Physical activity in the prevention and treatment of obesity and its comorbidities: evidence report of independent panel to assess the role of physical activity in the treatment of obesity and its comorbidities

Mental health around retirement: evidence of Ashenfelter's dip

BACKGROUND

Mental health issues among retirees have become increasingly concerning because the aging population presents a significant challenge globally, particularly in Western countries. Previous studies on this issue are plagued with bias owing to lacking panel data and estimation strategies. This study investigated the depression levels of European adults around the time of retirement.

METHODS

We used data obtained from Waves 1-7 of the Survey of Health, Ageing, and Retirement in Europe (SHARE) to create panel data covering the 2004-2017 period. Wave 3 (SHARELIFE) was excluded from the sample because it provided mismatched information. Fixed-effects (FE) and fixed-effects instrumental variables (FE-IV) models with multiple imputations were employed to examine the impacts of retirement on mental health before and after retirement, where being over pension age (normal and early) was used as the instrument variable.

RESULTS

Our results indicated that retirement based on aspirational motivations (β =  - 0.115, p < 0.001) and positive circumstances (β =  - 0.038, p < 0.001) significantly reduced depression, whereas retiring under negative circumstances could deteriorate one's mental health (β = 0.087, p < 0.001). FE and FE-IV models indicated that overall, retiring reduced retirees' depression (β =  - 0.096, p < 0.001 and β =  - 0.261, p < 0.001, respectively). The results of FE-IV models showed that adults planning to retire in the next two years experienced less depression compared with others in the workforce (λ =  - 0.313, p < 0.01). These adults must have adjusted their lifestyles in response to their impending retirement, thereby evincing Ashenfelter's dip. Two years after retirement, when the "honeymoon" phase was over, retirees may have completely adapted to their new lives and the effect of retirement was no longer important.

CONCLUSIONS

Retirement improves mental health before it happens, but not after. Increasing the pension eligibility age may postpone the beneficial effects of retirement on health. However, policy implications should be tailored according to the unique situations of each country, job sector, and population. Providing flexible schemes regarding retirement timing decisions would be better than a generalized retirement policy.

Home-Based Exergaming on Preschoolers' Energy Expenditure, Cardiovascular Fitness, Body Mass Index and Cognitive Flexibility: A Randomized Controlled Trial

PURPOSE

The effects of exergaming-based physical activity (PA) interventions on preschoolers' health outcomes and cognition remain largely unexplored. Therefore, we conducted a randomized controlled trial to discern the effectiveness of a home-based educational exergaming intervention on preschoolers' energy expenditure, fitness, body mass index, and cognition.

METHODS

Participants were 32 preschoolers (16 girls; 59.4% Asian; M_age = 4.72, SD = ±0.73) recruited from the Twin Cities area in Minnesota. During baseline testing, we measured preschooler's daily energy expenditure (EE), cardiovascular fitness, body mass index, and cognitive flexibility using validated instruments. Participants were then randomly assigned to one of two conditions: (1) the exergaming intervention condition; or (2) control condition. The intervention program requested children participate in home-based educational exergaming using the LeapTV gaming console for at least 30 min/session 5 times/week. The control condition asked children to maintain regular PA patterns without any exergaming gameplay. Each condition lasted 12 weeks. We conducted identical outcome assessments for all children at baseline and post-intervention.

RESULTS

Analysis of covariance with repeated measures yielded significant time x group interaction effects for cognitive flexibility, Wilks' Lambda = 0.81, F(1, 29) = 6.98, p = 0.01, η² = 0.19, suggesting children in the exergaming group demonstrated significantly greater increases in cognitive flexibility as compared to those in the control group over time. There were no significant differences for time x group changes between the two groups for EE, Wilks' Lambda = 0.92, F(1, 29) = 2.29, p = 0.14, η² = 0.08; cardiovascular fitness, Wilks' Lambda = 0.96, F(1, 29) = 1.07, p = 0.31, η² = 0.04; and BMI, Wilks' Lambda = 0.99, F(1, 29) = 0.05, p = 0.82, η² = 0.01. However, our data did suggest a marginal effect of time for EE, Wilks' Lambda = 0.89, F(1, 29) = 3.26, p = 0.08, η² = 0.08, indicating that children's daily EE increased from baseline to post-intervention.

CONCLUSIONS

Home-based educational exergaming may positively impact cognitive flexibility in preschoolers. Studies with larger sample sizes in multiple geographic locations are needed, with our study suggesting a longer intervention period might also be warranted.

Acute effects of exercise intensity on subsequent substrate utilisation, appetite, and energy balance in men and women

Exercise is capable of influencing the regulation of energy balance by acutely modulating appetite and energy intake coupled to effects on substrate utilization. Yet, few studies have examined acute effects of exercise intensity on aspects of both energy intake and energy metabolism, independently of energy cost of exercise. Furthermore, little is known as to the gender differences of these effects. One hour after a standardised breakfast, 40 (19 female), healthy participants (BMI 23.6 ± 3.6 kg·m−2, V̇O2peak 34.4 ± 6.8 mL·kg−1·min−1) undertook either high-intensity intermittent cycling (HIIC) consisting of 8 repeated 60 s bouts of cycling at 95% V̇O2peak or low-intensity continuous cycling (LICC), equivalent to 50% V̇O2peak, matched for energy cost (∼950 kJ) followed by 90 mins of rest, in a randomised crossover design. Throughout each study visit, satiety was assessed subjectively using visual analogue scales alongside blood metabolites and GLP-1. Energy expenditure and substrate utilization were measured over 75 min postexercise via indirect calorimetry. Energy intake was assessed for 48 h postintervention. No differences in appetite, GLP-1, or energy intakes were observed between HIIC and LICC, with or without stratifying for gender. Significant differences in postexercise nonesterified fatty acid concentrations were observed between intensities in both genders, coupled to a significantly lower respiratory exchange ratio following HIIC (P = 0.0028), with a trend towards greater reductions in respiratory exchange ratioin males (P = 0.079). In conclusion, high-intensity exercise, if energy matched, does not lead to greater appetite or energy intake, but may exert additional beneficial metabolic effects that may be more pronounced in males.

Comparison of Measures of Maximal and Submaximal Fitness in Response to Exercise

INTRODUCTION

Adoption of physical activity (PA) consistent with current guidelines does not improve maximal cardiorespiratory fitness (mCRF; V˙O2peak) beyond the error of measurement for approximately 30% of adults. Whether PA improves measures of exercise tolerance at submaximal levels (submaximal cardiorespiratory fitness [sCRF]) independent of change in mCRF is unknown. Here we assessed the relationship between exercise-induced changes in mCRF and sCRF.

METHODS

Twenty-five physically inactive men 30-60 yrs old (mean ± SD = 44.3 ± 9.1 yr) completed 4 wk of supervised exercise consisting of 30 min of exercise, five times per week at 65% mCRF. mCRF was assessed using a maximal treadmill test. sCRF was measured as follows: 1) exercise tolerance, the distance traveled during a 12-min time trial on a treadmill, and 2) change in heart rate (HR) at submaximal work rates during the maximal treadmill test. Daily PA was measured by accelerometry at baseline and 4 wk.

RESULTS

mCRF (P = 0.009) and both measures of sCRF (P < 0.001) improved at 4 wk. No change in measures of daily PA was observed at 4-wk compared with baseline (P > 0.05). No association was observed between exercise-induced change in mCRF and change in either measure of sCRF (P > 0.05) after exercise training. In the group of participants who did not improve mCRF beyond the measurement error (n = 13, or 52%), we observed a significant improvement in both measures of sCRF (P < 0.001). Among these 13 individuals, all improved in at least one measure of sCRF.

CONCLUSION

Exercise-induced improvements in mCRF were not associated with improvements in either measure of sCRF. Improvements in submaximal measures of cardiorespiratory fitness are observed in the absence of change in mCRF. Measures of sCRF capture peripheral adaptations to exercise not captured by measures of mCRF alone.

Arginine and aerobic training prevent endothelial and metabolic alterations in rats at high risk for the development of the metabolic syndrome

Endothelial function is a key mechanism in the development of CVD. Arginine and exercise are important non-pharmacological strategies for mitigating the impact of metabolic changes in the metabolic syndrome, but the effect of their combined administration is unknown. Thus, the aim of this study was to investigate the isolated and combined effects of aerobic training and arginine supplementation on metabolic variables and vascular reactivity in rats at high risk for developing the metabolic syndrome. Wistar rats were divided into two groups: control and fructose (F – water with 10 % fructose). After 2 weeks, the F group was divided into four groups: F, fructose+arginine (FA, 880 mg/kg per d of l-arginine), fructose+training (FT) and fructose+arginine+training (FTA); treatments lasted for 8 weeks, and no difference was observed in body mass gain. Arginine did not improve the body protein content, and both the FA and FT groups show a reversal of the increase in adipose tissue. Insulin increase was prevented by training and arginine, without additive effect, and the increase in serum TAG was prevented only by training. The F group showed impaired endothelium-dependent vasodilation and hyperreactivity to phenylephrine, but arginine and training were capable of preventing these effects, even separately. Higher nitric oxide level was observed in the FA and FT groups, and no potentiating effect was detected. Thus, only training was able to prevent the increase in TAG and improve the protein mass, and training and arginine exert similar effects on fat content, insulin and endothelial function, but these effects are not additive.

Effect of Active Videogames on Underserved Children's Classroom Behaviors, Effort, and Fitness

OBJECTIVE

The purpose of this study was to examine the effect of active videogames (AVGs) on underserved minority children's on-task classroom behavior, academic effort, and fitness.

MATERIALS AND METHODS

A one group pre- and posttest repeated measures design was used. In Fall 2013, 95 fourth grade children (57 boys, 38 girls; 96% of minority) from three classes at an underserved urban elementary school participated in teacher-supervised AVG activities (e.g., Wii Sports, Xbox Just Dance). Specifically, students participated in a 50-minute weekly AVG program at school for 6 weeks. Children's academic effort was evaluated by classroom teachers using a validated scale that assessed activity, attention, conduct, and social/emotional behavior. Moreover, children's classroom behavior was observed immediately before and after each AVG session by trained researchers. Finally, cardiovascular fitness was also measured.

RESULTS

A paired t-test was used to assess teacher-rated student effort, while one-way (gender) analysis of variance (ANOVA) with repeated measures was performed to analyze children's on-task classroom behavior. There was a significant effect on children's effort between the first (mean = 3.24, SD = 0.75) and last week (mean = 3.41, SD = 0.73) assessments, t = 2.42, P = 0.02. In addition, there was a significant effect on classroom behavior, F = 33.103, P < 0.01. In detail, children scored significantly higher on on-task behavior during the post-AVG observation (mean = 81.4, SD = 12.3) than seen during the pre-AVG observation (mean = 69.8, SD = 14.9). However, no main effect was indicated for gender, F = 0.39, P = 0.54. No significant improvement in cardiovascular fitness was observed, although slight improvements were seen.

CONCLUSION

Offering an AVG program at school could improve underserved minority children's classroom on-task behavior and academic effort. Future studies may include a control group to further confirm the effectiveness of AVG activities. Practical implications for educators and other stakeholders are provided.

Urban Park Development and Pediatric Obesity Rates: A Quasi-Experiment Using Electronic Health Record Data

INTRODUCTION

Childhood obesity affects ~20% of children in the United States. Environmental influences, such as parks, are linked with increased physical activity (PA).

OBJECTIVE

To examine whether changes in Body Mass Index (BMI) z-score were associated with construction of a new park.

METHODS

A quasi-experimental design was used to determine whether living in proximity of a park was associated with a reduction in BMI z-score. Children were selected from health clinics within an 11 mile radius of the park. A repeated-measure ANOVA was employed for analysis of the relationship between exposure (new park) and BMI z-score.

RESULTS

Participants were 1443 (median age 10.3 range (2-17.9 years), BMI: z-score 0.84 ± 1.09) African American (77.4%) adolescents. Change in BMI z-score was not statistically different for children living at different distances from the park after controlling for age, gender, race, ethnicity, or payer type (p = 0.4482). We did observe a small 0.03 increase in BMI z-score from pre- to post-park (p = 0.0007). There was a significant positive association between child's baseline age and BMI z-score (p < 0.001).

CONCLUSIONS

This study found proximity to a park was not associated with reductions in BMI z-score. Additional efforts to understand the complex relationship between park proximity, access, and PA are warranted.

Effects of insufficient physical activity on mortality and life expectancy in Jiangxi province of China, 2007-2010

BACKGROUND

Physical inactivity remains an under-researched field in terms of studying burden of disease at provincial level, and no studies have examined the effects of inactivity on life expectancy (LE) in China. The purpose of this study was to estimate mortality risk and LE effects associated with insufficient levels of physical activity in Jiangxi province.

METHODS/FINDINGS

Prevalence of risk factors and mortality counts were extracted from Chronic Diseases and Risk Factors Surveillance Survey (CDRFSS) and Disease Surveillance Points system (DSP), respectively. Insufficient physical activity (IPA) was defined as less than 150 minutes of moderate-intensity physical activity or 60 minutes of vigorous-intensity physical activity per week, accumulated across work, home, transport and discretionary domains. Population-attributable fractions (PAF) were used to calculate the mortality attributable to risk factors, and life table methods were used to estimate the LE gains and LE shifts. Monte Carlo simulation techniques were used for uncertainty analysis. Overall, 5 885 (95% uncertainly interval (UI), 5 047-6 506) and 8 578 (95% UI, 8 227-9 789) deaths in Jiangxi province were attributable to IPA in 2007 and 2010, respectively. The LE gains for elimination of attributable deaths were 0.68 (95% UI, 0.61-076) in 2007, and increased to 0.91 (95% UI, 0.81-1.10) in 2010. If the prevalence of IPA in 2010 had been decreased by 50% or 30%, 3 678 (95% UI, 3 220-4 229) or 2 090 (95% UI, 1 771-2 533) deaths would be avoided, and 0.40 (95% UI, 0.34-0.53) or 0.23 (95% UI, 0.16-0.31) years of LE gained, respectively.

CONCLUSIONS

Adults in Jiangxi province of China have a high and increasing prevalence of IPA. Due to the deaths and potential LE gains associated with IPA, there is an urgent need to promote physical activity, one of the most modifiable risk factors, within China's health care reform agenda.

Peer-delivered physical activity interventions: an overlooked opportunity for physical activity promotion

The purpose of this systematic review was to catalogue and synthesize published studies that have examined the effects of peer-delivered physical activity interventions on physical activity behavior. Ten published studies were identified that met the inclusion criteria. The following information was extracted from each study: study design and duration; characteristics of the sample, peers, and interventions; and physical activity outcomes. In all articles reporting within-groups analyses, peer-delivered interventions led to increases in physical activity behavior. When compared to alternatives, peer-delivered interventions were just as effective as professionally delivered interventions and more effective than control conditions for increasing physical activity. Only three studies included measures of social cognitive variables, yielding some evidence that peers may enhance self-efficacy and self-determined forms of motivation. Based on these findings, interventionists are encouraged to include peer mentors in their intervention delivery models. Investigators are encouraged to pursue a more comprehensive understanding of factors that can explain and maximize the impact of peer-delivered activity interventions.

Noni-based nutritional supplementation and exercise interventions influence body composition

Background:

The prevalence of obesity and overweight in the Unites States has reached unprecedented levels, and so has the need for effective exercise and nutritional programs for prevention of unhealthy weight gain or safe weight loss.

Aims:

The present study was conducted in overweight men and women to assess the impact of noni-based nutritional supplementation and exercise interventions on body composition.

Materials and Methods:

Twenty two participants (16 women and 6 men), ages 18-65, were enrolled in a 12-week, open-label trial of a weight-loss program involving noni-based dietary supplements, gender-specific daily calorie restriction, and exercise interventions. Weight, percent body fat, and body mass index were measured before and after the trial.

Results:

All participants experienced weight loss. The average decrease in fat mass was highly significant (P < 0.0001), as were decreases in percent body fat and body mass index. Individual weight and fat mass losses were 17.55 ± 9.73 and 21.78 ± 8.34 lbs., respectively, and individual percent body fat and body mass index decreases were 8.91 ± 3.58 % and 2.6 ± 1.32, respectively.

Conclusion:

The nutritional and exercise interventions significantly influenced body composition among participants.

Access to environmental resources and physical activity levels of adults in Hawaii

PURPOSE

Examine associations between physical activity (PA) and spatial accessibility to environmental PA resources in Hawaii.

METHODS

Metabolic equivalents (METs) of mild, moderate, and strenuous PA were compared for accessibility with environmental PA resources within a population-based sample of Hawaiian adults (n = 381). Multiple linear regression estimated differences in PA levels for residing further from a PA resource or residing in an area with a greater number of resources.

RESULTS

No associations were found in the total sample. Analyses within subsamples stratified by ethnicity revealed that greater spatial accessibility to a PA resource was positively associated with strenuous PA among Caucasians (P = .04) but negatively associated with moderate PA among Native Hawaiians (P = .00).

CONCLUSION

The lack of association in the total sample may be a consequence of Hawaii's unique environment. Results of stratified sample analyses are unique, providing groundwork for future examinations within parallel environments and among similar ethnic groups.

A Research Agenda to Examine the Efficacy and Relevance of the Transtheoretical Model for Physical Activity Behavior

Regular physical activity (PA) decreases the risk of several chronic diseases including some cancers, type II diabetes, obesity, and cardiovascular disease; however, the majority of US adults are not meeting the recommended levels to experience these benefits. To address this public health concern, the underlying mechanisms for behavior change need to be understood, translated and disseminated into appropriately tailored interventions. The Transtheoretical Model (TTM) provides a framework for both the conceptualization and measurement of behavior change, as well as facilitating promotion strategies that are individualized and easily adapted. The purpose of this manuscript is to present the constructs of the TTM as they relate to PA behavior change. We begin with a brief synopsis of recent examinations of the TTM constructs and their application. Subsequent to its introduction, we specifically present the TTM within the PA context and discuss its application and usefulness to researchers and practitioners. Criticisms of the TTM are also noted and presented as opportunities for future research to enhance the valid application of the TTM. We offer general study design recommendations to appropriately test the hypothesized relationships within the model. With further examinations using appropriate study design and statistical analyses, we believe the TTM has the potential to advance the public health impact of future PA promotion interventions.

Associations between patterns of objectively measured physical activity and risk factors for the metabolic syndrome

PURPOSE

To determine whether certain patterns of objectively measured physical activity (PA) are associated with the risk factors for or the diagnosis of the metabolic syndrome (MS).

DESIGN

Latent class analysis, including assessment of the associations between latent PA classes and risk factors for the MS.

SETTING

Random sample from throughout the United States using data from the 2003-2004 National Health and Nutrition Examination Survey.

SUBJECTS

A total of 3458 civilian adult noninstitutionalized U.S. citizens.

MEASURES

Daily minutes of moderate-to-vigorous PA across a 7-day week based on accelerometer measurements, as well as high blood pressure, blood glucose levels, triglyceride levels, and body mass index, along with low levels of high density lipoproteins, using clinical cut points.

RESULTS

Membership in the more active PA classes was consistently associated with lower odds of all risk factors for the MS. However, when participants were categorized into quartiles of the coefficients of variation of PA across 7 days, few differences were seen in any of the risk factors.

CONCLUSIONS

Accumulating the total weekly recommended amount of PA is consistently associated with positive health profiles, and more PA than the recommended amounts may be even better. However, the manner in which this activity is accumulated, either spread over most days of the week or compressed into just a couple of days, may have similar associations with the risk factors for the MS.

Perceived community environment and physical activity involvement in a northern-rural Aboriginal community

BACKGROUND

Type 2 diabetes disproportionately affects Aboriginal peoples in Canada. Ample evidence shows that regular physical activity (PA) plays an important role in the prevention and treatment of type 2 diabetes. Evidence is beginning to emerge linking PA to the physical environment but little is known about the relationship between remote rural environments and PA involvement in Aboriginal peoples. This study's purpose was to investigate the relationship between perceptions of the environment and PA and walking patterns in Aboriginal adults in order to inform the planning and implementation of community-relevant PA interventions.

METHODS

Two hundred and sixty three residents (133 women, mean age = 35.6 years, SD = 12.3 and 130 men, mean age = 37.2 years, SD = 13.1) from Moose Factory, Ontario were asked about environmental factors related to walking and PA involvement. Survey items were drawn from standardized, validated questionnaires. Descriptive statistics (means, standard deviations, percentages) were calculated. A series of hierarchical multiple regressions were performed to determine associations between walking and overall PA with perceived environmental variables.

RESULTS

Hierarchical multiple regression to predict walking revealed significant associations between walking and perceived safety and aesthetics. Owning home exercise equipment predicted strenuous PA. Different aspects of the physical environment appear to influence different types of physical activities. The significant amount of variance in behaviour accounted for by perceived environmental variables (5.3% walking) included safety, aesthetics, convenience, owning home exercise equipment and comfortable shoes for walking.

CONCLUSION

Results suggest that a supportive physical environment is important for PA involvement and that walking and activities of different intensity appear to be mediated by different perceived environmental variables. Implications for PA promotion in rural environments where Aboriginal people face many unique environmental features (e.g., bears, mosquitoes, extreme cold) are discussed.

Physical Activity, Obesity Status, and Glycemic Control

PURPOSE

We aimed to evaluate the relationship of physical activity and obesity with glycemic control and insulin resistance.

METHODS

A randomized, population-based, cross-sectional health and nutrition survey was conducted in the province of Athens, Greece. Subjects included 1514 men and 1528 women without evidence of cardiovascular or other chronic disease. Participants were classified as inactive, minimally active, or health-enhancing physical activity (HEPA) active based on the International Physical Activity Questionnaire. Insulin sensitivity was assessed by the homeostatic model (HOMA), and overweight or obesity was assessed according to BMI (BMI >or= 25). Related social, biological, and lifestyle factors were also recorded and used as potential confounders.

RESULTS

Five hundred sixty-five (37.3%) men and 493 (32.3%) women were classified as physically active. From the 1058 (34.8%) subjects who were classified as active, 306 (10.1%) met the criteria for HEPA active, and the rest were minimally active. HEPA active and minimally active subjects smoked less and had lower BMI, waist, and waist-to-hip ratio. Lean and overweight or obese subjects with sedentary lifestyle had greater levels of glucose, insulin, and insulin resistance [corrected] However, overweight or obese volunteers with physical activity levels classified as HEPA had similar levels of glucose and insulin sensitivity, with lower insulin than lean inactive individuals. Linear regression analysis between HOMA and physical activity, taking into consideration several social and biological factors, showed that physical activity (MET x min x wk(-1)), age, BMI, and total energy intake are important predictors of HOMA, whereas other factors such as waist circumference did not reach statistical significance.

CONCLUSION

Our data show that physical activity is a significant factor on insulin sensitivity, whereas increased physical activity may ameliorate the well-known effects of obesity on insulin sensitivity.

Effects of eight weeks of exercise training and orlistat therapy on body composition and maximal exercise capacity in obese females

A comparative assessment was made of the short-term effects of orlistat therapy and exercise training on body composition and aerobic fitness in obese females. A total of 24 obese patients were enrolled in to the study; 12 received orlistat therapy (DO) and 12 participated in a regular aerobic exercise-training programme (DE). All patients were on hypocaloric diets. Each patient performed three incremental ramp exercise tests (one at Week 0, one at the end of Week 4 and one at the end of Week 8) to exhaustion using an electromagnetically braked cycle ergometer to determine their anaerobic threshold and maximal exercise (Wmax) capacity. Patients in the DE group performed continuous exercise at a work rate that corresponded to the anaerobic threshold. Weight loss and loss of fat mass after 8 weeks were -6.4% (P=0.002) and -13.4% (DE) vs -5.8% (P=0.002) and -6.4% (P=0.008) (DO), respectively. Wmax capacity was 90.8+/-5 W (basal) vs 92.9+/-5 W (Week 4, P=0.1) and 100.4+/-6 W (Week 8, 10.5%, P=0.04) in the DO group, and 96.2+/-6 W (basal) vs 129.1+/-4 W (Week 4, 34.1%, P=0.002) and 137.5+/-5 W(Week 8, 42.9%, P=0.002) in the DE group. Despite similar decreases in body weight in both groups, patients in the DE group achieved a markedly higher level of Wmax, reflecting a better improvement in cardiopulmonary fitness, compared with patients in the DO group. Considering the improvement of aerobic fitness in the short term, an aerobic exercise-training programme should be considered for sedentary obese patients to improve their aerobic fitness and thereby reduce the negative outcomes of obesity.

Aerobic exercise training and cardiovascular reactivity to psychological stress in sedentary young normotensive men and women

Forty-five (22 women) sedentary young (18-30 years old) nonsmoking normotensive volunteers engaged in either 6 weeks of aerobic training (AT), weight training (WT), or a no-treatment (NT) condition to determine whether AT lowers systolic (SBP) and diastolic (DBP) blood pressure, heart rate (HR), and rate-pressure product (RPP) during rest, psychological stress, and recovery periods. Estimated VO(2)max increased for the AT (32.1+/-1.1 to 38.4+/-1.0 ml.kg(-1).min(-1)). A smaller increase for the WT (30.5+/-1.1 to 33.8+/-1.0) was likely due to increased leg strength, and VO(2)max did not change for the NT (32.5+/-1.1 to 32.9+/-1.0). Heart rate and RPP levels were lower during psychological stress and recovery after training for AT relative to the WT and NT. Overall SBP was also lower in the AT relative to the NT but not the WT. In conclusion, aerobic training lowered cardiovascular activity levels during psychological stress and recovery in healthy young adults, implying a protective role against age-related increases in coronary heart disease for individuals who adopt aerobic exercise early in life and maintain the behavior across the life span.

Exercise and diet in obesity treatment: an integrative system dynamics perspective

PURPOSE

Demonstrate the utility of System Dynamics computer modeling to study and gain insight into the impacts of physical activity and diet on weight gain and loss.

METHODS

A holistic System Dynamics computer model is presented that integrates the processes of human metabolism, hormonal regulation, body composition, nutrition, and physical activity. These processes are not independent of one another, and the model captures the complex interdependencies between them in the regulation of body weight and energy metabolism. The article demonstrates how such an integrative simulation model can serve as a viable laboratory tool for controlled experimentation to investigate the impacts of physical activity and diet on body weight and composition.

RESULTS

In one experiment, weight loss from a moderate level of daily exercise was slightly less than the loss from dieting. Although exercise did have a favorable impact on body composition by protecting against the loss in fat-free mass (FFM), it, however, failed to blunt the drop in resting energy expenditure (REE) that accompanies diet-based weight loss. The smaller loss in FFM did indeed induce a smaller drop in REE, however, the preservation of FFM also affected a relatively larger loss in FM, which, in turn, induced a larger adaptive reduction in the metabolic rate. The two adaptations almost totally offset one another, causing minimal differences in REE. In a second experiment, exercise regimens of moderate- to high-level intensity proved counterproductive as weight-reducing strategies. However, when the diet was changed from a balanced composition to one that was highly loaded with carbohydrates, it became possible to sustain the intense exercise regimen over the experimental period and achieve a significant drop in body weight.

CONCLUSION

The results underscore the significant interaction effects between physical activity, diet, and body composition and demonstrate the utility of computer-based experimentation to study, gain insight into, and make predictions about their dynamics.

Physical health correlates of overprediction of physical discomfort during exercise

This study sought to determine if overprediction of physical discomfort prior to and following exercise was related to a number of self-report and objective measures of physical health status in a general population sample. Cross-sectional findings indicated a significant and specific relation between patterns of discomfort overprediction (vs under- or accurate prediction) and negative self-reported health status and attitudes to exercise, lower levels of physical activity, as well as poorer scores for resting heart rate, cardiorespiratory fitness and body mass index (but not waist:hip ratio). Females were more likely to overpredict discomfort, were less active and had poorer physical health than males. The potential usefulness of the prediction match-mismatch paradigm for studying exercise-related appraisal processes as proximal determinants of physical activity are discussed. Information obtained from such studies could prove useful in public health education campaigns aimed at increasing levels of physical activity in the general population, particularly among the less active.

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.

G protein beta 3 polymorphism and hemodynamic and body composition phenotypes in the HERITAGE Family Study

A C825T polymorphism of the G protein beta3 (GNB3) gene has been reported to be associated with hypertension and obesity. We analyzed the associations between the GNB3 C825T polymorphism and hemodynamic and body composition phenotypes in the sedentary state and their responses to endurance training in mainly normotensive white (n = 473) and black (n = 255) men and women. Blood pressure (BP) and heart rate (HR) were measured at rest and during submaximal exercise at constant power output (50 W), and stroke volume and cardiac output were obtained during exercise. Body composition was assessed with underwater weighing. Baseline systolic BP (SBP) at 50 W was slightly higher in the white CC homozygotes (P = 0.036), whereas in blacks the CC genotype was associated with a lower resting HR (P = 0.012). In blacks, the CC homozygotes showed a greater training-induced reduction in HR at 50 W (P = 0.013) and a similar trend was observed also in whites (P = 0.053). Black women carrying the CC genotype showed significantly greater reductions in resting SBP and diastolic BP (DBP) than the TT homozygotes, whereas in black men the changes in resting BP were similar across the genotypes (P < 0.05 for sex-by-GNB3 interactions). The GNB3 genotype was not associated with baseline body composition in blacks or whites. In blacks, the TT genotype was associated with a greater training-induced decrease in fat mass (P = 0.012) and percent body fat (P = 0.006). These data suggest that DNA sequence variation in the GNB3 locus is not a major modifier of endurance training-induced changes in hemodynamic and body composition phenotypes in healthy but previously sedentary subjects. The GNB3 genotype may play a minor role in HR and body fatness regulation in blacks and in responsiveness of resting BP to endurance training in black women.

A new accelerometric method to assess the daily walking practice

OBJECTIVE

To describe a method to obtain a profile of the duration and intensity (speed) of walking periods over 24 hours in women under free-living conditions.

DESIGN

A new method based on accelerometry was designed for analyzing walking activity. In order to take into account inter-individual variability of acceleration, an individual calibration process was used. Different experiments were performed to highlight the variability of acceleration vs walking speed relationship, to analyze the speed prediction accuracy of the method, and to test the assessment of walking distance and duration over 24-h.

SUBJECTS

Twenty-eight women were studied (mean+/-s.d.) age: 39.3+/-8.9 y; body mass: 79.7+/-11.1 kg; body height: 162.9+/-5.4 cm; and body mass index (BMI) 30.0+/-3.8 kg/m(2).

RESULTS

Accelerometer output was significantly correlated with speed during treadmill walking (r=0.95, P<0.01), and short unconstrained walks (r=0.86, P<0.01), although with a large inter-individual variation of the regression parameters. By using individual calibration, it was possible to predict walking speed on a standard urban circuit (predicted vs measured r=0.93, P<0.01, s.e.e.=0.51 km/h). In the free-living experiment, women spent on average 79.9+/-36.0 (range: 31.7-168.2) min/day in displacement activities, from which discontinuous short walking activities represented about 2/3 and continuous ones 1/3. Total walking distance averaged 2.1+/-1.2 (range: 0.4-4.7) km/day. It was performed at an average speed of 5.0+/-0.5 (range: 4.1-6.0) km/h.

CONCLUSION

An accelerometer measuring the anteroposterior acceleration of the body can estimate walking speed together with the pattern, intensity and duration of daily walking activity.

Determining the amount of physical activity needed for long-term weight control

OBJECTIVE

To evaluate prospectively the influence of habitual physical activity on body weight of men and women and to develop a model that defines the role of physical activity on longitudinal weight change.

DESIGN AND SETTING

Occupational cohort study conducted for a mean of 5.5 y.

SUBJECTS

A total of 496 (341 male and 155 female) NASA/Johnson Space Center employees who completed the 3 month education component of the employee health-related fitness program and remained involved for a minimum of 2 y.

MEASUREMENTS

Body weights were measured at baseline (T1) and follow-up (T2), and habitual physical activity was obtained from the mean of multiple ratings of the 11-point (0-10) NASA Activity Scale (NAS) recorded quarterly between T1 and T2. Other measures included age, gender, VO(2 max) obtained from maximal treadmill testing, body mass index (BMI), and body fat percentage.

RESULTS

Multiple regression demonstrated that mean NAS, T1 weight, aging and gender all influence long-term T2 weight. T1 age was significant for the men only. Independently, each increase in mean NAS significantly (P<0.01) reduced T2 weight in men (b=-0.91 kg; 95% CI:-1.4 to-0.42 kg) and women (b=-2.14 kg; 95% CI:-2.93 to-1.35 kg). Mean NAS had a greater effect on T2 weight as T1 weight increased, and the relationship was dose-dependent.

CONCLUSIONS

Habitual physical activity is a significant source of long-term weight change. The use of self-reported activity level is helpful in predicting long-term weight changes and may be used by health care professionals when counseling patients about the value of physical activity for weight control.