consumed either the 6% CHO-E solution or a non-carbohydrate (CHO) placebo (5 ml kg(-1) BM) during the 5 min pre-trial and after each 15-min period of part A (2 ml kg(-1) BM). Time to fatigue was increased by 24.4% during part B when CHO was ingested (5.1 +/- 1.8 vs. 4.1 +/- 1.6 min, P < 0.05), with distance covered in part B also significantly greater in the CHO trial (851 +/- 365 vs. 694 +/- 278 m, P < 0.05). No significant between-trials differences were observed for mean 15-m sprint time (P = 0.35), peak sprint time (P = 0.77), or heart rate (P = 0.08) during part A. These results demonstrate, for the first time, that ingestion of a CHO-E solution significantly improves the intermittent, high-intensity endurance running capacity of adolescent team games players during an exercise protocol designed to simulate the physiological demands of team games.

Pediatric sports nutrition: an update

PURPOSE OF REVIEW

There is a growing interest in the field of pediatric sports nutrition because of the will to lead the child athlete to high achievements, with minimal impairment of growth and development. In this article, we review some of the new data concerning the possible short-term and long-term effects of nutrition on children's performance, current and future health.

RECENT FINDINGS

Growing children engaged in strenuous exercise have several physiologic and metabolic characteristics that distinguish them from adults and require specific nutritional considerations. There is currently not enough evidence to support either carbohydrate loading or increased protein intake in the diet of the child athlete. Creatine use, although common among youth, is not recommended. Adequate hydration is essential to optimal performance. Consumption of iron-rich foods should be encouraged, as depleted iron stores are common in young athletes. In female athletes, nutritional deficiencies could lead to athletic amenorrhea and bone loss, and the resolution of energy deficits can restore normal bone formation and the return of menses.

SUMMARY

In the highly competitive world of the child athlete, proper nutrition is of essence. Unfortunately, most of the knowledge in this field is based on adult literature. Age-specific research would lead to a better understanding of what constitutes 'a healthy diet' in the context of the growing athlete and may be a first step toward achieving these necessary insights.

Fat oxidation rate and the exercise intensity that elicits maximal fat oxidation decreases with pubertal status in young male subjects

The range of exercise intensities that elicit high fat oxidation rates (FOR) in youth and the influence of pubertal status on peak FOR are unknown. In a longitudinal design, we compared FOR over a range of exercise intensities in a small cohort of developing prepubertal male subjects. Five boys all at Tanner stage 1 (ages 11-12 yr) and nine men (ages 20-26 yr) underwent an incremental cycle ergometry test to volitional exhaustion. FOR curves were determined from indirect calorimetry during the final 30 s of each increment. The same protocol was duplicated annually in the boys as they progressed through puberty. The peak FOR was considerably higher (P<0.05) in boys at Tanner 1 (8.6+/-1.5 mg.kg lean body mass(-1).min(-1)) (mean+/-SD) compared with men (4.2+/-1.1 mg.kg lean body mass(-1).min(-1)). FOR dropped as boys developed through puberty (Tanner 2/3 peak rate=7.6+/-0.6 mg.kg lean body mass(-1).min(-1); Tanner 4 peak rate=5.4+/-1.8 mg.kg lean body mass(-1).min(-1), main effect of Tanner stage; P<0.05) to the levels found in men (not significant). The exercise intensity that elicited peak FOR was higher in the boys at Tanner 1 [56+/-6% peak aerobic power (VO2 peak)] than in men (31+/-4% VO2 peak) (P<0.001). This value tended to decrease by Tanner stage 4 (45+/-10% VO2 peak, main effect of Tanner stage; P=0.06). We conclude that, compared with men, prepubertal boys have higher relative FOR throughout a wide range of exercise intensities and that FOR drops as boys develop through puberty.

The endocrine response and substrate utilization during exercise in children and adolescents

Adolescence is a time of rapid growth caused by significant changes in hormone levels. For many, it is also a time of increased physical activity and sport that places a large demand on energy reserves. Exercise is known to cause perturbations in endocrine and metabolic systems in children and adolescents, yet careful characterization of these responses is only now being conducted. It does not appear that prepubertal youth have a different muscle composition than adults. However, these youth do have a lower anaerobic capacity and a greater reliance on aerobic metabolism during activity. Prepubertal adolescents may have an immature glucose regulatory system that influences glycemic regulation at the onset of moderate exercise. During heavy exercise, muscle and blood lactate levels are lower in children than in adults and there is a greater reliance on fat as fuel. The exercise intensity that causes maximal fat oxidation rate and the relative rate of fat oxidation decreases as adolescents develop through puberty. The mechanism for the attenuated lipid utilization with the advancement of puberty, and the impact that this may have on body composition, are unknown. Surprisingly, prepubertal adolescents have relatively high rates of exogenous glucose oxidation, perhaps because of their smaller endogenous carbohydrate reserves. Further study is needed to determine the optimal exogenous carbohydrate feeding regimen for peak performance in adolescence. Studies are also needed to determine whether physical activity, at an intensity targeted to maximize fat oxidation, help to lower body adiposity in overweight youth.

La recherche qui éclaire les guides sur l’activité physique au Canada : introductionCet article est tiré d’un supplément intitulé Advancing physical activity measurement and guidelines in Canada: a scientific review and evidence-based foundation for the future of Canadian physical activity guidelines (Favoriser les lignes directrices et la mesure de l’activité physique au Canada: examen scientifique et justification selon les données probantes pour l’avenir des lignes directrices de l’activité physique canadienne) publié par Physiologie appliquée, nutrition et métabolisme et la Revue canadienne de santé publique. On peut aussi mentionner Appl. Physiol. Nutr. Metab. 32 (Suppl. 2F) ou Can. J. Public Health 98 (Suppl. 2)

La Société canadienne de physiologie de l’exercice (SCPE), en collaboration avec Santé Canada et d’autres organismes, a publié en 1998 le premier guide d’activité physique canadien à l’intention des adultes ; d’autres guides conçus spécifiquement à l’intention des aînés et des enfants ont vu le jour en 1999 et 2002 respectivement. La recherche en sciences de l’activité physique (recherche fondamentale, sur le comportement, sur la relation dose–effet, en épidémiologie, en promotion de la santé et en évaluation de l’activité physique) ne cesse de progresser depuis. Une revue détaillée de la littérature s’avère donc pertinente pour vérifier si les directives et les guides sont toujours d’actualité ou nécessitent d’être mis à jour. Cet article énumère selon une approche chronologique les événements justifiant la préparation de ce numéro spécial pour la revue incluant une prise de position et un aperçu du contenu et de son organisation. Puis, en guise d’introduction aux autres articles, on y lit une brève discussion sur les objectifs des directives et des guides, sur les issues anticipées aux plans biologiques, psychologiques et comportementaux et sur les modalités de suivi.

Research that informs Canada’s physical activity guides: an introductionThis article is part of a supplement entitled Advancing physical activity measurement and guidelines in Canada: a scientific review and evidence-based foundation for the future of Canadian physical activity guidelines co-published by Applied Physiology, Nutrition, and Metabolism and the Canadian Journal of Public Health. It may be cited as Appl. Physiol. Nutr. Metab. 32(Suppl. 2E) or as Can. J. Public Health 98(Suppl. 2)

The Canadian Society for Exercise Physiology (CSEP), in partnership with Health Canada and others, released Canada’s first physical activity guide for adults in 1998, with specific versions for older adults in 1999 and for children and youth in 2002. Research in the physical activity sciences (e.g., basic science, behavioural assessment, dose–response relationships, epidemiology, health messaging, physical activity measurement) has advanced rapidly since these publications. A detailed review of relevant current research is thus required, to assess whether the existing guidelines and resulting guides need revision or renewal. This introductory paper provides a brief chronology of events leading to the preparation of this journal supplement, including a statement of purpose and an overview of organization and content. A brief discussion of the purpose of the physical activity guidelines and guides, intended biological, psychological, and behavioural outcomes, and the way in which guidelines relate to on-going measurement and surveillance is provided as a context for the papers that follow.

Energy substrate utilization during prolonged exercise with and without carbohydrate intake in preadolescent and adolescent girls

Little information is available on energy metabolism during exercise in girls, particularly the contribution of exogenous carbohydrate (CHOexo). The purpose of this study was to determine substrate utilization during exercise with and without CHOexo intake in healthy girls. Twelve-yr-old preadolescent (YG; n = 12) and 14-yr-old adolescent (OG; n = 10) girls consumed flavored water (WT) or 13C-enriched 6% CHO (CT) while cycling for 60 min at ∼70% maximal aerobic power (V̇o2max). Substrate utilization was calculated for the final 15 min of exercise. CHOexo decreased fat oxidation by ∼50% in YG but not in OG ( P < 0.001) and decreased endogenous CHO oxidation by ∼15% in OG but not in YG ( P = 0.006). Endogenous CHO oxidation was lower in YG than in OG regardless of trial ( P ≤ 0.01), whereas fat oxidation was higher in YG only during WT ( P < 0.001). CHOexo oxidation rate was similar between YG and OG (7.1 ± 0.5 and 6.8 ± 0.4 mg·kg−1·min−1, respectively, P = 0.67), contributing ∼19% to total energy expenditure. Serum estradiol levels in all girls correlated with fat ( r = −0.50 to −0.59, P = 0.03 to 0.005) and endogenous CHO oxidation ( r = 0.50 to 0.63, P = 0.03 to 0.005) but not with CHOexo oxidation ( r = −0.09, P = 0.71). We conclude that CHOexo influences endogenous substrate utilization in an age-dependent manner in healthy girls but that total CHOexo oxidation during exercise is not different between YG and OG. Our results also point to potential sex-related differences in energy substrate utilization even during childhood.