Changes In Percent Body Fat Research Articles

CHANGE IN BODY MASS OR BODY FAT MAY CONFOUND THE INTERPRETATION OF CHANGE IN DEXA TBMC 634

Dual energy x-ray absorptiometry (DEXA) is widely used to measure total body bone mineral content (TBMC) and bone mineral density (BMD). Accurate measurement and interpretation of the change in TBMC and BMD in response to specific interventions such as exercise, drug therapy or calcium supplementation is important. The purpose of this study was to investigate the correlation between change in TBMC, body mass and body fat percentage in United States Naval Academy (USNA) midshipmen (midn). 74 male midn age 18.8±1.0yo and 63 female midn age 18.3±0.7yo were recruited to this study in August 1992. Midn received a total body Norland XR-26 DEXA scan each year, in a repeated measures design, until their graduation in May 1996. Mean TBMC, percent change in TBMC, percent change in body fat, the correlation between percent change in TBMC and percent change in body fat, and percent change in body mass are shown in Table 1. Change in individual midn TBMC was directional with change in percent body fat and body mass. Change in TBMC was significantly (p<.001) correlated to change in percent body fat and body mass. Miles run per week, other exercise activities or change in height were not related to TBMC. We conclude that DEXA measurement of TBMC may be confounded with change in body mass and/or change in body fat percentage. Caution should be exercised in the interpretation of an intervention therapy on change in TBMC measured by DEXA.

Pharmacokinetics of TCDD in veterans of Operation Ranch Hand: 10-year follow-up.

Using multiple measurements from serum collected over 10 yr (1982, 1987, and 1992), we estimated the half-life of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) in 213 veterans of Operation Ranch Hand, the Air Force unit responsible for the aerial spraying of Agent Orange in Vietnam. The potential influences of age, percent body fat, and changes in percent body fat on the half-life estimate were also examined. The mean decay rate of TCDD for these veterans is 0.0797 per year with 95% confidence interval 0.0727 to 0.0868 per year; the corresponding half-life estimate is 8.7 yr with 95% confidence interval 8.0-9.5 yr. Half-life increased significantly with increasing body fat, but not with age or relative changes in percent body fat.

β-Adrenergically mediated thermogenic and heart rate responses: Effect of obesity and weight loss

β-Adrenergically mediated thermogenic and heart rate (HR) responses, as assessed by stepwise intravenous infusion of the β-agonist isoprenaline (ISO), were evaluated by partial regression analysis in a group of men with a wide range of body fat (n = 30) and in a subgroup of 16 obese men after weight loss. β-Adrenergically mediated thermogenesis (open-circuit ventilated-hood system) was blunted in obese subjects, as reflected by a significant positive correlation between percent body fat (hydrostatic weighing) and the plasma ISO concentration needed to increase resting energy expenditure (EE) by 15% ( P < .001). The magnitude of the β-adrenergically mediated HR response was (negatively) associated with the basal plasma norepinephrine (NE) concentration ( P < .001). Weight reduction resulted in a significant increase in thermogenic and HR responses in obese subjects. Furthermore, the increase in thermogenic response as a result of weight loss was negatively related to the magnitude of thermogenic response ( P < .01) and positively related to the initial percent body fat ( P < .05). The increase in HR response as a result of weight loss was positively related to the decrease in basal NE ( P < .01) and the change in percent body fat ( P < .05). In conclusion, the degree of adiposity was shown to be negatively related to the magnitude of β-adrenergically mediated thermogenesis, whereas the HR response was merely related to basal NE. Since weight loss resulted in a significant increase in the thermogenic response, the blunted β-adrenergically mediated thermogenesis does not seem to be a primary factor contributing to the development of obesity.

Effects of a 10‐week step aerobic training program on the aerobic power and body composition of college‐age women

This study determined the effect of a 10‐week step aerobics training program on aerobic power and body composition of college‐age women (mean age, 19.4 years). Subjects in the experimental group (n = 21) exercised three times per week for 10 weeks, at an intensity that represented 76% of maximal heart rate. A control group (n = 28) did not exercise. All subjects performed a maximal treadmill test, were hydrostatically weighed, and were measured for maximal buttocks, thigh, and calf girth prior to and on completion of the study. Compared with the control group, the experimental group showed significant (p ≤0.05) improvement in peak oxygen consumption (11.7%), maximal minute ventilation (6.7%), and time to exhaustion on the treadmill (33.1%). There was no significant (p >0.05) change in percent body fat in either group. Thus, it appears that step aerobic training can be an effective method of improving aerobic power in college‐age women. However, while the acute caloric requirement of step aerobics compares...

Energy and nutrient intakes during high-altitude acclimatization

Information on the food intake of free living individuals during the initial stage of an expedition, when the diet is based on fresh and locally available foods, is scarce. A weighed dietary survey was carried out by 10 healthy unacclimatized male subjects who walked from an altitude of 2430 m to Everest Base Camp (5400 m) in 10 days. All food and fluids consumed during the study period were weighed using dietary scales and recorded in food record books. The mean daily energy intake was 10.03 (SE 1.26) MJ. The average body weight loss was 2.07 (SE 0.6) kg and there was no change in percentage body fat calculated from skinfold thickness measurements. The percentage energy from carbohydrates in the diet was significantly higher ( p &lt; 0.05) in the final 3 days (59%, SE 2.0) compared with the first 3 days of the study period (51%, SE 3.6). It is likely that the high carbohydrate intake reflected the availability of foods at this time. With the exception of folic acid and vitamin C, the mean daily intakes of B vitamins, iron, and zinc exceeded the UK Dietary Reference Values. However, these values refer to healthy populations but not to those exposed to high altitude when nutrient requirements may be increased.

Determinants of TCDD half-life in veterans of operation ranch hand.

The half-life of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) changed significantly with body fat and age in 337 members of Operation Ranch Hand, the Air Force unit responsible for the aerial spraying of Agent Orange in Vietnam. Using paired TCDD measurements derived from serum collected in 1982 and in 1987, we investigated how TCDD half-life varied with percent body fat (PBF), relative changes in PBF, and age. We found that half-life increased significantly with increasing PBF and decreased significantly with increasing relative change in PBF and with age. The median observed half-life of TCDD for these 337 veterans is 11.3 yr with a nonparametric 95% confidence interval of 10.0-14.1 yr.

Ability of the Army Circumference Method to Detect Changes in Subcutaneous Fat Over a 9-Week Period

The Army Circumference Method (ACM), used to estimate percent body fat for soldiers, has been shown to have questionable validity as applied to women. This study's primary purpose was to examine the ability of this method to detect changes in subcutaneous fat over a 9-week period with men (N = 55) and women (N = 51) enrolled in a weight management program. Changes in percent body fat, based on the ACM, were correlated with the corresponding ones from the Jackson/Pollock skinfold method. Results indicated that the male ACM (r2 = 0.548) could more satisfactorily detect changes in subcutaneous fat than the female ACM (r2 = 0.135).

A Function of Pretraining Concentration

Previous endurance training studies lack sufficient sample size to adequately assess changes, in total cholesterol concentrations (ΔTC) subsequent to endurance exercise training as a function of the pretraining value. Meta-analysis techniques have previously been employed in an attempt to overcome this problem, and have suggested that pretraining TC values are significant predictors of ΔTC after training. This retrospective study was designed to identify significant predictors of ΔTC after an endurance training program, after adjusting for the pretraining cholesterol concentration. Subjects included an intact population of apparently healthy men (n = 327) and women (n = 215) ranging in age from 20 to 75 years, who completed approximately 16 to 20 weeks of endurance training in a university-based adult exercise program between 1973 and 1986. The training stimulus consisted of individualized aerobic exercise (walking, walk-jog, or running) at approximately 75% to 85% maximal heart rate reserve for 30 to 50 minutes four times per week. Pre-post training TC values were 227 (±48) vs 217 (±42) and 210 (±44) vs 205 (±40) mg /dl (P < 0.03.) for the men and the women, respectively. Significant zero-order correlations (P < 0.05) were found between ΔTC and pretraining TC (r = −0.512), change in body weight (ΔBW; r = 0.265), change in percent body fat (ΔBF; r = 0.144) and change in VO2max(ΔVO2max; r = −0.263). After adjustment for the pretraining TC, age became, and ΔBW, ΔBF, and Δ2max remained significant first-order predictors of ΔTC for the combined male and female cohort. Gender-specific regression analysis revealed differences between men and women for predictors of ΔTC. After adjustment for the pretraining TC, ΔBW (r = 0.332), ΔBF (r = 0.223), and VO2max (r = −0.201) were significant predictors of ΔTC for the men, but only age (r = 0.135) remained a predictor of ΔTC for the women. Curvilinear trend analysis failed to reveal a threshold pretraining TC concentration above which favorable changes could be expected. However, classification into the National Cholesterol Education Program (NCEP) categories (e.g., < 200; 201–239; ± 240 mg/dl) showed that individuals in the high cholesterol category had ΔTC of −9.9% and −9.2% for the men and the women, respectively (P < 0.01). These results confirm the importance of pretraining TC levels in assessing the potential for a favorable ΔTC subsequent to endurance training, and suggest that the equivocal results found in previous studies may have been due, in part, to the use of samples with normal pretraining TC, or of small samples with a wide range of pretraining TC such that the treatment effect for those with high TC may have been diluted by the rest of the sample.

Lactation and reproductive performance of mares fed added dietary fat during late gestation and early lactation

Eighteen pregnant mares were randomly allotted to one of two treatment groups. The control group was fed a conventional concentrate and the fat group was fed a concentrate containing 5% feed-grade rendered fat. Both concentrates had the same nutrient:calorie ratio and were fed in amounts required to maintain zero change in percent body fat of the mares. During the study, which began 60 d prior to expected foaling date and ended 60 d postpartum, mares were monitored for feed intake, body weight, rump fat thickness, ration digestibility, plasma glucose and lipid concentrations, milk composition and reproductive efficiency. Birth weight, growth rate, and plasma glucose and lipid concentrations were also measured in foals. Mares fed fat consumed less concentrate (P<.09 during the last 60 d of gestation but consumed similar amounts of concentrate over 60 d of lactation. Protein and ether extract digestion was higher (P<.05 and P<.09, respectively) in the mares fed fat during the postpartum period. Dietary treatment had no influence on plasma glucose or lipid concentrations of the mares or plasma glucose concentrations of their foals, but foals whose dams were fed fat had higher plasma lipid concentrations at birth (P<.01), d 10 and d 30 (P<.05). Percent fat was higher in milk samples from mares fed fat at d 10 (P<.09, 1.23 vs .99%) and d 60 (P<.01, .72 vs .43%) of lactation. Reproductive performance was not significantly different between treatment groups, however there was a trend for a shorter postpartum interval and fewer cycles per pregnancy in the mares fed added fat. Foals from both groups were of similar size and weight at birth and had similar weight gains over 60 d, however, foals nursing mares fed fat tended to gain more weight in the first week of life (1.85 vs 1.56 kg/d) and have more rump fat at d 60 (.53 vs .44 cm) than foals nursing control mares.

Percent body fat in obese white females predicted by anthropometric measurements

The percent body fat (PBF) and 15 anthropometric measurements were measured in 221 obese white females randomly assigned to validation and cross-validation groups. Two new anthropometric equations for the prediction of the percent of body fat were generated by multiple regression. Equation 1 includes the residual lung volume (RV) as a factor and had a correlation coefficient (r) of 0.85 and a standard error of the estimate (SEE) of 3.9%. Equation 2 does not include the RV and has an r of 0.82 and an SEE of 4.3%. Both equations were more precise than two previous widely used equations. In a subgroup of 37 subjects who underwent weight loss, equation 1 gave a more precise estimate of the change in PBF. We conclude that the new equations permit a better prediction of the PBF in obese white females.

New approach for estimating excess body fat from changes in abdominal girth.

A new method is proposed for determining changes in percent body fat (%BF) based on the difference between an initial value for abdominal girth (AG) and a calculated "target" AG based on a desired %BF. Group data from large-scale anthropometric surveys in the military were used to derive specific reference values for Q, defined as the ratio of AG at a desired %BF to F(√BMkg /Htm ). For an individual, Q*F resulted in an AG that corresponded to a desired %BF (set at approximately 20% for males and 30% for females). The method was applied to professional football players, longshoremen, shot-put and weight-lifting athletes, and obese males and females who reduced body mass and altered their body composition. The results showed that changes in AG with body mass loss were proportional to percentage changes in total body fat loss. These relationships permitted extrapolation to a projected target AG that corresponded to a desired %BF. The proposed method differs from the traditional approach that first determines %BF, and then the individual attempts to achieve a desired change in body mass or body composition. The objective of the new method is straightforward; the individual endeavors to attain a target AG that corresponds to a desired %BF.

Validity of anthropometric percent fat prediction equations for use with pregnant women.

The purpose of this investigation was to determine the validity of five different skinfold prediction equation for use in forecasting the percent body fat of pregnant women. Twenty-one pregnant women underwent hydrostatic and skinfold thickness determinations of percent body fat at 6-10, 16, and 28 weeks of gestation. The correlations between hydrostatic and anthropometric determinations of percent body fat were high during the three test periods (r= .78 to r = .89). The slopes of the line of best fit between the criterion (hydrostatic weighing) and predicted variable (prediction equation) decreased across pregnancy. The anthropometric prediction equations tended to overestimate percent body fat changes in comparison to the hydrostatically determined percent body fat changes. Skinfold thickness measurements can be used as a prepregnancy aid in determining recommended weight gain during pregnancy and as a measure of subcutaneous fat status during pregnancy. However, anthropometric prediction equations should not be used during the later stages of pregnancy to estimate percent fat or percent fat changes.

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Fourteen untrained females (age 19 +/- 1, range 18-21) were studied to examine the heart rate-VO2 relationship during a single aerobic dance training session. These findings were used to help explain the changes in VO2max resulting from an aerobic dance training program. VO2max and body composition were determined before and after an 8 wk training period. In addition, the heart rate-VO2 responses to an aerobic dance training session were monitored and compared to the heart rate responses of treadmill jogging performed at the same VO2. The aerobic dance session elicited a significantly lower oxygen pulse than did treadmill exercise (7.2 +/- 0.3 vs 8.1 +/- 0.8 ml.beat-1; P less than 0.01). There were no significant changes in percent body fat, whereas VO2max increased by 11% (34.4 +/- 0.9 vs 38.1 +/- 0.8 ml.kg-1.min-1; P less than 0.05). No significant changes in any of the parameters tested were observed in 10 untrained controls. These findings indicate that the heart rate elicited from aerobic dance represents a lower relative exercise intensity (VO2) than that of running. Therefore, the assumption that aerobic dance training produces the same cardiovascular adaptations as running training when performed at the same target rate may be unwarranted.

Effects of a Rebound Exercise Training Program on Aerobic Capacity and Body Composition.

In brief: Training on rebound exercise equipment (minitrampolines) is a popular new approach to aerobic conditioning, but its physiological benefits have been a matter of debate. This study was designed to determine if rebound aerobic dancing is an effective way to improve aerobic capacity and body composition. A group of previously sedentary college women who trained on rebound equipment three times a week for eight weeks showed a 9% increase in max but no significant change in percent body fat. A control group showed no significant changes. The improvement was similar to results produced by conventional aerobic dance programs of like intensity but moderate in comparison to other established forms of aerobic exercise.

Increased exercise level and plasma lipoprotein concentrations: A one-year, randomized, controlled study in sedentary, middle-aged men

Eighty-one sedentary but healthy men aged 30–55 participated in a 1 yr randomized study of the effects of exercise on plasma lipoprotein concentrations. Forty-eight were assigned to a running program, while 33 remained as sedentary controls (an approximately 3:2 ratio). After 1 yr the running group had become significantly fitter and leaner than the control group. Lipoprotein concentration changes in the runners (vs. controls) uniformly favored reduced risk of coronary heart disease, but were not significant when all 46 participants with complete data were included. However, the 25 men who averaged at least eight miles (12.9 kilometers) per wk of running increased their plasma high-density-lipoprotein (HDL) cholesterol level by 4.4 mg/dl ( p = 0.045) and their HDL 2 mass level by 33 mg/dl ( p = 0.059), vs. controls. Significant correlations were found for distance run per wk vs. change in plasma HDL-cholesterol ( r = 0.48), HDL 2 ( r = 0.41), and low-density-lipoprotein cholesterol ( r = −0.31). Changes in percent body fat and in HDL-cholesterol were correlated ( r = −0.47) in runners. There appears to be a threshold at about 8 miles per wk above which a 1-yr running program leads to beneficial lipoprotein changes.

Left ventricular size following endurance, sprint, and strength training

Left ventricular size following endurance, sprint, and strength training. Med. Sci. Sports Exercise, Vol. 14, No. 5, pp. 344-347, 1982. Left ventricular dimensions in adolescent boys were determined before and after three types of training regimens: endurance (END), N = 8, means = 16.8 yr; sprint (SPR), N = 8, means = 16.3 yr; strength (STR), N = 12, means = 18.7 yr. With training the END group significantly increased VO2max in 1 X min-1 (3.71 +/- 0.27 to 4.16 +/- 0.57, P less than 0.05) and in ml X min-1 X kg-1 (58.4 +/- 5.6 to 64.2 +/- 5.5, P less than 0.05). The SPR group increased VO2max in 1 X min-1 (3.63 +/- 0.63 to 3.98 +/- 0.78, P less than 0.05) but not in ml X min-1 X kg-1 (59.5 +/- 4.1 to 63.2 +/- 5.4) because body weight increased from 61.2 +/- 10.5 to 63.1 +/- 10.7 kg (P less than 0.05) with no change in percent body fat. The STR training group significantly improved upper body strength. Despite these specific training adaptations no significant modifications were found for interventricular and left ventricular posterior wall thickness or for left ventricular internal diameter in either training group. However, calculated left ventricular mass was slightly but significantly higher by 10% and 4% in the END and STR training groups, respectively. These small increases in calculated left ventricular mass with short-term training are probably caused by small but insignificant increases in left ventricular internal diameter secondary to a training bradycardia (END group: 76 +/- 8 to 64 +/- 1 beats X min-1) and to increased diastolic filling time rather than to true cardiac hypertrophy. Significant increases in aerobic capacity and in strength can occur without modification of left ventricular dimensions.

Blood pressure and body composition changes in women

To determine which of two measures of adiposity change (total weight or percentage fat determined by volume displacement) is more strongly associated with change in blood pressure, a longitudinal study was made of 68 women aged 15–59. The initial physical characteristics of the subjects were the following: mean age, 41.2 years; average weight, 127.1 lb; average percentage body fat, 24.4%; mean systolic blood pressure, 119.8 mm Hg; and mean diastolic blood pressure, 77.8 mm Hg. Changes over an average period of 25 months consisted of a mean weight loss of 2.0 lb, percentage body fat decrease of 1.3%, and systolic and diastolic blood pressure lowering of 1.5 and 1.4 mm Hg. For all women, the correlation coefficient for change in systolic blood pressure with change in percentage body fat by volume displacement was r = 0.28 ( P < 0.05). This value, although slightly higher than that obtained using body weight in this study, is not significantly different from it. Results for diastolic blood pressure were similar. Partial correlation, adjusting for age, initial weight, and percentage body fat did not change the values. These findings suggest that the use of change in percentage body fat did not provide any improvement in the relationship between changes in blood pressure and in weight.