Glucose ingestion and substrate utilization during exercise in boys with IDDM

Cardiorespiratory Fitness and Physical Activity in Pediatric Diabetes: A Systemic Review and Meta-Analysis

Importance

It is unclear whether cardiorespiratory fitness (CRF) and physical activity are lower among youths with type 1 diabetes (T1D) and type 2 diabetes (T2D) compared with youths without diabetes.

Objective

To describe the magnitude, precision, and constancy of the differences in CRF and physical activity among youths with and without diabetes.

Data Sources

MEDLINE, Embase, CINAHL, and SPORTDiscus were searched from January 1, 2000, to May 1, 2022, for eligible studies.

Study Selection

Observational studies with measures of CRF and physical activity in children and adolescents aged 18 years or younger with T1D or T2D and a control group were included.

Data Extraction and Synthesis

Data extraction was completed by 2 independent reviewers. A random-effects meta-analysis model was used to estimate differences in main outcomes. The pooled effect estimate was measured as standardized mean differences (SMDs) with 95% CIs. The Preferred Reporting Items for Systematic Review and Meta-Analyses guideline was followed.

Main Outcomes and Measures

The main outcomes were objectively measured CRF obtained from a graded maximal exercise test and subjective or objective measures of physical activity. Subgroup analyses were performed for weight status and measurement type for outcome measures.

Results

Of 7857 unique citations retrieved, 9 studies (755 participants) with measures of CRF and 9 studies (1233 participants) with measures of physical activity for youths with T2D were included; for youths with T1D, 23 studies with measures of CRF (2082 participants) and 36 studies with measures of PA (12 196 participants) were included. Random-effects models revealed that directly measured CRF was lower in youths with T2D (SMD, -1.06; 95% CI, -1.57 to -0.56; I2 = 84%; 9 studies; 755 participants) and in youths with T1D (SMD, -0.39; 95% CI, -0.70 to -0.09; I2 = 89%; 22 studies; 2082 participants) compared with controls. Random-effects models revealed that daily physical activity was marginally lower in youths with T1D (SMD, -0.29; 95% CI, -0.46 to -0.11; I2 = 89%; 31 studies; 12 196 participants) but not different among youths with T2D (SMD, -0.56; 95% CI, -1.28 to 0.16; I2 = 91%; 9 studies; 1233 participants) compared with controls. When analyses were restricted to studies with objective measures, physical activity was significantly lower in youths with T2D (SMD, -0.71; 95% CI, -1.36 to -0.05; I2 = 23%; 3 studies; 332 participants) and T1D (SMD, -0.67; 95% CI, -1.17 to -0.17; I2 = 93%; 12 studies; 1357 participants) compared with controls.

Conclusions and Relevance

These findings suggest that deficits in CRF may be larger and more consistent in youths with T2D compared with youths with T1D, suggesting an increased risk for cardiovascular disease-related morbidity in adolescents with diabetes, particularly among those with T2D. The findings reinforce calls for novel interventions to empower youths living with diabetes to engage in regular physical activity and increase their CRF.

An Overview of Diet and Physical Activity for Healthy Weight in Adolescents and Young Adults with Type 1 Diabetes: Lessons Learned from the ACT1ON Consortium

The prevalence of overweight and obesity in young people with type 1 diabetes (T1D) now parallels that of the general population. Excess adiposity increases the risk of cardiovascular disease, which is already elevated up to 10-fold in T1D, underscoring a compelling need to address weight management as part of routine T1D care. Sustainable weight management requires both diet and physical activity (PA). Diet and PA approaches must be optimized towards the underlying metabolic and behavioral challenges unique to T1D to support glycemic control throughout the day. Diet strategies for people with T1D need to take into consideration glycemic management, metabolic status, clinical goals, personal preferences, and sociocultural considerations. A major barrier to weight management in this high-risk population is the challenge of integrating regular PA with day-to-day management of T1D. Specifically, exercise poses a substantial challenge due to the increased risk of hypoglycemia and/or hyperglycemia. Indeed, about two-thirds of individuals with T1D do not engage in the recommended amount of PA. Hypoglycemia presents a serious health risk, yet prevention and treatment often necessitates the consumption of additional calories, which may prohibit weight loss over time. Exercising safely is a concern and challenge with weight management and maintaining cardiometabolic health for individuals living with T1D and many healthcare professionals. Thus, a tremendous opportunity exists to improve exercise participation and cardiometabolic outcomes in this population. This article will review dietary strategies, the role of combined PA and diet for weight management, current resources for PA and glucose management, barriers to PA adherence in adults with T1D, as well as findings and lessons learned from the Advancing Care for Type 1 Diabetes and Obesity Network (ACT1ON).

Maximal Fat Oxidation During Exercise Is Already Impaired in Pre-pubescent Children With Type 1 Diabetes Mellitus

Objective: We evaluated substrate utilization during submaximal exercise, together with glycemic responses and hormonal counter-regulation to exercise, in children with type 1 diabetes mellitus (T1DM).

Methods: Twelve pre-pubescent children with T1DM and 12 healthy children were matched by sex and age. Participants completed a submaximal incremental exercise test to determine their fat and carbohydrate oxidation rates by indirect calorimetry. Levels of glycemia, glucagon, cortisol, growth hormone, noradrenaline, adrenaline, and insulin were monitored until 120 min post-exercise.

Results: Absolute peak oxygen uptake (VO₂ peak) was significantly lower in the children with T1DM than in the healthy controls (1131.4 ± 102.5 vs. 1383.0 ± 316.6 ml.min⁻¹, p = 0.03). Overall carbohydrate and lipid oxidation rates were the same in the two groups, but for exercise intensities, higher than 50% of VO₂ peak, fat oxidation rate was significantly lower in the children with T1DM. The absolute maximal lipid oxidation rate was significantly lower in the T1DM children (158.1 ± 31.6 vs. 205.4 ± 42.1 mg.min⁻¹, p = 0.005), and they reached a significantly lower exercise power than the healthy controls (26.4 ± 1.2 vs. 35.4 ± 3.3 W, p = 0.03). Blood glucose responses to exercise were negatively correlated with pre-exercise blood glucose concentrations (r = −0.67; p = 0.03).

Conclusion: Metabolic and hormonal responses during sub-maximal exercise are impaired in young children with T1DM.

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.

Carbohydrate supplementation: a critical review of recent innovations

PURPOSE

To critically examine the research on novel supplements and strategies designed to enhance carbohydrate delivery and/or availability.

METHODS

Narrative review.

RESULTS

Available data would suggest that there are varying levels of effectiveness based on the supplement/supplementation strategy in question and mechanism of action. Novel carbohydrate supplements including multiple transportable carbohydrate (MTC), modified carbohydrate (MC), and hydrogels (HGEL) have been generally effective at modifying gastric emptying and/or intestinal absorption. Moreover, these effects often correlate with altered fuel utilization patterns and/or glycogen storage. Nevertheless, performance effects differ widely based on supplement and study design. MTC consistently enhances performance, but the magnitude of the effect is yet to be fully elucidated. MC and HGEL seem unlikely to be beneficial when compared to supplementation strategies that align with current sport nutrition recommendations. Combining carbohydrate with other ergogenic substances may, in some cases, result in additive or synergistic effects on metabolism and/or performance; however, data are often lacking and results vary based on the quantity, timing, and inter-individual responses to different treatments. Altering dietary carbohydrate intake likely influences absorption, oxidation, and and/or storage of acutely ingested carbohydrate, but how this affects the ergogenicity of carbohydrate is still mostly unknown.

CONCLUSIONS

In conclusion, novel carbohydrate supplements and strategies alter carbohydrate delivery through various mechanisms. However, more research is needed to determine if/when interventions are ergogenic based on different contexts, populations, and applications.

Hyperglycemia But Not Hyperinsulinemia Is Favorable for Exercise in Type 1 Diabetes: A Pilot Study

OBJECTIVE

To distinguish the effects of hyperglycemia and hyperinsulinemia on exercise-induced increases in R_d and endogenous glucose production (EGP) in type 1 diabetes.

RESEARCH DESIGN AND METHODS

We studied six participants without diabetes and six participants with type 1 diabetes on three visits in random order for the following: euglycemia, low insulin (EuLoI); euglycemia, high insulin (EuHiI); and hyperglycemia, low insulin (HyLoI). Glucose fluxes were measured using [6,6-²H₂] glucose before, during, and after 60 min of exercise.

RESULTS

R_d increased (P < 0.01) with exercise within groups, while peak R_d during exercise was lower (P < 0.01) in participants with type 1 diabetes than participants without diabetes during all visits. In type 1 diabetes participants, EGP increased (P < 0.001) with exercise during EuLoI and HyLoI but not during EuHiI. This demonstrates that hyperinsulinemia, but not hyperglycemia, blunts the compensatory exercise-induced increase in EGP in type 1 diabetes.

CONCLUSIONS

The data from this pilot study indicate that 1) exercise-induced compensatory increase in EGP was inhibited in participants with type 1 diabetes with hyperinsulinemia but not with hyperglycemia; 2) in contrast, in participants without diabetes, exercise-induced increase in EGP was inhibited only during combined hyperinsulinemia and hyperglycemia. Taken together, these results suggest that low insulin coupled with euglycemia or modest hyperglycemia appear to be the most favorable milieu for type 1 diabetes during exercise.

Exercise Management for Young People With Type 1 Diabetes: A Structured Approach to the Exercise Consultation

Regular physical activity during childhood is important for optimal physical and psychological development. For individuals with Type 1 Diabetes (T1D), physical activity offers many health benefits including improved glycemic control, cardiovascular function, blood lipid profiles, and psychological well-being. Despite these benefits, many young people with T1D do not meet physical activity recommendations. Barriers to engaging in a physically active lifestyle include fear of hypoglycemia, as well as insufficient knowledge in managing diabetes around exercise in both individuals and health care professionals. Diabetes and exercise management is complex, and many factors can influence an individual's glycemic response to exercise including exercise related factors (such as type, intensity and duration of the activity) and person specific factors (amount of insulin on board, person's stress/anxiety and fitness levels). International guidelines provide recommendations for clinical practice, however a gap remains in how to apply these guidelines to a pediatric exercise consultation. Consequently, it can be challenging for health care practitioners to advise young people with T1D how to approach exercise management in a busy clinic setting. This review provides a structured approach to the child/adolescent exercise consultation, based on a framework of questions, to assist the health care professional in formulating person-specific exercise management plans for young people with T1D.

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.

Exercise modes and their association with hypoglycemia episodes in adults with type 1 diabetes mellitus: a systematic review

OBJECTIVE

Type 1 diabetes mellitus rates are rising worldwide. The health benefits of physical exercise in this condition are many, but more than 60% do not participate, mainly from fear of hypoglycemia. This systematic review explores the effects of physical exercise modes on blood glucose levels in adults for hypoglycemia prevention.

RESEARCH DESIGN AND METHODS

Predefined inclusion criteria were randomized or non-randomized cross-over trials of healthy non-obese adults with type 1 diabetes mellitus. Exercise interventions used standardized protocols of intensity and timing. Outcomes included hypoglycemia during or after exercise, and acute glycemic control. Medline, Cumulative Index to Nursing and Allied Health Literature, Allied and Complementary Medicine Database, SPORTDiscus, CochraneCENTRAL (1990 to 11 January 2018), and Embase (1988 to 9 April 2018) were searched using keywords and Medical Subject Heading (MeSH) terms. Inclusions, data extraction and quality assessment using the Critical Appraisal Skills Programme checklists were done by one researcher and checked by a second. Review Manager (V.5.3) was used for meta-analysis where four or more outcomes were reported.

RESULTS

From 5459 citations, we included 15 small cross-over studies (3 non-randomized), 13 assessing aerobic (intermittent high-intensity exercise (IHE) vs continuous, or continuous vs rest) and 2 assessing resistance exercise versus rest. Study quality was good, and all outcome measures were reported. Thirteen gave hypoglycemia results, of which five had no episodes. Meta-analysis of hypoglycemia during or after IHE compared with continuous exercise showed no significant differences (n=5, OR=0.68 (95% CI 0.16 to 2.86), I²=56%). For blood glucose there was little difference between groups at any time point.

CONCLUSION

IHE may be safer than continuous exercise because of lesser decline in blood glucose, but more research needs to demonstrate if this would be reflected in hypoglycemic episode rates.

TRIAL REGISTRATION NUMBER

CRD42018068358.

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.

Glucagon responses to exercise-induced hypoglycaemia are improved by somatostatin receptor type 2 antagonism in a rat model of diabetes

AIMS/HYPOTHESIS

Regular exercise is at the cornerstone of care in type 1 diabetes. However, relative hyperinsulinaemia and a blunted glucagon response to exercise promote hypoglycaemia. Recently, a selective antagonist of somatostatin receptor 2, PRL-2903, was shown to improve glucagon counterregulation to hypoglycaemia in resting streptozotocin-induced diabetic rats. The aim of this study was to test the efficacy of PRL-2903 in enhancing glucagon counterregulation during repeated hyperinsulinaemic exercise.

METHODS

Diabetic rats performed daily exercise for 1 week and were then exposed to saline (154 mmol/l NaCl) or PRL-2903, 10 mg/kg, before hyperinsulinaemic exercise on two separate occasions spaced 1 day apart. In the following week, animals crossed over to the alternate treatment for a third hyperinsulinaemic exercise protocol.

RESULTS

Liver glycogen content was lower in diabetic rats compared with control rats, despite daily insulin therapy (p < 0.05). Glucagon levels failed to increase during exercise with saline but increased three-to-six fold with PRL-2903 (all p < 0.05). Glucose concentrations tended to be higher during exercise and early recovery with PRL-2903 on both days of treatment; this difference did not achieve statistical significance (p > 0.05).

CONCLUSIONS/INTERPRETATION

PRL-2903 improves glucagon counterregulation during exercise. However, liver glycogen stores or other factors limit the prevention of exercise-induced hypoglycaemia in rats with streptozotocin-induced diabetes.

Current perspectives on physical activity and exercise for youth with diabetes

Regular physical activity (PA) for youth with diabetes improves cardiorespiratory fitness, body composition, bone health, insulin sensitivity, and psychosocial well-being. However many youth with diabetes or pre-diabetes fail to meet minimum PA guidelines and a large percentage of youth with diabetes are overweight or obese. Active youth with type 1 diabetes tend to have lower HbA1c levels and reduced insulin needs, whereas activity in adolescents at-risk for type 2 diabetes improves various measures of metabolism and body composition. Insulin and nutrient adjustments for exercise in type 1 diabetes is complex because of varied responses to exercise type and because of the different times of day that exercise is performed. This review highlights the benefits of exercise and the established barriers to exercise participation in the pediatric diabetes population. A new exercise management algorithm for insulin and carbohydrate intake strategies for active youth with type 1 diabetes is presented.

Patients with type 1 diabetes oxidize fat at a greater rate than age- and sex-matched controls

INTRODUCTION

Elevated patient blood glucose and exogenous insulin administration may affect substrate oxidation in patients with type 1 diabetes mellitus (T1DM); however, this has not been demonstrated with conviction. We examined substrate oxidation during incremental exercise in a group of subjects with T1DM and compared the results to those of an age- and sex-matched control group of subjects.

METHODS

A group of subjects with T1DM (n = 29; 10 men, 19 women) was recruited for metabolic testing from a weeklong fitness camp. An age- and sex-matched control group of subjects (n = 29; 10 men, 19 women) was recruited from the local community. Subjects were required to avoid strenuous exercise for 48 hours and fast for 2 hours prior to metabolic testing. An incremental test to exhaustion on either a stationary cycle or treadmill was administered to all subjects. Maximum oxygen consumption of subjects was measured (T1DM subjects: 41.4 ± 1.9 mL/kg/min; control subjects: 48.4 ± 1.3 mL/kg/min). Blood glucose was recorded at 20 and 5 minutes before the exercise test, and at 5 and 20 minutes after the exercise test.

RESULTS

The T1DM and control subjects were matched for age, height, weight, and body composition. Subject blood glucose levels were higher in the group of subjects with T1DM than the control group at all times measured (P < 0.001). At all relative intensities of exercise (50%-80% maximum oxygen consumption; P < 0.050), absolute fat oxidation was higher in the group of subjects with T1DM (P < 0.050) and absolute carbohydrate oxidation was higher in the control group.

CONCLUSION

Our data indicate that subjects with T1DM oxidize fat at a higher rate and carbohydrates at a lower rate when compared with age- and sex-matched controls at the same relative intensity of exercise, despite the elevated pre-exercise blood glucose of subjects with T1DM.

Whole-body glucose oxidation rate during prolonged exercise in type 1 diabetic patients under usual life conditions

OBJECTIVE

Fuel oxidation during exercise was studied in type 1 insulin-dependent (T1DM) patients mainly under quite constant insulin and glycemia; these protocols, however, likely do not reflect patients' usual metabolic conditions. The glucose oxidation rate (GLUox) in T1DM patients under usual life conditions was thus investigated during prolonged exercise (3-h) and its behavior was described mathematically.

MATERIALS/METHODS

Whole-body GLUox was determined in eight T1DM patients (4/8 M; aged 35-59 years) and eight well-matched healthy subjects. Venous blood was drawn prior to and every 30 min until the end of exercise; glycemia, insulin, cortisol, and growth hormone concentrations were determined. Oxygen consumption, carbon dioxide production, and ventilation were measured at rest and thereafter every 30 min of the exercise. To prevent hypoglycemia, patients were given fruit fudge (93% sucrose) prior to / during exercise.

RESULTS

Insulin concentration and glycemia were significantly higher in patients across the entire exercise period (group effect, p<0.001 for both). GLUox decreased significantly with increasing exercise duration (time effect, p<0.001), but no significant difference was detected between the two groups (group effect, p=NS). GLUox, expressed as the percentage of the starting value, was described by an exponential function showing a time constant of 90 min (n=96; mean corrected R(2)=0.666).

CONCLUSIONS

GLUox in T1DM patients was not significantly different from the rate observed in the control subjects. The function describing the time course of GLUox may be useful to correct an estimated GLUox for the duration of exercise and help T1DM patients avoiding exercise-induced glycemic imbalances.

Orange juice limits postprandial fat oxidation after breakfast in normal-weight adolescents and adults

Caloric beverages may promote weight gain by simultaneously increasing total energy intake and limiting fat oxidation. During moderate intensity exercise, caloric beverage intake depresses fat oxidation by 25% or more. This randomized crossover study describes the impact of having a caloric beverage with a typical meal on fat oxidation under resting conditions. On 2 separate days, healthy normal-weight adolescents (n = 7) and adults (n = 10) consumed the same breakfast with either orange juice or drinking water and sat at rest for 3 h after breakfast. The meal paired with orange juice was 882 kJ (210 kcal) higher than the meal paired with drinking water. Both meals contained the same amount of fat (12 g). For both age groups, both meals resulted in a net positive energy balance 150 min after breakfast. Resting fat oxidation 150 min after breakfast was significantly lower after breakfast with orange juice, however. The results suggest that, independent of a state of energy excess, when individuals have a caloric beverage instead of drinking water with a meal, they are less likely to oxidize the amount of fat consumed in the meal before their next meal.

Continuous moderate-intensity exercise with or without intermittent high-intensity work: effects on acute and late glycaemia in athletes with Type 1 diabetes mellitus

AIMS

Individuals with Type 1 diabetes mellitus are susceptible to hypoglycaemia during and after continuous moderate-intensity exercise, but hyperglycaemia during intermittent high-intensity exercise. The combination of both forms of exercise may have a moderating effect on glycaemia in recovery. The aims of this study were to compare the physiological responses and associated glycaemic changes to continuous moderate-intensity exercise vs. continuous moderate-intensity exercise + intermittent high-intensity exercise in athletes with Type 1 diabetes.

METHODS

Interstitial glucose levels were measured in a blinded fashion in 11 trained athletes with Type 1 diabetes during two sedentary days and during 2 days in which 45 min of afternoon continuous moderate-intensity exercise occurred either with or without intermittent high-intensity exercise. The total amount of work performed and the duration of exercise was identical between sessions.

RESULTS

During exercise, heart rate, respiratory exchange ratio, oxygen utilization, ventilation and blood lactate levels were higher during continuous moderate-intensity + intermittent high-intensity exercise vs. continuous moderate-intensity exercise (all P < 0.05). Despite these marked cardiorespiratory differences between trials, there was no difference in the reduction of interstitial glucose or plasma glucose levels between the exercise trials. Nocturnal glucose levels were higher in continuous moderate-intensity + intermittent high-intensity exercise and in sedentary vs. continuous moderate-intensity exercise (P < 0.05). Compared with continuous moderate-intensity exercise alone, continuous moderate-intensity + intermittent high-intensity exercise was associated with less post-exercise hypoglycaemia (5.2 vs. 1.5% of the time spent with glucose < 4.0 mmol/l) and more post-exercise hyperglycaemia (33.8 vs. 20.4% of time > 11.0 mmol/l).

CONCLUSIONS

Although the decreases in glucose level during continuous moderate-intensity exercise and continuous moderate-intensity + intermittent high-intensity exercise are similar, the latter form of exercise protects against nocturnal hypoglycaemia in athletes with Type 1 diabetes.

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.

Exercise and glucose metabolism in persons with diabetes mellitus: perspectives on the role for continuous glucose monitoring

Exercise causes profound changes in glucose homeostasis. For people with type 1 diabetes, aerobic exercise usually causes blood glucose concentration to drop rapidly, while anaerobic exercise may cause it to rise, thereby making glycemic control challenging. Having the capacity to know their glucose levels and the direction of change during exercise increases self-efficacy in these persons who are prone to hypo- and hyperglycemia. For people with type 2 diabetes, learning first hand that regular exercise improves glucose levels may be a motivating factor in getting them to be more active. Continuous glucose monitoring is a potentially useful adjunct to diabetes management for the active person with either forms of diabetes. This review aims to guide the reader to use this technology to its maximum advantage by providing an overview of technical features, performance characteristics, and clinical utility, all balanced against the limitations that may be more prominent during physical activity.

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.

Fat and carbohydrate metabolism during submaximal exercise in children

During exercise, the contribution of fat and carbohydrate to energy expenditure is largely modulated by the intensity of exercise. Age, a short- or long-term diet enriched in carbohydrate or fat substrate stores, training and gender are other factors that have also been found to affect this balance. These factors have been extensively studied in adults from the perspective of improving performance in athletes, or from a health perspective in people with diseases. During the last decade, lifestyle changes associated with high-energy diets rich in lipid and reduced physical activity have contributed to the increase in childhood obesity. This lifestyle change has emerged as a serious health problem favouring the early development of cardiovascular diseases, insulin resistance or type 2 diabetes mellitus. Increasing physical activity levels in young people is important to increase energy expenditure and promote muscle oxidative capacity. Therefore, it is surprising that the regulation of balance between carbohydrate and lipid use during exercise has received much less attention in children than in adults. In this review, we have focused on the factors that affect carbohydrate and lipid metabolism during exercise and have identified areas that may be relevant in explaining the higher contribution of lipid to energy expenditure in children when compared with adults. Low muscle glycogen content is possibly associated with a low activity of glycolytic enzymes and high oxidative capacity, while lower levels of sympathoadrenal hormones are likely to favour lipid metabolism in children. Changes in energetic metabolism occurring during adolescence are also dependent on pubertal events with an increase in testosterone in boys and estrogen and progesterone in girls. The profound effects of ovarian hormones on carbohydrate and fat metabolism along with their effects on oxidative enzymes could explain that differences in substrate metabolism have not always been observed between girls and women. Finally, although the regulatory mechanisms of fat and carbohydrate balance during exercise are quite well identified, there are a lack of data specific to children and most of the evidences reported in this review were drawn from studies in adults. Isotope tracer techniques and nuclear magnetic resonance will allow non-invasive investigation of the metabolism of the different substrate sources in skeletal muscle.

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.

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.

Substrate source utilization during moderate intensity exercise with glucose ingestion in Type 1 diabetic patients

Substrate oxidation and the respective contributions of exogenous glucose, glucose released from the liver, and muscle glycogen oxidation were measured by indirect respiratory calorimetry combined with tracer technique in eight control subjects and eight diabetic patients (5 men and 3 women in both groups) of similar age, height, body mass, and maximal oxygen uptake, over a 60-min exercise period on cycle ergometer at 50.8% (SD 4.0) maximal oxygen uptake [131.0 W (SD 38.2)]. The subjects and patients ingested a breakfast (containing ∼80 g of carbohydrates) 3 h before and 30 g of glucose (labeled with 13C) 15 min before the beginning of exercise. The diabetic patients also received their usual insulin dose [Humalog = 9.1 U (SD 0.9); Humulin N = 13.9 U (SD 4.4)] immediately before the breakfast. Over the last 30 min of exercise, the oxidation of carbohydrate [1.32 g/min (SD 0.48) and 1.42 g/min (SD 0.63)] and fat [0.33 g/min (SD 0.10) and 0.30 g/min (SD 0.10)] and their contribution to the energy yield were not significantly different in the control subjects and diabetic patients. Exogenous glucose oxidation was also not significantly different in the control subjects and diabetic patients [6.3 g/30 min (SD 1.3) and 5.2 g/30 min (SD 1.6), respectively]. In contrast, the oxidation of plasma glucose and oxidation of glucose released from the liver were significantly lower in the diabetic patients than in control subjects [14.5 g/30 min (SD 4.3) and 9.3 g/30 min (SD 2.8) vs. 27.9 g/30 min (SD 13.3) and 21.6 g/30 min (SD 12.8), respectively], whereas that of muscle glycogen was significantly higher [28.1 g/30 min (SD 15.5) vs. 11.6 g/30 min (SD 8.1)]. These data indicate that, compared with control subjects, in diabetic patients fed glucose before exercise, substrate oxidation and exogenous glucose oxidation overall are similar but plasma glucose oxidation is lower; this is associated with a compensatory higher utilization of muscle glycogen.

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

Substrate utilization during exercise is known to differ between children and adults, but whether these differences are related to pubertal status is unclear. The objective of this study was to investigate the effects of pubertal status on endogenous (CHOendo) and orally ingested exogenous (CHOexo) carbohydrate and fat oxidation rates during exercise. Twenty boys at the same chronological age (12 y) were divided into three pubertal groups (pre-pubertal, PP: n = 7; early-pubertal, EP: n = 7; mid- to late-pubertal, M-LP: n = 6) and consumed either a placebo or13C-enriched 6% CHO drink while cycling for 60 min at ~70% of their maximal aerobic power (VO2 max). Another group of 14-year-old boys (pubertal, n = 9) completed all procedures. Substrate utilization was calculated for the final 15 min of exercise using indirect calorimetry and stable isotope methodology. CHOexodecreased fat (p < 0.001) and increased total CHO (p < 0.001) oxidation, irrespective of group. Fat oxidation was higher (p = 0.01) in younger boys than in older boys, but similar (p ≥ 0.33) among PP, EP, and M-LP boys. CHOexocontributed to ~30% of energy expenditure (EE) in PP and EP, but to only 24% in M-LP (p = 0.02), which was identical to the older boys (24%). CHOexooxidation rate as a percentage of EE was inversely related to testosterone levels (r = −0.51, p = 0.005, n = 29). It was concluded that reliance on CHOexoduring exercise is particularly sensitive to pubertal status, with the highest oxidation rates observed in pre- and early-pubertal boys, independent of chronological age.

Role of physical exercise in children and adolescents with diabetes mellitus

During the past 50 years several studies have underlined the central role of physical exercise in the management of patients with both type 1 and type 2 diabetes mellitus. The numerous benefits described in normal individuals who practise regular exercise have also been demonstrated in patients with diabetes who obtained significant physical and psychological advantages for the care of the underlying disease. Despite physical and psychological benefits, the occurrence of acute complications and some important effects on diabetes-related vascular complications may often discourage patients from participation in sports activities. However, even though adverse events may occur, exercise is still judged one of the most important components in the treatment of patients with diabetes. Thus, children, adolescents and young adults with diabetes must be educated on the metabolic changes occurring during physical activity in order to be able to acquire the ability to individually modulate their diet and insulin therapy before and after exercise. Appropriate education may allow a proper and correct approach to physical exercise.

Substrate oxidation during exercise: type 2 diabetes is associated with a decrease in lipid oxidation and an earlier shift towards carbohydrate utilization

OBJECTIVES

Exercise is a recommended treatment for type 2 diabetes but the actual pattern of metabolic adaptation to exercise in this disease is poorly known and not taken in account in the protocols used. Metabolic defects involved in the pathways of substrate oxidation were described in type 2 diabetes. We hypothesized that type 2 diabetes, regardless of age, gender, training status and weight, could influence by its own the balance of substrates at exercise.

METHODS

30 sedentary type 2 diabetic subjects and 38 sedentary matched control subjects were recruited. We used exercise calorimetry to determine lipid and carbohydrate oxidation rates. We calculated two parameters quantifying the balance of substrates induced by increasing exercise intensity: the maximal lipid oxidation point (PLipoxMax) and the Crossover point (COP), intensity from which the part of carbohydrate utilization providing energy becomes predominant on lipid oxidation.

RESULTS

Lipid oxidation was lower in the diabetic group, independent of exercise intensity. PLipoxMax and COP were lower in the diabetic group [PLipoxMax=25.3+/-1.4% vs. 36.6+/-1.7% %Wmax (P<0.0001)] - COP =24.2+/-2.2% vs. 38.8+/-1.9% %Wmax (P<0.0001).

CONCLUSIONS

Type 2 diabetes is associated with a decrease in lipid oxidation at exercise and a shift towards a predominance of carbohydrate oxidation for exercise intensities lower than in control subjects. Taking into account these alterations could provide a basis for personalizing training intensity.

Physical activity, sport, and pediatric diabetes

The benefits derived from regular physical activity include improved cardiovascular fitness, increased lean mass, improved blood lipid profile, enhanced psychosocial well-being, and decreased body adiposity. The benefits for children with diabetes may also include blood glucose control and enhanced insulin sensitivity. However, for these children, engagement in vigorous physical activity and sport must be properly controlled through modifications in insulin therapy and nutritional intake so that the benefits of exercise outweigh the risks. The following review describes the various physiological and metabolic factors which occur both during exercise and during sport while describing specific recommendations to control glucose excursions by proper insulin management and diet.

Impact of exercise on overnight glycemic control in children with type 1 diabetes mellitus

OBJECTIVE

To examine the effect of exercise on overnight hypoglycemia in children with type 1 diabetes mellitus (T1DM).

STUDY DESIGN

At 5 clinical sites, 50 subjects with T1DM (age 11 to 17 years) were studied in a clinical research center on 2 separate days. One day included an afternoon exercise session on a treadmill. On both days, frequently sampled blood glucose levels were measured at the DirecNet central laboratory. Insulin doses were similar on both days.

RESULTS

During exercise, plasma glucose levels fell in almost all subjects; 11 (22%) developed hypoglycemia. Mean glucose level from 10 pm to 6 am was lower on the exercise day than on the sedentary day (131 vs 154 mg/dL; P=.003). Hypoglycemia developed overnight more often on the exercise nights than on the sedentary nights (P=.009), occurring on the exercise night only in 13 (26%), on the sedentary night only in 3 (6%), on both nights in 11 (22%), and on neither night in 23 (46%). Hypoglycemia was unusual on the sedentary night if the pre-bedtime snack glucose level was>130 mg/dL.

CONCLUSIONS

These findings indicate that overnight hypoglycemia after exercise is common in children with T1DM and support the importance of modifying diabetes management after afternoon exercise to reduce the risk of hypoglycemia.

Exercise with and without an insulin pump among children and adolescents with type 1 diabetes mellitus

BACKGROUND

The use of insulin pumps is becoming a popular technique for insulin delivery among patients with type 1 diabetes mellitus (T1DM), but there is no consensus regarding the guidelines for proper pump use during exercise.

OBJECTIVE

To investigate the physiologic responses and risk of hypoglycemia among children and adolescents with T1DM when exercising with the pump on (PO) (50% of the basal rate) or pump off (PF).

METHODS

Ten subjects with T1DM (6 female subjects and 4 male subjects), 10 to 19 years of age, performed prolonged exercise (40-45 minutes) on a cycle ergometer approximately 2 hours after a standard breakfast and an insulin (Lispro) bolus. Complex carbohydrates (20 g) were provided before and after the exercise. Each patient exercised once with PO and once with PF, in a randomized, crossover (single-blind) manner. During exercise and 45 minutes of recovery, subjects were monitored for cardiorespiratory, metabolic, and hormonal responses. Blood glucose concentrations were recorded for 24 hours after exercise, with a continuous glucose monitoring system, to document late hypoglycemic events.

RESULTS

During exercise, blood glucose concentrations decreased by 59 +/- 58 mg/dL (mean +/- SD: 29 +/- 24%) with PF and by 74 +/- 51 mg/dL (35.5 +/- 18%) with PO (not significant). No significant differences were found in cortisol, growth hormone, or noradrenaline levels between PO and PF. There were no differences in cardiorespiratory parameters, blood lactate concentrations, or free fatty acids concentrations between pump modes. Hypoglycemic events during exercise were asymptomatic and occurred for 2 subjects with PO and 2 with PF. Nine subjects had late hypoglycemia after PO, compared with 6 after PF (not significant).

CONCLUSIONS

We found no advantage for subjects with either PO or PF during exercise, and we noted that late hypoglycemia was more common than hypoglycemia during exercise. However, PO was associated with a trend of increased risk for late hypoglycemia. We recommend that the pump be removed or turned off during prolonged exercise and that blood glucose concentrations be monitored for several hours after exercise, regardless of the pump mode.

Efeito da hidratação com carboidratos na resposta glicêmica de diabéticos tipo 1 durante o exercício

Não está claro se a ingestão de carboidratos (CHO) através de bebidas esportivas pode manter a glicemia em diabéticos tipo 1. A finalidade deste estudo foi examinar a glicemia em adolescentes com diabetes tipo 1 que ingeriram bebidas esportivas com 6% de CHO durante e após o exercício. Dez adolescentes (5 meninas e 5 meninos, 15,3 ± 2,4 anos) com o diabetes controlado (HbA1c < 12%), e sem complicações da doença, exercitaram-se em um cicloergômetro a 55-60% do pico máximo de consumo de O2 (VO2pico) durante 60 minutos em dois dias separados. Em ordem randomizada e desenho duplo-cego, os sujeitos ingeriram (5ml·kg-1 antes do exercício, e 2ml·kg-1 a cada 15 minutos de exercício) bebida esportiva com 6% de CHO ou água com sabor sem CHO (placebo) com cor e sabor similares aos da bebida esportiva. Após uma hora de exercício, a glicemia não diminuiu significativamente quando foi ministrada bebida esportiva (CHO-6%) (221,0 ± 78 para 200,5 ± 111mg·dL-1, p > 0,05), e diminuiu significativamente na situação placebo (282,9 ± 85 para 160,2 ± 77mg·dL-1, p < 0,05) (9 vs. 43,2%). Após 30 minutos de recuperação, a glicemia foi de 177,2 ± 107mg·dL-1 com CHO e 149,1 ± 69,6mg·dL-1 com placebo, representando 20,1% e 47,3% dos níveis pré-exercício. Não foram encontradas diferenças significativas entre as situações na freqüência cardíaca, taxa de percepção de esforço, na insulina e eletrólitos sanguíneos. Não foram encontradas alterações no hematócrito e hemoglobina durante o exercício, indicando que os sujeitos permaneceram euidratados. Em conclusão, o uso de bebidas contendo 6% de CHO atenuou a redução da glicemia induzida pelo exercício em adolescentes com diabetes tipo 1.

Benefit and risk of exercise on myocardial function in diabetes

Regular physical activity promotes cardiorespiratory fitness and has been considered a cornerstone for non-pharmacological treatment of more than 17 million Americans with diabetes mellitus. Physical exercise has been shown to positively affect certain cardiovascular risk factors such as insulin resistance, glucose metabolism, blood pressure and body fat composition, which are closely associated with diabetes and heart disease. With the increasingly sedentary life style in our society, routine daily exercise of moderate intensity is highly recommended to reduce cardiovascular risk, the leading cause of death in diabetic patients. Exercise produces many beneficial effects to the heart function such as reduced incidence of coronary heart disease, attenuated severity of diabetic cardiomyopathy, improved cardiac performance, cardiac reserve and autonomic regulation. Nevertheless, many diabetic patients do not appear to gain much benefit from exercise or may even be at risk of performing physical exercise. This review summarizes the benefit and risk of exercise on diabetic heart function, with a special emphasis on myocardial and autonomic function.

Altered energetic properties in skeletal muscle of men with well-controlled insulin-dependent (type 1) diabetes

This study asked whether the energetic properties of muscles are changed by insulin-dependent diabetes mellitus (or type 1 diabetes), as occurs in obesity and type 2 diabetes. We used (31)P magnetic resonance spectroscopy to measure glycolytic flux, oxidative flux, and contractile cost in the ankle dorsiflexor muscles of 10 men with well-managed type 1 diabetes and 10 age- and activity-matched control subjects. Each subject performed sustained isometric muscle contractions lasting 30 and 120 s while attempting to maintain 70-75% of maximal voluntary contraction force. An altered glycolytic flux in type 1 diabetic subjects relative to control subjects was apparent from significant differences in pH in muscle at rest and at the end of the 120-s bout. Glycolytic flux during exercise began earlier and reached a higher peak rate in diabetic patients than in control subjects. A reduced oxidative capacity in the diabetic patients' muscles was evident from a significantly slower phosphocreatine recovery from a 30-s exercise bout. Our findings represent the first characterization of the energetic properties of muscle from type 1 diabetic patients. The observed changes in glycolytic and oxidative fluxes suggest a diabetes-induced shift in the metabolic profile of muscle, consistent with studies of obesity and type 2 diabetes that point to common muscle adaptations in these diseases.

Effect of water polo practice on cytokines, growth mediators, and leukocytes in girls

PURPOSE

The effects of exercise on growth and development are mediated through a complex interaction between the endocrine, immune, and nervous systems. Very little is known about how these systems respond to exercise in children or adolescents. Moreover, there are few studies that have examined growth factors, inflammatory cytokines, and leukocyte responses to "real-life" or field exercise solely in girls. Thus, the goal of the present study was to determine the acute exercise-induced alterations in the growth hormone --> insulin-like growth factor-I axis, inflammatory cytokines, and certain aspects of immune function in a group of adolescent girls after a typical water polo practice.

METHODS

Ten, healthy, high-school female subjects, 14-16 yr old, performed a single, typical, 1.5-h water polo practice session. Blood was sampled before and after the session.

RESULTS

The exercise resulted in an increase in HR (from 82 +/- 2 to 161 +/- 5 beats.min(-1) at 30 min, P < 1.4.10(-6) ), as well as in circulating lactate levels (375 +/- 66%, P < 0.0005). Significant increases where noted in circulating IL-6 (396 +/- 162%, P < 0.005) and IL-1ra (71 +/- 20%, P < 0.015). A substantial increase in the level of IGFBP-1 (1344 +/- 344%, P < 0.001) was also observed. Interestingly, TNF-alpha levels decreased after the exercise (-10.4 +/- 3.8%, P < 0.04) as did insulin (55 +/- 12%, P < 0.005). The exercise led to significant increases in granulocytes, monocytes, and lymphocytes. The exercise significantly influenced adhesion molecules (such as CD62L and CD54), which has not been previously studied in adolescent girls.

CONCLUSIONS

These data demonstrate that an intense "real-life" exercise bout in adolescent females leads to profound increases in inflammatory cytokines and reductions in anabolic mediators with substantial alterations in white blood cell subpopulations and adhesion molecules. The role of these frequent, almost daily immune and cytokine changes on growth and development have yet to be determined.

Oxidation rate of exogenous carbohydrate during exercise is higher in boys than in men

To determine whether the relative utilization of exogenous carbohydrate (CHO(exo)) differs between children and adults, substrate utilization during 60 min of cycling at 70% peak O(2) uptake was studied in 12 pre- and early pubertal boys (9.8 +/- 0.1 yr) and 10 men (22.1 +/- 0.5 yr) on two occasions. Subjects consumed either a placebo or a (13)C-enriched 6% CHO(exo) beverage (total volume per trial: 24 ml/kg). Substrate utilization was calculated for the final 30 min of exercise. During both trials, total fat oxidation was higher (5.4 +/- 0.5 vs. 3.0 +/- 0.4 mg x kg(-1) x min(-1), P < 0.001) and total CHO oxidation lower (27.4 +/- 1.5 vs. 34.8 +/- 1.2 mg x kg(-1) x min(-1), P < 0.001) in boys than in men, respectively. During the CHO(exo) trial, CHO(exo) oxidation was higher (P < 0.001) in boys (8.8 +/- 0.5 mg x kg(-1) x min(-1)) than in men (6.2 +/- 0.5 mg x kg(-1) x min(-1)) and provided a greater (P < 0.001) relative proportion of total energy in boys (21.8 +/- 1.4%) than in men (14.6 +/- 0.9%). These results suggest that, although endogenous CHO utilization during exercise is lower, the relative oxidation of ingested CHO is considerably higher in boys than in men. The greater reliance on CHO(exo) in boys may be important in preserving endogenous fuels and may be related to pubertal status.

Effect of intense exercise on inflammatory cytokines and growth mediators in adolescent boys

OBJECTIVE

Exercise can enhance growth and development in children, but recent investigations have revealed an intriguing paradox. Namely, the early (4-5 weeks) response to training programs in children lead to a catabolic, growth hormone (GH)-resistant state rather than the expected anabolic activation of the GH-->insulin-like growth factor-I (IGF-I) axis. This paradox led us to hypothesize that single bouts of exercise in children could stimulate proinflammatory cytokines known to inhibit directly anabolic activity of the GH-->IGF-1 axis (interleukin [IL]-6, IL-1beta, and tumor necrosis factor-alpha [TNF-alpha]).

METHODS

Eleven healthy high school-age boys, age 14 to 18.5 years, performed a single, typical, 1.5-hour wrestling practice session. Blood was sampled before and after the session.

RESULTS

We found significant decreases in anabolic mediators: total IGF-I (-11.2 +/- 2.3%), bound IGF-I (-11.2 +/- 2.4%), and insulin (-42 +/- 10%. However, there was no change in unbound IGF-I. Remarkable increases were found in proinflammatory cytokines IL-6 (795 +/- 156%), TNF-alpha (30 +/- 12%), and IL-1beta (286 +/- 129%) and in IGF-binding protein-1 (835 +/- 234%), which itself is stimulated by inflammatory cytokines and is known to inhibit IGF-I. Evidence for compensatory mechanisms to counter the antianabolic inflammatory response to acute exercise were also noted: IL-1ra increased (80 +/- 20%) and IGF-binding protein-3 proteolysis (which can maintain unbound, biologically active IGF-I despite losses in total IGF-I) increased significantly (101 +/- 39%) as well.

CONCLUSIONS

These data demonstrate that an intense exercise bout in male adolescents leads to reductions in anabolic mediators and profound increases in inflammatory cytokines. This might explain the development of what seems to be a paradoxical catabolic state in the initial phases of exercise training programs.

Substrate utilization during exercise with glucose and glucose plus fructose ingestion in boys ages 10--14 yr

We measured substrate utilization during exercise performed with water (W), exogenous glucose (G), and exogenous fructose plus glucose (FG) ingestion in boys age 10-14 yr. Subjects (n = 12) cycled for 90 min at 55% maximal O(2) uptake while ingesting either W (25 ml/kg), 6% G (1.5 g/kg), or 3% F plus 3% G (1.5 g/kg). Fat oxidation increased during exercise in all trials but was higher in the W (0.28 +/- 0.023 g/min) than in the G (0.24 +/- 0.023 g/min) and FG (0.25 +/- 0.029 g/min) trials (P = 0.04). Conversely, total carbohydrate (CHO) oxidation decreased in all trials and was lower in the W (0.63 +/- 0.05 g/min) than in the G (0.78 +/- 0.051 g/min) and FG (0.74 +/- 0.056 g/min) trials (P = 0.009). Exogenous CHO oxidation, as determined by expired (13)CO(2), reached a maximum of 0.36 +/- 0.032 and 0.31 +/- 0.030 g/min at 90 min in G and FG, respectively (P = 0.04). Plasma insulin levels decrease during exercise in all trials but were twofold higher in G than in W and FG (P < 0.001). Plasma glucose levels decreased transiently after the onset of exercise in all trials and then returned to preexercise values in the W and FG (approximately 4.5 mmol/l) trials but were elevated by approximately 1.0 mmol/l in the G trial (P < 0.001). Plasma lactate concentrations decreased after the onset of exercise in all trials but were lower by approximately 0.5 mmol/l in W than in G and FG (P = 0.02). Thus, in boys exercising at a moderate intensity, the oxidation rate of G plus F is slightly less than G alone, but both spare endogenous CHO and fat to a similar extent. In addition, compared with flavored W, the ingestion of G alone and of G plus F delays exhaustion at 90% peak power by approximately 25 and 40%, respectively, after 90 min of moderate-intensity exercise.