Effects of resistance training and endurance training on insulin sensitivity in nonobese, young women: a controlled randomized trial.

We examined the effects of a 6-month randomized program of endurance training (n = 14), resistance training (n = 17), or control conditions (n = 20) on insulin sensitivity in nonobese, younger women (18-35 yr). To examine the possible mechanism(s) related to alterations in insulin sensitivity, we measured body composition, regional adiposity, and skeletal muscle characteristics with computed tomography. We observed no changes in total body fat, sc abdominal adipose tissue, or visceral adipose tissue with endurance or resistance training. Insulin sensitivity, however, increased with endurance training (pre, 421 +/- 107; post, 490 +/- 133 mg/min; P < 0.05) and resistance training (pre, 382 +/- 87; post, 417 +/- 89 mg/min; P = 0.06). When the glucose disposal rate was expressed per kg fat-free mass (FFM), the improved insulin sensitivity persisted in endurance-trained (pre, 10.5 +/- 2.7; post, 12.1 +/- 3.3 mg/min x kg FFM; P < 0.05), but not in resistance-trained (pre, 9.7 +/- 1.9; post, 10.2 +/- 1.8 mg/min x kg FFM; P = NS) women. Muscle attenuation ratios increased (P < 0.05) in both endurance- and resistance-trained individuals, but this was not related to changes in insulin sensitivity. Moreover, the change in insulin sensitivity was not related to the increased maximum aerobic capacity in endurance-trained women (r = 0.24; P = NS). We suggest that both endurance and resistance training improve glucose disposal, although by different mechanisms, in young women. An increase in the amount of FFM from resistance training contributes to increased glucose disposal probably from a mass effect, without altering the intrinsic capacity of the muscle to respond to insulin. On the other hand, endurance training enhances glucose disposal independent of changes in FFM or maximum aerobic capacity, suggestive of an intrinsic change in the muscle to metabolize glucose. We conclude that enhanced glucose uptake after physical training in young women occurs with and without changes in FFM and body composition.

Respiratory fitness, free living physical activity, and cardiovascular disease risk in older individuals: a doubly labeled water study.

The objective of this study was to examine the importance of cardiorespiratory fitness vs. physical activity energy expenditure on selected cardiovascular disease risk factors in older individuals. One hundred and seventeen older individuals, 53 men (68 +/- 9 yr) and 63 women (67 +/- 7 yr), participated in the study. This cohort was divided into 4 groups: 1) high cardiorespiratory fitness and high physical activity, 2) high cardiorespiratory fitness and low physical activity, 3) low cardiorespiratory fitness and high physical activity, and 4) low cardiorespiratory fitness and low physical activity. Cardiorespiratory fitness (VO2max) was determined from a graded exercise test, physical activity energy expenditure was measured by doubly labeled water and indirect calorimetry, body composition was determined by dual energy x-ray absorptiometry, and dietary practices were determined by a 3-day recall. Cardiorespiratory fitness exerted greater effects on the cardiovascular disease risk profile than physical activity. That is, older individuals with higher levels of cardiorespiratory fitness, regardless of their physical activity levels, showed lower levels of fasting insulin (P < 0.01), triglycerides (P < 0.05), total cholesterol (P < 0.05), total to high density lipoprotein cholesterol ratio (P < 0.05), low density lipoprotein (P < 0.05), and lower waist circumference (P < 0.01). Moreover, individuals with a high cardiorespiratory fitness but low physical activity energy expenditure displayed a more favorable cardiovascular disease risk profile than individuals with low cardiorespiratory fitness and high physical activity energy expenditure. The results suggest that higher levels of cardiorespiratory fitness have greater cardioprotective effects than higher levels of free living physical activity in older individuals. Although these findings do not discount the health benefits of being physically active, it is possible that greater emphasis should be placed on aerobic exercise to increase cardiorespiratory fitness in the elderly.

Energy expenditure, energy intake, and weight loss in Alzheimer disease.

Alzheimer disease is one of the leading causes of death among older individuals. Unexplained weight loss and cachexia are frequent clinical findings in patients with Alzheimer disease. Thus, it has been postulated that Alzheimer disease may be associated with dysfunction in body weight regulation. This brief review examines the interrelations among energy intake, energy expenditure, and body composition in Alzheimer disease. We explored whether abnormally high daily energy expenditures, low energy intakes, or both contribute to unexplained weight loss and a decline in nutritional status. Specifically, we considered studies that examined energy intake, body composition, and daily energy expenditure and its components. The application of doubly labeled water and indirect calorimetry to understand the etiology of wasting has increased our knowledge regarding the relation among energy expenditure, physical activity levels, and body composition in Alzheimer disease patients. Although the number of studies are limited, results do not support the notion that a hypermetabolic state contributes to unexplained weight loss in Alzheimer disease, even in cachectic patients. Recent findings are presented suggesting an association between abnormally elevated levels of physical activity energy expenditure and elevated appendicular skeletal muscle mass and energy intake in Alzheimer disease patients. Clinical strategies aimed at developing lifestyle and dietary interventions to maintain adequate energy intake, restore energy balance, and maintain skeletal muscle mass should be a future area of investigation in Alzheimer disease research.

Phenotypic characteristics associated with insulin resistance in metabolically obese but normal-weight young women.

Metabolically obese, normal-weight (MONW) individuals are a hypothesized subgroup of the general population. These normal-weight individuals potentially display a cluster of obesity-related features, although this has not been systematically tested in young women. We hypothesized that MONW young women would display higher levels of total and visceral fat and lower levels of physical activity than normal women. In a cohort of 71 healthy nonobese women (21-35 years old), we identified MONW women based on cut points for insulin sensitivity (normal = glucose disposal >8 mg x min(-1) x kg(-1) of fat-free mass [FFM], n = 58; impaired = glucose disposal <8 ml x min(-1) x kg(-1) of FFM, n = 13). Thereafter, we measured body composition (dual energy X-ray absorptiometry) and body fat distribution (computed tomography), cardiorespiratory fitness (VO2max on a treadmill), physical activity energy expenditure (doubly labeled water and indirect calorimetry), glucose tolerance (oral glucose tolerance test), serum lipid profile, and dietary intake. We found a higher body fat percentage (32 +/- 6 vs. 27 +/- 6%, P = 0.01) and higher subcutaneous (213 +/- 61 vs. 160 +/- 78 cm2, P = 0.03) and visceral (44 +/- 16 vs. 35 +/- 14 cm2, P < 0.05) abdominal adiposity in the MONW group versus the normal group. The MONW group showed a lower physical activity energy expenditure (2.66 +/- 0.92 vs. 4.39 +/- 1.50 MJ/day, P = 0.01), but no difference in cardiorespiratory fitness was noted between groups. In conclusion, despite a normal body weight, a subset of young, apparently healthy women displayed a cluster of risky phenotypic characteristics that, if left untreated, may eventually predispose them to type 2 diabetes and cardiovascular disease.

Obesity-related phenotypes and the beta3-adrenoceptor gene variant in postmenopausal women.

We examined the hypothesis that postmenopausal women with the beta3-adrenoceptor gene variant (Trp64Arg) have reduced total daily energy expenditure (TEE), altered free fatty acid kinetics, and increased intra-abdominal fat. A secondary objective was to examine whether the obese state masks the effect of the variant on resting metabolic rate (RMR). There were 23 obese heterozygous women with the genetic variant (age 58 +/- 6 years; BMI 36 +/- 7 kg/m2) who were compared with 19 homozygous obese women with the normal allele (age 56 +/- 4 years; BMI 36 +/- 3 kg/m2). Daily energy expenditure was determined from doubly labeled water and indirect calorimetry, lipolysis from infusion of [1-13C]palmitate, and body fat distribution from computed tomography. No significant differences were found in TEE, RMR, energy expenditure of physical activity, the thermic effect of a meal, fat oxidation as estimated by fasting and postprandial respiratory quotients (RQs), or rate of lipolysis. Similarly, no difference was found in visceral adipose tissue and abdominal subcutaneous fat areas. When RMR was compared between obese (n = 23) and never-obese women with the Trp64Arg variant (n = 16), we found a 317 kcal/day lower RMR in never-obese women after controlling for fat mass, fat-free mass, and age (P < 0.0017). These results do not support the hypothesis that already obese women with the Trp64Arg polymorphism of the beta3-adrenergic receptor gene have lower daily energy expenditure, altered lipolysis, and increased abdominal obesity. On the other hand, the lower RMR in never-obese women suggests that the obese state may mask a moderate effect of the Trp64Arg variant on energy expenditure. Although these results need to be confirmed in other populations, the obese state may have been a confounding factor in previous studies of the beta3-adrenoceptor Trp64Arg variant and energy expenditure.

Appendicular skeletal muscle mass, physical activity, and cognitive status in patients with Alzheimer's disease.

OBJECTIVE: To examine the interrelations among appendicular skeletal muscle mass and physical activity, energy intake, and cognitive status in free-living patients with AD. BACKGROUND: Increasing disease severity in AD patients may contribute to poor nutritional status and loss of skeletal muscle mass. This may lead to impaired physical function and loss of functional independence. METHODS: Participants in our study were 30 noninstitutionalized AD patients (74 +/- 8 years) and 30 healthy age- and body mass index-matched control subjects (73 +/- 7 years). We measured appendicular skeletal muscle mass by dual-energy X-ray absorptiometry, energy expenditure by doubly labeled water, and energy intake by food diaries. RESULTS: As expected, the AD group had lower Mini-Mental State Examination scores than the control subjects (p < 0.05). No differences in energy intake or energy expenditure and its components were noted between the groups. Higher levels of appendicular muscle mass in AD patients were associated with increased energy expenditure of physical activity (r = 0.52, p < 0.01) and daily energy intake (r = 0.49, p = 0.01). Cognitive status was not related to appendicular muscle mass, daily energy intake, or energy expenditure of physical activity in AD patients. CONCLUSIONS: Higher levels of physical activity and energy intake are associated with higher appendicular skeletal muscle mass in AD patients. Nutritional and physical activity interventions may represent practical and inexpensive strategies in their therapeutic management.

Norepinephrine kinetics in older women: relationship to physical activity and blood pressure.

The sympathetic nervous system participates in the regulation of carbohydrate, lipid, and energy metabolism, and has been implicated in the pathogenesis of hypertension and obesity. Increased sympathetic nervous system activity with age may alter disease risk and contribute to the development of certain chronic diseases. Thus, we examined possible determinants of sympathetic nervous system activity in older normotensive women from infusions of tritiated norepinephrine (NE) to estimate rates of norepinephrine appearance and clearance. A secondary aim was to examine the association between norepinephrine kinetics and mean supine arterial blood pressure. Twenty-two older women (65.7 +/- 5.7 years) were characterized for resting NE kinetics, body composition, body fat distribution, peak aerobic capacity, leisure time physical activity energy expenditure (LTA), dietary carbohydrates, and daily energy intake. Analysis of univariate correlations revealed that only the LTA was significantly correlated with plasma NE appearance (r = 0.54, p < 0.01). Stepwise regression analysis identified LTA as the only significant predictor of plasma NE appearance rate with a total R2 = 0.29. The waist-to-hip ratio was selected as the only significant predictor of mean arterial blood pressure with an R2 = 0.30. When forced into the model, plasma NE appearance explained only 1% of the unique variance in mean arterial blood pressure. In summary, we found that: (1) higher levels of physical activity are related to higher plasma NE appearance in older women; (2) greater central body fatness is an independent predictor of mean arterial blood pressure; and (3) plasma NE appearance rate is a minor contributor to variation in mean arterial blood pressure in older, normotensive women.

Measurement and prediction of sympathetic nervous system activity in humans.

The measurement of norepinephrine (NE) kinetics has broadened our understanding of sympathetic nervous system activity involvement in energy expenditure, blood pressure regulation and substrate utilization. This methodology, however, has several disadvantages that include administration of radioactivity to volunteers, its expense, and time consuming laboratory analyses. Thus, we developed an equation to predict plasma NE appearance rate (NEAP) derived from infusions of tritiated norepinephrine performed in 113 healthy men (18-78 yr.). The accuracy of the equation was tested using cross-validation procedures. Age, fat mass, plasma [NE], waist circumference, and body weight (BW) correlated significantly with plasma NE appearance rate. The resulting prediction equation in the validation group was: NEAP = 0.00003148 BW [NE], with R2 = 0.76 and was successfully cross-validated. Using pooled data from both groups the prediction equation was: NEAP (microg/min) = 0.00003108 x [NE (pg/ml)] x [Body weight (kg)] with an R2 = 0.70 and SEE = 0.096 microg/min. The magnitude of error associated with this equation allows for detection of age-associated, exercise-induced changes and blood pressure-related differences in plasma NE appearance rate published in the literature. We provide an equation that offers a relatively simple and accurate alternative to estimate plasma NE appearance from the measurement of arterialized plasma [NE] and body weight.

Energy expenditure in Alzheimer's disease.

Alzheimer's disease type dementia is a growing health problem and is one of the leading causes of death among elderly people. Unexplained weight loss and cachexia is a frequent clinical finding in patients with Alzheimer's disease. It has been postulated that Alzheimer's disease may by characterized by dysfunction in body weight regulation. This brief review examines energy intake, energy expenditure and body composition in Alzheimer's disease. We consider whether inappropriately high levels of energy expenditure may contribute to unexplained weight loss and decline in nutritional status. Specifically, we will consider studies that have examined body composition, daily energy expenditure and its components. The application of doubly labeled water and indirect calorimetry to problems of "wasting" has increased our knowledge regarding energy expenditure and physical activity levels in Alzheimer's patients. Although the number of studies are limited, results do not support the notion that a "hypermetabolic" state contributes to unexplained weight loss in Alzheimer's disease, even in cachectic patients. Clinical strategies aimed at developing feeding strategies to maintain adequate caloric intake and the restoration of energy balance should be a future area of investigation in Alzheimer's research.