Weight loss does not affect the sit-to-stand metabolic cost in adolescents with obesity.

PURPOSE: There is considerable interest in simple and effective methods to reduce sitting time and increase energy expenditure, and standing breaks have emerged as a realisable approach in individuals with obesity. The aim of the present study was to determine the extent to which energy expenditure in standing differs from sitting, and whether this energetic and metabolic-related responses are modified following a weight loss program in adolescents with obesity. METHODS: After body composition assessment (DXA), cardiorespiratory and metabolic variables were continuously recorded (indirect calorimetry) during 10 min while sitting and then during 5 min standing posture before (n = 21; T1) and at the end of a multidisciplinary intervention (n = 17; T2) in adolescents with obesity. RESULTS: Before and after the intervention, energy expenditure and fat oxidation rates were significantly increased in standing compared with sitting. Weight loss did not change the relationship between sitting and standing energy expenditure. Sitting energy expenditure represented 1.0 and 1.1 Metabolic Equivalent of Task at T1 and T2, and increased to 1.1 and 1.2 during standing at T1 and T2, respectively. The percentage of change of android fat mass between T1 and T2 was positively associated with the percentage of change in energy expenditure from sitting to standing at T2. CONCLUSION: The vast majority of the adolescents with obesity significantly increased their energy expenditure between sitting and standing, both before and after a weight loss intervention. However, the standing posture did not allow breaking the sedentary threshold. Abdominal fat mass is associated with energic profile.

Is the SPARTACUS 15-15 test an accurate proxy for the assessment and tracking of maximal aerobic capacities in adolescents with obesity?

[Purpose] While there is a need for reliable field tests for the evaluation of physical fitness in pediatric obesity, the present work i) evaluates the validity of the Spartacus 15-15 test in indirectly assessing maximal aerobic capacity in adolescents with obesity and ii) evaluates its sensibility to weight loss. [Participants and Methods] Fifty-five 11-16 year-old adolescents with obesity (Tanner 3-4) were enrolled in a 12-week weight-management intervention. Maximal Aerobic fitness (VO2peak test + Spartacus test) and body composition (Dual X-ray absorptiometry) were assessed at baseline and after 12 weeks. [Results] Moderate correlations were found at baseline between VO2peak (2,231.90 ± 465.6 mL/min) and Spartacus stage (6.83 ± 1.8 stage, r=0.52; p≤0.05), speed (12.85 ± 1.8 km/h, r=0.52 ; p≤0.05) and time (20.6 ± 5.4 min; r=0.50; p≤0.05). The intervention favored significant improvements for VO2peak, Spartacus Rate of Perceived Exertion final stage, maximal speed and time. Change over time in VO2peak and Spartacus variables were not correlated. [Conclusion] The Spartacus test can be used as a proxy for VO2peak at baseline and can be used to estimate VO2peak using the proposed equation. The Spartacus 15-15 test might be a better indicator for changes in functional capacity than an indicator of VO2peak changes in youth with obesity.

Maturation-related changes in the development and etiology of neuromuscular fatigue.

PURPOSE: The aim of the present study was to investigate the role of maturation on the etiology of neuromuscular fatigue induced by repeated maximal voluntary isometric contractions (MVIC). METHODS: Nine prepubertal boys (9.9 ± 1.3 years), eight male adolescents (13.6 ± 1.3 years) and eleven men (23.4 ± 3.0 years) performed a series of repeated isometric MVICs of the knee extensors until the MVIC torque reached 60% of its initial value. Magnetic stimulations were delivered to the femoral nerve every five MVICs to follow the course of voluntary activation level (VA) and the potentiated twitch torque (Qtwpot). RESULTS: Task failure was reached after 52.9 ± 12.7, 42.6 ± 12.5, and 26.6 ± 6.3 repetitions in boys, adolescents and men, respectively. VA remained unchanged in men whereas it decreased significantly and similarly in boys and adolescents (p < 0.001). In contrast, Qtwpot remained unchanged in boys and decreased significantly less in adolescents than adults (p < 0.05). CONCLUSIONS: Children and adolescents experience less peripheral and more central fatigue than adults. However, adolescents experience more peripheral fatigue than children for a comparable amount of central fatigue. This finding supports the idea that the tolerance of the central nervous system to peripheral fatigue could increase during maturation.

Effect of Exercise Duration on Subsequent Appetite and Energy Intake in Obese Adolescent Girls.

There is a growing interest regarding the effect of exercise on appetite and energy intake in youth. While the role of exercise intensity has been a primary focus of study, the effect of exercise duration on subsequent food intake has not been fully examined in obese adolescents. On three separate mornings in a randomly assigned order, obese adolescent girls (n = 20) aged 12-15 years old were asked to perform a rest session (control, CON) or two cycling sessions for 20 (EX20) or 40 min (EX40) set at their ventilatory threshold. Absolute and relative energy intake were measured from an ad libitum lunch meal 30 min after rest or exercise and appetite feelings assessed using visual analogue scales throughout the day. Hunger, satiety, and prospective food consumption were not significantly different between conditions. Absolute energy intake (kcal) did not differ between conditions, while relative energy intake on EX40 (571 ± 381 kcal) was significantly lower than during CON (702 ± 320 kcal; p < .05) and EX20 (736 ± 457 kcal; p < .05). Fat ingestion (in grams) was significantly lower on CON (7.8 ± 3.2 g) compared with EX20 (10.3 ± 4.6 g; p < .01). Protein intake (in grams) was higher on EX20 (37.0 ± 16.6 g) compared with both CON (29.5 ± 11.7 g; p < .01) and EX40 (33.1 ± 10.9 g; p < .05). However, the percentage of total energy derived from each macronutrient was not different between conditions. Obese adolescent girls do not compensate for an acute bout of exercise set at their ventilatory threshold by increasing energy intake, regardless of the exercise duration.

Obesity-related differences in neuromuscular fatigue in adolescent girls.

PURPOSE: The aim of this study was to investigate the effect of obesity on neuromuscular fatigue in adolescent girls. METHODS: Twelve lean (13.6 ± 0.8 years) and 12 obese (13.9 ± 0.9 years) girls repeated 5-s maximal voluntary contractions (MVC) of the knee extensors until the generated torque reached 55 % of its initial value. Magnetic stimulations were delivered to the femoral nerve every five MVCs to follow the course of voluntary activation (VA) and potentiated twitch torque (Qtwpot). RESULTS: Torque reached 55 % of its initial value after 52.6 ± 20.4 and 74.9 ± 22.8 repetitions in obese and lean girls, respectively (p < 0.01). Furthermore, the decline of VA was smaller in obese girls (p < 0.001). In contrast, Qtwpot decreased to a greater extent in obese girls (p < 0.05). CONCLUSIONS: Obese girls fatigue faster than their lean counterparts. The peripheral factors mainly account for fatigue in obese girls, whereas central factors are mainly involved in lean girls.

The effectiveness of multidisciplinary weight loss interventions is associated with initial cardiorespiratory fitness in adolescents with obesity.

BACKGROUND: The identification of predictive parameters of the success of multidisciplinary weight loss interventions (MWLI) appears essential to optimize obesity management. The association between baseline cardiorespiratory fitness (CRF) and changes in anthropometric parameters and body composition during MWLI remains underexplored in adolescents with obesity. OBJECTIVES: To assess whether baseline CRF was associated with the effectiveness of a 16-week MWLI measured through improved body mass, body mass index (BMI) and body composition (percentage of total fat mass (FM) as the main criterion). METHODS: Cardiorespiratory fitness and body composition were respectively measured by peak oxygen consumption (VO2peak) during maximal exercise tests and dual-photon x-ray absorptiometry (DXA), before (T0) and after (T1) a 16-week MWLI in 165 adolescents (aged 13.3 ± 1.38 years, 61.2% female, BMI 35.11 ± 5.16 kg/m2). RESULTS: Reductions in BMI and total FM percentage between T0 and T1 were greater in subjects with a baseline VO2peak ≥ 3rd quartile compared to the first quartile (p < 0.001) and the interquartile range (p < 0.05 and p < 0.001, respectively). Baseline VO2peak and VO2 at the first ventilator threshold were positively correlated with the reductions in body mass, BMI and total and visceral FM percentages and with the increase in lean mass (LM) percentage between T0 and T1 after adjustment for age and gender (p < 0.001). CONCLUSION: Initial CRF is associated with the success of MWLI in adolescents with obesity. Improving their aerobic fitness before starting a MWLI might be a promising strategy to optimize its benefits.

Bone Response to High-Intensity Interval Training versus Moderate-Intensity Continuous Training in Adolescents with Obesity.

INTRODUCTION: Since adolescents with obesity are prone to bone fragility during weight loss, the aim was to compare the impact of high-intensity interval training (HIIT) versus moderate-intensity continuous training (MICT) on bone density, geometry, and strength. METHODS: Sixty-one adolescents were randomly assigned to 2 cycling trainings (HIIT and MICT) and a control (CTR, without training) group. Anthropometry, dual-energy X-ray absorptiometry with hip structural analysis and the trabecular bone score (TBS) were assessed before and after the 16-week intervention. RESULTS: Body mass index (BMI) and fat mass (FM) percentage decreased at T1 versus T0 in both training groups (p < 0.001 for HIIT, p = 0.01 for MICT), though to a larger extent in HIIT (p < 0.05). Total body bone mineral density (BMD) and bone mineral content (BMC) increased in both training groups (p < 0.001), but to a greater extent in HIIT for BMC (p < 0.05). Lumbar spine BMD and BMC increased in both training groups (p < 0.001 for HIIT, p < 0.01 for MICT), with a time × group interaction between HIIT and CTR (p < 0.05) only. TBS increased in both training groups (p < 0.01 for HIIT, p < 0.05 for MICT). Hip BMD and BMC increased in both HIIT (p < 0.001 and p < 0.01) and MICT (p < 0.01 and p < 0.05). At the narrow neck (NN), endocortical diameter, width (p < 0.01), cross-sectional moment of inertia, and section modulus (Z) (p < 0.05) increased only in the HIIT group, such as BMD and Z (p < 0.05) at the intertrochanteric region (IT) and average cortical thickness (p < 0.001) and width (p < 0.05) at the femoral shaft. At the NN and IT, the buckling ratio decreased only in the HIIT group (p < 0.05), predicting higher resistance to fracture. CONCLUSIONS: In addition to inducing greater BMI and FM percentage decreases in comparison to MICT, HIIT improves multisite bone density, geometry, and strength, which heighten the justification for HIIT as part of weight loss interventions in adolescents with obesity.

Designing, Implementing, and Evaluating a Home-Based, Multidisciplinary, Family-Centered Pediatric Obesity Intervention: The ProxOb Program.

Although family-based interventions have been suggested as promising approaches for preventing and treating pediatric obesity, available studies failed to include the whole family in its own natural environment and routine. This paper aims to detail the development, implementation, and evaluation phases of the ProxOb home-based, family-centered program and present its feasibility and early results. ProxOb provides families with a 6-month multidisciplinary, home-based, and family-centered intervention followed by an 18-month maintenance phase. A global psychosocial, clinical, and behavior evaluation was conducted at baseline (T0) at the end of the 6-month intervention (T1) and after the 18-month maintenance phase (T2). A total of 130 families with at least one child with obesity completed the ProxOb program so far, and more than 90% of them also presented at least one parent with overweight or obesity. Being part of a single-parent family seemed to increase the chance of completing the intervention (63.0% vs. 33.3% in the drop-outers subgroup, p = 0.03). The BMI z-score for children with obesity (T0 = 4.38 ± 1.05; T1 = 4.06 ± 1.07; T2 = 4.29 ± 1.12) significantly decreased between T0 and T1, followed by weight regain at T2. ProxOb proposes a feasible and replicable real-life approach to address childhood obesity while involving the children's family.

Psycho-Physiological Responses to a 4-Month High-Intensity Interval Training-Centered Multidisciplinary Weight-Loss Intervention in Adolescents with Obesity.

BACKGROUND: To evaluate the impact of 4 months of a high-intensity interval training (HIIT)-centered weightmanagement intervention on health-related quality of life (HR-QOL), health perception (HP) and physical selfperception (PSP) in adolescents with obesity. METHODS: Fifty-six adolescents with obesity (28 girls; mean body mass index [BMI], 35±4.89 kg/m2; z-BMI, 2.3±0.3; 11-17 years) followed a multidisciplinary weight-management intervention composed of nutritional counseling, HIIT program, and health-related therapeutic education. Anthropometric parameters, body composition (dual X-ray absorptiometry), and maximal aerobic capacities (maximal oxygen consumption [VO2peak]) were assessed, and self-reported questionnaires were used to assess HR-QOL (36-item short form survey), HP and PSP at baseline (T0) and post-intervention (T1). RESULTS: Body weight (92.6±18.9 to 85.9±16.2 kg), BMI (35.0±4.8 to 32.1±4.5 kg/m2), z-BMI (2.3±0.3 to 2.1±0.3) and fat mass percentage (36.0%±9.1% to 30.4%±7.8%) were significantly decreased (P<0.001) between T0 and T1. There was a tendency for VO2peak to increase from 26.35±5.81 mL/kg/min at T0 to 28.79±6.59 mL/kg/min at T1 (P=0.06). Physical functioning (P=0.002), physical limitation (P=0.048), general health (P<0.001) and bodily pain (P=0.030) were improved at T1. A significant improvement occurred in dimensions of HP such as physical condition (P=0.001), adiposity (P<0.001), alimentation (P<0.001), general health (P=0.038), and perceived general health (P=0.001). In addition, there was an improvement in items of PSP such as self-perceived coordination (P=0.022), endurance (P=0.001) and activity (P=0.001), global self-concept (P=0.015), and appearance (P=0.016). Physical but not mental HR-QOL domains, HP and PSP were associated with weight reduction. CONCLUSION: While HIIT favors improved HR-QOL, HP status and PSP in adolescents with obesity, physical but not mental HR-QOL, HP and PSP were associated with weight reduction.

Effect of HIIT versus MICT on body composition and energy intake in dietary restrained and unrestrained adolescents with obesity.

High-intensity interval training (HIIT) has been suggested as an effective alternative to traditional moderate-intensity continuous training (MICT) that can yield improvements in a variety of health outcomes. Yet, despite the urgent need to find effective strategies for the treatment of pediatric obesity, only a few studies have addressed the impact of HIIT on eating behaviors and body composition in this population. This study aimed to compare the effect of HIIT versus MICT on eating behaviors in adolescents with obesity and to assess if the participants' baseline dietary status is associated with the success of the intervention. Forty-three adolescents with obesity were randomly assigned to a 16-week MICT or HIIT intervention. Body composition and 24-h ad libitum energy intake were assessed at baseline and at the end of the program. Restrained eating, emotional eating, and external eating were assessed using the Dutch Eating Behavior Questionnaire at baseline. Both interventions led to significant weight, body mass index (BMI), and fat mass percentage (FM%) reductions, with better improvements in FM% in the HIIT group; whereas 24-h ad libitum energy intake increased to a similar extent in both groups. HIIT provides better body composition improvements over MICT, despite a similar increase in energy intake. Restrained eaters experienced less weight loss and smaller BMI reduction compared with unrestrained eaters; higher baseline cognitively restrained adolescents showed a greater increase of their ad libitum energy intake. Novelty HIIT favors better body composition improvements compared with MICT. Both MICT and HIIT increased ad libitum energy intake in adolescents with obesity. Weight loss achievement is better among unrestrained eaters.

The accuracy of bioelectrical impedance to track body composition changes depends on the degree of obesity in adolescents with obesity.

The aim of the present study was to assess the sensitivity of bio-impedance (BIA) in tracking body composition changes in adolescents with various degrees of obesity. We hypothesized that while BIA provides a reliable measure of body composition, its accuracy decreases with increasing obesity and its ability to track changes might be reduced with higher degree of body weight and body composition. Whole-body and segmental body composition were assessed by bio-impedance analysis (BIA-Tanita MC-780) and dual x-ray absorptiometry (DXA, Hologic) among 196 obese adolescents (Tanner stage 3-5) aged 14 ±â€¯0.9 years old, before and after a 3-month weight loss program. Except for the measurement of FFM (kg) (r = 0.03; P = .721; ρ = 0.107; P = .246), the percentage of variation between M0 and M3 for FM% (r = 0.41, P < .001; ρ = 0.534; P < .001) and FMkg (r = 0.64 P < .001; ρ = 0.572; P < .001) are significantly correlated and show significant concordance between DXA and BIA. FMkg and FM% changes between M0 and M3 are similarly tracked by DXA and BIA whatever the initial degree of obesity (based on initial weight, BMI, FM% and FFMkg tertiles). The higher the degree of changes and the higher are the differences between the two devices in measuring FM% and FMkg changes. We found inconsistent and low correlations and concordances between the two devices when tracking FM% changes whatever the degree of weight and FM (kg and %) variations. The accuracy of body composition assessment using BIA decreases with increasing obesity, and its reliability to track changes is reduced with high initial or variations of body weight, FM, FFM and BMI.

Nutritional compensation to exercise- vs. diet-induced acute energy deficit in adolescents with obesity.

BACKGROUND: To compare the energy and macronutrient intake responses to equivalent energy deficits induced by diet (food restriction) and exercise in adolescents with obesity. METHODS: Fourteen 12-15years old obese adolescents completed three experimental conditions (08:00am to 07:30pm) in a randomized crossover design: i) control session (CON); ii) diet-induced 25% energy depletion (Def-EI), iii) and an exercise-induced 25% energy depletion (Def-EX). The sessions order was either CON/Def-EI/Def-EX or CON/Def-EX/Def-EI as the deficit corresponded to 25% of the energy ingested at lunch on the control day (CON) and was imposed either by exercise (Def-EX) or diet (Def-EI). Ad libitum EI and macronutrients preferences were assessed at dinner and appetite sensations assessed using visual analogue scales. RESULTS: Mean BMI was 36.6±5.0kg/m2 (z-BMI: 2.40±0.29). The individually calibrated 25% energy deficit represented 254±92kcal. Ad libitum EI was significantly higher during both Def-EX (971±225kcal) and Def-EI (949±246kcal) compared with CON (742±297) (p<0.05). The relative energy ingested derived from fat was significantly higher on both Def-EX (36.6±10.9%) and Def-EI (36.9±13.1%) compared with CON (21.6±7.8%) (p<0.05). The energy derived from carbohydrates was significantly lower on both Def-EX (48.3±9.0%) and Def-EI (44.4±17.3%) compare with CON (61.1±10.1%) (p<0.05). Appetite sensations were not different between conditions. The induced energy deficit was negatively correlated with the ad libitum EI difference between the exercise and the control session (EI Def-EX - EI CON) (r=-0,643 p<0.05) and positively correlated with the EI difference between the dietary restriction and the control session (EI Def-EI - EI CON) (r=0,569 p<0.05). CONCLUSION: Equicaloric exercise- or diet-induced energy deficits could lead to similar EI compensation in obese adolescents but this EI compensation might be influenced by the magnitude of the deficit.

Bioelectrical impedance is an accurate method to assess body composition in obese but not severely obese adolescents.

The aim of this study was to compare total and segmental body composition results between bioimpedance analysis (BIA) and dual x-ray absorptiometry (DXA) scan and to test the reproducibility of BIA in obese adolescents. We hypothesized that BIA offers an accurate and reproducible method to assess body composition in adolescents with obesity. Whole-body and segmental body compositions were assessed by BIA (Tanita MC-780) and DXA (Hologic) among 138 (110 girls and 28 boys) obese adolescents (Tanner stage 3-5) aged 14±1.5years. The BIA analysis was replicated on 3 identical occasions in 32 participants to test the reproducibility of the methods. Whole-body fat mass percentage was significantly higher using the BIA method compared with DXA (40.6±7.8 vs 38.8±4.9%, P<.001), which represents a 4.8% overestimation of the BIA technique compared with DXA. Similarly, fat mass expressed in kilograms is overestimated by 2.8% using BIA (35.8±11.7kg) compared with the DXA measure (34.3±8.7kg) (P<.001), and fat-free mass is underestimated by -6.1% using BIA (P<.001). Except for the right arm and leg percentage of fat mass, all the segmental measures of body composition are significantly different between the 2 methods. Intraclass correlation coefficient and Lin coefficient showed great agreement and concordance between both methods in assessing whole-body composition. Intraclass correlation coefficient between the 3 BIA measures ranged from 0.99 to 1 for body weight, body fat, and fat-free mass. Bioimpedance analysis offers an acceptable and reproducible alternative to assess body composition in obese adolescents, with however a loss of correlation between BIA and DXA with increasing body fat; its validity remains uncertain for segmental analysis among obese youth.

Effect of muscle length on voluntary activation level in children and adults.

PURPOSE: The aim of the present study was to compare the effect of muscle length on the level of voluntary activation (VA) at short and long muscle lengths between children and adults. METHODS: Thirteen prepubertal boys (10.2 ± 1.1 yr) and 10 men (23.9 ± 2.9 yr) performed 5-s maximal isometric voluntary contractions of the knee extensor muscles at three muscular angles (20°, 90°, 100°; 0°, full extension) interspersed with at least 60-s passive recovery periods. Single magnetic stimulations were delivered to the femoral nerve during maximal isometric voluntary contractions to determine the level of VA using the twitch interpolation technique. The specific torque was calculated as the absolute torque divided by thigh muscle mass, as assessed using dual-energy x-ray absorptiometry. Finally, the theoretical specific torque that could be produced with a complete (i.e., 100%) activation level (specific torque at 100% VA) was estimated from the values of specific torque and VA. RESULTS: Results showed a higher specific torque in adults at 90° and 100° but not at 20°. Accordingly, VA was significantly higher in adults at 90° (94% ± 4% vs 88% ± 8%, P < 0.05) and 100° (93% ± 6% vs 86% ± 8%, P < 0.05), whereas no significant difference was observed at 20°. Interestingly, the specific torque at 100% VA was not different between groups whatever the joint angle. CONCLUSIONS: The lower ability of children to fully activate their motor units at long muscle length could account for their lower specific torque because no difference in theoretical specific torque was observed between groups at 90° and 100°.

Insights into the Mechanisms of Neuromuscular Fatigue in Boys and Men.

PURPOSE: The aim of the present study was to investigate the role of central and peripheral factors in neuromuscular fatigue induced by repeated maximal contractions in children and adults. METHODS: Eleven boys (9.9 ± 1.2 yr) and 12 men (23.9 ± 3.5 yr) completed a fatigue protocol consisting in a repetition of 5-s maximal isometric voluntary contractions (MVC) of the knee extensors separated by 5-s passive recovery periods until the generated torque reached 60% of its initial value. Single magnetic stimulations were delivered to the femoral nerve every five MVC to follow the course of voluntary activation level and the amplitude of the potentiated twitch torque (Qtw(pot)) and vastus lateralis and rectus femoris concomitant M-waves (Mmax). RESULTS: Torque reached 60% of initial value after 49.5 ± 16.8 and 34.0 ± 19.6 repetitions in boys and men, respectively (P < 0.05). Furthermore, men showed significantly higher knee extensor MVC decline than boys between 50% and 90% of total repetitions (P < 0.05). Voluntary activation remained unchanged in men, whereas it decreased significantly in boys (P < 0.05). In contrast, whereas Qtw(pot) remained unchanged in boys, Qtw(pot) decreased progressively up to 60% of total repetitions in men (P < 0.001). Finally, Mmax remained unchanged for vastus lateralis and rectus femoris muscles in both groups. CONCLUSIONS: Children experienced no apparent peripheral fatigue and higher central fatigue than adults. The greater fatigue resistance in children could be related to a strategy of the CNS aimed at limiting the recruitment of motor units to prevent any extensive peripheral fatigue.