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The aim of this study was to examine the effect of delayed evening mealtime on sleep quality in young athletes. Twelve rugby players (age 15.8 ± 0.7 years) participated in a crossover within-participant design. Adolescents spent five consecutive days in each of two conditions, separated by a 2-week washout period: routine dinner (3.5 hr before bedtime) and late dinner (LD, 1.5 hr before bedtime). Other mealtimes as well as bedtime and wake-up time were usual and remained the same in both conditions. Their schedules, dietary intakes, and physical activity were controlled and kept constant throughout the study. Sleep was assessed using polysomnography on the first and the last nights in the individual rooms of the boarding school. An increase in total sleep time by 24 min (p = .001, d = 1.24) and sleep efficiency by 4.8% was obtained during LD (p = .001, d = 1.24). Improvement in sleep efficiency was mainly due to a lower wake after sleep onset (−25 min, p = .014, d = −3.20), a decrease of microarousals (−25%, p = .049, d = −0.64), and awakenings ≥90 s (−30%, p d = −0.97) in LD compared to routine dinner. There were no significant differences in sleep architecture except for a shorter slow-wave sleep (N3) latency (−6.9 min, p = .03, d = −0.778) obtained during LD. In this study, evening dinner 1.5 hr before bedtime leads to better quality and less fragmented sleep compared to evening dinner 3.5 hr before bedtime in young athletes.

This study compares the effectiveness of a 12-week moderate exercise training program (METP), performed in the morning versus the evening, on sleep, physical activity, physical fitness, sleepiness, fatigue and health-related quality of life (HRQoL) in overweight and obese patients. Sedentary and inactive overweight/obese adults (n = 36) were included in METP and randomized into two groups: morning group (GM) and evening group (GE). Twenty-eight participants successfully completed METP (3 × 90 min exercise session per week for 12 weeks, completion rates80%). Sleep, physical activity, and bedtime temperature were measured using accelerometry and infrared tympanic temperature during 3 separate weeks of the study (Week1, Week6, and Week12). Participants also took part in baseline and endpoint assessments including physical fitness as well as subjective physical activity, chronotype, sleep quality, sleepiness, fatigue and HRQoL. METP did not impact objective sleep quality differently between the two groups (morning vs evening). Bedtime and mid-sleep were advanced when METP was done in the morning whereas they were delayed when METP was practiced in the early evening (

Sleep is bi-directionally linked to energy balance. This crossover study design will evaluate the acute effect of a moderate energy deficit (500 kcal) induced by diet, exercise, or mixed (−250 kcal by diet and 250 kcal by exercise) on sleep and the next morning’s appetitive responses. The study sample comprises 24 healthy young adults. The experimental measurements will be conducted in a naturalistic, momentary manner and partly assessed by the participants. The participants will undergo a run-in period in order to stabilize their sleep schedules and provide them with training on the study protocol and measurements. Indirect calorimetry will be used to determine their resting metabolic rate and peak oxygen consumption (VO2 peak). Then, they will take part in a control session (CTL), followed by three energy deficit sessions in random order: a diet-induced energy deficit session (DED), an exercise-induced energy deficit session (EED), and a mixed energy deficit session (MED). All experimental sessions will be separated by a one-week washout. The participants’ sleep will be monitored by ambulatory polysomnography, and the next morning’s appetitive response will be evaluated via ad libitum food intake, appetite sensations, and food reward, measured by a food liking and wanting computerized test.

In recent years, running has dramatically increased in children and adolescents, creating a need for a better understanding of running gait in this population; however, research on this topic is still limited. During childhood and adolescence multiple factors exist that likely influence and shape a child’s running mechanics and contribute to the high variability in running patterns. The aim of this narrative review was to gather together and assess the current evidence on the different factors that influence running gait throughout youth development. Factors were classified as organismic, environmental, or task-related. Age, body mass and composition, and leg length were the most researched factors, and all evidence was in favour of an impact on running gait. Sex, training, and footwear were also extensively researched; however, whereas the findings concerning footwear were all in support of an impact on running gait, those concerning sex and training were inconsistent. The remaining factors were moderately researched with the exception of strength, perceived exertion, and running history for which evidence was particularly limited. Nevertheless, all were in support of an impact on running gait. Running gait is multifactorial and many of the factors discussed are likely interdependent. Caution should therefore be taken when interpreting the effects of different factors in isolation.

This study aimed to determine the short-term effect of two isocaloric diets differing in the ratio of protein–carbohydrate on melatonin levels, sleep, and subsequent dietary intake and physical activity in healthy young men. Twenty-four healthy men took part in a crossover design including two sessions of three days on isocaloric diets whether high-protein, low-carbohydrate (HPLC) or low-protein, high-carbohydrate (LPHC) followed by 24-h free living assessments. Sleep was measured by ambulatory polysomnography pre-post-intervention. Melatonin levels were assessed on the third night of each session on eight-point salivary sampling. Physical activity was monitored by accelerometry. On day 4, participants reported their 24-h ad-libitum dietary intake. LPHC resulted in better sleep quality and increased secretion of melatonin compared to HPLC. A significant difference was noted in sleep efficiency (p < 0.05) between the two sessions. This was mainly explained by a difference in sleep onset latency (p < 0.01) which was decreased during LPHC (PRE: 15.8 ± 7.8 min, POST: 11.4 ± 4.5 min, p < 0.001). Differences were also noted in sleep staging including time spent on REM (p < 0.05) and N1 (p < 0.05). More importantly, REM latency (PRE: 97.2 ± 19.9 min, POST 112.0 ± 20.7 min, p < 0.001) and cortical arousals (PRE: 7.2 ± 3.9 event/h, POST 8.5 ± 3.3 event/h) increased in response to HPLC diet but not LPHC. On day 4, 24-h ad-libitum energy intake was higher following HPLC compared to LPHC (+64 kcal, p < 0.05) and explained by increased snacking behavior (p < 0.01) especially from carbohydrates (p < 0.05). Increased carbohydrates intake was associated with increased cortical arousals.

BACKGROUND Although adolescence and obesity are related to impaired sleep duration and quality, exercise was admitted as a nonpharmacological treatment for sleep and better control of energy balance. OBJECTIVES To investigate the acute effects of intense exercise on sleep and subsequent dietary intake. METHODS Sixteen adolescent girls with obesity (age 13.7 ± 1.1 years, weight 82.7 ± 10.2 kg, body mass index (BMI) 30.5 ± 3.4 kg/m2 , fat mass (FM) 39.2 ± 3.1%, Pittsburgh Sleep Quality Index (PSQI) 8.6 ± 2.8, paediatric daytime sleepiness scale (PDSS) 19.6 ± 5.9) took part in two experimental sessions in a random order: Control (CTL) and Exercise (EX). The two sessions were identical except for a continuous ergocycle exercise bout lasting 40 minutes and performed at 70% VO2max at the end of the morning of EX. Energy expenditure and sleep were measured by accelerometry and next-morning dietary intake in an ad libitum meal. RESULTS Higher sleep duration (P

Juvenile idiopathic arthritis (JIA) is a chronic inflammatory disease characterized by persistent joint inflammation that manifests as joint pain and swelling and limited range of joint motion. In healthy subjects, the literature reports that physical activity has an anti-inflammatory effect. In JIA patients, exercise could be used as a therapeutic tool to counteract disease-related inflammation and thereby improve clinical symptoms, although transient flare of pain could be the price to pay. Indeed, in patients with a chronic inflammatory disease, physical activity is prone to exacerbate underlying inflammatory stress. Physical activity improves quality of life and symptoms in JIA patients, but the mechanisms of action remain unclear. This review focuses on the mechanisms underlying exercise-induced immune and hormonal changes. Data on the impact of acute and chronic physical activities on the secretion of hormones and other molecules such as miRNA or peptides involved in the inflammatory process in JIA was compiled and summarized, and the key role of the biological effect of muscle-derived interleukin 6 in the exercise-induced modulation of pro/anti-inflammatory balance is addressed. We also go on to review the effect of training and type of exercise on cytokine response. This review highlights the beneficial effect of physical exercise in children with JIA and potential effect of exercise on the balance between pro- and anti-inflammatory response.

Acute exercise has been shown to induce nutritional adaptations in obese and lean inactive youth but it remains unclear whether youth with a high level of physical activity experience such exercise-induced energy intake and appetite modifications.14 (15- to 16-year-old) male elite rugby players completed sessions on three separate occasions: (1) a control session (CON); (2) an exercise session (EX) and; (3) a rugby session (RUGBY). The energy induced by the rugby and exercise sessions was matched (Polar Team2 pro technology), and participants' energy intake, food preferences (ad libitum buffet meals) and appetite feelings (Visual Analogue Scales) were assessed throughout the experimental days.The energy intake during lunch and snack time was not different between conditions. Dinner time energy intake was significantly increased after RUBGY compared to CON with respectively 969 ± 145 kcal and 777 ± 183 kcal (p 0.05). The energy intake at dinner time was significantly increased during EX (1185 ± 199 kcal) compared to both CON (p 0.001) and RUGBY (p 0.01). None of the appetite feelings investigated were modified between sessions.Adolescent elite rugby players regulate their energy intake differently depending on the nature of their training; independently of the energy expended. This demonstrates the need for energetic and nutritional education to optimize their physical fitness and performance.

Background Acute intensive exercise has been shown to induce a decreased subsequent daily energy intake in obese adolescents without altering the subjective appetite feelings. It is however unclear whether or not those nutritional adaptations to acute exercise are affected by the adolescents' weight status. The aim of this study was to compare the energy intake and macronutrient preferences, appetite feeling and energy expenditure response to acute exercise between lean and obese adolescents. Methods Ten obese and nine normal weight 12-15 year old adolescents randomly completed a session with a 30 minute cycling exercise at 75% VO2max and a sedentary session. During both sessions energy expenditure was assessed using Armband, ad libitum energy intake measured by weighing at both lunch and dinner time and appetite feelings assessed using visual analog scales. Results Daily, morning and afternoon energy expenditure were significantly higher in obese than in normal weight adolescents (p < 0.001). Total energy expenditure was significantly higher during EX (1086 ± 157 kcal) compared to SED (853 ± 154 kcal) in lean (p < 0.05) but not significantly different in obese (respectively 1865 ± 222 and 1803 ± 232 kcal). Afternoon energy expenditure was significantly lower during EX compare to SED in obese (p < 0.05) but not in normal weight adolescents. Lunch, dinner and total daily energy intake were significantly reduced after the exercise session in obese (p > 0.05) but not in lean adolescents. No group or condition effects were observed on subjective appetite feelings. Discussion Post exercise spontaneous energy intake and energy expenditure are reduced in obese but not in normal weight adolescents, without appetite feeling changes. Acute exercise may have a greater impact on energy balance through the induced decreased energy intake in the absence of significant change in energy expenditure in obese youth.

International audience; Our purpose was to investigate the effect of obesity in prepubertal children on the hormonal response to exercise performed under different conditions of nutrient availability. Prepubertal obese (age, 10.3 +/- 1.8 years; % body fat, 36.1 +/- 6.1; n = 9) and lean (age, 9.2 +/- 1.6 years; % body fat, 22.2 +/- 4.1; n = 7) children completed 2 experimental sessions in which they performed a 30 min of cycling exercise at 50% of their maximal aerobic power either 1 h (T1h) or 3 h (T3h) after a standardized breakfast. Plasma insulin-like growth factor 1 (IGF-1), IGF binding protein 1 (IGFBP-1), and IGFBP-3 levels were assessed at baseline and after exercise. Urine was collected during the sessions, and catecholamine and glucocorticoid excretions were analyzed. A significant time effect was observed for IGFBP-1; postexercise levels decreased in lean and obese children (p

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

International audience; 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 (EX(2)) was conducted following 6 weeks of diet modification and physical activity (3 x 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), EX(2) 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

International audience; Although physical activity is primarily considered for its effects on energy expenditure for prevention and treatment of both overweight and obesity, its role in the regulation and control of energy balance seems more complex. Not only does physical activity affect energy expenditure, it also leads to modifications in energy intake and appetite that have been identified in children and that should be considered for weight loss. It also appears that it may not systematically favor increased energy expenditure due to individual differences in compensatory responses. This brief paper summarizes the pediatric evidence regarding those potential compensatory responses to physical activity and suggests that these compensatory responses of increasing physical activity levels may depend on children’s adiposity status.

International audience; Purpose: This study was performed to investigate whether changes in biomechanical parameters of walking explain the reduction in net metabolic cost after weight loss in obese adolescents.Methods: Body composition and metabolic and mechanical energy costs of walking at 1.25 m·s(-1) were assessed in 16 obese adolescents before and after a weight loss. Center of mass (COM) and foot accelerations were measured using two inertial sensors and integrated twice to determine COM and foot velocities and displacements. Potential and kinetic energy fluctuations of the COM and the external mechanical work were calculated. Lateral leg swing was calculated from foot displacements.Results: As expected, the decrease in net metabolic cost was greater, which would have been expected on the basis of the amount of weight loss. The smaller lateral leg swing after weight loss did not explain part of the decrease in net metabolic cost. The reduced body mass required less leg muscle work to raise and accelerate the COM as well as to support body weight. The decrease in body mass seems also associated with a lesser leg muscle work required to raise the COM because of smaller vertical motions. As a result of the inverted pendulum mechanism, the decrease in vertical motions (hence in potential energy fluctuations) was probably related to the decrease in mediolateral kinetic energy fluctuations. Moreover, the lesser amount of fat mass in the gynoid region seems related to the decrease in net metabolic cost of walking.Conclusions: The reduction in net metabolic cost of walking after weight loss in weight-reduced adolescents is associated with changes in the biomechanical parameters of walking.

Background Obesity is increasing worldwide, reaching alarming proportions. Eating habits have changed over time and nowadays children and adolescents' environment favours the adoption of unhealthy eating behaviours leading to metabolic impairment. Objective To explore the impact of eating risk factors and their cumulative effect on anthropometric characteristics in French primary school children. Methods A total of 278 healthy French children (7.50 ± 0.67 years old) and their legal representatives agreed to take part in this study. Parents were asked to fill in an eating habits clinical questionnaire with questions about skipping breakfast, snacking between meals, eating in front of the TV and sugar-sweetened beverage consumption. On the basis of the answers, children were classified into four categories as a function of the number of eating risk factors they presented. Body mass index (BMI), the sum of four skinfolds (Σ4 skinfolds: tricipital, bicipital, sub-scapular and supra-iliac) and waist circumference (WC) were measured. BMI was transformed into z-BMI for each child. Results anova and unpaired t-test provided significantly higher z-BMI, Σ4 skinfolds and WC in children who were used to skipping breakfast, snacking, watching TV while eating and consuming sugar-sweetened beverages. The more children accumulated eating risk factors, the higher were their z-BMI, Σ4 skinfolds and WC (manova: P

Defining and detecting the metabolic syndrome in children and adolescents is difficult because of ongoing discussion of components and thresholds. The aim of this work was to highlight the limitations of a dichotomous definition of the metabolic syndrome, leading to considerable overlap between those with and without the metabolic syndrome, by computing different continuous scores.A total of 50 children and adolescents ages 6-16 years were studied. Height and weight were measured; body mass index (BMI) was calculated, and obesity was defined by age- and sex-specific 97(th) percentiles of French reference values. Metabolic syndrome prevalence was based on the criteria reported by Chen et al. in 2006 and compared with five scores reflecting specific metabolic syndrome components (MetScores): Fat mass, waist circumference, BMI, homeostasis model assessment (HOMA), and systolic blood pressure.Using a standard clinical definition, 48% of obese children and adolescents were diagnosed with metabolic syndrome. The prevalence of metabolic syndrome in the sample was much higher using specific MetScores: Fat mass, 92%; waist circumference, 94%; BMI, 94%; HOMA, 98%; and systolic blood pressure, 84%. Insulin resistance (IR), assessed as a high HOMA index, was present in 68% of the sample, and was the metabolic syndrome component with the highest prevalence.The use of a continuous indicator of the metabolic syndrome, such as MetScores, may help to overcome limitations imposed by dichotomous definitions, particularly among obese children and adolescents. A high prevalence of IR indicates the relevance of HOMA in detection of the metabolic syndrome.

Aim: To fight overweight and obesity in childhood, this study proposes an additional physical activity (PA) in young children aged 6‐10 years. The objective was to evaluate the effect of school-based PA on the body composition according to body mass index (BMI) categories (nonobese vs. obese) and gender. Methods: This 6-month study examined the effect of this intervention on body composition in 425 children in 14 primary schools (2 weekly PA sessions of 1 h each) compared to 5 control schools. Adiposity indices were evaluated or calculated: BMI, BMI z-score, waist circumference, sum of skinfolds and fat-free mass. Results: No difference in the prevalence of obesity and anthropometric characteristics was found between the intervention and control groups at baseline. In girls, PA intervention had significant effect on all anthropometric variables (p < 0.05 to p < 0.001), except on BMI. In contrast, in boys only BMI z-score (p < 0.001) and fat-free mass (p < 0.001) were affected. Conclusions: Six months of preventive PA intervention offer an effective means to improve body composition in obese children. The pattern of response related to PA was similar between girls and boys. In contrast, the pattern was different according to BMI category, with a higher response in obese than nonobese children.

International audience; This pilot study compared the rating of perceived exertion scores (RPE) in young girls for two modalities of exercises (running vs cycling) performed at the same absolute heart rate. 23 girls, ages 8 to 11 years, from a gymnastic club performed graded, intermittent, and submaximal running and cycling exercises at a similar absolute heart rate (±5 bpm). These exercises consisted of three stages of 3 min. duration separated by 1-min. recovery intervals. RPE was estimated using the Children's Effort Rating Table scale at the end of each stage of each exercise. Mean ratings were only significantly different during cycling, compared to running for the Stage 3 (cycling 5.3 ± 2.7 and running 7.0 ± 1.9, p < .05). During low exercise intensity, measured as heart rate, the modality of exercise does not seem to affect RPE. In contrast, with high heart rates, RPE are higher during cycling than running, so it is necessary to take account of the type of exercise.

The aim of the present study was to compare physiological data obtained during cycling using a noncircular "Harmonic" chainring versus a standard circular chainring over a range of speeds and slopes in endurance-trained cyclists. Thirteen male subnational cyclists (16-45 years) performed two maximal graded exercises on their own bicycle: one with a circular chainring, the other with a Harmonic chainring with the same gearwheel (52 teeth). The two chainrings were randomly assigned to avoid learning effects. The tests were carried out on a simulator. Speeds and/or slopes were increased every 2 min 30 s until exhaustion of the subject. Ventilation, oxygen uptake, carbon dioxide output, respiratory exchange ratio, and heart rate were continuously measured during the tests. Blood lactate concentration was measured during the last 30 s of each level. No significant difference was observed in any of the submaximal parameters measured during the tests ( P>0.05). Similarly, maximal values were not statistically different ( P>0.05). In conclusion, although the design of the Harmonic chainring was based on optimization analysis, comparison of the physiological response in this study did not translate into an advantage of the Harmonic over circular chainring during submaximal and maximal pedaling in trained cyclists.

The aim of this study was to examine the consistency or reproducibility of measuring cycling peak power in children and adults. Twenty-seven pre-pubertal girls and boys and 27 female and male physical education students (age 9.8 +/- 0.5 and 24.4 +/- 4.3 years, respectively; mean +/- s) participated in the study. All participants performed five tests over 15 days and underwent a habituation session before the study. Each test included four sprints against four different braking forces. We found that braking forces of 7.5% of body weight in children and 10% of body weight in adults were too high for most of the participants to elicit maximal cycling power. Unlike the children, the physical education students improved their performance between session 1 and session 2 (1025 +/- 219 vs 1069 +/- 243 W; P0.001). Therefore, to obtain reproducible measures of cycling peak power, a habituation session including a complete test protocol (i.e. warm-up plus three sprints) is highly recommended. When the protocol included three sprints in children and at least two sprints in adults, measurement of cycling peak power was found to be highly reliable (test-retest coefficient of variation approximately 3%). Finally, to avoid performance fluctuations, especially over several consecutive evaluations (e.g. longitudinal studies), it is necessary to maintain high motivation in children.

Resume Introduction L'objectif est d'evaluer les effets d'un programme d'activite physique multidisciplinaire sur la perception de la contrainte d'un exercice aerobie et anaerobie chez l'enfant en fonction de son statut ponderal. Methode La population d'etude est composee de 56 enfants (28 obeses vs 28 non obeses) qui ont participe pendant 11 semaines a deux seances d'une heure d'activite physique hebdomadaires. Des mesures anthropometriques, d'aptitudes physiques aerobie et anaerobie ainsi que de la perception de la contrainte au cours de ces tests ont ete effectuees. Resultats L'intervention a ameliore significativement les parametres de la composition corporelle, les performances aerobie et anaerobie ainsi que le niveau de la perception de contrainte imposee. Conclusion Ces resultats suggerent que le statut ponderal doit etre pris en compte dans les programmes d'activite physique multidisciplinaire de prevention de l'obesite infantile, afin de promouvoir les activites physiques a long terme.

International audience

The imbalance between energy expenditure and energy intake is the main factor accounting for the progression of obesity. For many years, physical activity has been part of weight-loss programmes to increase energy expenditure. It is now recognized that exercise can also affect appetite and energy consumption. In the context of seeking new obesity treatments, it is of major interest to clarify the impact of physical exercise on energy intake. Many reviews on this topic have been published regarding both lean and overweight adults, and this review focuses on the relationships between acute exercise and the short-term regulation of energy intake in lean and overweight or obese youths. The current literature provides very few data regarding the impact of exercise on subsequent energy intake and perceived and measured appetite in children and adolescents, mainly because of methodological difficulties in the assessment of both energy intake and expenditure. It has been long suggested that energy intake was regulated after exercise in order to compensate for the exercise-induced energy expenditure and then preserve energy balance. This overview underlines that the energy expended during exercise is not the main parameter that influences subsequent energy intake in both lean and overweight/obese children and adolescents, and that factors such as the duration or intensity of exercise may have larger impact. The effects of acute exercise on the following nutritional adaptations (energy intake and appetite feelings) remain inconclusive in lean youths, mainly due to the lack of data and the disparity of the methodologies used. Studies in overweight or obese children and adolescents are confronted with the same difficulties, and the few available data suggest that intensive exercise (>70% maximal oxygen consumption) can induce a reduction in daily energy balance, as a result of its anorexigenic effect in obese adolescents. However, further studies are needed to clarify the impact of acute exercise on subsequent nutritional adaptations and appetite-related hormones in children and adolescents, and to investigate the effect of chronic exercise programmes.

The aim of the present study was to determine whether differences in age-related heart rate recovery (HRR) kinetics were associated with differences in power output, blood lactate concentration ([La]b), and acidosis among children, adolescents, and adults. Ten prepubertal boys (aged 9.6 ± 0.7 years), 6 pubertal boys (aged 15.2 ± 0.8 years), and 7 men (aged 20.4 ± 1.0 years) performed 10 repeated 10-s all-out cycling sprints, interspersed with 5-min passive recovery intervals. Mean power output (MPO) was measured during each sprint, and HRR, [La]b, and acidosis (pHb) were determined immediately after each sprint. Children displayed a shorter time constant of the primary component of HRR than adolescents and adults (17.5 ± 4.1 vs. 38.0 ± 5.3 and 36.9 ± 4.9 s, p < 0.001 for both), but no difference was observed between adolescents and adults (p = 1.00). MPO, [La]b, and pHb were also lower in children compared with the other 2 groups (p < 0.001 for both). When data were pooled, HRR was significantly correlated with MPO (r = 0.48, p < 0.001), [La]b (r = 0.58, p < 0.001), and pHb (r = –0.60, p < 0.001). Covarying for MPO, [La]b, or pHb abolished the between-group differences in HRR (p = 0.42, p = 0.19, and p = 0.16, respectively). Anaerobic glycolytic contribution and power output explained a significant portion of the HRR variance following high-intensity intermittent exercise. The faster HRR kinetic observed in children appears to be related, at least in part, to their lower work rate and inherent lack of anaerobic metabolic capacity.

Net metabolic cost of walking normalized by body mass ( CW·BM−1; in J·kg−1·m−1) is greater in obese than in normal-weight individuals, and biomechanical differences could be responsible for this greater net metabolic cost. We hypothesized that, in obese individuals, greater mediolateral body center of mass (COM) displacement and lower recovery of mechanical energy could induce an increase in the external mechanical work required to lift and accelerate the COM and thus in net CW·BM−1. Body composition and standing metabolic rate were measured in 23 obese and 10 normal-weight adolescents. Metabolic and mechanical energy costs were assessed while walking along an outdoor track at four speeds (0.75–1.50 m/s). Three-dimensional COM accelerations were measured by means of a tri-axial accelerometer and gyroscope and integrated twice to obtain COM velocities, displacements, and fluctuations in potential and kinetic energies. Last, external mechanical work (J·kg−1·m−1), mediolateral COM displacement, and the mechanical energy recovery of the inverted pendulum were calculated. Net CW·BM−1was 25% higher in obese than in normal-weight subjects on average across speeds, and net CW·BM−67(J·kg−0.67·m−1) was significantly related to percent body fat ( r2= 0.46). However, recovery of mechanical energy and the external work performed (J·kg−1·m−1) were similar in the two groups. The mediolateral displacement was greater in obese subjects and significantly related to percent body fat ( r2= 0.64). The mediolateral COM displacement, likely due to greater step width, was significantly related to net CW·BM−67( r2= 0.49). In conclusion, we speculate that the greater net CW·BM−67in obese subjects may be partially explained by the greater step-to-step transition costs associated with wide gait during walking.