Cardiorespiratory function during exercise in obese children

Comprehensive cardiac evaluation to maximal exercise in a contemporary population of prepubertal children

BACKGROUND

Heart rate (HR) is a biomarker used to measure physiological function, health status and cardiovascular autonomic function. The purpose of this study was to determine sex- and age-specific reference values for cardiac autonomic function at rest, during maximal exercise and the recovery phase in prepubertal children.

METHODS

Five hundred and twelve healthy children 7-11 years of age performed a Léger test. A heart RR-interval monitor recorded the heart data and a specific software analysed the cardiac autonomic response through HR and HR variability (HRV). It analysed HR before the test (resting HR, RHR), during the test (HR_peak) and HR recovery (HRR) in the first minute (HRR1) and the fifth minute (HRR5). The values are mean ± SD.

RESULTS

Collectively, 91.2% of girls and 92.3% of boys were within the recommended ranges regarding RHR. The average HR_peak was 199 ± 10.83 b.p.m. and 96.8% of girls and 95.3% of boys were within the minimum threshold value recommended (180 b.p.m.). Boys showed lower values of RHR than girls (p < 0.001) and larger values of HRR 1 and HRR5 (p < 0.001).

CONCLUSIONS

This study comprehensively provides a reference set of data for the most important HR variables that can be obtained during exercise testing in prepubertal children regarding age and sex and in a field setting.

IMPACT

This is the first study to provide reference values of autonomic cardiac function at rest, during maximal exercise and during the recovery period in prepubertal children aged 7-11 years. Despite the early age of participants, cardiorespiratory fitness, RHR and HRR are different according to sex. Aerobic performance and HR_peak have a negative correlation with body mass index and cardiometabolic risk.

The Effect of Body Mass Index on Acute Cardiometabolic Responses to Graded Exercise Testing in Children: A Narrative Review

Although the beneficial role of exercise for health is widely recognized, it is not clear to what extent the acute physiological responses (e.g., heart rate (HR) and oxygen uptake (VO₂)) to a graded exercise test are influenced by nutritional status (i.e., overweight vs. normal-weight). Therefore, the main objectives of the present narrative review were to examine the effect of nutritional status on acute HR, and VO₂ responses of children to exercise testing. For this purpose, we examined existing literature using PubMed, ISI, Scopus, and Google Scholar search engines. Compared with their normal-body mass index (BMI) peers, a trend of higher HRrest, higher HR during submaximal exercise testing, and lower HRmax was observed among overweight and obese children (according to BMI). Independent from exercise mode (walking, running, cycling, or stepping), exercise testing was metabolically more demanding (i.e., higher VO₂) for obese and overweight children than for their normal-weight peers. Considering these cardiometabolic differences according to BMI in children might help exercise specialists to evaluate the outcome of a graded exercise test (GXT) (e.g., VO2max, HRmax) and to prescribe optimal exercise intensity in the context of development of exercise programs for the management of body mass.

Exercise intolerance in obese children and adolescents

Background: Abnormal lung function has been reported in the obese population and is associated with the severity of obesity.

Objectives: To identify abnormal lung function in obese children and adolescents, and examine the cardiopulmonary response of those who have abnormal lung functions during exercise, and to reveal predictors of exercise intolerance in this population.

Methods: Fifty obese participants aged 8–18 years (56% male; mean age 13.2 ± 2.0 years; mean BMI 33.0 ± 3.6 kg/m2, mean BMI z score 3.1 ± 0.3) underwent spirometry, lung volume evaluation, and a cardiopulmonary exercise test.

Results: Lung function abnormalities and exercise intolerance because of pulmonary limitations were found in 36% and 74% of the participants, respectively. A comparison of participants with normal and abnormal lung functions revealed a lower breathing reserve and a higher ventilatory equivalent for CO2 production (VE/VCO2) during exercise in those who had lung function abnormalities (18 ± 15 vs 30±10%, P <0.001 and 30.3 ± 3.3 vs 29.6 ± 3.1; P = 0.02, respectively). Exercise intolerant participants had a higher BMI z score compared with those who were not (3.1 ± 0.3 vs 2.9 ± 0.3; P = 0.03). BMI z score ≥ 2.84 had an 80% sensitivity and 67% specificity for predicting exercise intolerance in this population.

Conclusions: Evaluations of lung function and exercise capacity should be included in the follow-up planning for obese children and adolescents. A BMI z score ≥ 2.84 was most sensitive for predicting exercise intolerance in this population.

Physiological response is similar in overweight and normoweight boys during cycling: a longitudinal study

The purpose of this study was to determine whether metabolic cost is similar in overweight and normoweight children when workload during exercise on a cycle-ergometer is adjusted relative to an objectively determined second ventilatory threshold (VT2) or the maximal workload (Pmax). The tests were conducted every 2 years: first at the age of 10 years and the third test at around the age of 14 years. The levels of maximal oxygen consumption (VO(2)max), Pmax, and the VT2 were determined by means of graded tests on a cycle ergometer. The main test consisted of two 6-minute exercises of submaximal constant intensity (below and above VT2) performed on a cycle ergometer, with a 4-minute recovery between efforts. The workload during cycling was adjusted individually for each participant and adjusted to the values determined in the graded test: workload at VT2 and Pmax. Physiological response (absolute and relative to free-fat mass oxygen uptake, heart rate, pulmonary ventilation, tidal volume, and breathing frequency) is similar in overweight and normoweight boys when workload on a cycle ergometer is adjusted to VT2. The only significant intergroup difference was seen in relative to body mass oxygen intake.

Obesity: the new childhood disability?

This review addresses the impact of obesity on paediatric physical functioning utilizing the World Health Organization International Classification of Functioning, Disability and Health Framework (ICF). The ICF encompasses functioning (as it relates to all body functions and structures), activities (undertaking a particular task) and participation (in a life situation) with disability referring to impairments in body functions/structures, activity restrictions or participation limitations. Electronic databases were searched for peer-reviewed studies published in English prior to May 2009 that examined aspects of physical functioning in children (≤18 years). Eligible studies (N = 104) were ranked by design and synthesized descriptively. Childhood obesity was found to be associated with deficits in function, including impaired cardiorespiratory fitness and performance of motor tasks; and there was some limited evidence of increased musculoskeletal pain and decrements in muscle strength, gait and balance. Health-related quality of life and the subset of physical functioning was inversely related to weight status. However, studies investigating impacts of obesity on wider activity and participation were lacking. Further research utilizing the ICF is required to identify and better characterize the effects of paediatric obesity on physical function, activity and participation, thereby improving targets for intervention to reduce disability in this population.

Effectiveness of weight management interventions in children: a targeted systematic review for the USPSTF

CONTEXT

Targeted systematic review to support the updated US Preventive Services Task Force (USPSTF) recommendation on screening for obesity in children and adolescents.

OBJECTIVES

To examine the benefits and harms of behavioral and pharmacologic weight-management interventions for overweight and obese children and adolescents.

METHODS

Our data sources were Ovid Medline, PsycINFO, the Education Resources Information Center, the Database of Abstracts of Reviews of Effects, the Cochrane databases, reference lists of other reviews and trials, and expert recommendations. After 2 investigators reviewed 2786 abstracts and 369 articles against inclusion/exclusion criteria, we included 15 fair- to good-quality trials in which the effects of treatment on weight, weight-related comorbidities, and harms were evaluated. Studies were quality rated by 2 investigators using established criteria. Investigators abstracted data into standard evidence tables.

RESULTS

In the available research, obese (or overweight) children and adolescents aged 4 to 18 years were enrolled, and no studies targeted those younger than 4 years. Comprehensive behavioral interventions of medium-to-high intensity were the most effective behavioral approach with 1.9 to 3.3 kg/m(2) difference favoring intervention groups at 12 months. More limited evidence suggests that these improvements can be maintained over the 12 months after the end of treatments and that there are few harms with behavioral interventions. Two medications combined with behavioral interventions resulted in small (0.85 kg/m(2) for orlistat) or moderate (2.6 kg/m(2) for sibutramine) BMI reduction in obese adolescents on active medication; however, no studies followed weight changes after medication use ended. Potential adverse effects were greater than for behavioral interventions alone and varied in severity. Only 1 medication (orlistat) has been approved by the US Food and Drug Administration for prescription use in those aged > or =12 years.

CONCLUSIONS

Over the past several years, research into weight management in obese children and adolescents has improved in quality and quantity. Despite important gaps, available research supports at least short-term benefits of comprehensive medium- to high-intensity behavioral interventions in obese children and adolescents.

Limiar de variabilidade da freqüência cardíaca em adolecentes obesos e não-obesos

A obesidade na adolescência está associada à disfunção simpato-vagal cardíaca em repouso, embora existam poucas informações sobre a resposta autonômica durante o exercício nestes adolescentes. OBJETIVO: Comparar a modulação autonômica durante teste de esforço físico dinâmico incremental em amostras de adolescentes obesos e não-obesos, e analisar a relação entre o limiar de variabilidade da freqüência cardíaca (LiVFC) e o limar ventilatório (LV). MÉTODOS: Dez adolescentes obesos e 19 adolescentes não-obesos do sexo masculino com idades entre 13 e 18 anos foram submetidos à teste de esforço físico progressivo máximo em esteira rolante para estudo da variabilidade da freqüência cardíaca (VFC) e para identificação do LV. A VFC foi estudada mediante análise do desvio-padrão da variabilidade instantânea batimento-a-batimento (SD1) da Plotagem de Poincaré. O LiVFC foi identificado na intensidade de esforço físico em que o SD1 atingiu valor menor que 3 ms. RESULTADOS: O índice SD1 diminuiu progressivamente em ambos os grupos até aproximadamente 50-60% do VO2pico, sendo que os adolescentes obesos apresentaram valores significativamente menores (p<0,001) somente na intensidade relativa a 20% do VO2pico, Os adolescentes obesos apresentaram valores relativos (mL.kg-1.min-1) de VO2pico e LV significativamente menores (p<0,05) que os adolescentes não-obesos. Em ambos os grupos, não foram observadas diferenças significativas entre o ponto de ocorrência do LV e do LiVFC, expressos em valores relativos e absolutos de VO2. Contudo, não foram encontradas correlações significativas entre o ponto de ocorrência do LV e do LiVFC, tanto em valores relativos quanto em valores absolutos de VO2. CONCLUSÕES: A obesidade na adolescência parece não estar associada à alteração da modulação autonômica durante o exercício físico. Torna-se possível determinar o LiVFC mediante análise da Plotagem de Poincaré em adolescentes obesos e não-obesos. Entretanto, a ausência de associação estatística entre o LiVFC e o LV demonstra que parece não haver relação causal entre estes eventos.

Energy cost of walking in boys who differ in adiposity but are matched for body mass

PURPOSE

To compare the energy cost of treadmill walking, in pairs of obese and lean adolescents who were matched for total body mass.

METHODS

Metabolic energy expenditure was determined at 67, 83, and 100 m.min-1, in nine obese and nine nonobese 11- to 18-yr-old boys. Total adiposity and fat distribution in the trunk and limbs were assessed using DXA.

RESULTS

There were no intergroup differences in the net (exercise minus rest) energy cost at the two lower speeds, but the obese boys expended more energy at 100 m.min-1 (12%, P < 0.05). Heart rate was consistently higher in the obese boys: 18% at 67 m.min-1, 22% at 83 m.min-1, and 28% at 100 m.min-1. Pooling all subjects together, body mass, rather than adiposity, was the main predictor of energy cost: 89.1%, 76.3%, and 62.1% (P < 0.05 for all) of the total variance at 67, 83, and 100 m.min-1, respectively. The variance explained by total body fat was only 2.1%, 8.4%, and 16%, respectively. There was no relationship between [OV0312]O(2net) and the proportion of fat in body segments.

CONCLUSION

It is total body mass, more than adiposity (total and regional) per se, that affects the energy cost of locomotion in obese boys.

Physical fitness and physical activity in obese and nonobese Flemish youth

OBJECTIVE

To assess different aspects of physical fitness and physical activity in obese and nonobese Flemish youth.

RESEARCH METHODS AND PROCEDURES

A random sample of 3214 Flemish schoolchildren was selected and divided into an "obese" and "nonobese" group based on body mass index and sum of skinfolds. Physical fitness was assessed by the European physical fitness test battery. Physical activity was estimated by a modified version of the Baecke Questionnaire.

RESULTS

Obese subjects had inferior performances on all tests requiring propulsion or lifting of the body mass (standing-broad jump, sit-ups, bent-arm hang, speed shuttle run, and endurance shuttle run) compared with their nonobese counterparts (p < 0.001). In contrast, the obese subjects showed greater strength on handgrip (p < 0.001). Both groups had similar levels of leisure-time physical activity; however, nonobese boys had a higher sport index than their obese counterparts (p < 0.05).

DISCUSSION

Results of this study show that obese subjects had poorer performances on weight-bearing tasks, but did not have lower scores on all fitness components. To encourage adherence to physical activity in obese youth, it is important that activities are tailored to their capabilities. Results suggest that weight-bearing activities should be limited at the start of an intervention with obese participants and alternative activities that rely more on static strength used.

Total body fat does not influence maximal aerobic capacity

OBJECTIVE

The objective of this study was to examine the influence of body weight and body composition on aspects of aerobic fitness. Our hypothesis was that increased body weight, specifically increased fat mass (FM), would not limit VO2max relative to fat-free mass (FFM), but would reduce maximal and sub-maximal VO2max relative to body weight.

DESIGN

We used data from two ongoing studies. In Study 1 a cross-sectional analysis of 129 children across a wide spectrum of body composition was performed. In Study 2 we examined data from 31 overweight women before and after weight loss.

METHODS

VO2max was measured using a treadmill test. Sub-maximal aerobic capacity was evaluated with respiratory exchange ratio (RER), heart-rate (HR), and oxygen uptake relative to VO2max at a given workload (%VO2max). Body composition was assessed using dual energy X-ray absorptiometry (DXA) (Study 1) and a four-compartment model (Study 2).

RESULTS

In Study 1, FFM was the strongest determinant of VO2max (r=0.87; P<0.0001). After adjusting for FFM, there was no significant influence of FM on VO2max. After separating children into lean and obese sub-groups, absolute VO2max was significantly higher in the obese (1.24+/-0.27 vs 1.56+/-0.40) and VO2max relative to body weight was significantly lower (44.2+/-3.2 vs 32.0+/-4.1 ml/(kg-min)), whereas there was no significant difference when expressed relative to FFM (57.9+/-5.8 vs 59.2+/-4.9 ml/(kgFFM-min)). Sub-maximal aerobic capacity was significantly lower in the obese children, as indicated by a higher HR and %VO2max; time to exhaustion was significantly lower in the obese children (15.3+/-2.9 vs 11.1+/-2.1 min). In Study 2, FFM was also the strongest determinant of VO2max before and after weight loss. The relationship between VO2max and FFM was identical before and after weight loss so that VO2max relative to FFM was identical before and after weight loss (43.8+/-4.9 vs 45.5+/-6.4 ml/(kgFFM-min)). However, sub-maximal aerobic capacity was lower in the obese state, as indicated by a significantly higher RER (0.85+/-0.06 vs 0.79+/-0.05), HR (124+/-14 vs 102+/-11 bpm), and %VO2max (44% vs 36%).

CONCLUSION

The major influence of body weight on VO2max is explained by FFM; FM does not have any effect on VO2max. Fatness and excess body weight do not necessarily imply a reduced ability to maximally consume oxygen, but excess fatness does have a detrimental effect on submaximal aerobic capacity. Thus, fatness and VO2max should be considered independent entities.

Gait and postural stability in obese and nonobese prepubertal boys

OBJECTIVE

To examine differences in gait and postural stability of obese and nonobese prepubertal boys.

DESIGN

Percentage of gait cycle in double support was examined to determine significant differences. Postural stability was compared using temporal and frequency measures of the center of pressure in static stance.

SETTING

Gait was examined using videography on a 30-meter walkway. Postural stability was examined using a measurement platform.

PARTICIPANTS

Ten obese (>95th percentile in body mass index) and 10 nonobese (15th to 90th percentile in body mass index) prepubertal boys aged 8 to 10yrs.

INTERVENTION

Participants were examined at three walking cadences as determined by preferred gait cadence. Full vision, darkness, and visually confused conditions were used to accentuate static postural stability differences.

MAIN OUTCOME MEASURES

In the presence of dynamic stability differences (gait), static stability measures further investigated stability differences.

RESULTS

Obese boys spent significantly (p < .02) greater percentage of gait cycle in dual stance. Obese boys showed significantly (p < .01) greater sway areas, energy, and variability primarily in the medial/lateral direction.

CONCLUSIONS

Dual stance differences suggest diminished dynamic stability in obese boys. Greater sway areas in medial/lateral direction in obese boys and the absence of significant frequency measures suggest that the instability observed in obese boys is caused by excess weight rather than underlying postural instability.

Maximal aerobic power during running and cycling in obese and non-obese children

The maximal aerobic capacity while running and cycling was measured in 22 prepubertal children (mean age +/- SD 9.5 +/- 0.8 years): 14 obese (47.3 +/- 10 kg) and 8 non-obese (31.1 +/- 6.1 kg). Oxygen consumption (VO2) and carbon dioxide production were measured by an open circuit method. Steady state VO2 was determined at different levels of exercise up to the maximal power on the cycloergometer (92 W in obese and 77 W in non-obese subjects) and up to the maximal running speed on the treadmill at a 2% slope (8.3 km/h in obese and 9.0 km/h in lean children). Expressed in absolute values, the VO2max in obese children was significantly higher than in controls (1.55 +/- 0.29 l/min versus 1.23 +/- 0.22 l/min, p < 0.05) for the treadmill test and comparable in the two groups (1.4 +/- 0.2 l/min versus 1.16 +/- 0.2 l/min, ns) for the cycloergometer test. When VO2max was expressed per kg fat free mass, the difference between the two groups disappeared for both tests. These data suggest that obese children had no limitation of maximal aerobic power. Therefore, the magnitude of the workload prescribed when a physical activity program is intended for the therapy of childhood obesity, it should be designed to increase caloric output rather than to improve cardiorespiratory fitness.

The effect of fasting hyperinsulinaemia on physical fitness in obese children

Treadmill stress testing was carried out according to the Bruce protocol on 14 non-hyperinsulinaemic and 11 hyperinsulinaemic obese children and on 43 age-matched controls. The obese groups were matched for body weight, body composition, physical activity and plasma lipid values. Body composition was calculated on the basis of four skinfold measurements. Exercise duration and physical working capacity corrected for body weight and lean body mass were decreased in the obese children (P less than 0.01). The hyperinsulinaemic obese children had lower physical working capacities (in absolute values and when corrected for body weight and lean body mass) than the non-hyperinsulinaemic obese children (P less than 0.05). The exercise period was not significantly different in the two obese subgroups. While fasting plasma insulin levels showed a significant negative correlation with exercise duration and relative physical working capacity in the obese children, the anthropometric parameters did not. It is suggested that the decreased physical fitness in obese children is further aggravated in those with hyperinsulinaemia.

Are obese children truly unfit? Minimizing the confounding effect of body size on the exercise response

To test the hypothesis that obese children are unfit (i.e., have abnormal responses to exercise testing consistent with reduced levels of habitual physical activity), we used new analytic strategies in studies of 18 obese children performing cycle ergometry. The subject's weight (mean +/- SD) was 168 +/- 24% that predicted by height, and the age range was 9 to 17 years. Size-independent measures of exercise (e.g., the ratio of oxygen uptake (VO2) to work rate during progressive exercise and the temporal response of VO2, carbon dioxide output (VCO2), and minute ventilation (VE) at the onset of exercise) were used. The ability to perform external mechanical work was corrected for VO2 at unloaded pedaling (change in maximum oxygen uptake (delta VO2max) and in anaerobic threshold (delta AT). On average, obese children's responses were in the normal range: delta VO2max, 104 +/- 41% (+/- SD) predicted (by age); delta AT, 85 +/- 51%; ratio of change in VE to change in VCO2, 111 +/- 21% and ratio of change in VO2 to change in work rate, 100 +/- 24%, but six of the obese children had values of delta VO2max or delta AT that were more than 2 SD below normal. In addition, obese children did not have increased delta VO2max or delta AT with age as observed in nonobese children. Although the response time of VO2 was normal (99 +/- 32% of predicted), those for both VCO2 and VE were prolonged. We conclude that the finding of obesity in a child is not a reliable indicator of poor fitness but that testing cardiorespiratory responses to exercise can be used to identify subjects with serious impairment and to individualize therapy.

Exercise therapy and hypocaloric diet in the treatment of obese children and adolescents

Fourteen obese children and adolescents were treated with a combined therapy of low calorie diet and exercise and their progress compared to that of 11 obese children treated with diet only. Children treated with combination therapy were encouraged to perform aerobic exercises daily, for a period of time which was calculated to consume approximately 250 kcal per exercise session. After 4 months of therapy, a significantly (P less than 0.05) larger decrease of % overweight was observed in the group of children treated with diet and exercise (-25 +/- 13.5%) than in those treated with diet only (-15.8 +/- 10.5%). Treatment compliance was better in the group treated with diet and exercise than in the group which followed a low calorie diet only. We think that unsupervised exercise therapy can be successfully combined with a low calorie diet in the treatment of childhood obesity.

Gas exchange during exercise in obese children

Twenty-three obese children, aged 9 to 14 years, ranging in percentage overweight from 26% to 83% (median 51.6% +/- 16.3%), and 37 normal-weight children, matched for sex, age and height, performed a maximal exercise test on a treadmill. Cardiorespiratory performance was assessed by determination of the ventilatory anaerobic threshold (VAT) expressed in ml O2/min per kg and as a percent of maximal oxygen uptake (% VO2max). VAT and VO2max related to body weight were significantly lower (P less than 0.01) in the obese than in the normal-weight children. VAT % VO2max was similar in the two groups. A significant correlation was found between VAT and VO2max both in the obese (r = 0.85) and in the control groups (r = 0.79). The habitual level of physical activity was lower in the obese subjects compared to the control subjects (P less than 0.001). In conclusion our study shows that physical fitness of overweight children is quantitatively lowered and that it can be assessed by VAT. VAT does not require a maximal test and is particularly useful in the ergometric study of subjects with exercise intolerance.

Metabolic evaluation of obese and nonobese siblings

OBJECTIVE

To test the hypotheses that obese adolescents have a lower resting metabolic rate and less aerobic endurance than their nonobese siblings.

DESIGN

Case-referent study of obese and nonobese siblings from the same kindred.

SETTING

Tertiary referral center.

PARTICIPANTS

Telephone screening of community volunteers resulted in a consecutive sample of 16 kindreds. Obese and nonobese siblings were similar in age, height, and pubertal status. Significantly more female subjects were in the obese group (p less than 0.01).

MEASUREMENTS AND MAIN RESULTS

Body composition studies revealed that the obese siblings had higher body fat (p less than 0.001) but that fat-free mass was similar to that of the lean siblings. Resting metabolic rates determined by indirect calorimetry for the obese and nonobese pairs did not differ. Although the obese siblings appeared less fit when maximal oxygen consumption was measured in relation to total weight, maximal oxygen consumption did not differ when values were standardized for fat-free mass.

CONCLUSIONS

The obese adolescents did not have a reduced resting metabolic rate. As in adults, the relationship between resting metabolic rate and fat-free mass was similar for obese and nonobese children and adolescents. Any decreased sport participation by the obese siblings was not due to inherent reductions in aerobic capacity.