Total body fat does not influence maximal aerobic capacity

Responses of lean and obese boys to repeated summer exercise in the heat bouts

PURPOSE

To determine the degree of natural acclimatization and artificially induced acclimation-related changes during repeated exercise in the heat bouts in seven lean and seven obese 9- to 12-yr-old boys during summer months.

METHODS

Beginning at random times during the summer, subjects underwent a 70-min exercise (30% VO(2max)) in the heat exposure (38 degrees C, 50% relative humidity) on six separate days.

RESULTS

On day 1, obese children were less naturally acclimatized as indicated by significantly higher baseline core temperatures (T(c)) (obese = 37.62 +/- 0.06 vs lean = 37.41 +/- 0.06; P < 0.004). By day 6 versus day 1, significant reductions in baseline T(c) were evident in both groups (obese = 37.41 +/- 0.04 vs lean = 37.18 +/- 0.04; both P < 0.05). Baseline T(c) in obese subjects by day 6 was similar to that of lean subjects on day 1. Daily reductions in exercise T(c) were evident in both groups (final exercising T(c) day 1 vs day 6: obese = 38.15 +/- 0.05 vs 37.89 +/- 0.05; lean = 38.17 +/- 0.09 vs 37.72 +/- 0.06 degrees C; both P < 0.001), occurring at a significantly slower rate in obese subjects (final exercise T(c) day 6 - day 1: obese vs lean = -0.26 +/- 0.04 vs -0.45 +/- 0.08 degrees C; P < 0.05). Significant reductions in exercising heart rate (HR) occurred in the lean but not the obese subjects by day 6 (final exercising HR day 1 vs day 6: obese = 132 +/- 3 vs 131 +/- 3, P > 0.05; lean = 138 +/- 3 vs 127 +/- 3 bpm; P < 0.001).

CONCLUSIONS

During summer months, obese children are less naturally heat-acclimatized and subsequently acclimate at a slower rate.

Insulin sensitivity, VO2max and body composition in severely obese Swedish children and adolescents

AIM

The aim of this study was to identify relationships between insulin sensitivity (SI), cardiorespiratory fitness and body composition in severely obese Swedish children and adolescents.

METHODS

Two hundred and twenty-eight obese children (119 girls, 8-16 years, body mass index (BMI) 23.2-57.0 kg/m(2)) performed a frequently sampled intravenous glucose tolerance test (FSIVGTT), a submaximal bicycle ergometry test and a dual-energy X-ray absorptiometry (DEXA).

RESULTS

Mean SI (SD) was 0.38 (0.32) (x10(-5)/min/pM). SI correlated positively with relative body mass (BM) VO(2)max (r = 0.42) (p < 0.001), relative fat-free mass (FFM) VO(2)max (r = 0.36) (p < 0.001) and negatively with body mass index standard deviation score (BMI SDS) (r =-0.22) (p = 0.001). SI did not correlate with percent body fat (r =-0.01) and absolute VO(2)max (r = 0.01). In multiple regression analyses with SI as dependent variable, VO(2)max and body composition, together with gender, age and Tanner stage, explained 20-26% of the variance.

CONCLUSION

Relative (BM) VO(2)max and relative (FFM) VO(2)max were stronger predictors of SI than percent body fat in severely obese children and adolescents. The study confirms that cardiorespiratory fitness is of importance for the metabolic syndrome in the studied population. Efforts to improve SI should include physical activity targeting cardiorespiratory fitness also in severely obese children and adolescents.

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

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

Femoral artery remodeling after aerobic exercise training without weight loss in women

Background

It is currently unclear whether reductions in adiposity mediate the improvements in vascular health that occur with aerobic exercise. The purpose of this longitudinal study of 13 healthy women (33 ± 4 years old) was to determine whether 14 weeks of aerobic exercise would alter functional measures of vascular health, namely resting aortic pulse wave velocity (aPWV, an index of arterial stiffness), femoral artery diameter (D_FA), and femoral artery blood flow (BF_FA) independent of changes in adiposity.

Methods

Aerobic fitness was assessed as VO₂peak normalized to fat-free mass, and adiposity (percent body fat) was determined by dual energy x-ray absorptiometry. Serum concentrations of proteins associated with risk for cardiovascular disease, including C-reactive protein (CRP), soluble intercellular adhesion molecule-1 (sICAM-1), and leptin, were also measured. Subjects cycled for 50 minutes, 3 times per week.

Results

Aerobic fitness normalized to fat-free mass increased 6% (P = 0.03) whereas adiposity did not change. Resting D_FA increased 12% (P < 0.001) and resting shear rate decreased 28% (P = 0.007). Aortic PWV, and serum sICAM-1, CRP and leptin did not change with training.

Conclusion

Significant reductions in adiposity were not necessary for aerobic exercise training to bring about improvements in aerobic fitness and arterial remodeling. Peripheral arterial remodeling occurred without changes in central arterial stiffness or markers of inflammation.

Acquired obesity and poor physical fitness impair expression of genes of mitochondrial oxidative phosphorylation in monozygotic twins discordant for obesity

Defects in expression of genes of oxidative phosphorylation in mitochondria have been suggested to be a key pathophysiological feature in familial insulin resistance. We examined whether such defects can arise from lifestyle-related factors alone. Fourteen obesity-discordant (BMI difference 5.2 +/- 1.8 kg/m(2)) and 10 concordant (1.0 +/- 0.7 kg/m(2)) monozygotic (MZ) twin pairs aged 24-27 yr were identified among 658 MZ pairs in the population-based FinnTwin16 study. Whole body insulin sensitivity was measured using the euglycemic hyperinsulinemic clamp technique. Transcript profiles of mitochondrial genes were compared using microarray data of fat biopsies from discordant twins. Body composition of twins was determined using DEXA and maximal oxygen uptake (Vo(2max)) and working capacity (W(max)) using a bicycle ergometer exercise test with gas exchange analysis. The obese cotwins had lower insulin sensitivity than their nonobese counterparts (M value 6.1 +/- 2.0 vs. 9.2 +/- 3.2 mg x kg LBM(-1) x min(-1), P < 0.01). Transcript levels of genes involved in the oxidative phosphorylation pathway (GO:0006119) in adipose tissue were lower (P < 0.05) in the obese compared with the nonobese cotwins. The obese cotwins were also less fit, as measured by Vo(2max) (50.6 +/- 6.5 vs. 54.2 +/- 6.4 ml x kg LBM(-1) x min(-1), for obese vs. nonobese, P < 0.05), W(max) (3.9 +/- 0.5 vs. 4.4 +/- 0.7 W/kg LBM, P < 0.01) and also less active, by the Baecke leisure time physical activity index (2.8 +/- 0.5 vs. 3.3 +/- 0.6, P < 0.01). This implies that acquired poor physical fitness is associated with defective expression of the oxidative pathway components in adipose tissue mitochondria.

Pictorial and verbal category-ratio scales for effort estimation in children

BACKGROUND

Research on the diverse aspects of exercise performance in childhood in the past 20 years has included an increase in the study of perceived exertion.

OBJECTIVE

The aim of this study was to compare children's ratings of effort perception by means of the Borg Category-Ratio Perceived Exertion (CR-10) Scale and a pictorial version of the Children's Effort Rating Table (Pictorial-CERT) scale, and to assess the long-term repeatability of the two scales.

METHODS

Fifty healthy children (25 girls and 25 boys; initially aged 10.4 +/- 0.5 years) participated in three incremental treadmill tests until volitional exhaustion or a maximal gradient of 22% at 5.4 km/h was attained. The first two tests (T1 and T2) were at an interval of 1 month. The third test (T3) took place 3 years later and utilized exactly the same protocol.

RESULTS

Perceived exertion correlated significantly with measures of exercise intensity - minute ventilation, heart rate and oxygen uptake for the whole group. The range of correlations for all tests was significantly higher for the Pictorial-CERT (r = 0.62-0.88 and r = 0.59-0.71 for the Pictorial-CERT and CR-10 respectively). Intraclass correlation coefficients between T1 and T2 were significantly higher for the Pictorial-CERT in comparison with the CR-10 (0.77 vs. 0.54, respectively; z = -2.07; P = 0.038).

CONCLUSION

The Pictorial-CERT is more appropriate for use with children of this age range and appears to be more reproducible than the Borg CR-10 Scale. Concurrent and construct validity evidence promotes the use of the Pictorial-CERT by junior children.

Cardiovascular fitness in adolescents: The influence of sexual maturation status—The AVENA and EYHS studies

The purposes were: (1) to determine the influence of sexual maturation status and body composition by comparing cardiovascular fitness (CVF) level in two adolescent populations from the south and the north of Europe; (2) to describe the associations between CVF and sexual maturation status in adolescence. A total of 1,867 Spanish adolescents from the AVENA study and 472 from the Swedish part of the EYHS were selected for this report (aged 14-16 years). CVF (expressed by the maximal oxygen consumption) was estimated from 20 m shuttle run test in the AVENA study and from a maximal ergometer cycle test in the EYHS. Sexual maturation status was classified according to Tanner stages. Body fat percentage (BF%) was estimated from skinfold thicknesses. Expressing CVF in different ways (in absolute value and in relation to weight or fat free mass; FFM) resulted in two different results with regard to CVF interpretation and comparison between the study populations. A higher CVF, as expressed in relation to FFM, was observed in the Spanish when compared to Swedish adolescents (P = 0.001). However, after adjusting for both sexual maturation status and BF%, the difference disappeared in males, while it remained significant in females (P = 0.001). CVF was negatively associated with sexual maturation status in males (P = 0.001). However, after adjusting for BF%, the association disappeared in males, while it was significant in females (P = 0.05). These results suggest that for CVF comparisons and interpretation in adolescent populations, sexual maturation status and BF%, as well as the way to express the CVF, should be taken into account.

An exploratory study of cardiac function and oxygen uptake during cycle ergometry in overweight children

OBJECTIVE

Obesity has been proposed to negatively impact cardiac function in overweight (OW) individuals. The relationship between diastolic dysfunction and oxygen uptake (Vo(2)) kinetics is equivocal. This exploratory investigation evaluated the relationship between resting left ventricular function and Vo(2) kinetics during cycle ergometry in OW and non-overweight (NO) children and adolescents.

RESEARCH METHODS AND PROCEDURES

Fourteen OW (>85 percentile for BMI for age and gender) children, 10 boys and 4 girls (age, 11.7 +/- 1.9 years; body mass, 80.6 +/- 45.5 kg) and 10 NO children (4 boys, 6 girls) volunteered to participate in the study (age, 12.5 +/- 2.1 years; body mass, 45.8 +/- 13.8 kg). Resting cardiovascular structure and function were assessed using spectral Doppler echocardiography. All subjects underwent two sub-maximal exercise stages on a cycle ergometer (3 minutes unloaded and 5 minutes at 50 W, both at a cadence of 50 rpm). Respiratory data were measured on a breath-by-breath basis at both workloads and the mean response time (MRT) was calculated.

RESULTS

Analysis of the MRT data demonstrated that there were no significant differences between OW and NO (OW, 52.6 +/- 11.7 seconds vs. NO, 45.6 +/- 7.4 seconds). Significant correlations (p < 0.05) were obtained between MRT Vo(2) and echocardiographic-derived mitral valve inflow pressure half-time (r = 0.55) and between MRT Vo(2), and mitral valve inflow deceleration time (r = 0.55).

DISCUSSION

The evidence from this research suggests a possible link between left ventricular diastolic function at rest and oxygen uptake kinetics during sub-maximal exercise in OW and NO children and adolescents.

Oxygen-uptake efficiency slope as a determinant of fitness in overweight adolescents

PURPOSE

Peak oxygen uptake (VO2peak) is frequently difficult to assess in overweight individuals; therefore, submaximal measures that predict VO2peak are proposed as substitutes. Oxygen uptake efficiency slope (OUES) has been suggested as a submaximal measurement of cardiorespiratory fitness that is independent of exercise intensity. There are few data examining its value as a predictor of V O2peak in severely overweight adolescents.

METHODS

One hundred seven severely overweight (BMI Z 2.50 +/- 0.34) and 43 nonoverweight (BMI Z 0.13 +/- 0.84) adolescents, performed a maximal cycle ergometer test with respiratory gas-exchange measurements. OUES was calculated through three exercise intensities: lactate inflection point (OUES LI), 150% of lactate inflection point (OUES 150), and VO2peak (OUES PEAK).

RESULTS

When adjusted for lean body mass, VO2peak and OUES at all exercise intensities were lower in overweight subjects (VO2peak: 35.3 +/- 6.4 vs 46.8 +/- 7.9 mL.kg(-1) LBM.min(-1), P < 0.001; OUES LI: 37.9 +/- 10.0 vs 43.7 +/- 9.2 mL.kg(-1) LBM.min(-1).logL(-1) P < 0.001; OUES 150: 41.6 +/- 9.0 vs 49.8 +/- 11.1 mL.kg(-1) LBM.min(-1).logL(-1) P < 0.001; and OUES PEAK: 45.1 +/- 8.7 vs 52.8 +/- 9.6 mL.kg(-1) LBM.min(-1).logL(-1) P < 0.001). There was a significant increase in OUES with increasing exercise intensity in both groups (P < 0.001). OUES at all exercise intensities was a significant predictor of VO2peak for both groups (r2 = 0.35-0.83, P < 0.0001). However, limits of agreement for predicted VO2peak relative to actual VO2peak were wide (+/- 478 to +/- 670 mL.min(-1)).

CONCLUSIONS

OUES differs significantly in overweight and nonoverweight adolescents. The wide interindividual variation and the exercise intensity dependence of OUES preclude its use in clinical practice as a predictor of VO2peak.

Aerobic exercise in adolescents with obesity: preliminary evaluation of a modular training program and the modified shuttle test

BACKGROUND

Increasing activity levels in adolescents with obesity requires the development of exercise programs that are both attractive to adolescents and easily reproducible. The aim of this study was to develop a modular aerobic training program for adolescents with severe obesity, with a focus on variety, individual targets and acquiring physical skills. We report here the effects on aerobic fitness from a pilot study. Furthermore, we examined the feasibility of the modified shuttle test (MST) as an outcome parameter for aerobic fitness in adolescents with severe obesity.

METHODS

Fifteen adolescents from an inpatient body weight management program participated in the aerobic training study (age 14.7 +/- 2.1 yrs, body mass index 37.4 +/- 3.5). The subjects trained three days per week for 12 weeks, with each session lasting 30-60 minutes. The modular training program consisted of indoor, outdoor and swimming activities. Feasibility of the MST was studied by assessing construct validity, test-retest reliability and sensitivity to change.

RESULTS

Comparing pretraining and end of training period showed large clinically relevant and significant improvements for all aerobic indices: e.g. VO2 peak 17.5%, effect size (ES) 2.4; Wmax 8%, ES 0.8. In addition, a significant improvement was found for the efficiency of the cardiovascular system as assessed by the oxygen pulse (15.8%, ES 1.6). Construct validity, test-retest reliability and sensitivity to change of the MST were very good. MST was significantly correlated with VO2 peak (r = 0.79) and Wmax (r = 0.84) but not with anthropometric measures. The MST walking distance improved significantly by 32.5%, ES 2.5. The attendance rate at the exercise sessions was excellent.

CONCLUSION

This modular, varied aerobic training program has clinically relevant effects on aerobic performance in adolescents with severe obesity. The added value of our aerobic training program for body weight management programs for adolescents with severe obesity should be studied with a randomized trial. This study further demonstrated that the MST is a reliable, sensitive and easy to administer outcome measure for aerobic fitness in adolescent body weight management trials.

Fitness is a stronger predictor of fasting insulin levels than fatness in overweight male middle-school children

OBJECTIVE

We studied the relationship between % body fat (%BF), cardiovascular fitness (CVF), and insulin resistance (IR) in overweight middle-school children.

STUDY DESIGN

Middle school children (n = 106, body mass index [BMI] > 95th percentile for age) underwent evaluation of body composition, maximal volume of oxygen utilization (VO2) uptake/kg lean body mass (VO2max/kgLBM), and fasting glucose and insulin (FI) concentrations and derived homeostasis model assessment index (HOMA(IR)).

RESULTS

Both %BF (r = .33, P < .001) and VO2max/kgLBM (r = -0.42, P < .0001) were significantly correlated with FI. Bivariate regression analysis revealed %BF (P = .008 vs FI, P = .035 vs HOMA(IR)) and VO2max/kgLBM (P < .001 vs FI, P = .009 vs HOMA(IR)) to be independent predictors of insulin sensitivity. In males, VO2max/kgLBM was a better predictor of FI and HOMA(IR) than %BF.

CONCLUSIONS

In obese middle-school children, both %BF and VO2max/kgLBM are independent predictors of FI levels. The relationship between CVF and FI levels was significant in both sexes but was particularly profound and stronger than %BF in males. Efforts to reduce risk of type 2 diabetes mellitus in an increasingly obese child population should include exercise intervention sustained enough to improve CVF.

Age and gender differences in VO2max in Swedish obese children and adolescents

AIM

To describe age and gender differences in estimated maximum oxygen uptake (VO2max) and participation in organized physical activity in Swedish obese children and adolescents, and compare the results with an age-matched reference group representative of the general population.

METHODS

Two hundred and nineteen obese children (102 boys, 117 girls, aged 8-16 years, Body Mass Index (BMI) 24.3-57.0 kg.m-2) performed a submaximal bicycle ergometry test and an interview concerning participation in organized physical activity.

RESULTS

The obese children had lower relative VO2max (p<0.001) than the reference group. In contrast to the reference group no age or gender differences were detected in the obese children aged 11-13 years and 14-16 years. With increased age (after 11 years) the obese children participated less in organized physical activity than the reference group (p<0.001). In obese adolescents, participation in organized physical activity in leisure time explained 7% and BMI 45% of the variance in relative VO2max.

CONCLUSION

The obese children had lower relative VO2max, and participated less in organized physical activity than the reference group. The variance in relative VO2max was primarily explained by BMI. Obese adolescents, especially boys, were found to be at risk of physical inactivity.

Muscle fatigue during high-intensity exercise in children

Children are able to resist fatigue better than adults during one or several repeated high-intensity exercise bouts. This finding has been reported by measuring mechanical force or power output profiles during sustained isometric maximal contractions or repeated bouts of high-intensity dynamic exercises. The ability of children to better maintain performance during repeated high-intensity exercise bouts could be related to their lower level of fatigue during exercise and/or faster recovery following exercise. This may be explained by muscle characteristics of children, which are quantitatively and qualitatively different to those of adults. Children have less muscle mass than adults and hence, generate lower absolute power during high-intensity exercise. Some researchers also showed that children were equipped better for oxidative than glycolytic pathways during exercise, which would lead to a lower accumulation of muscle by-products. Furthermore, some reports indicated that the lower ability of children to activate their type II muscle fibres would also explain their greater resistance to fatigue during sustained maximal contractions. The lower accumulation of muscle by-products observed in children may be suggestive of a reduced metabolic signal, which induces lower ratings of perceived exertion. Factors such as faster phosphocreatine resynthesis, greater oxidative capacity, better acid-base regulation, faster readjustment of initial cardiorespiratory parameters and higher removal of metabolic by-products in children could also explain their faster recovery following high-intensity exercise.From a clinical point of view, muscle fatigue profiles are different between healthy children and children with muscle and metabolic diseases. Studies of dystrophic muscles in children indicated contradictory findings of changes in contractile properties and the muscle fatigability. Some have found that the muscle of boys with Duchenne muscular dystrophy (DMD) fatigued less than that of healthy boys, but others have reported that the fatigue in DMD and in normal muscle was the same. Children with glycogenosis type V and VII and dermatomyositis, and obese children tolerate exercise weakly and show an early fatigue. Studies that have investigated the fatigability in children with cerebral palsy have indicated that the femoris quadriceps was less fatigable than that of a control group but the fatigability of the triceps surae was the same between the two groups. Further studies are required to elucidate the mechanisms explaining the origins of muscle fatigue in healthy and diseased children. The use of non-invasive measurement tools such as magnetic resonance imaging and magnetic resonance spectroscopy in paediatric exercise science will give researchers more insight in the future.

The energy cost of cycling in young obese women

In order to evaluate the difference in the energy cost of submaximal cycling between normal weight (NW) and obese (OB) females, nine OB (age 23.2 years+/-1.6 SE, BMI 40.4+/-1.2 kg/m2) and nine NW (age 25.6 years+/-1.8, BMI 21.7+/-0.6 kg/m2) healthy young women were studied during a graded bicycle ergometer test at 40, 60, 80, 100 and 120 W. At rest and at all workloads, oxygen uptake VO2 was higher in OB than in NW women (Student's t test, P<0.05-0.01), as well as respiratory quotient during all exercise levels (P<0.05-0.01), while similar values of heart rate, pulmonary ventilation and breathing efficiency were found between the two groups. Maximal VO2 and anaerobic threshold were higher in OB women, and they also explained the higher oxygen pulse observed during submaximal exercise, but no difference was found when the values were adjusted for fat-free mass. While net mechanical efficiency (ME) was significantly lower in OB (ANOVA, P<0.05), delta ME was similar in both groups, indicating no substantial derangement of muscle intrinsic efficiency in obesity, but suggesting that the increased mass of body segments involved in cycling movements may be chiefly responsible for the higher energy cost of this type of exercise. Comparison of the actual VO2 presently measured with that predicted by available cycle ergometry equations at the different workloads indicated inaccuracy of various degrees ranging from 8.4 to -31.9%. It is concluded that the lower mechanical efficiency displayed by obese women in cycling has to be taken into account when prescribing exercise through methods predicting the metabolic load.

Increased exercise capacity after surgically induced weight loss in morbid obesity

OBJECTIVE

To investigate the effects of surgically induced weight loss on exercise capacity in patients with morbid obesity (MO).

RESEARCH METHODS AND PROCEDURES

A prospective 1-year follow-up study was carried out, with patients being their own controls. A symptom-limited cardiopulmonary exercise stress test was performed in 31 MO patients (BMI > 40 kg/m2) before and 1 year after undergoing bariatric surgery.

RESULTS

At 1 year after surgery, weight was reduced from 146 +/- 33 to 95 +/- 19 kg (p < 0.001), and BMI went from 51 +/- 4 to 33 +/- 6 kg/m2 (p < 0.001). After weight loss, obese patients performed each workload with lower oxygen consumption, heart rate, systolic arterial pressure, and ventilatory volume (p < 0.001). This reduced energy expenditure allowed them to increase the duration of their effort test from 13.8 +/- 3.8 to 21 +/- 4.2 minutes (p < 0.001). Upon finishing the exercise, MO patients before surgery were able to reach only 83% of their age-predicted maximal heart rate, and their respiratory exchange ratio was 0.87 +/- 0.06. After weight loss, those values were 90% and 1 +/- 0.08, respectively (p < 0.01). When we compared the peak O2 pulse corrected by fat free mass before and after surgery, no significant differences between the groups were found.

DISCUSSION

After surgically induced weight loss, MO patients markedly improved their exercise capacity. This is due to the fact that they were able to perform the external work with lower energy expenditure and also to increase cardiovascular stress, optimizing the use of cardiac reserve. There were no differences in cardiac function before and after surgery.

Influence of excess adiposity on exercise fitness and performance in overweight children and adolescents

OBJECTIVE

Relatively little is known about how excess body mass affects adolescents' capacity to perform sustained exercise. We hypothesized that most of the difficulty that severely overweight adolescents have with sustained exercise occurs because the metabolic costs of moving excess mass result in use of a high proportion of their total oxygen reserve.

METHODS

We compared results from a maximal cycle ergometry fitness test in 129 severely overweight adolescents who had BMIs of 41.5 +/- 9.7 kg/m2 and ages of 14.5 +/- 1.8 years (range: 12.1-17.8 years) and 34 nonoverweight adolescents who had BMIs of 20.1 +/- 2.9 kg/m2 and ages of 14.5 +/- 1.5 years (range: 12.0-18.1 years). Oxygen uptake (Vo2) was compared at 3 times: during a 4-minute period of unloaded cycling (ULVo2), at the lactate threshold estimated by gas exchange (LTVo2), and at maximal exertion (Vo2 max). Heart rate was obtained at rest and at Vo2 max. Participants also completed a 12-minute walk/run performance test to obtain distance traveled (D12) and heart rate.

RESULTS

Absolute LTVo2 and Vo2 max and LTVo2 as a percentage of Vo2 max were not different in overweight and nonoverweight adolescents during the cycle test. However, absolute ULVo2 was significantly greater in overweight adolescents: ULVo2 accounted for 35 +/- 8% of Vo2 max (and 63 +/- 15% of LTVo2) in overweight adolescents but only 20 +/- 5% of Vo2 max (and 39 +/- 12% of LTVo2) in nonoverweight adolescents. Resting heart rate before initiating the cycle test was significantly greater in overweight than nonoverweight adolescents (94 +/- 14 vs 82 +/- 15 beats per minute). However, maximal heart rate during the cycle test was significantly lower in overweight adolescents (186 +/- 13 vs 196 +/- 11 beats per minute). During the walk/run test, mean D12 was significantly shorter for overweight than for nonoverweight adolescents (1983 +/- 323 vs 1159 +/- 194 m). D12 was negatively related to BMI SDS (r = -0.81) and to ULVo2 (r = -0.98).

DISCUSSION

Overweight and nonoverweight adolescents had similar absolute Vo2 at the lactate threshold and at maximal exertion, suggesting that overweight adolescents are more limited by the increased cardiorespiratory effort required to move their larger body mass through space than by cardiorespiratory deconditioning. The higher percentage of oxygen consumed during submaximal exercise indicates that overweight adolescents are burdened by the metabolic cost of their excess mass. Their greater oxygen demand during an unloaded task predicted poorer performance during sustained exercise. Exercise prescriptions for overweight adolescents should account for the limited exercise tolerance imposed by excess body mass, focusing on activities that keep demands below lactate threshold so that exercise can be sustained.

Oxygen uptakes adjusted for body composition in normal-weight and obese adolescents

OBJECTIVE

To test whether resting oxygen uptake (VO(2)), submaximal VO(2), and maximal VO(2) (VO(2max)) differs between obese adolescents (n = 18; BMI > 30) and a matched normal-weight control group after adjustment for differences in fat-free mass (FFM) and fat mass (FM).

RESEARCH METHODS AND PROCEDURES

FFM and FM were assessed by DXA. Resting VO(2), submaximal VO(2), and VO(2max) were measured by indirect calorimetry.

RESULTS

There was no difference in resting VO(2) between groups after adjusting for FFM and FM. Submaximal VO(2) did not differ between groups after adjusting for body weight. Percentage VO(2max) and NET VO(2) (VO(2max) - resting VO(2)) were significantly higher in the obese group during submaximal exercise, however not after adjusting for body weight. VO(2max) was not significantly different between groups after adjusting for FFM.

DISCUSSION

When body compositions are appropriately controlled for, resting VO(2), submaximal VO(2), and VO(2max) do not differ between obese and normal-weight adolescents. These data suggested that the higher relative VO(2) observed in obese adolescent subjects is due to their higher FM and not to an impaired VO(2max) even though they may be less physically active.

Effects of a multidisciplinary weight loss intervention on anaerobic and aerobic aptitudes in severely obese adolescents

OBJECTIVE

To investigate if a multidisciplinary weight loss programme in adolescents suffering severe obesity allows an improvement of anaerobic and aerobic aptitudes.

DESIGN

In all, 55 adolescents (33 girls and 22 boys) suffering from severe obesity were enrolled in an interdisciplinary weight reduction programme lasting 6-12 months. Progressive submaximal physical activity was performed and national dietary allowances for adolescents with low levels of physical activity were provided.

MEASUREMENTS

Total and regional body composition and anaerobic aptitudes (handgrip strength (HGS), vertical jump height (VJH)) and aerobic aptitudes (maximal aerobic power (MAP), maximal oxygen uptake (VO(2max))) were measured before and after weight loss.

RESULTS

The mean reduction of body mass index (BMI) was similar in girls (21.4+/-5.9%) and boys (23.7+/-6.4%). Fat mass (FM) steepest drop was observed in the trunk (-63.2+/-10.1% in boys and -51.5+/-11.4% in girls). The total lean mass (LM) did not vary in both sexes. Right HGS and VJH increased in both sexes (P<0.05), whereas left HGS increased only in boys. MAP and VO(2max) per kg BW increased (P< 0.0001) in both sexes (2.3+/-0.3 vs 1.7+/-0.3 W/kg and 32.8+/-4.5 vs 26.7+/-4.1 ml/min/kg in girls and 2.8+/-1.9 vs 1.9+/-0.4 W/kg and 39.1+/-6.3 vs 27.9+/-5.1 ml/min/kg in boys, respectively), whereas MAP and VO(2max) in absolute value and per kg LM increased only in boys (P=0.04). Total LM was the strongest determinant of HGS, VJH, MAP and VO(2max) in both sexes (P<0.005).

CONCLUSIONS

Multidisciplinary weight reduction programme including moderate dietary restriction in combination with regular physical training induced an improvement of anaerobic and aerobic aptitudes, a marked reduction of obesity and a preservation of LM in severely obese adolescents.

Brisk Walking Speed in Older Adults Who Walk for Exercise

OBJECTIVES

To determine the self-selected exercise intensity of older adults who report that they walk briskly for exercise. An additional aim of the study was to assess the contribution of self-reported physical activity to self-selected exercise intensity.

DESIGN

Observational.

SETTING

walking path.

PARTICIPANTS

Subjects consisted of 212 participants in the Study of Physical Performance and Age-Related Changes in Sonomans who stated in a detailed home interview that they walked briskly for exercise.

MEASUREMENTS

Observed brisk walking speed was measured as the time it took participants to walk half a mile at "normal brisk walking speed." Self-reported physical activity was categorized as metabolic equivalent of the task (MET) in minutes of exercise reported in the previous 7 days. Physiological measures and body composition were obtained through laboratory evaluation.

RESULTS

Men walked at an average speed+/-standard deviation of 5.72+/-0.69 km/h and women walked at an average speed of 5.54+/-0.64 km/h. Self-reported physical activity was not associated with brisk walking speed when adjusted for age and ratio of lean to fat mass.

CONCLUSION

This study found that older adults who report that they walk briskly for exercise do so at a pace considered moderate or greater in absolute intensity as indicated by their walking speed (4.83 km/h). Ninety-eight percent of men (93/95) and 97% of women (113/117) had an observed walking speed equivalent to 3 or more METs based on their calculated walking speed.

Changes in fat mass, fat-free mass and aerobic fitness in severely obese children and adolescents following a residential treatment programme

The purpose of this study was to describe changes in fat mass (FM), fat-free mass (FFM) and aerobic fitness in severely obese children and adolescents during residential treatment in the Medical Paediatric Centre Zeepreventorium. Treatment consisted of moderate dietary restriction, physical activity and psychological support. This study was a clinical observation of 20 severely obese children and adolescents (8 boys and 12 girls, aged 15.4+/-1.8 years) who completed the 10-month residential programme. Height, weight, FM, FFM and aerobic fitness was measured four times during the intervention: at baseline, 11 weeks, 24 weeks and at 33 weeks (at the end of the programme ). The mean decrease in level of overweight was 46% (P<0.001), with a mean loss of 8.9% FM (P<0.001). Submaximal performance (PWC150) improved from 123+/-35 Watt to 152+/-37 Watt (P<0.001). Maximal performance levels increased (performance time: from 14+/-2.9 min to 15.3+/-3.5 min, peak power: from 186+/-38 Watt to 205+/-45 Watt, P<0.01) without an improvement in absolute VO(2 peak).

CONCLUSION

A moderate dietary restriction in combination with physical activity and psychological support in severely obese children and adolescents is effective in decreasing body fat and improving physical performance. Further research is needed to evaluate the longer-term effects of such a programme.

[Cardiopulmonary function and exercise capacity in patients with morbid obesity]

INTRODUCTION AND OBJECTIVES

The effect of obesity on cardiac function is still under discussion. The objective of this study was to assess cardiopulmonary capacity in morbidly obese patients. Patients and method. A symptom-limited cardiopulmonary exercise stress test was carried out in 31 morbidly obese patients (BMI 50 9 kg/m2) and 30 normal controls (BMI 24 2 kg/m2. Cardiovascular function was evaluated using the oxygen pulse (oxygen uptake/heart rate).

RESULTS

There were no differences in age, sex and height between both groups. During the effort the obese subjects presented greater oxygen uptake, heart rate, systolic arterial pressure and minute ventilation and shorter test duration than control group (14 3 vs 27 4 min; p < 0.001). Oxygen pulse values were higher in obese patients. However, after oxygen uptake indexation by fat free mass, these differences disappeared, suggesting a similar cardiovascular function. At the end of the exercise, the control group reached 96% of their age-predicted maximal heart rate and their respiratory exchange ratio was 1 0.2. Obese patients only reached 86% and 0.87 0.2, respectively.

CONCLUSIONS

Due to their need of more energy output to move total body mass morbidly obese patients have a reduced exercise capacity. They finish the test having done a submaximal exercise. However, during this effort they show a normal cardiopulmonar capacity.

Physical activity in free-living, overweight white and black women: divergent responses by race to diet-induced weight loss

BACKGROUND

Black women are at greater risk of obesity than are white women, perhaps because of their lower levels of physical activity.

OBJECTIVE

We compared free-living activity energy expenditure (AEE) in sedentary white and black women (in overweight and normal-weight states) and in never-overweight control subjects.

DESIGN

Subjects included 46 women (23 white, 23 black) studied while overweight and after reaching a normal weight and 38 female control subjects (23 white, 15 black). Diet, without exercise training, resulted in a mean weight loss of 13 kg and a body mass index (in kg/m(2)) < 25. Body composition, sleeping energy expenditure, free-living total energy expenditure, and the energy cost of activity and aerobic capacity were assessed before and after weight loss under 4-wk, diet-controlled, weight-stable conditions and in the control subjects. AEE was defined as above-sleep energy expenditure.

RESULTS

No significant racial differences in body composition, before or after weight loss, were found. After weight loss, AEE and aerobic capacity increased in the white women and decreased in the black women (P < 0.05 and P < 0.02, respectively). After weight loss, but not before, the white women had a significantly higher mean AEE than did the black women (2448 +/- 979 and 1728 +/- 1373 kJ/d, respectively; P < 0.05), approximating AEEs in the white (2314 +/- 1105) and black (2310 +/- 1251) control subjects.

CONCLUSIONS

Relative to the responses of the white women to diet-induced weight loss, the black women became less fit and less physically active. Induction of a normal body weight in overweight black women appeared to produce a more obesity-prone state, favoring weight relapse.

Perceptual versus physiological heat strain during exercise-heat stress

PURPOSE

The physiological strain index (PSI) has been proposed as a universally applicable measure of exercise-heat strain. Unknown is whether this index, based on normalized increases in core temperature and heart rate, is matched by its perceptual analog.

METHODS

By using a similar mathematical construct to the PSI, the perceptions of thermal sensation and perceived exertion were combined, and the resultant index, PeSI, was compared with its physiological counterpart, denoted as PhSI, for the exercise-heat stress specific to this study. Twenty-six young and healthy subjects wore semi-impermeable clothing and walked (3.5 km.h(-1)) under hot conditions (40 degrees C and 30% RH) until exhaustion or when their core temperature reached 39.5 degrees C. Subjects were divided into two fitness groups [endurance trained (T) and untrained (U)] comprised of 10 men and 3 women each. U subjects had a higher level of body fatness (mean +/- SD 18.1 +/- 5.3 vs 12.6 +/- 4.5%; P=0.010) and a lower level of aerobic fitness ((.)VO(2max)= 43.6 +/- 3.8 +/- vs 59.0 +/- 6.2 mL.min(-1).kg(-1); P<0.001).

RESULTS

During the first hour of exposure, there was no group difference in PhSI, yet T perceived their physiological strain (PeSI) lower than U (P=0.002). Further, the indices were not different for U whereas PhSI was higher than PeSI for T (P=0.008). At the end of the exposure, T had a higher value of PhSI than U (8.23 +/- 0.72 vs 6.74 +/- 1.47; = 0.002), but there was no group difference in PeSI. Although the indices were again not different for U, PhSI at the end was higher than PeSI for T (6.14 +/- 1.68; P<0.001).

CONCLUSION

T underestimated and U consistently perceived their physiological strain, as defined by PhSI, in accordance with the measured increases in core temperature and heart rate throughout an exposure to uncompensable exercise-heat stress.

Ventilatory efficiency and rate of perceived exertion in obese and non-obese children performing standardized exercise

Sixty children, in the age span 6-17 years originally divided into two groups, matched by age, sex and height--30 obese subjects [15 girls/15 boys; body mass index (BMI) = 27.4 +/- 4.5 m kg-2; ideal body weight (IBW) range = 122-185%] and 30 controls (BMI = 18.8 +/- 2.7 m kg-2) performed incremental treadmill exercise test. Perceived exertion was assessed by means of Category-Ratio Borg scale. The duration of the exercise for the children in the obesity group was significantly shorter than controls (P = 0.010) but obese children have greater absolute values for oxygen uptake (VO2peak ml min-1 = 1907 +/- 671 versus 1495 +/- 562; P = 0.013) and ventilatory variables (VE, VT), which adjusted for body mass decrease significantly (VO2/kg ml min-1 kg-1 = 29.2 +/- 3.8 versus 33.6 +/- 3.5; P < 0.001). Among the various methods for 'normalizing' absolute values of VO2peak for body size, dividing it by body surface area (BSA) yielded the best results (VO2/BSA ml min-1 m-2 = 43.5 +/- 4.6 versus 44.7 +/- 5.6; P = 0.335). The ventilatory efficiency determined either as a slope of VE versus VCO2 or as a simple ratio at anaerobic threshold did not differ between obese and non-obese children in the incremental and recovery periods of exercise. There was a negative correlation of VE/VCO2 slope with age and anthropometric parameters. Obese children rated perceived exertion significantly higher than controls despite the standard workload (Borg score = 6.2 +/- 1.2 versus 5.2 +/- 1.1; P = 0.001). In conclusion, the absolute metabolic cost of exercise is higher in the obesity group compared with the control subjects. Both groups have similar ventilatory efficiency but an increased awareness of fatigue that furthermore limits their physical capacity.

Factors that alter body fat, body mass, and fat-free mass in pediatric obesity

PURPOSE

The purpose of this study was to quantify the effects of exercise treatment programs on changes in body mass, fat-free mass, and body fat in obese children and adolescents.

METHODS

By using the meta-analytic approach, studies that met the following criteria were included in our analyses: 1) at least six subjects per group; 2) subject groups consisting of children in the 5- to 17-yr age range; 3) pretest and posttest values for either body mass, percent body fat, or fat-free mass (FFM); 4) used exercise as a mode of treatment (e.g., walking, jogging, cycle ergometry, high-repetition resistance exercise, and combinations); 6) training programs >or= 3 wk; 7) full-length publications (not conference proceedings); 8) apparently "healthy" children (i.e., free from endocrine diseases and disorders); and 9) published studies in English language journals only.

RESULTS

A total of 120 investigations were located that addressed the issue of exercise as a method of treatment in pediatric obesity. Of those, 30 met our criteria for inclusion. Across all designs and categories, fixed-effects modeling yielded significant decreases in the following dependent variables: 1) percent body fat (mean = 0.70 +/- 0.35; 95% CI = 0.21 to 1.1); 2) FFM (mean = 0.50 +/- 0.38; 95% CI = 0.03 to 0.57); 3) body mass (mean = 0.34 +/- 0.18; 95% CI = 0.01 to 0.46); 4) BMI (mean = 0.76 +/- 0.55; 95% CI = 4.24 to 1.7), and 5) VO2max (mean = 0.52 +/- 0.16; 95% CI = 0.18 to 0.89), respectively. Significant differences were found as a function of the type intervention groups (exercise vs exercise + behavioral modification; P < 0.04); body composition assessment methods (skinfold vs hydrostatic weighing, DEXA, and total body water; P < 0.006); exercise intensity (60-65%, vs >or= 71% VO2max; P < 0.01); duration (<or= 30 min vs > 30 min; P < 0.03); and mode (aerobic vs aerobic + resistance training; P < 0.02). Stepwise linear regression suggested that initial body fat levels (or body mass), type of treatment intervention, exercise intensity, and exercise mode accounted for most of the variance associated with changes in body composition after training.

CONCLUSIONS

Exercise is efficacious for reducing selected body composition variables in children and adolescents. The most favorable alterations in body composition occurred with 1) low-intensity, long-duration exercise; 2) aerobic exercise combined with high-repetition resistance training; and 3) exercise programs combined with a behavioral-modification component.

Free-living activity energy expenditure in women successful and unsuccessful at maintaining a normal body weight

BACKGROUND

Although physical inactivity is believed to contribute to the rising prevalence of obesity, the role and magnitude of its contribution to weight gain are unknown.

OBJECTIVE

We compared total free-living activity energy expenditure (AEE) and physical activity level in women successful and unsuccessful at maintaining a normal body weight.

DESIGN

Premenopausal, generally sedentary women were studied at their normal weight and 1 y later after no intervention. Two groups were identified on the basis of extreme weight changes: maintainers (n = 27) had a weight gain of less-than-or-equal 3% of their initial body weight ( less-than-or-equal 2 kg/y) and gainers (n = 20) had a weight gain of >10% (>6 kg/y). At baseline and follow-up, evaluations were conducted during 4 wk of diet-controlled, energy-balance conditions. Free-living AEE and physical activity were assessed with the use of doubly labeled water, exercise energy economy and muscle strength with the use of standardized exercise tests, and sleeping EE and substrate utilization with the use of chamber calorimetry.

RESULTS

Maintainers lost a mean (plus minusSD) of 0.5 plus minus 2.2 kg/y and gainers gained 9.5 plus minus 2.1 kg/y. Gainers had a lower AEE (P < 0.02), a lower physical activity level (P < 0.01), and less muscle strength (P < 0.001); these differences between groups remained significant from baseline to follow-up. Sleeping EE, exercise economy, and sleeping or 24-h substrate utilization were not significantly different between the 2 groups. A lower AEE in the gainers explained approximately 77% of their greater weight gain after 1 y.

CONCLUSION

The general US population should increase their daily physical activity levels to decrease the rising prevalence of obesity.

Aerobic fitness, not energy expenditure, influences subsequent increase in adiposity in black and white children

BACKGROUND

Low levels of energy expenditure and aerobic fitness have been hypothesized to be risk factors for obesity. Longitudinal studies to determine whether energy expenditure influences weight gain in whites have provided conflicting results. To date, no studies have examined this relationship in blacks or whether aerobic fitness influences weight gain in white or black children.

METHODS

One hundred fifteen children, 72 white (55 girls and 17 boys) and 43 black (24 girls and 19 boys) were recruited for this study. Aerobic fitness, resting, total, and activity-related energy expenditure and body composition were measured at baseline. The children returned annually for 3 to 5 repeated measures of body composition. The influence of the initial measures of energy expenditure and fitness on the subsequent rate of increase in adiposity was examined, adjusting for initial body composition, age, ethnicity, gender, and Tanner stage. Because 20 children did not attain maximum oxygen consumption, the sample size for the combined analysis was 95.

RESULTS

Initial fat mass was the main predictor of increasing adiposity in this cohort of children, with greater initial fat predicting a higher rate of increase of adiposity. There was also a significant negative relationship between aerobic fitness and the rate of increasing adiposity (F(1,82) = 3.92). With every increase of.1 L/minute of fitness, there was a decrease of.081 kg fat per kg of lean mass gained. None of the measures of energy expenditure significantly predicted increasing adiposity in white or black children.

CONCLUSIONS

Initial fat mass was the dominant factor influencing increasing adiposity; however, aerobic fitness was also a significant independent predictor of increasing adiposity in this cohort of children. Resting, total, or activity-related energy expenditure did not predict increasing adiposity. It seems that aerobic fitness may be more important than absolute energy expenditure in the development of obesity in white or black children. energy expenditure, fitness, longitudinal, obesity.