Georges Jabbour

Catecholamines and Obesity: Effects of Exercise and Training

Excess body fat in obese individuals can affect the catecholamine response to various stimuli. Indeed, several studies report lower plasma catecholamine concentrations in obese subjects compared with nonobese subjects in response to submaximal or maximal exercise. This low catecholamine response reflects decreased sympathetic nervous system (SNS) activity. Although the relationship between the SNS and obesity is not well established, some authors have suggested that low SNS activity may contribute to the development of obesity. A decreased catecholamine response could affect α- and β-adrenoceptor sensitivity in adipose tissue, reducing lipolysis and increasing fat stores. Few studies have examined the effects of obesity on the plasma catecholamine response at rest and during exercise in adolescents. It is interesting to note that the effects of age, sex, and degree of obesity and the impact of very intense exercise on the catecholamine response have not yet been well examined. Moreover, the hormonal concentrations measured in the majority of obesity studies did not take into account plasma volume changes. This methodological factor can also undoubtedly influence plasma catecholamine results.

Catecholamine Response to Exercise in Obese, Overweight, and Lean Adolescent Boys

INTRODUCTION The aim of this study was to examine the effect of body fat percentage on the plasma catecholamine response to a cycling sprint test (CST) in sedentary adolescent boys. METHODS In this study, 31 adolescent boys (9 obese (% body fat = 31.0% ± 3.0%), 11 overweight (% body fat = 24.0% ± 1.6%), and 11 lean (% body fat = 16.0% ± 1.9%)), matched for peak oxygen consumption, completed a CST consisting of six 6-s maximal sprints with 2 min of passive rest between each repetition. Performance of each subject was determined as the mean power output (PO(mean)) developed during the CST. Plasma lactate, epinephrine, and norepinephrine concentrations were determined successively at rest, after a 10-min warm-up, immediately after the CST, and after 20 min of passive recovery. RESULTS Although groups were not different in age, height, or peak oxygen consumption (mL·kg(-1) fat-free mass·min(-1)), maximal epinephrine concentration was significantly (P < 0.05) higher in lean vs obese and was negatively correlated to body fat percentage (r = -0.60, P < 0.05). Maximal norepinephrine values were higher in lean versus overweight and obese, and a negative relationship was found between maximal norepinephrine concentration and body fat percentage (r = -0.60, P < 0.05). Maximal lactate concentration was higher in lean versus overweight and obese (14.7 ± 3.3, 10.4 ± 2.7, and 10.2 ± 2.5 mM in lean, overweight, and obese, respectively). A significant relationship was also obtained between maximal norepinephrine and maximal epinephrine values with both maximal lactate concentration (r = 0.60 and r = 0.60, P < 0.05, respectively) and PO(mean) (r = 0.65 and r = 0.6, P < 0.05). CONCLUSIONS Our results show that the catecholamine response to a CST was affected by body fat percentage, with reduced epinephrine and norepinephrine values in overweight and obese adolescents.

Barriers to Active Lifestyles in Children with Type 1 Diabetes

OBJECTIVES To identify the main barriers to active lifestyles in children with type 1 diabetes based on known barriers in adults with type 1 diabetes. METHODS Children with type 1 diabetes (n=201) recruited from the Centre Hospitalier Universitaire (CHU) Sainte-Justine Diabetes Clinic answered a specific questionnaire, the Barriers to Physical Activity in Type 1 Diabetes (BAPAD1), which assesses perceived barriers and parental support in the childrens adoption of active lifestyles. RESULTS In younger individuals (those younger than 12 years of age), the highest barrier scores were loss of control of diabetes, fear of hypoglycemia, work schedule and external temperature. In the older group (those ≥12 years of age), fear of hypoglycemia, external temperature, loss of control of diabetes and low fitness levels were the most important. Greater parental support was associated with lower overall barrier scores in younger and older children alike (r=-0.71 and r=-0.65, respectively; p<0.001). CONCLUSIONS There are some differences in barriers to active lifestyles between younger and older children with type 1 diabetes. Parental support appears to be the key to active lifestyles in their children.

Effects of Acute Supramaximal Cycle Exercise on Plasma FFA Concentration in Obese Adolescent Boys

Aims The aims of the present study are 1) to evaluate the free fatty acid (FFA) profile and 2) to determine the relative anaerobic and aerobic contributions to total energy consumption during repeated supramaximal cycling bouts (SCE) in adolescent boys with different body weight statuses. Materials and Methods Normal-weight (NW), overweight (OW), and obese (OB) adolescent boys (n =15 per group) completed a SCE sessions consisted of 6 x 6s maximal sprints with 2 min of passive rest between each repetition. Plasma FFA levels were determined at rest, immediately after a 10 min warm-up, and immediately at the end of SCE. The anaerobic and aerobic contributions (%) were measured via repeated SCE bouts. Insulin resistance was calculated using the homoeostatic model assessment (HOMA-IR) index. Results The FFA concentrations measured immediately after SCE were higher in the OB group than in the OW and NW (p<0.01 and p<0.01, respectively) groups. Moreover, the anaerobic contributions to SCE were significantly lower in obese adolescents (p<0.01) and decreased significantly during the 2nd, 3rd and 4th repetitions. The FFA levels were significantly associated with the HOMA-IR index and aerobic contribution among adolescent boys (r=0.83 and r=0.91, respectively, p<0.01). Conclusion In contrast to the NW and OW groups, there is an increase in lipid mobilization and sift to aerobic energy metabolism during SCE in the OB group.

Effect of supramaximal exercise training on metabolic outcomes in obese adults

ABSTRACT The purpose of this study was to evaluate the effects of 6 weeks of supramaximal exercise training (SET) on performance variables and metabolic changes in sedentary obese adults. Twenty-four obese adults were randomly allocated into a non-trained (NT) [n = 12; body mass index (BMI) = 33(3)] and SET group [n = 12; BMI = (33(2)]. After baseline metabolic and fitness measurements, the participants completed a 6-week SET intervention. Metabolic, anthropometric, and fitness assessments were repeated post-intervention. For SET, fasting glucose (4.64(0.15) vs. 4.32(0.22) mmol · l–1; P < 0.01), insulin (23.2(4.6) vs. 13.8(3.3) µmol · ml–1; P < 0.01), homoeostasis model assessment-insulin resistance index (4.78(1.2) vs. 2.65(1.5); P < 0.01) and systolic blood pressure (127(3) vs. 120(3) mmHg; P < 0.01) were significantly lower 24-h post-intervention than at baseline and for the NT group, and these changes remained significant at 72-h and 2-weeks post-intervention (P < 0.01, respectively). Interestingly, nonesterified fatty acids (0.62(0.09) vs. 0.71(0.11) mmol · l–1; P < 0.01) and resting fat oxidation rate (57(11) vs. 63(4)%; P < 0.01) increased significantly from baseline 24-h post-intervention in the SET group and from baseline at 72-h (P < 0.01, respectively) and 2-weeks post-intervention (P < 0.01, respectively). Six weeks of SET improved a number of metabolic and vascular risk factors in obese, sedentary adults, highlighting the potential of SET to provide an alternative exercise model for the improvement of metabolic health in this population.

Mechanical efficiency during a cycling test is not lower in children with excess body weight and low aerobic fitness

The aims of this study were to assess the association between (i) body weight status and mechanical efficiency (ME); and (ii) ME and aerobic fitness in children aged 8‐10 years.

High‐intensity interval training improves performance in young and older individuals by increasing mechanical efficiency

This study evaluated the effects of 6 weeks of high‐intensity interval training (HIIT) on mechanical efficiency (ME) in young and older groups. Seventeen healthy young adults [26.2(2.4) year], and thirteen healthy older adults [54.5(2.3) year] completed a 6‐week HIIT intervention (three sessions per week) on an electromagnetically braked cycle ergometer. Each HIIT session contained six repetitions of supramaximal exercise intervals (6 seconds each) with 2 min of passive recovery between each repetition. ME (%) were computed in net terms across stages corresponding to ventilator thresholds 1 (VT1) and 2 (VT2) and at 100% of maximal oxygen consumption (VO2max) of an incremental maximal cycling test. After 6 weeks, the ME values did not differ between the two groups and were significantly higher than the ones at baseline (P < 0.01). In this study, the multiple linear regression analysis demonstrated the increases in maximal power (Pmax) contributed significantly to ME increases over 6 weeks at VT1, VT2 and at 100% of VO2max. This model accounted respectively for 28, 38, and 42%, of the increases. In older adults, ME determined during incremental maximal cycling test increases at VT1, VT2 and at 100% over 6‐week HIIT intervention, and the increment appeared to be related to increases in Pmax. HIIT can be recommended as a strategy aimed at improving muscle efficiency among older adults.

Mechanical efficiency improvement in relation to metabolic changes in sedentary obese adults.

Purpose Mechanical efficiency (ME) refers to the ability of an individual to transfer energy consumed by external work. This performance indicator is impaired by obesity and is associated with decreased high-intensity exercise performance. However, it is unclear if ME may be improved in response to high intensity training (HIT). This study aimed to determine if ME increases in response to HIT in obese adults and to identify the factors associated with these changes. Methods 24 obese adults (body mass index=∼33 kg/m2) were randomised into control (n=12) and trained (n=12) groups. Following baseline metabolic, anthropometric, fitness and ME measurements, the participants completed a 6-week exercise intervention that included 18 sessions of six repeats of 6 s supramaximal sprints on an electromagnetically braked cycle ergometer. The metabolic, anthropometric and fitness assessments were repeated postintervention. ME (expressed as a %) was calculated during an incremental maximal cycling test at stages of 25, 50, 75, 100 and 125 W. Results ME did not differ across the groups at 25 and 50 W. Following HIT, ME increased significantly at 75, 100 and 125 W (p<0.01, respectively) compared with the control group (p<0.01, respectively). Although no changes in fat-free mass were observed following HIT, the increases in ME at 75, 100 and 125 W correlated positively with both homeostasis model assessment-estimated insulin resistance index decreases (r=0.9; r=0.89 and r=0.88, p<0.01, respectively) and peak power increases (r=0.87, r=0.88 and r=0.9, p<0.01, respectively). Conclusions Although there were no changes in the participants’ anthropometric variables, HIT improved ME in obese adults, an enhancement that appears to be related to increases in muscle strength and metabolic adaptations.

Aerobic Fitness Indices of Children Differed Not by Body Weight Status but by Level of Engagement in Physical Activity

BACKGROUND Moderate-to-vigorous physical activity (MVPA) improves aerobic fitness in children, which is usually assessed by maximal oxygen consumption. However, other indices of aerobic fitness have been understudied. OBJECTIVE To compare net oxygen (VO2net), net energy consumption (Enet), net mechanical efficiency (MEnet), and lipid oxidation rate in active and inactive children across body weight statuses. DESIGN The sample included normal-weight, overweight, and obese children of whom 44 are active (≥30 min of MVPA/d) and 41 are inactive (<30 min of MVPA/d). VO2net, Enet, MEnet and lipid oxidation rate were determined during an incremental maximal cycling test. RESULTS Active obese participants had significantly lower values of VO2net and Enet and higher MEnet than inactive obese participants at all load stages. In addition, active obese participants showed a significantly higher lipid oxidation rate compared with inactive obese and active overweight and normal-weight participants. VO2net, Enet, and MEnet were similar across active children, regardless of body weight status. CONCLUSIONS Thirty minutes or more of MVPA per day is associated with a potentiation of aerobic fitness indicators in obese prepubertal children. Moreover, the indices of aerobic fitness of inactive obese children are significantly different from those of active obese and nonobese ones.

Increased lipid oxidation during exercise in obese pubertal girls: A QUALITY study

This study explores differences in LO rates between pre‐pubertal and pubertal girls of three body weight status groups.