Fat distribution and cardiovascular disease risk in African-American women

We have previously shown that in Caucasian men and women fat in the trunk, and especially visceral fat, was related to cardiovascular disease (CVD) risk even after adjusting for fat in other depots. We also found that leg fat was negatively related to CVD. In order to determine if these relationships also exist in African-American women, blood lipids, insulin, and blood pressure in 26 pre-menopausal African-American women were evaluated. In addition, magnetic resonance imaging measured fat distribution was evaluated from the lateral malleolus to top of the shoulder. Percent fat was related to VLDL cholesterol, VLDL3 cholesterol, triglycerides, insulin, and diastolic blood pressure. Inclusion of visceral and trunk fat together in multiple regression did little to improve the relationship with CVD risk. Leg fat, however, tended to be negatively related to CVD risk after adjusting for trunk fat and visceral fat. Partial correlations indicated that leg fat was negatively related to VLDL cholesterol (r = -0.36), triglycerides (r = -0.36), insulin (r = -0.46), and diastolic blood pressure (r = -0.43). These results indicate that in African-American women, visceral fat may be less atherogenic than in Caucasian men and women since it was poorly related to CVD risk after adjusting for fat in the trunk. In addition, consistent with results from Caucasians, leg fat is inversely related to CVD risk after adjusting for fat in other parts of the body. Caution must be made in the interpretation of correlational data. Further research is warranted to explore these intriguing relationships.

Do adaptive changes in metabolic rate favor weight regain in weight-reduced individuals? An examination of the set-point theory

BACKGROUND

Obese persons generally regain lost weight, suggesting that adaptive metabolic changes favor return to a preset weight.

OBJECTIVE

Our objective was to determine whether adaptive changes in resting metabolic rate (RMR) and thyroid hormones occur in weight-reduced persons, predisposing them to long-term weight gain.

DESIGN

Twenty-four overweight, postmenopausal women were studied at a clinical research center in four 10-d study phases: the overweight state (phase 1, energy balance; phase 2, 3350 kJ/d) and after reduction to a normal-weight state (phase 3, 3350 kJ/d; phase 4, energy balance). Weight-reduced women were matched with 24 never-overweight control subjects. After each study phase, assessments included RMR (by indirect calorimetry), body composition (by hydrostatic weighing), serum triiodothyronine (T(3)), and reverse T(3) (rT(3)). Body weight was measured 4 y later, without intervention.

RESULTS

Body composition-adjusted RMR and T(3):rT(3) fell during acute (phase 2) and chronic (phase 3) energy restriction (P: < 0.01), but returned to baseline in the normal-weight, energy-balanced state (phase 4; mean weight loss: 12.9 +/- 2.0 kg). RMR among weight-reduced women (4771 +/- 414 kJ/d) was not significantly different from that in control subjects (4955 +/- 414 kJ/d; P: = 0.14), and lower RMR did not predict greater 4-y weight regain (r = 0.27, NS).

CONCLUSIONS

Energy restriction produces a transient hypothyroid-hypometabolic state that normalizes on return to energy-balanced conditions. Failure to establish energy balance after weight loss gives the misleading impression that weight-reduced persons are energy conservative and predisposed to weight regain. Our findings do not provide evidence in support of adaptive metabolic changes as an explanation for the tendency of weight-reduced persons to regain weight.

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.

Racial differences in insulin secretion and sensitivity in prepubertal children: role of physical fitness and physical activity

OBJECTIVE

To investigate in prepubertal children whether physical fitness and/or physical activity are: 1) associated with insulin secretion and sensitivity and 2) account for racial differences in insulin secretion and sensitivity.

RESEARCH METHODS AND PROCEDURES

Subjects included 34 African American and 34 white nondiabetic children aged 5 to 11 years. Data were divided into two sets according to the availability of VO2max and physical activity data. Body composition was measured by dual-energy X-ray absorptiometry. Subcutaneous abdominal adipose tissue and intra-abdominal adipose tissue were examined by computed tomography. Insulin sensitivity (S1) and acute insulin response (AIR) were determined by a frequently sampled intravenous glucose tolerance test. An all-out, progressive treadmill exercise test was used for measuring VO2max. Physical activity data were collected by questionnaire.

RESULTS

African American children had lower SI and higher AIR than white children, after adjusting for total body fat mass. African Americans reported higher levels of physical activity (hours/wk) than whites, but had a lower VO2max. In multiple linear regression analysis, hours/wk of activity and hours/wk of vigorous activity, but not moderate activity, were independently related to SI and AIR after adjusting for race, total body fat mass or fat distribution, and total lean tissue mass. VO2max was not related to AIR, and was inversely related to SI, after adjusting for body composition. Race remained significantly associated with both SI and AIR, even after adjusting for body composition, fat distribution, and hours/wk of activity or hours/wk of vigorous activity.

DISCUSSION

In summary, overall physical activity and, especially, vigorous activity were associated with insulin secretion and sensitivity. However, neither physical activity nor VO2max explained the racial difference in insulin secretion (higher in African Americans) and sensitivity (lower in African Americans). Thus, racial (African American to white) differences in aspects of insulin action seem to be due to factors other than body composition, fat distribution, cardiovascular fitness, and amount of physical activity.

Resistance training increases total energy expenditure and free-living physical activity in older adults

The purpose of this study was to determine what effects 26 wk of resistance training have on resting energy expenditure (REE), total free-living energy expenditure (TEE), activity-related energy expenditure (AEE), engagement in free-living physical activity as measured by the activity-related time equivalent (ARTE) index, and respiratory exchange ratio (RER) in 61- to 77-yr-old men (n = 8) and women (n = 7). Before and after training, body composition (four-compartment model), strength, REE, TEE (doubly labeled water), AEE (TEE - REE + thermic response to meals), and ARTE (AEE adjusted for energy cost of standard activities) were evaluated. Strength (36%) and fat-free mass (2 kg) significantly increased, but body weight did not change. REE increased 6.8%, whereas resting RER decreased from 0.86 to 0.83. TEE (12%) and ARTE (38%) increased significantly, and AEE (30%) approached significance (P = 0.06). The TEE increase remained significant even after adjustment for the energy expenditure of the resistance training. In response to resistance training, TEE increased and RER decreased. The increase in TEE occurred as a result of increases in both REE and physical activity. These results suggest that resistance training may have value in increasing energy expenditure and lipid oxidation rates in older adults, thereby improving their metabolic profiles.

Total body fat does not influence maximal aerobic capacity

OBJECTIVE

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

DESIGN

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

METHODS

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

RESULTS

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

CONCLUSION

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

Evaluation of the strength-size relationship in vivo using various muscle size indices

PURPOSE

It is well accepted that maximum strength is related to muscle size. The primary purpose of this study was to determine whether anthropometric or dual-energy x-ray absorptiometry (DEXA) estimates of muscle size were valid predictors of plantar flexor maximum voluntary contraction (MVC) strength and could be used in lieu of more sophisticated techniques (e.g., magnetic resonance imaging (MRI)). Additionally, we compared the relationship among MVC and three MRI-determined muscle size measures; anatomical (ACSA) and physiological (PCSA) cross-sectional areas; and muscle volume (VOLm).

METHODS

We measured plantar flexor MVC at 1.83 rad and various indices of muscle size: 1) body weight, 2) total body lean mass (LM) (DEXA), 3) lower leg LM (DEXA), 4) lower leg circumference, 5) estimated muscle+bone cross-sectional area (CSA) from circumference and calf skin-fold, 6) triceps surae ACSA, 7) triceps surae PCSA, and (8) triceps surae volume (VOLm), in 39 premenopausal women (mean +/- SD: 36 +/- 8 yr, 165 +/- 6 cm, and 65 +/- 9 kg).

RESULTS

Zero-order correlations showed significant (P < 0.05) associations between MVC and total body LM (r = 0.365), lower leg LM (r = 0.381), circumference (r = 0.584), estimated muscle+bone CSA (r = 0.447), ACSA (r = 0.733), PCSA (r = 0.715), and VOLm (r = 0.649). By using the Fisher Z-transformation, ACSA and PCSA correlated significantly higher with MVC (P < 0.05) than anthropometric and DEXA indices. Further, only ACSA and PCSA regressed to the origin, indicating the ability to predict MVC was greatest with these two measures.

CONCLUSIONS

The MRI-determined muscle size indices, which were specific to the triceps surae, correlated with strength better than whole limb anthropometric and DEXA indices. In this group of women, both ACSA and PCSA appeared superior to VOLm for predicting strength. PCSA was not found to be more precise than ACSA. ACSA appears to provide adequate precision for estimating plantar flexor specific tension in vivo.

Energy expenditure and free-living physical activity in black and white women: comparison before and after weight loss

BACKGROUND

The prevalence of obesity is higher in black than in white women. Differences in energy economy and physical activity may contribute to this difference.

OBJECTIVE

The objective of this study was to compare free-living energy expenditure and physical activity in black and white women before and after weight loss.

DESIGN

Participants were 18 white and 14 black women with body mass indexes (in kg/m(2)) between 27 and 30. Diet, without exercise, was used to achieve a weight loss of >/=10 kg and a body mass index <25. After 4 wk of energy balance in overweight and normal-weight states, body composition was assessed by using a 4-compartment model, sleeping and resting energy expenditures were assessed by using a chamber calorimeter, physiologic stress of exercise and exercise economy were measured by using standardized exercise tasks, and daily energy expenditure was assessed by using doubly labeled water.

RESULTS

Weight loss averaged 12.8 kg. Sleeping and resting energy expenditures decreased in proportion to changes in body composition. Weight reduction significantly improved physiologic capacity for exercise in both groups of women, making it easier for them to be physically active. Black women had lower body composition-adjusted energy requirements than did white women-both before and after weight loss-during sleep (9% lower, 519 kJ/d; P < 0.001), at rest (14% lower, 879 kJ/d; P < 0.001), during exercise (6% lower; P < 0. 05), and as a daily total (9% lower, 862 kJ/d; P < 0.06). By contrast, free-living physical activity was similar between the groups.

CONCLUSIONS

Weight-reduced women had metabolic rates appropriate for their body sizes. Black women had lower resting and nonresting energy requirements in both overweight and normal-weight states than did white women and did not compensate with greater physical activity, potentially predisposing them to greater weight regain.

Reliability of treadmill measures and criteria to determine VO2max in prepubertal girls

PURPOSE

The main objective of this study was to determine the reliability of measuring treadmill exercise economy (VO2submax) and the maximal oxygen uptake (VO2max) in prepubertal girls tested twice, 6 wk apart. We also wanted to examine the percentage of young girls who were able to reach the criteria for achieving VO2max and to describe methods that would allow a high proportion of young children to achieve criteria for reaching a true VO2max.

METHODS

We studied 61 normal-weight, prepubertal girls with a mean (+/- SD) age 7.3+/-1.3 yr (range 4.8 to 10.3 yr). VO2submax was determined while walking for 4 min at 2.5 mph with 0% grade. VO2max was measured during a progressive, all-out, continuous treadmill test using standardized procedures and criteria. Heart rate (HR) was measured using a Polar monitor. Respiratory rate (RR), respiratory exchange ratio (RER), ventilation (V), and VO2 were measured using a Sensormedics metabolic monitor.

RESULTS

There were no significant differences between visits I and 2 in mean HR, RR, RER, V, VO2submax (421 vs 422 mL x min(-1), respectively), and VO2max (1036 vs 1049 mL x min(-1), respectively). Intra-individual coefficients of variation (CV) between visits 1 and 2 for submaximal tests were: HR = 5.1%, RR = 12.4%, RER = 7.2%, V = 12.5%, and VO2 = 12.4%. Intra-individual CVs for the maximum tests were: HRmax = 2.1%, RRmax = 10.8%, RERmax = 5.3%, Vmax = 11.7%, and VO2max = 7.5%. A high proportion of the girls reached criteria for VO2max [RER> 1.00, HR>85% of age predicted maximum, and plateauing of VO2max] in both visits: 99% reached one of three criteria, 92% reached two of three criteria, and 70% reached all three criteria. Twenty girls [mean age 7.2+/-1.2 yr] reached at least two criteria in both visits, whereas 32 girls [mean (+/- SD) age 8.6+/-1.0 yr] reached three criteria in both visits.

CONCLUSION

Exercise measurements using treadmill testing were reliable in healthy, normal-weight, prepubertal girls. Older girls when compared to the younger girls were able to reach criteria for VO2max more often. Thus, we recommend that one testing should give researchers an accurate measure of walking economy and aerobic capacity, and that two criteria are enough for determining VO2max.

Tetrameric and dimeric malate dehydrogenase isoenzymes in Trypanosoma cruzi epimastigotes

Two malate dehydrogenase isoforms, named MDH1 and MDH2, have been purified to homogeneity from Trypanosoma cruzi epimastigotes. Both enzymes consist of subunits with a molecular mass close to 33 kDa; native molecular mass determination by gel filtration, however, indicated that MDH1 is a dimer, whereas MDH2 is a tetramer. Both isoforms did not cross-react immunologically. The N-termini of both MDH isoforms and several tryptic peptides of MDH1 (amounting to about one third of the complete molecule) have been sequenced by automated Edman degradation. The tryptic digests of both enzymes have also been analysed by mass spectrometry (MALDI-TOF MS). The apparent Km values in both directions of the reaction have been determined, as well as the possible inhibition by excess of the substrate oxaloacetate. The sequence data, together with the pI values and the presence or absence of oxaloacetate inhibition indicate that the dimeric MDH1 is the mitochondrial isoenzyme, whereas the tetrameric MDH2 is the glycosomal isoenzyme. No evidence was found for the presence of a cytosolic isoform.

Validation of the BOD POD with hydrostatic weighing: influence of body clothing

OBJECTIVE

Whole body air-displacement plethysmography (BOD POD), a new body composition technique, was validated against hydrodensitometry (UWW) in 67 women wearing a one-piece swimsuit (OP) who represent a wide range of body fatness and age. Additionally, the effect of trapped isothermic air in clothing while in the BOD POD was examined by comparing different clothing schemes (a one-piece swimsuit (OP), two-piece swimsuit (TP), a hospital gown (HG), and a hospital gown previously included in a volume calibration (GC)) in a subset of 25 women.

DESIGN

Cross-sectional data analysis.

SUBJECTS

67 healthy Caucasian females.

MEASUREMENTS

Body density g/cm3 (Db) by BOD POD and UWW.

RESULTS

In 67 females UWW Db (1.030+/-0.020 g/cm3) was higher (P<0.01) than BOD POD Db (1. 028+/-0.020 g/cm3). This is a difference of 1.0% fat. The R2 was 0. 94, SEE was 0.005 g/cm3 and the regression between Db by UWW and BOD POB did not significantly deviate from the line of identity. In the subset group of 25 subjects, OP Db (1.040+/-0.014 g/cm3) and TP Db (1.040+/-0.014 g/cm3) were significantly lower (P<0.01) than UWW Db (1.044+/-0.014 g/cm3) or a difference of 1.9% fat. The R2 was 0.86 and the SEE was 0.005 g/cm3 and the regression between Db by UWW and both OP and TP did not significantly deviate from the line of identity. HG Db (1.056+/-0.016 g/cm3) and GC Db (1.037+/-0.016 g/cm3) were significantly different (P<0.01) from UWW Db (1.044+/-0. 014 g/cm3). This difference in density translates to a difference of 5.5% and 3.2% fat respectively. The regression between Db by UWW and both HG and GC significantly deviated from the line of identity.

CONCLUSION

This study supports the use of the BOD POD as a substitute for UWW. However, caution should be made in using the BOD POD if subjects are clothed in anything other than a tight fitting swimsuit.

Racial differences in energy expenditure and aerobic fitness in premenopausal women

BACKGROUND

Aerobic fitness, or maximal oxygen uptake (f1.gif" BORDER="0">O(2)max), and energy expenditure (EE) may be lower in African Americans than in whites.

OBJECTIVE

The objective of this study was to compare sleeping EE (SEE), resting EE (REE), free-living total EE (TEE), and f1.gif" BORDER="0">O(2)max in African American and white women after adjustment for body composition and free-living activity-related energy expenditure (AEE).

DESIGN

Eighteen African American and 17 white premenopausal women were matched for weight, percentage body fat, and age. SEE and REE were measured in a room calorimeter and f1.gif" BORDER="0">O(2)max was measured on a treadmill. Fat-free mass (FFM) and fat mass (FM) (4-compartment model), AEE (doubly labeled water and SEE), and regional lean tissue (dual-energy X-ray absorptiometry) were used as adjustment variables in SEE, REE, TEE, and f1.gif" BORDER="0">O(2)max comparisons.

RESULTS

The African American women had significantly more limb lean tissue and significantly less trunk lean tissue than did the white women. The African American women also had significantly lower SEE (6.9%), REE (7.5%), TEE (9.6%), and f1.gif" BORDER="0">O(2)max (13.4%) than did the white women. Racial differences persisted after adjustment for f1.gif" BORDER="0">O(2)max, AEE, FFM, and limb lean tissue but disappeared after adjustment for trunk lean tissue. The f1.gif" BORDER="0">O(2)max difference was independent of all body-composition variables and of AEE.

CONCLUSIONS

African American women had lower aerobic fitness than did white women, independent of differences in lean tissue or AEE. Diminished racial differences in SEE, REE, and TEE after adjustment for trunk lean tissue suggest that low EE in African American women is mediated by low volumes of metabolically active organ mass.

31P MRS measurement of mitochondrial function in skeletal muscle: reliability, force-level sensitivity and relation to whole body maximal oxygen uptake

The reliability, relation to whole-body maximal oxygen uptake (VO(2max)), and force-level sensitivity of (31)P MRS markers of mitochondrial function were studied in 39 normal-weight women. Following 90 s isometric plantar-flexion exercises at 45, 70 and 100% of maximum voluntary contraction, skeletal muscle mitochondrial function was determined from the phosphocreatine recovery time constant (TC(PCr)), the ADP recovery time constant (TC(ADP)), and the rate of change in PCr during the first 14 s of recovery (OxPhos). VO(2max) was measured on a treadmill. Test-retest measurements were obtained in a subset of seven women. Overall, TC(PCr), TC(ADP) and OxPhos were reproducible for all exercises (coefficients of variation = 2.3-19.3%). With increasing force-level, TC(PCr) was prolonged (29.0 +/- 8.2, 31.9 +/- 9.0 and 35.4 +/- 9.5 s), OxPhos was increased (0.159 +/- 0.081, 0.247 +/- 0.090 and 0.310 +/- 0.114), and TC(ADP) was shortened (22.4 +/- 7.9, 21.3 +/- 6.2, and 19.5 +/- 6.7; p < 0.01). All MRS markers of mitochondrial function were correlated with VO(2max) (r = 0.41-0.72; p < 0.05). These results suggest that measurements of TC(PCr), TC(ADP) and OxPhos yield reproducible results that correlate with whole-body VO(2max) and that vary in force-level sensitivity.

Effect of weight reduction, obesity predisposition, and aerobic fitness on skeletal muscle mitochondrial function

We used (31)P magnetic resonance spectroscopy to measure maximal mitochondrial function in 12 obesity-prone women before and after diet-induced weight reduction and in 12 matched, never-obese, and 7 endurance-trained controls. Mitochondrial function was modeled after maximum-effort plantar flexion from the phosphocreatine recovery time constant (TC(PCr)), the ADP recovery time constant (TC(ADP)), and the rate of change in PCr during the first 14 s of recovery (OxPhos). Weight reduction was not associated with a significant change in mitochondrial function by TC(PCr), TC(ADP), or OxPhos. Mitochondrial function was not different between postobese and never-obese controls by TC(PCr) [35.1 +/- 2.5 (SE) vs. 34.6 +/- 2.5 s], TC(ADP) (22.9 +/- 1.8 vs. 21.2 +/- 1.8 s), or OxPhos (0.26 +/- 0. 03 vs. 0.25 +/- 0.03 mM ATP/s), postobese vs. never-obese, respectively. However, TC(ADP) was significantly faster (14.5 +/- 2. 3 s), and OxPhos was significantly higher (0.38 +/- 0.04 mM ATP/s) in the endurance-trained group. These results suggest that maximal mitochondrial function is not impaired in normal-weight obesity-prone women relative to their never-obese counterparts but is increased in endurance-trained women.

Effects of strength training on intra-abdominal adipose tissue in obese prepubertal girls

PURPOSE

The purpose of this study was to determine the effects of strength training on fat distribution and its relationship to glucose tolerance in obese prepubertal girls.

METHODS

A strength training intervention study was designed in which the children exercised three times per week for 5 months. Twelve healthy, obese prepubertal girls (ages 7-10 yr, > 95th percentile weight for height) were enrolled in the study. Body composition was measured by dual-energy x-ray absorptiometry and computed tomography, and glucose tolerance was measured by a 3-h oral glucose tolerance test at baseline and after training.

RESULTS

Significant increases in height, weight, fat-free mass, fat mass, and subcutaneous abdominal adipose tissue occurred after training (P < 0.05), whereas intra-abdominal adipose tissue (IAAT) remained stable (N = 11). Insulin area was highly correlated with IAAT before (r = 0.91) and after (r = 0.90) training (both P < 0.01, N = 9).

CONCLUSION

In growing obese prepubertal girls undergoing a strength training program, IAAT remains unchanged, whereas subcutaneous abdominal fat and total body fat increased; insulin area is related to IAAT in these children.

Variability of abdominal adipose tissue measurements using computed tomography in prepubertal girls

OBJECTIVE

To determine the variability of measuring regional adipose tissue area using abdominal computed tomography (CT) in normal-weight, prepubertal girls.

DESIGN

Measurements of abdominal CT were performed twice, 6 weeks apart.

SUBJECTS

Sixty-one normal-weight, prepubertal girls (age: 4.8-10.3 y, mean (s.d.) BMI: 16.7 +/- 1.5 kg/m2).

MEASUREMENTS

Abdominal adipose tissue by CT at baseline and 6 weeks later.

RESULTS

There were no significant differences between visits 1 and 2 with regard to the children's average abdominal CT derived intraabdominal adipose tissue (21.64 cm2 vs 23.74 cm2) and subcutaneous adipose tissue (62.49 cm2 vs 65.28 cm2). The Pearson coefficient of correlation (r), P-value, total coefficient of variation (CV) and standard error of the difference (SEdelta) for intra-individual measurements between visits 1 and 2 by abdominal CT were: total abdominal adipose tissue, r = 0.94, P < 0.0001, CV = 12.34%, SEdelta 2.25 cm2; subcutaneous abdominal adipose tissue, r = 0.96, P < 0.0001, CV = 10.67%, SEdelta = 1.57 cm2; and intraabdominal adipose tissue, r = 0.67, P < 0.0001, CV = 21.5%, SEdelta = 1.11 cm2. The mean ratios of intraabdominal to subcutaneous adipose tissue on visits 1 and 2 were 0.42 +/- 0.2 and 0.44 +/- 0.24, respectively.

CONCLUSION

Regional adipose tissue area measurements using abdominal CT were reliable in healthy, normal-weight, prepubertal girls.

The etiology of obesity: relative contribution of metabolic factors, diet, and physical activity

Three major factors modulate body weight: metabolic factors, diet, and physical activity, each influenced by genetic traits. Despite recent advances in these areas, the prevalence of obesity in Westernized societies has increased. In contrast to monogenic animal models and rare human genetic syndromes, predisposition to common forms of obesity is probably influenced by numerous susceptibility genes, accounting for variations in energy requirements, fuel utilization, muscle metabolic characteristics, and taste preferences. Although recent increases in obesity prevalence cannot be explained by changes in the gene pool, previously "silent" genetic variants may now play important permissive roles in modern societies. Available data suggest that variations in resting energy expenditure, thermic effect of food, and fuel utilization exist but, by themselves, are unlikely to explain the onset of obesity. Regarding diet, the best available trend survey data indicate that fat and energy intake have fallen, in this and other Westernized countries. Diverging trends of decreasing energy intake and increasing body weight suggest that reduced physical activity may be the most important current factor explaining the rising prevalence of obesity. Subsistence in modern societies requires extreme adaptations in previously useful energy-conserving diet and exercise behaviors. Recognizing the difficulties in sustaining energy-restricted diets in the presence of fast foods and social feasts, the current trend toward increasing body weight is not likely to be reversed solely through recommendations for further reductions in energy intake. In all likelihood, activity levels will have to increase in response to an environment engineered to be more physically demanding.

Serum leptin concentrations and weight gain in postobese, postmenopausal women

OBJECTIVE

This study was designed to determine if serum leptin concentrations (adjusted for fat mass) after weight loss on a low-calorie diet predict subsequent weight gain.

RESEARCH METHODS AND PROCEDURES

Body composition and serum leptin concentrations were determined on 14 moderately obese, postmenopausal, nondiabetic women with a familial predisposition to obesity. Assessments were obtained under tightly controlled metabolic ward conditions of macronutrient intake and weight maintenance both before (obese state) and after a mean weight loss of 12.0 kg to normal body weight (postobese state). Four years later, without intervention, body weight and body composition were reassessed.

RESULTS

Weight loss resulted in significant decreases in fat mass (29.7 +/- 5.4 vs. 20.3 +/- 4.7; kg), body mass index (27.7 +/ 1.6 vs. 23.0 +/- 1.5; kg/m2), percent body fat (40.7 +/- 4.3 vs. 33.1 +/- 5.0), and serum leptin concentrations (31.8 +/- 16.0 vs. 11.5 +/- 5.4; ng/mL). Serum leptin concentrations were positively correlated (p<0.05) with fat mass in both the obese and postobese states (r=0.67 and r=0.56, respectively). However, residual serum leptin concentrations (adjusted for fat mass) in the obese and postobese states were not related to changes in body weight (p = 0.61 and 0.52), fat mass (p = 0.72 and 0.42), body mass index (p = 0.59 and 0.33), or percent body fat (p=0.84 and 0.46) over the follow-up period.

DISCUSSION

These finding do not support the hypothesis that relatively low concentrations of leptin predict weight regain after weight loss. However, because the number of subjects in this study was limited, further studies are warranted.

Fitness and energy expenditure after strength training in obese prepubertal girls

PURPOSE

The purpose of this study was to determine the effects of a school-based, low-volume strength training program on energy expenditure, strength, and physical fitness in obese prepubertal girls.

METHODS

A longitudinal, 5-month strength training exercise program was undertaken by healthy, obese (> 95th percentile weight-for-height, N = 11) girls age 7-10 yr. The following were measured: strength by the one-repetition maximum test; fitness (VO2peak) by a treadmill exercise test; resting metabolic rate (RMR), 24-h sedentary energy expenditure (SEE), and sleeping metabolic rate (SMR) by room respiration calorimetry; and total energy expenditure (TEE) by the doubly labeled water method. Physical activity energy expenditure (AEE) was calculated as TEE-(RMR + 0.1.TEE) and physical activity level (PAL) as TEE/RMR. An age-matched, nonoverweight control group was measured for (VO2peak) and RMR over the same time period.

RESULTS

Strength increased by 19.6 and 20.0% in the upper and lower body (P < 0.01), respectively. (VO2peak) (mL.min-1) increased in both groups over time (P < 0.05), but not when covaried for fat-free mass (FFM) or weight. After adjusting for FFM or weight, RMR did not change, but SMR and 24-h SEE decreased significantly in the exercise group. There were no changes in nonprotein respiratory quotient or substrate oxidation. No changes in TEE, AEE, and PAL occurred, either unadjusted or adjusted for FFM or weight.

CONCLUSION

This long-term, school-based, low-volume strength training program favorably increases strength in obese prepubertal girls but does not increase their daily energy expenditure.

A role for high intensity exercise on energy balance and weight control

The objective of this commentary is to remark on the impact, exercise intensity has on energy expenditure and its potential for body weight control. Exercise intensity can favorably impact on energy expenditure in a number of ways. First, exercise-associated energy expenditure is increased by decreasing exercise efficiency and increasing work rate. Second, resistance training that increases muscle mass, in turn increases resting energy expenditure. Third, aerobic exercise > 70% VO2max, increases resting energy expenditure separate from any change in muscle mass. High-intensity exercise training has the added benefit of improving fitness, thus making low-intensity exercise less difficult and more easily tolerated. Although continuous intense exercise is difficult to maintain for extended periods of time, intense interval exercise can be easily endured and may be an important adjunct to lifestyle modifications for body weight control.

Energy expenditure and physical fitness in overweight vs non-overweight prepubertal girls

OBJECTIVE

To determine whether overweight children have lower physical activity energy expenditure (EE) and fitness levels than non-overweight children.

STUDY DESIGN

Twenty-four healthy girls aged 7-10 y were divided into overweight (> 95th percentile weight-for-height) and non-overweight (10-90th percentile) groups. Basal metabolic rate (BMR), sleeping metabolic rate (SMR), 24 h sedentary EE (SEE) and total EE (TEE) were measured by room respiration calorimetry and doubly labelled water. Physical activity EE and physical activity level (PAL) were calculated. Fitness (VO2peak) was measured by a treadmill exercise test.

RESULTS

The overweight group had significantly higher body weight, percent fat, fat mass and fat-free mass (FFM) (P < 0.001). The overweight girls had higher BMR, SMR, SEE and TEE (P < 0.001), but not after adjustment for FFM. Physical activity EE and PAL were not significantly different between groups. After adjusting for FFM or weight, submaximal and peak VO2 were not significantly different between groups.

CONCLUSIONS

We conclude that these overweight girls do not have lower physical activity EE or fitness levels than the non-overweight prepubertal girls, however, the rather high body fat of the non-overweight group may have precluded us from finding any differences between groups.

Resistive training maintains bone mineral density in postmenopausal women

We examined the effects of a total body resistive training program (RT) on total and regional bone mineral density (BMD) in older women. Twenty-seven healthy postmenopausal women (mean age 62 +/- 1 years) participated in a strength training program three times/week for 16 weeks. Strength was assessed before and after training by either one or three repetition maximum (1RM and 3RM) tests. Both upper and lower body strength significantly increased by 36-65% and 32-98%, respectively, after training. There was a small but significant decrease in body weight and body mass index after training (P < 0. 05), with no change in the waist-to-hip ratio. BMD, assessed by dual-energy X-ray absorptiometry, did not change over the duration of the training period in the anterioposterior spine (L2-L4), femoral neck, Ward's triangle, and greater trochanter. BMD of the total body, lateral spine (B2-B4), and the regions of the radius (1/3 radius and ultradistal radius) also did not fall in subsets of these women. Muscular strength of both the leg and chest press were significantly associated with L2-L4, femoral neck, Ward's triangle, and greater trochanter BMD (range r = 0.57-0.84, all P < 0.005). Markers of bone turnover, namely, bone-specific alkaline phosphatase, osteocalcin, and urinary aminoterminal cross-linked telopeptide of type I collagen did not change significantly. In conclusion, a resistive training program maintains BMD and improves muscular strength in healthy, older women. This may be important in preventing the negative health outcomes associated with the age-related loss of bone density.

Crystallization and preliminary X-ray analysis of tyrosine aminotransferase from Trypanosoma cruzi epimastigotes

Tyrosine aminotransferase from Trypanosoma cruzi has been crystallized from PEG 4000 at pH 6.8. The crystals belong to the monoclinic space group P21 and have lattice constants of a = 59.1, b = 103.0, c = 77.8 A, beta = 113.1 degrees for a data set measured at 138 K. The presence of a non-crystallographic twofold axis together with a Matthews parameter Vm of 2.5 A3 Da-1 indicates that the asymmetric unit contains one dimeric molecule. The crystals diffract to at least 2.7 A and are stable in the X-ray beam in a shock-frozen state. Native data sets have been collected at temperatures of 285 and 138 K using a Siemens X1000 detector on a rotating-anode generator.

Resistance exercise prevents plantar flexor deconditioning during bed rest

Because resistance exercise (REX) and unloading induce opposing neuromuscular adaptations, we tested the efficacy of REX against the effects of 14 d of bed rest unloading (BRU) on the plantar flexor muscle group. Sixteen men were randomly assigned to no exercise (NOE, N = 8) or REX (N = 8). REX performed 5 sets x 6-10 repetitions to failure of constant resistance concentric/eccentric plantar flexion every other day during BRU. One-repetition maximum (1RM) strength was tested on the training device. The angle-specific torque-velocity relationship across 5 velocities (0, 0.52, 1.05, 1.75, and 2.97 rad.s-1) and the full range-of-motion power-velocity relationship were assessed on a dynamometer. Torque-position analyses identified strength changes at shortened, neutral, and stretched muscle lengths. Concentric and eccentric contractile work were measured across ten repetitions at 1.05 rad.s-1. Maximal neural activation was measured by surface electromyography (EMG). 1RM decreased 9% in NOE and improved 11% in REX (P < 0.05). Concentric (0.52 and 1.05 rad.s-1), eccentric (0.52 and 2.97 rad.s-1), and isometric angle-specific torques decreased (P < 0.05) in NOE, averaging 18%, 17%, and 13%, respectively. Power dropped (P < 0.05) in NOE at three eccentric (21%) and two concentric (14%) velocities. REX protected angle-specific torque and average power at all velocities. Concentric and eccentric strength decreased at stretched (16%) and neutral (17%) muscle lengths (P < 0.05) in NOE while REX maintained or improved strength at all joint positions. Concentric (15%) and eccentric (11%) contractile work fell in NOE (P < 0.05) but not in REX. Maximal plantar flexor EMG did not change in either group. In summary, constant resistance concentric/eccentric REX completely prevented plantar flexor performance deconditioning induced by BRU. The reported benefits of REX should prove useful in prescribing exercise for astronauts in microgravity and for patients susceptible to functional decline during bed- or chair-bound hospital stays.