Impact of high- and low-intensity targeted exercise training on the type of substrate utilization in obese boys submitted to a hypocaloric diet

Toward Exercise Guidelines for Optimizing Fat Oxidation During Exercise in Obesity: A Systematic Review and Meta-Regression

BACKGROUND

Exercise training performed at maximal fat oxidation (FATmax) is an efficient non-pharmacological approach for the management of obesity and its related cardio-metabolic disorders.

OBJECTIVES

Therefore, this work aimed to provide exercise intensity guidelines and training volume recommendations for maximizing fat oxidation in patients with obesity.

METHODS

A systematic review of original articles published in English, Spanish or French languages was carried out in EBSCOhost, PubMed and Scopus by strictly following the Preferred Reporting Items for Systematic reviews and Meta-Analyses (PRISMA) statement. Those studies that analyzed maximal fat oxidation (MFO) and FATmax in patients with obesity (body fat > 25% for men; > 35% for women) by calculating substrate oxidation rates through indirect calorimetry during a graded exercise test with short-duration stages (< 10 min) were selected for quantitative analysis. The accuracy of relative oxygen uptake (% peak oxygen uptake [%[Formula: see text]O2peak]) and relative heart rate (% peak heart rate [%HRpeak]) for establishing FATmax reference values was investigated by analyzing their intra-individual and inter-study variation. Moreover, cluster analysis and meta-regression were used for determining the influence of biological factors and methodological procedures on MFO and FATmax.

RESULTS

Sixty-four manuscripts were selected from 146 records; 23 studies only recruited men (n = 465), 14 studies only evaluated women (n = 575), and 27 studies included individuals from both sexes (n = 6434). The majority of the evaluated subjects were middle-aged adults (aged 40-60 y; 84%) with a poor cardiorespiratory fitness (≤ 43 mL·kg-1·min-1; 81%), and the reported MFO ranged from 0.27 to 0.33 g·min-1. The relative heart rate at FATmax (coefficient of variation [CV]: 8.8%) showed a lower intra-individual variation compared with relative oxygen uptake (CV: 17.2%). Furthermore, blood lactate levels at FATmax ranged from 1.3 to 2.7 mmol·L-1 while the speed and power output at FATmax fluctuated from 4 to 5.1 km·h-1 and 42.8-60.2 watts, respectively. Age, body mass index, cardiorespiratory fitness, FATmax, the type of ergometer and the stoichiometric equation used to calculate the MFO independently explained MFO values (R2 = 0.85; p < 0.01). The MFO in adolescents was superior in comparison with MFO observed in young and middle-aged adults. On the other hand, the MFO was higher during treadmill walking in comparison with stationary cycling. Body fat and MFO alone determined 29% of the variation in FATmax (p < 0.01), noting that individuals with body fat > 35% showed a heart rate of 61-66% HRpeak while individuals with < 35% body fat showed a heart rate between 57 and 64% HRpeak. Neither biological sex nor the analytical procedure for computing the fat oxidation kinetics were associated with MFO and FATmax.

CONCLUSION

Relative heart rate rather than relative oxygen uptake should be used for establishing FATmax reference values in patients with obesity. A heart rate of 61-66% HRpeak should be recommended to patients with > 35% body fat while a heart rate of 57-64% HRpeak should be recommended to patients with body fat < 35%. Moreover, training volume must be higher in adults to achieve a similar fat oxidation compared with adolescents whereas exercising on a treadmill requires a lower training volume to achieve significant fat oxidation in comparison with stationary cycling.

Beyond the Calorie Paradigm: Taking into Account in Practice the Balance of Fat and Carbohydrate Oxidation during Exercise?

Recent literature shows that exercise is not simply a way to generate a calorie deficit as an add-on to restrictive diets but exerts powerful additional biological effects via its impact on mitochondrial function, the release of chemical messengers induced by muscular activity, and its ability to reverse epigenetic alterations. This review aims to summarize the current literature dealing with the hypothesis that some of these effects of exercise unexplained by an energy deficit are related to the balance of substrates used as fuel by the exercising muscle. This balance of substrates can be measured with reliable techniques, which provide information about metabolic disturbances associated with sedentarity and obesity, as well as adaptations of fuel metabolism in trained individuals. The exercise intensity that elicits maximal oxidation of lipids, termed LIPOXmax, FATOXmax, or FATmax, provides a marker of the mitochondrial ability to oxidize fatty acids and predicts how much fat will be oxidized over 45–60 min of low- to moderate-intensity training performed at the corresponding intensity. LIPOXmax is a reproducible parameter that can be modified by many physiological and lifestyle influences (exercise, diet, gender, age, hormones such as catecholamines, and the growth hormone-Insulin-like growth factor I axis). Individuals told to select an exercise intensity to maintain for 45 min or more spontaneously select a level close to this intensity. There is increasing evidence that training targeted at this level is efficient for reducing fat mass, sparing muscle mass, increasing the ability to oxidize lipids during exercise, lowering blood pressure and low-grade inflammation, improving insulin secretion and insulin sensitivity, reducing blood glucose and HbA_1c in type 2 diabetes, and decreasing the circulating cholesterol level. Training protocols based on this concept are easy to implement and accept in very sedentary patients and have shown an unexpected efficacy over the long term. They also represent a useful add-on to bariatric surgery in order to maintain and improve its weight-lowering effect. Additional studies are required to confirm and more precisely analyze the determinants of LIPOXmax and the long-term effects of training at this level on body composition, metabolism, and health.

Substrate Oxidation Is Altered by Obesity During Submaximal Cycling in Prepubertal and Early Pubertal Children: A Quality Study

BACKGROUND

To examine substrate oxidation in prepubertal and early pubertal children as a function of body weight, body composition, and sex during an exhaustive cycling test.

METHODS

This study included 320 children in prepubertal and early puberty (Tanner stage 1 or 2; n = 188 males) who completed a minimum of 4 stages (2-5 min/stage) of an adapted version of the McMaster exhaustive exercise protocol on an upright cycle ergometer. Substrate utilization, relative to individual VO2peak, was determined using VO2 and VCO2 data, obtained with breath-by-breath gas analysis during exercise.

RESULTS

Both peak (mg/kg lean body mass·min) and submaximal lipid oxidation (mg/kg lean body mass·min) were highest (P < .01) in children with healthy weight (HW), then overweight, and lowest in obese (OB). Both females with HW (compared with males with HW) and females with OB (compared with males with OB) had higher (P < .01) peak and submaximal lipid oxidation. In children with OB, fat-free mass correlated positively (P < .01) with submaximal lipid oxidation (r = .50). In contrast, in children with HW and overweight, fat-free mass correlated positively (P < .01) with carbohydrate oxidation (r = .52 and r = .47, respectively).

CONCLUSION

Obesity during childhood may alter substrate oxidation during exercise. These results may have implications in the implementation of exercise programs in prepubertal or early puberty to control adiposity.

Are Prepubertal Children Metabolically Comparable to Well-Trained Adult Endurance Athletes?

It is well acknowledged that prepubertal children have smaller body dimensions and a poorer mechanical (movement) efficiency, and thus a lower work capacity than adults. However, the scientific evidence indicates that prepubertal children have a greater net contribution of energy derived from aerobic metabolism in exercising muscle and reduced susceptibility to muscular fatigue, which makes them metabolically comparable to well-trained adult endurance athletes. For example, the relative energy contribution from oxidative and non-oxidative (i.e. anaerobic) sources during moderate-to-intense exercise, the work output for a given anaerobic energy contribution and the rate of acceleration of aerobic metabolic machinery in response to submaximal exercise are similar between prepubertal children and well-trained adult endurance athletes. Similar conclusions can be drawn on the basis of experimental data derived from intra-muscular measurements such as type I fibre percentage, succinate dehydrogenase enzyme activity, mitochondrial volume density, post-exercise phosphocreatine re-synthesis rate and muscle by-product clearance rates (i.e. H⁺ ions). On a more practical level, prepubertal children also experience similar decrements in peak power output as well-trained adult endurance athletes during repeated maximal exercise bouts. Therefore, prepubertal children have a comparable relative oxidative contribution to well-trained adult endurance athletes, but a decrease in this relative contribution occurs from childhood through to early adulthood. In a clinical context, this understanding may prove central to the development of exercise-based strategies for the prevention and treatment of many metabolic diseases related to mitochondrial oxidative dysfunction (e.g. in obese, insulin-resistant and diabetic patients), which are often accompanied by muscular deconditioning during adolescence and adulthood.

High-intensity interval training in overweight and obese children and adolescents: systematic review and meta-analysis

INTRODUCTION

While High Intensity Interval Training is praised in many populations for its beneficial effects on body composition and cardiometabolic health, its use among obese youth remain uncertain. This study aimed at determining whether HIIT is effective to improve aerobic fitness and reduce cardiometabolic risk factors in overweight and obese youth.

EVIDENCE ACQUISITION

A systematic search was conducted and articles reporting studies that investigated the effects of HIIT in 6 to 18-year-old youth were eligible. Meta-analyses were performed when appropriate.

EVIDENCE SYNTHESIS

Fifteen studies were included for the systematic review and meta-analyses. HIIT significantly improves maximal oxygen uptake (1.117 [95% CI: 0.528 to 1.706], P<0.001), and reduces body mass (-0.295 [95% CI: -0.525 to -0.066], P<0.05), body fat (-0.786 [95% CI: -1.452 to -0.120], P<0.05), systolic and diastolic blood pressure (-1.026 [95% CI: -1.370 to -0.683], P<0.001; -0.966 [95% CI: -1.628 to -0.304], P<0.01 respectively), and the HOMA-IR (-1.589 [95% CI: -2.528 to -0.650], P<0.01). However, there is significant heterogeneity, and low to high inconsistency for most cardiometabolic risk factors and aerobic fitness.

CONCLUSIONS

Although few studies have reported cardiometabolic risks, HIIT may also be as effective as traditional endurance continuous training to decrease blood pressure and insulin resistance. HIIT is effective to improve aerobic fitness, body composition, and cardiometabolic risk factors in obese youth, but data are insufficient to determine whether it is more effective than traditional continuous submaximal intensity exercise training.

High-Intensity Interval Training in Normobaric Hypoxia Leads to Greater Body Fat Loss in Overweight/Obese Women than High-Intensity Interval Training in Normoxia

A moderate hypoxic stimulus is considered a promising therapeutic modality for several pathological states including obesity. There is scientific evidence suggesting that when hypoxia and physical activity are combined, they could provide benefits for the obese population. The aim of the present study was to investigate if exposure to hypoxia combined with two different protocols of high-intensity interval exercise in overweight/obese women was more effective compared with exercise in normoxia. Study participants included 82 overweight/obese women, who started a 12 week program of 36 sessions, and were randomly divided into four groups: (1) aerobic interval training in hypoxia (AitH; FiO₂ = 17.2%; n = 13), (2) aerobic interval training in normoxia (AitN; n = 15), (3) sprint interval training in hypoxia (SitH; n = 15), and (4) sprint interval training in normoxia (SitN; n = 18). Body mass, body mass index, percentage of total fat mass, muscle mass, basal metabolic rate, fat, and carbohydrate oxidation, and fat and carbohydrate energy were assessed. Outcomes were measured at baseline (T1), after 18 training sessions (T2), 7 days after the last session (T3), and 4 weeks after the last session (T4). The fat mass in the SitH group was significantly reduced compared with the SitN group from T1 to T3 (p < 0.05) and from T1 to T4 (p < 0.05) and muscle mass increased significantly from T1 to T4 (p < 0.05). Fat mass in the AitH group decreased significantly (p < 0.01) and muscle mass increased (p = 0.022) compared with the AitN group from T1 to T4. All training groups showed a reduction in the percentage of fat mass, with a statistically significant reduction in the hypoxia groups (p < 0.05). Muscle mass increased significantly in the hypoxia groups (p < 0.05), especially at T4. While fat oxidation tended to increase and oxidation of carbohydrates tended to decrease in both hypoxia groups, the tendency was reversed in the normoxia groups. Thus, high-intensity interval training under normobaric intermittent hypoxia for 12 weeks in overweight/obese women seems to be promising for reducing body fat content with a concomitant increase in muscle mass.

Effect of Low- Versus High-Intensity Exercise Training on Biomarkers of Inflammation and Endothelial Dysfunction in Adolescents With Obesity: A 6-Month Randomized Exercise Intervention Study

PURPOSE

To investigate the effects of a low- versus high-intensity aerobic training on biomarkers of inflammation and endothelial dysfunction in adolescents with obesity.

METHODS

Sixty-two adolescents with obesity [age = 15 (14) y, body mass index = 34.87 (4.22) kg·m^-2] were randomized to receive either a high-intensity training (HIT, n = 31) or a low-intensity training (LIT, n = 31) for 24 weeks. All participants also received nutritional, psychological, and clinical counseling. Leptin, total and subtype leukocyte counts, tumor necrosis factor-alpha, interleukin-6, myeloperoxidase, soluble intercellular adhesion molecule-1, and soluble vascular cell adhesion molecule-1 were obtained at baseline and after 24 weeks.

RESULTS

HIT reduced neutrophils [from 4.4 (1.9) to 3.6 (1.3) µL^-1 × 10³; P = .01] and monocytes [from 7.2 (2.5) to 5.2 (1.8) µL^-1 × 10²; P < .01], but LIT increased neutrophils [from 4.5 (1.7) to 5.2 (3.3) µL^-1 × 10³; P = .01]. Although tumor necrosis factor-alpha increased in LIT [from 13.3 (7.5) to 17.7 (10.8) pg·mL^-1; P = .01], it decreased in HIT [from 12.4 (7.5) to 11.3 (6.2) pg·mL^-1; P = .01]. No changes in leukocyte counts, soluble intercellular adhesion molecule-1, soluble vascular cell adhesion molecule-1, and homeostasis assessment model for insulin resistance were observed.

CONCLUSIONS

Both HIT and LIT improved the inflammatory profile. The study, however, indicated that the number of biomarkers and the magnitude of changes were higher in the HIT compared with LIT.

Effects of high-intensity interval training on physical capacities and substrate oxidation rate in obese adolescents

PURPOSE

To investigate the effects of a 3-week weight-management program entailing moderate energy restriction, nutritional education, psychological counseling and three different exercise training (a: low intensity, LI: 40 % V'O₂max; b: high intensity, HI: 70 % V'O₂max; c: high-intensity interval training, HIIT), on body composition, energy expenditure and fat oxidation rate in obese adolescents.

METHODS

Thirty obese adolescents (age: 15-17 years, BMI: 37.5 kg m^-2) participated in this study. Before starting (week 0, W0) and at the end of the weight-management program (week 3, W3), body composition was assessed by an impedancemeter; basal metabolic rate (BMR), energy expenditure and substrate oxidation rate were measured during exercise and post-exercise recovery by indirect calorimetry.

RESULTS

At W3, body mass (BM) and fat mass (FM) decreased significantly in all groups, the decreases being significantly greater in the LI than in the HI and HIIT subgroups (BM: -8.4 ± 1.5 vs -6.3 ± 1.9 vs -4.9 ± 1.3 kg and FM: -4.2 ± 1.9 vs -2.8 ± 1.2 vs -2.3 ± 1.4 kg, p < 0.05, respectively). V'O₂peak, expressed in relative values, changed significantly only in the HI and HIIT groups by 0.009 ± 0.005 and 0.007 ± 0.004 L kg FFM^-1 min^-1 (p < 0.05). Furthermore, the HI and HIIT subgroups exhibited a greater absolute rate of fat oxidation between 50 and 70 % V'O₂peak at W3. No significant changes were observed at W3 in BMR, energy expenditure during exercise and post-exercise recovery.

CONCLUSION

A 3-week weight-management program induced a greater decrease in BM and FM in the LI than in the HI and HIIT subgroups, and greater increase in V'O₂peak and fat oxidation rate in the HI and HIIT than in the LI subgroup.

Severely obese adolescent girls rely earlier on carbohydrates during walking than normal-weight matched girls

The purpose of this study was to determine the substrate oxidation rate and the exercise intensity at which maximal lipid oxidation and ventilatory threshold (VT) occur in obese (BMI: 36.6 ± 6.3 kg · m(-2)) and normal-weight adolescent girls (BMI: 18.7 ± 1.6 kg · m(-2)) aged 14-18 years. Substrate oxidation rate was determined by gas exchange using an incremental field test involving walking. Body composition was assessed by bioelectrical impedance. Carbohydrate oxidation rates were significantly higher in obese than in normal-weight girls at speeds ranging from 4 to 6 km · h(-1) (P < 0.05), whereas no significant differences were observed between groups regarding lipid oxidation rates. The crossover point of substrate utilisation and the VT were significantly lower in obese than in normal-weight adolescents (P < 0.05). Maximal lipid oxidation rate was observed at 46 ± 15 and 53 ± 15 %EVO2max in obese and normal-weight adolescents, respectively. At these intensities, the Lipox(max) was significantly lower in obese than in normal-weight girls (6.7 ± 2.3 versus 8.9 ± 3.5 mg · min(-1) · kg(-1) FFM, P < 0.05, 95% CI: -3.7 to -0.7, d = -0.74). The present results have implications in designing interventions to promote lipid oxidation and energy expenditure during walking in severely obese adolescent girls.

Reproducibility of Fatmax and fat oxidation rates during exercise in recreationally trained males

Aerobic exercise training performed at the intensity eliciting maximal fat oxidation (Fat(max)) has been shown to improve the metabolic profile of obese patients. However, limited information is available on the reproducibility of Fat(max) and related physiological measures. The aim of this study was to assess the intra-individual variability of: a) Fat(max) measurements determined using three different data analysis approaches and b) fat and carbohydrate oxidation rates at rest and at each stage of an individualized graded test. Fifteen healthy males [body mass index 23.1 ± 0.6 kg/m(2), maximal oxygen consumption (VO2max) 52.0 ± 2.0 ml/kg/min] completed a maximal test and two identical submaximal incremental tests on ergocycle (30-min rest followed by 5-min stages with increments of 7.5% of the maximal power output). Fat and carbohydrate oxidation rates were determined using indirect calorimetry. Fat(max) was determined with three approaches: the sine model (SIN), measured values (MV) and 3rd polynomial curve (P3). Intra-individual coefficients of variation (CVs) and limits of agreement were calculated. CV for Fat(max) determined with SIN was 16.4% and tended to be lower than with P3 and MV (18.6% and 20.8%, respectively). Limits of agreement for Fat(max) were -2 ± 27% of VO2max with SIN, -4 ± 32 with P3 and -4 ± 28 with MV. CVs of oxygen uptake, carbon dioxide production and respiratory exchange rate were <10% at rest and <5% during exercise. Conversely, CVs of fat oxidation rates (20% at rest and 24-49% during exercise) and carbohydrate oxidation rates (33.5% at rest, 8.5-12.9% during exercise) were higher. The intra-individual variability of Fat(max) and fat oxidation rates was high (CV>15%), regardless of the data analysis approach employed. Further research on the determinants of the variability of Fat(max) and fat oxidation rates is required.

The influence of 2 weeks of low-volume high-intensity interval training on health outcomes in adolescent boys

The present study aimed to establish whether 2 weeks of high-intensity interval training would have a beneficial effect on aerobic fitness, fat oxidation, blood pressure and body mass index (BMI) in healthy adolescent boys. Ten adolescent boys (15.1 ± 0.3 years, 1.3 ± 0.2 years post-estimated peak height velocity) completed six sessions of Wingate-style high-intensity interval training over a 2-week period. The first session consisted of four sprints with training progressed to seven sprints in the final session. High-intensity interval training had a beneficial effect on maximal O2 uptake (mean change, ±90% confidence intervals: 0.19 L · min(-1), ±0.19, respectively), on the O2 uptake at the gas exchange threshold (0.09 L · min(-1), ±0.13) and on the O2 cost of sub-maximal exercise (-0.04 L · min(-1), ±0.04). A beneficial effect on the contribution of lipid (0.06 g · min(-1), ±0.06) and carbohydrate (-0.23 g · min(-1), ±0.14) oxidation was observed during sub-maximal exercise, but not for the maximal rate of fat oxidation (0.04 g · min(-1), ±0.08). Systolic blood pressure (1 mmHg, ±4) and BMI (0.1 kg · m2, ±0.1) were not altered following training. These data demonstrate that meaningful changes in health outcomes are possible in healthy adolescent boys after just six sessions of high-intensity interval training over a 2-week period.

Physical activity targeted at maximal lipid oxidation: a meta-analysis

Exercise is recognized as a part of the management of obesity and diabetes. Various protocols of exercise are proposed for the management of obesity, diabetes, and other metabolic diseases. One of the strategies proposed by several authors is low intensity endurance training targeted at the level of maximal oxidation. Large series using this technique are lacking. Addressing this issue, we performed a meta-analysis of the studies on anthropometric measurements. From a database of 433 articles, 15 were selected, including 279 subjects with 6 different populations. Studies duration ranged from 2 months to 12 months. Concerning weight loss, in the intervention versus control analysis, five studies with 185 participants were included with a significant effect size favors exercise (P = 0.02) without significant heterogeneity (I² = 0.0%, P = 0.83). Further randomized controlled trials for comparing it with other exercise protocols and defining its dose effectiveness on large samples are needed.

Maximal lipid oxidation during exercise: a target for individualizing endurance training in obesity and diabetes?

This review summarizes the rationale for personalized exercise training in obesity and diabetes, targeted at the level of maximal lipid oxidation as can be determined by exercise calorimetry. This measurement is reproducible and reflects muscles' ability to oxidize lipids. Targeted training at this level is well tolerated, increases the ability to oxidize lipids during exercise and improves body composition, lipid and inflammatory status, and glycated hemoglobin, thus representing a possible future strategy for exercise prescription in patients suffering from obesity and diabetes.

Crossover and maximal fat-oxidation points in sedentary healthy subjects: methodological issues

AIM

Our study aimed to assess the influence of protocol on the crossover point and maximal fat-oxidation (LIPOX(max)) values in sedentary, but otherwise healthy, young men.

METHODS

Maximal oxygen intake was assessed in 23 subjects, using a progressive maximal cycle ergometer test. Twelve sedentary males (aged 20.5±1.0 years) whose directly measured maximal aerobic power (MAP) values were lower than their theoretical maximal values (tMAP) were selected from this group. These individuals performed, in random sequence, three submaximal graded exercise tests, separated by three-day intervals; work rates were based on the tMAP in one test and on MAP in the remaining two. The third test was used to assess the reliability of data. Heart rate, respiratory parameters, blood lactate, the crossover point and LIPOX(max) values were measured during each of these tests.

RESULTS

The crossover point and LIPOX(max) values were significantly lower when the testing protocol was based on tMAP rather than on MAP (P<0.001). Respiratory exchange ratios were significantly lower with MAP than with tMAP at 30, 40, 50 and 60% of maximal aerobic power (P<0.01). At the crossover point, lactate and 5-min postexercise oxygen consumption (EPOC(5 min)) values were significantly higher using tMAP rather than MAP (P<0.001). During the first 5 min of recovery, EPOC(5 min) and blood lactate were significantly correlated (r=0.89; P<0.001).

CONCLUSION

Our data show that, to assess the crossover point and LIPOX(max) values for research purposes, the protocol must be based on the measured MAP rather than on a theoretical value. Such a determination should improve individualization of training for initially sedentary subjects.

Effect of time interval between food intake and exercise on substrate oxidation during exercise in obese and lean children

BACKGROUND & AIMS

Exercise induces adaptations in fat metabolism favourable to the treatment of obesity. However, time interval between meal and exercise alters substrate bioavailability and oxidation during exercise. The aim of this study was therefore to investigate the effect of time interval between food intake and exercise on substrate oxidation rates in obese and lean children.

METHODS

The metabolic responses to exercise of nine obese children (10.3 ± 1.8 years; %body fat: 36.1 ± 6.1) and seven lean children (9.2 ± 1.6 years; %body fat: 22.2 ± 4.1) were compared 1 h (time interval 1, TI1) and 3 h (TI3) after a standardized breakfast.

RESULTS

Despite significantly lower plasma glucose and insulin concentrations and large effect size suggesting a higher plasma FFA availability (lean, 1.43, obese 0.98), fat oxidation was not significantly increased in TI3 compared to TI1 in both lean and obese children. Fat oxidation contributed marginally to energy expenditure during exercise (<20%) in both conditions and groups but was moderately increased during TI3 compared to TI1 in lean children (effect size: 0.54).

CONCLUSIONS

The low contribution of fat oxidation to energy expenditure during exercise in obese and lean children fed 3 h before exercise questions the efficacy of moderate intensity exercise to favourably affect fat balance.

Intensive exercise: a remedy for childhood obesity?

BACKGROUND

Acute exercise can affect the energy intake regulation, which is of major interest in terms of obesity intervention and weight loss.

OBJECTIVE

To test the hypothesis that intensive exercise can affect the subsequent energy intake and balance in obese adolescents.

DESIGN

The study was conducted in 2009 and enrolled 12 obese pubertal adolescents ages 14.4±1.5 years old. Two exercise and one sedentary sessions were completed. The first exercise (EX(1)) and sedentary session (SED) were randomly conducted 1 week apart. The second exercise session (EX₂) was conducted following 6 weeks of diet modification and physical activity (3×90 min/week) to produce weight loss. Energy intake was recorded, subjective appetite sensation was evaluated using Visual Analogue Scales and energy expenditure was measured using ActiHerats during EX(1), EX₂ and SED.

RESULTS

Total energy intake over the awakened period was significantly reduced by 31% and 18% during the EX(1) and EX(2) sessions compared with the SED session, respectively (p<0.01). Energy balance over the awakened period was negative during EX₁, neutral during EX₂ and positive during SED. There was no significant difference in terms of subjective appetite rates between sessions during the awakened hours.

CONCLUSIONS

Intensive exercise favors a negative energy balance by dually affecting energy expenditure and energy intake without changes in appetite sensations, suggesting that adolescents are not at risk of food frustration.

Determination of the maximal fat oxidation point in obese children and adolescents: validity of methods to assess maximal aerobic power

We aimed to examine the interchangeability of techniques used to assess maximal oxygen consumption (VO2max) and maximal aerobic power (MAP) employed to express the maximal fat oxidation point in obese children and adolescents. Rate of fat oxidation were measured in 24 obese subjects (13.0 +/- 2.4 years; Body Mass Index 30.2 +/- 6.3 kg m(-2)) who performed a five 4-min stages submaximal incremental cycling exercise. A second cycling exercise was performed to measure VO2max. Results are those of the 20 children who achieved the criterion of RER (>1.02) to assess the attainment of VO2max. Although correlations between results obtained by different methods were strong, Bland-Altman plots showed little agreement between the maximal fat oxidation point expressed as a percentage of measured VO2max and as % VO2max estimated according to ACSM guidelines (underestimation : -5.9%) or using the predictive equations of Wasserman (-13.9%). Despite a mean underestimation of 1.4% several values were out of the limits of agreement when comparing measured MAP and Theoretical MAP. Estimations of VO2max lead to underestimations of the maximal fat oxidation point.

Effects of an eight-month weight-control program on body composition and lipid oxidation rate during exercise in obese children

OBJECTIVE

To investigate the effects of an 8-month multidisciplinary weight-control program, including 2 h/week of moderate physical activity, nutritional education lessons and psychological follow-up, on body composition and lipid oxidation rate during exercise in obese children.

DESIGN

Nineteen (7 boys and 12 girls) obese children, aged 8-12 yr [mean body mass index (BMI) z-score: 2.3 and fat mass: 35.8%] participated in this study. Before and at the end of the weight-control period body composition was assessed by bioelectrical impedance, lipid oxidation rate by indirect calorimetry during a graded exercise test, and time devoted to various activities and energy intake in free-living conditions by questionnaire.

RESULTS

All children completed the study, at the end of which BMI decreased significantly by mean 0.6+/-0.5 and 0.5+/-0.8 kg/m2, in boys and girls, respectively (p<0.05), and fat mass (FM) decreased by 1.7+/-2.8 and 1.4+/-1.3 kg in boys and girls, respectively (p<0.05). In addition, lipid oxidation rate during exercise increased significantly throughout the graded exercise test up to 21% at maximal lipid oxidation rate which happened at 48+/-5% of maximal oxygen uptake (VO2max), corresponding to 64+/-5% of maximal heart rate. Time spent at sedentary and very light physical activities decreased (p<0.001) to the benefit of recreational activities at home.

CONCLUSIONS

Multidisciplinary weight-control program, with moderate-intensity physical activities, induced decreases in FM without decreases in free FM, increases in VO2max, lipid oxidation rate during exercise, and time devoted to recreational activities in free-living conditions.

Determination of "Fatmax"with 1 h cycling protocols of constant load

Several earlier studies were aimed at determining an exercise intensity that elicits maximal fat oxidation (Fatmax). However, these studies employed few different intensities or used exercise periods of too short a duration. All investigators described intensity with reference to maximal ergometric values, which might lead to metabolically inhomogeneous workloads between individuals. The aim of this study was to determine Fatmax by overcoming these methodological shortcomings of earlier investigations. Ten healthy recreational athletes (29 +/- 5 y; 75 +/- 6 kg; 1.81 +/- 0.04 m) conducted an initial incremental cycling test to determine VO2 peak (59.2 +/- 6.1 mL.min-1.kg-1) and individual anaerobic threshold (IAT; 221 +/- 476 W). Within 4 weeks, 5 constant-load tests of 1 h duration were carried out at 55%, 65%, 75%, 85%, and 95% IAT. During all tests indirect calorimetry (MetaMax I, Cortex, Leipzig, Germany) served to quantify fat oxidation. Capillary blood sampling for lactate measurements was conducted every 15 min. All subjects remained in a lactate steady state during the constant load tests, which minimized influences from excess CO2. There was no difference between the 5 intensities for the percentage of energy from fat metabolism (p = 0.12). Additionally, the intensities led to similar absolute amounts of oxidized fat (p = 0.34). However, there was a significant increase in fat metabolism with increasing exercise duration (p = 0.04). It is impossible to define one theoretical optimal intensity for fat oxidation that is true in all individuals. It is thus mandatory to perform an individual assessment with indirect calorimetry. Intra-individual day-to-day variation might render the use of several tests of long duration less applicable than incremental testing with stages of sufficient duration.

Metabolic training: new paradigms of exercise training for metabolic diseases with exercise calorimetry targeting individuals

For patients with metabolic diseases, as with other diseases, exercise training is a fully recognized therapy. Such training helps obese patients stabilize weight after slimming. For patients with type 2 diabetics, it is both a prevention and a glucose-lowering treatment and reduces health care costs. We propose a targeted training for individuals at the level of maximal lipid oxidation (LIPOXmax) with a protocol of exercise calorimetry (four 6-min workloads) based on Brooks and Mercier's crossover concept. Calorimetric interpretation of gas exchange at the fifth and sixth minutes of each stage shows a bell-shaped curve for lipid oxidation that peaks at LIPOXmax, a point that varies considerably among individuals. As well, glucose oxidation is a linear function of power (carbohydrate cost of the watt). Such a calculation predicts fairly actual lipid oxidation over 45 min at the same level. Other protocols, with 3-min workloads used in sports medicine, are not reliable for patients with metabolic diseases. For obese adults and teenagers, as well as those with type 2 diabetes, 2 months' training at the LIPOXmax (three sessions at 45 min per week) results in a net loss of fat mass, with preserved fat-free mass, and increased ability to oxidize lipids. At the end of this period, training can be "re-targeted" to be more effective and, possibly, associated with other strategies with stronger exercise intensities. Therefore, metabolic training is a viable option for patients with metabolic diseases, but the full concept is still evolving. However, the major challenge remains to transform inactive individuals into active ones.