BackgroundThe true causes of the obesity epidemic are not well understood and there are few longitudinal population-based data published examining this issue. The objective of this analysis was to examine trends in occupational physical activity during the past 5 decades and explore how these trends relate to concurrent changes in body weight in the U.S.Methodology/Principal FindingsAnalysis of energy expenditure for occupations in U.S. private industry since 1960 using data from the U.S. Bureau of Labor Statistics. Mean body weight was derived from the U.S. National Health and Nutrition Examination Surveys (NHANES). In the early 1960's almost half the jobs in private industry in the U.S. required at least moderate intensity physical activity whereas now less than 20% demand this level of energy expenditure. Since 1960 the estimated mean daily energy expenditure due to work related physical activity has dropped by more than 100 calories in both women and men. Energy balance model predicted weights based on change in occupation-related daily energy expenditure since 1960 for each NHANES examination period closely matched the actual change in weight for 40–50 year old men and women. For example from 1960–62 to 2003–06 we estimated that the occupation-related daily energy expenditure decreased by 142 calories in men. Given a baseline weight of 76.9 kg in 1960–02, we estimated that a 142 calories reduction would result in an increase in mean weight to 89.7 kg, which closely matched the mean NHANES weight of 91.8 kg in 2003–06. The results were similar for women.ConclusionOver the last 50 years in the U.S. we estimate that daily occupation-related energy expenditure has decreased by more than 100 calories, and this reduction in energy expenditure accounts for a significant portion of the increase in mean U.S. body weights for women and men.

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This review explores the role of physical activity (PA) and exercise training (ET) in the prevention of weight gain, initial weight loss, weight maintenance, and the obesity paradox. In particular, we will focus the discussion on the expected initial weight loss from different ET programs, and explore intensity/volume relationships. Based on the present literature, unless the overall volume of aerobic ET is very high, clinically significant weight loss is unlikely to occur. Also, ET also has an important role in weight regain after initial weight loss. Overall, aerobic ET programs consistent with public health recommendations may promote up to modest weight loss (~2 kg), however the weight loss on an individual level is highly heterogeneous. Clinicians should educate their patients on reasonable expectations of weight loss based on their physical activity program and emphasize that numerous health benefits occur from PA programs in the absence of weight loss.

The first part of this article intends to give an applicable framework for the evaluation of endurance capacity as well as for the derivation of exercise prescription by the use of two gas exchange thresholds: aerobic (AerTGE) and anaerobic (AnTGE). AerT GE corresponds to the first increase in blood lactate during incremental exercise whereas AnTGE approximates the maximal lactate steady state. With very few constraints, they are valid in competitive athletes, sedentary subjects, and patients. In the second part of the paper, the practical application of gas exchange thresholds in cross-sectional and longitudinal studies is described, thereby further validating the 2-threshold model. It is shown that AerTGE and AnTGE can reliably distinguish between different states of endurance capacity and that they can well detect training-induced changes. Factors influencing their relationship to the maximal oxygen uptake are discussed. Finally, some approaches of using gas exchange thresholds for exercise prescription in athletes, healthy subjects, and chronically diseased patients are addressed.

BackgroundIndividuals differ in the response to regular exercise. Whether there are people who experience adverse changes in cardiovascular and diabetes risk factors has never been addressed.Methodology/Principal FindingsAn adverse response is defined as an exercise-induced change that worsens a risk factor beyond measurement error and expected day-to-day variation. Sixty subjects were measured three times over a period of three weeks, and variation in resting systolic blood pressure (SBP) and in fasting plasma HDL-cholesterol (HDL-C), triglycerides (TG), and insulin (FI) was quantified. The technical error (TE) defined as the within-subject standard deviation derived from these measurements was computed. An adverse response for a given risk factor was defined as a change that was at least two TEs away from no change but in an adverse direction. Thus an adverse response was recorded if an increase reached 10 mm Hg or more for SBP, 0.42 mmol/L or more for TG, or 24 pmol/L or more for FI or if a decrease reached 0.12 mmol/L or more for HDL-C. Completers from six exercise studies were used in the present analysis: Whites (N = 473) and Blacks (N = 250) from the HERITAGE Family Study; Whites and Blacks from DREW (N = 326), from INFLAME (N = 70), and from STRRIDE (N = 303); and Whites from a University of Maryland cohort (N = 160) and from a University of Jyvaskyla study (N = 105), for a total of 1,687 men and women. Using the above definitions, 126 subjects (8.4%) had an adverse change in FI. Numbers of adverse responders reached 12.2% for SBP, 10.4% for TG, and 13.3% for HDL-C. About 7% of participants experienced adverse responses in two or more risk factors.Conclusions/SignificanceAdverse responses to regular exercise in cardiovascular and diabetes risk factors occur. Identifying the predictors of such unwarranted responses and how to prevent them will provide the foundation for personalized exercise prescription.

OBJECTIVE -To quantify the relation of fitness to mortality among men with diabetes, adjusted for BMI and within levels of BMI.RESEARCH DESIGN AND METHODS -In this observational cohort study, we calculated all-cause death rates in men with diabetes across quartiles of fitness and BMI categories. Study participants were 2,196 men with diabetes (average age 49.3 years, SD 9.5) who underwent a medical examination, including a maximal exercise test, during 1970 to 1995, with mortality follow-up to 31 December 1996.RESULTS -We identified 275 deaths during 32,161 person-years of observation. Risk of all-cause mortality was inversely related to fitness. For example, in the fully adjusted model, the risk of mortality was 4.5 (2.6 -7.6), 2.8 (1.6 -4.7), and 1.6 (0.93-2.76) for the first, second, and third fitness quartiles, respectively, with the fourth quartile (highest fitness level) as the referent (P for trend Ͻ0.0001). There was no significant trend across BMI categories for mortality after adjustment for fitness. Similar results were found when the fitness-mortality relation was examined within levels of body composition. In normal-weight men with diabetes, the relative risks of mortality were 6.6 (2.8 -15.0), 3.2 (1.4 -7.0), and 2.2 (1.1-4.6) for the first, second, and third quartiles of fitness, respectively, as compared with the fourth quartile (P for trend Ͻ0.0001). We found similar results in the overweight and obese weight categories.CONCLUSIONS -There was a steep inverse gradient between fitness and mortality in this cohort of men with documented diabetes, and this association was independent of BMI. Diabetes Care 27:83-88, 2004W hile the importance of physical activity and weight loss in the prevention of diabetes is now well established by randomized clinical trials, few studies have examined the relative contribution of weight and physical activity on morbidity and mortality in individuals with diabetes (1,2). A better understanding of the relative contributions of weight control and physical activity to mortality may guide clinical recommendations.We previously reported that low cardiorespiratory fitness and physical inactivity are independent predictors of allcause and cardiovascular disease (CVD) mortality in men with type 2 diabetes (3). However, this study examined these exposures in multivariable models and, thus, did not allow for evaluation of the relative values of physical activity, fitness, or weight as mortality predictors. We have performed additional follow-up and can now extend our previous work by examining the relation of fitness and mortality within BMI categories.The primary aims of this study of men with diabetes were to examine 1) the risk of mortality associated with fitness and BMI when examined as continuous and categorical variables and 2) the doseresponse relationship between fitness and mortality both with adjustment for BMI and within levels of BMI. RESEARCH DESIGN AND METHODS -The Aerobics CenterLongitudinal Study (ACLS) is a prospective epidemiologic investigation. Participan...

BackgroundIt has been suggested that exercise training results in compensatory mechanisms that attenuate weight loss. However, this has only been examined with large doses of exercise. The goal of this analysis was to examine actual weight loss compared to predicted weight loss (compensation) across different doses of exercise in a controlled trial of sedentary, overweight or obese postmenopausal women (n = 411).Methodology/Principal FindingsParticipants were randomized to a non-exercise control (n = 94) or 1 of 3 exercise groups; exercise energy expenditure of 4 (n = 139), 8 (n = 85), or 12 (n = 93) kcal/kg/week (KKW). Training intensity was set at the heart rate associated with 50% of each woman's peak VO2 and the intervention period was 6 months. All exercise was supervised. The main outcomes were actual weight loss, predicted weight loss (exercise energy expenditure/ 7700 kcal per kg), compensation (actual minus predicted weight loss) and waist circumference. The study sample had a mean (SD) age 57.2 (6.3) years, BMI of 31.7 (3.8) kg/m2, and was 63.5% Caucasian. The adherence to the intervention was >99% in all exercise groups. The mean (95% CI) weight loss in the 4, 8 and 12 KKW groups was −1.4 (−2.0, −0.8), −2.1 (−2.9, −1.4) and −1.5 (−2.2, −0.8) kg, respectively. In the 4 and 8 KKW groups the actual weight loss closely matched the predicted weight loss of −1.0 and −2.0 kg, respectively, resulting in no significant compensation. In the 12 KKW group the actual weight loss was less than the predicted weight loss (−2.7 kg) resulting in 1.2 (0.5, 1.9) kg of compensation (P<0.05 compared to 4 and 8 KKW groups). All exercise groups had a significant reduction in waist circumference which was independent of changes in weight.ConclusionIn this study of previously sedentary, overweight or obese, postmenopausal women we observed no difference in the actual and predicted weight loss with 4 and 8 KKW of exercise (72 and 136 minutes respectively), while the 12 KKW (194 minutes) produced only about half of the predicted weight loss. However, all exercise groups had a significant reduction in waist circumference which was independent of changes in weight.Trial RegistrationClinicalTrials.gov NCT 00011193