Although magnetic resonance imaging (MRI) can accurately measure lower limb skeletal muscle (SM) ... more Although magnetic resonance imaging (MRI) can accurately measure lower limb skeletal muscle (SM) mass, this method is complex and costly. A potential practical alternative is to estimate lower limb SM with dual-energy X-ray absorptiometry (DXA). The aim of the present study was to develop and validate DXA-SM prediction equations. Identical landmarks (i.e., inferior border of the ischial tuberosity) were selected for separating lower limb from trunk. Lower limb SM was measured by MRI, and lower limb fat-free soft tissue was measured by DXA. A total of 207 adults (104 men and 103 women) were evaluated [age 43 Ϯ 16 (SD) yr, body mass index (BMI) 24.6 Ϯ 3.7 kg/m 2 ]. Strong correlations were observed between lower limb SM and lower limb fat-free soft tissue (R 2 ϭ 0.89, P Ͻ 0.001); age and BMI were small but significant SM predictor variables. In the cross-validation sample, the differences between MRI-measured and DXApredicted SM mass were small (Ϫ0.006 Ϯ 1.07 and Ϫ0.016 Ϯ 1.05 kg) for two different proposed prediction equations, one with fat-free soft tissue and the other with added age and BMI as predictor variables. DXA-measured lower limb fatfree soft tissue, along with other easily acquired measures, can be used to reliably predict lower limb skeletal muscle mass.
We employed a whole body magnetic resonance imaging protocol to examine the influence of age, gen... more We employed a whole body magnetic resonance imaging protocol to examine the influence of age, gender, body weight, and height on skeletal muscle (SM) mass and distribution in a large and heterogeneous sample of 468 men and women. Men had significantly ( P < 0.001) more SM in comparison to women in both absolute terms (33.0 vs. 21.0 kg) and relative to body mass (38.4 vs. 30.6%). The gender differences were greater in the upper (40%) than lower (33%) body ( P < 0.01). We observed a reduction in relative SM mass starting in the third decade; however, a noticeable decrease in absolute SM mass was not observed until the end of the fifth decade. This decrease was primarily attributed to a decrease in lower body SM. Weight and height explained ∼50% of the variance in SM mass in men and women. Although a linear relationship existed between SM and height, the relationship between SM and body weight was curvilinear because the contribution of SM to weight gain decreased with increasing...
The American Journal of Clinical Nutrition, Sep 1, 2000
Background: Skeletal muscle (SM) is a large body compartment of biological importance, but it rem... more Background: Skeletal muscle (SM) is a large body compartment of biological importance, but it remains difficult to quantify SM with affordable and practical methods that can be applied in clinical and field settings. Objective: The objective of this study was to develop and cross-validate anthropometric SM mass prediction models in healthy adults. Design: SM mass, measured by using whole-body multislice magnetic resonance imaging, was set as the dependent variable in prediction models. Independent variables were organized into 2 separate formulas. One formula included mainly limb circumferences and skinfold thicknesses [model 1: height (in m) and skinfold-corrected upperarm, thigh, and calf girths (CAG, CTG, and CCG, respectively; in cm)]. The other formula included mainly body weight (in kg) and height (model 2). The models were developed and cross-validated in nonobese adults [body mass index (in kg/m 2) < 30]. Results: Two SM (in kg) models for nonobese subjects (n = 244) were developed as follows: SM = Ht ϫ (0.00744 ϫ CAG 2 + 0.00088 ϫ CTG 2 + 0.00441 ϫ CCG 2) + 2.4 ϫ sex Ϫ 0.048 ϫ age + race + 7.8, where R 2 = 0.91, P < 0.0001, and SEE = 2.2 kg; sex = 0 for female and 1 for male, race = Ϫ2.0 for Asian, 1.1 for African American, and 0 for white and Hispanic, and SM = 0.244 ϫ BW + 7.80 ϫ Ht + 6.6 ϫ sex Ϫ 0.098 ϫ age + race Ϫ 3.3, where R 2 = 0.86, P < 0.0001, and SEE = 2.8 kg; sex = 0 for female and 1 for male, race = Ϫ1.2 for Asian, 1.4 for African American, and 0 for white and Hispanic. Conclusion: These 2 anthropometric prediction models, the first developed in vivo by using state-of-the-art body-composition methods, are likely to prove useful in clinical evaluations and field studies of SM mass in nonobese adults.
Limited research has been done to explore differences between ethnic groups, including Hispanic A... more Limited research has been done to explore differences between ethnic groups, including Hispanic Americans (HAs), in the association between percentage body fat (PBF) and body mass index (BMI; in kg/m(2)); the numbers of HAs are increasing in the US population. We investigated whether the relation between PBF and BMI in adult HAs differed from that of African Americans (AAs) and European Americans (EAs). We used a multiple regression model in which PBF measured with dual energy X-ray absorptiometry was predicted by the reciprocal of BMI (1/BMI; in m(2)/kg) in a sample of 487 men (n(EA) = 192, n(AA) = 148, and n(HA) = 147) and 933 women (n(EA) = 448, n(AA) = 304, and n(HA) = 181). For men, our results showed no significant differences between HAs and EAs, AAs and EAs, or HAs and AAs in the slope of the line relating 1/BMI to PBF. In women, there were significant differences in PBF as predicted by BMI between HAs and EAs (P < 0.002) and AAs and HAs (P = 0.020), but not between AAs a...
The study objective was to compare the accuracy of portable and hospital or laboratory-based body... more The study objective was to compare the accuracy of portable and hospital or laboratory-based body composition methods, as well as to evaluate reference methods that may be necessary for the development of population-specific phenotyping equations in field-study settings. Subjects were healthy adults of mixed ethnicity from the greater New York metropolitan area. Adiposity was evaluated by whole-body magnetic resonance imaging (MRI), dual energy x-ray absorptiometry (DXA), underwater weighing (UWW), air displacement plethysmography (ADP), isotope dilution (ID), bioimpedance analysis (BIA), and anthropometry (ANTH). Anthopometric measurements included height, weight, and skinfolds. MRI was selected as the reference for assessing total body adiposity. Pearson correlation coefficients with MRI-derived adipose tissue mass and fat mass measured by the other methods were: DXA (r=0.98, n=251), ADP (r=0.98, n=73), UWW (r=0.96, n=216), ID (r=0.95, n=248), ANTH (r=0.94, n=235), and BIA (r=0.92...
Journal of applied physiology (Bethesda, Md. : 1985), 1999
Although there is growing interest in studying muscle distribution, regional skeletal muscle (SM)... more Although there is growing interest in studying muscle distribution, regional skeletal muscle (SM) mass measurement methods remain limited. The aim of the present study was to develop a new dual-energy X-ray absorptiometry (DEXA) model for estimating regional adipose tissue-free skeletal muscle mass (AT-free SM). Relationships were derived from Reference Man data between tissue-system- level components (i.e., AT-free SM, AT, skeleton, and skin) and molecular-level components including fat-free soft tissue, fat, and bone mineral. The proposed DEXA-SM model was evaluated by multiscan computerized axial tomography (CT). Twenty-seven male subjects [age, 36 +/- 12 (SD) yr; body mass, 73.2 +/- 12.4 kg; 20 were healthy, and 7 had acquired immunodeficiency syndrome] completed DEXA and CT studies. Identical landmarks for DEXA and CT measurements were selected in three regions, including calves, thighs, and forearms. There was a strong correlation for AT-free SM estimates between the new DEXA ...
Aging is associated with the onset of chronic diseases that lead to pathological expansion of the... more Aging is associated with the onset of chronic diseases that lead to pathological expansion of the extracellular water (ECW) compartment. Healthy aging, in the absence of disease, is also reportedly accompanied by a relative expansion of the ECW compartment, although the studies on which this observation is based are few in number, applied different ECW measurement methods, included small ethnically homogeneous subject samples, and failed to adjust ECW for non-age-related influencing factors. The aim of the current study was to examine, in a large ( n = 1,538) ethnically diverse [African American (AA), Asian, Caucasian, Hispanic] subject group the cross-sectional relationships between ECW and age after controlling first for other potential factors that may influence fluid distribution. ECW and intracellular water (ICW) were derived from measured total body water (isotope dilution) and potassium (40K whole body counting). The cross-sectional relationships between ECW, ICW, and ECW/ICW...
Despite research and clinical significance, limited information is available on the relations bet... more Despite research and clinical significance, limited information is available on the relations between skeletal muscle (SM) and age in adults, specifically among Hispanics, African Americans (AA), and Asians. The aim was to investigate possible sex and ethnic SM differences in adults over an age range of 60 years. Subjects were 468 male and 1280 female adults (≥18 years). SM was estimated based on DXA-measured appendicular lean-soft tissue using a previously reported prediction equation. Locally weighted regression smoothing lines were fit to examine SM trends and to localize age cutoffs; piecewise multiple linear regression models were then applied, controlling for weight and height, to identify age cutoffs for sex-specific changes in SM among the ethnic groups. The age of 27 years was identified for women and men as the cutoff after which SM starts to show a negative association with age. Both sexes had a similar ethnic pattern for expected mean SM at the age cutoff, with AA presenting the highest SM values, followed by Whites, Hispanics, and Asians. After the age cutoffs, the lowering of SM differed by ethnicity and sex: AA women showed the greatest SM lowering whereas Hispanic women had the least. Hispanic men tended to show a higher negative association of SM with age followed by AA and Whites. To conclude, significant sex and ethnic differences exist in the magnitude of negative associations of SM with age >27 years. Further studies using a longitudinal design are needed to explore the associations of ethnicity-related decline of SM with health risks. Skeletal muscle (SM), the largest component of adipose tissue-free body mass in humans, is central to the study of nutritional, physiologic, and metabolic processes (Janssen et al., 2000; Lukaski, 2005; Malina, 1996). Total-body and regional SM mass can now be accurately quantified with imaging methods, including computed axial tomography (CT) and magnetic resonance imaging (MRI) (Heymsfield et al., 1997; Lee et al., 2001). However, CT and MRI are costly methods and instrument access is limited. An alternative approach for measuring total-body SM is dual energy X-ray absorptiometry (DXA), because DXA instruments are widely available and are relatively inexpensive; and radiation exposure is also minimal (Lukaski, 2005; Pietrobelli et al., 1996; Wang et al., 1999). DXA systems provide a measure of appendicular lean soft tissue (ALST), a fat-and
A whole body skeletal muscle [(SM); kg] mass estimation model, based on total body potassium [(TB... more A whole body skeletal muscle [(SM); kg] mass estimation model, based on total body potassium [(TBK); mmol] measured by whole body (40)K counting (WBC) was developed (SM = 0.0082.TBK) and validated in adults in a previous study. It is unknown whether the adult TBK SM prediction model is applicable for pediatric use. The aim of this study was to derive and validate a pediatric TBK SM prediction equation. SM measured by MRI was used as the criterion and TBK was measured by WBC. The protocol was completed in 116 healthy children, 66 males and 50 females, 11.7 +/- 3.5 y (mean +/- SD, range = 5-17 y). A strong linear correlation was observed between TBK and SM (r = 0.984; P < 0.001). The SM:TBK ratio was 0.0071 +/- 0.0008 kg/mmol in the children studied, much lower than the corresponding value of 0.0082 kg/mmol in adults. An empirical SM prediction equation was developed using TBK alone: SM = 0.0085.TBK - 2.83, r(2) = 0.97, SEE = 1.39 kg. Bland-Altman analysis did not disclose a signif...
ABSTRACT Traditional techniques to measure whole-body composition divide the body into five level... more ABSTRACT Traditional techniques to measure whole-body composition divide the body into five levels – atomic, molecular, cellular, tissue and organ. Adiposity within the whole body is usually estimated via the body mass index or anthropometrically by measurement of body weight, stature, skinfolds and circumference. Visceral adipose tissue is an independent predictor of obesity health-related risk. All major tissues and organs can now be measured in vivo using computerized axial tomography or magnetic resonance imaging. At the cellular level, fat cell mass cannot be quantified in vivo; it is usually estimated by combining total body adipose tissue mass with biopsy-derived adipose tissue cell mass concentration. The concentration of molecular fat, or triglyceride, in the body is measured by either body volume analysis, labelled water dilution and dual-energy X-ray absorptiometry. Studies at the atomic level assess total body potassium or total body nitrogen and carbon. The most suitable method depends on the intended use of the data and the required degree of accuracy.
The study of human body composition is a branch of human biology which focuses on the in vivo qua... more The study of human body composition is a branch of human biology which focuses on the in vivo quantification of body components, the quantitative relationships between components, and the quantitative changes in these components related to various influencing factors. Accordingly, the study of human body composition is composed of three interrelated research areas, body composition rules, body composition methodology, and body composition alterations. This thesis describes the authors recent investigations related to the first two of the three research areas. In the rules area, this thesis begins with a comprehensive five-level model of body composition. The approximate 40 body components are systematically organized into five levels with increasing complexity: 1, atomic; 11, molecular; III, cellular; IV, tissue-system; and V 1 whole-body. Although each level and its multiple components are distinct, interconnections exist such that the model is consistent and functions as a whole. ...
The assumed "constancy" of fat-free body mass hydration is a cornerstone in the body-co... more The assumed "constancy" of fat-free body mass hydration is a cornerstone in the body-composition research field. Hydration, the observed ratio of total body water to fat-free body mass, is stable at approximately 0.73 in mammals and this constancy provides a means of estimating total body fat in vivo. This review examines both in vitro and in vivo data that support the hydration constancy hypothesis and provides a critique of applied methodology. Biological topics of interest are then examined and critical areas in need of future research are identified. These are important issues because water dilution is the only method currently available for estimating body fat in all mammals, which range in body mass by a factor of 10(4).
Objective: BMI (kilograms per meters squared) and waist circumference (WC) (measured in centimete... more Objective: BMI (kilograms per meters squared) and waist circumference (WC) (measured in centimeters) are each associated with the risk of developing cardiovascular disease (CVD). Therefore, a combination of the two may be more effective in identifying subjects at risk than either alone. The present study sought to identify the combination of BMI and WC that has the strongest association with CVD risk factors in whites. Research Methods and Procedures: Subjects were 8712 white men and women from the Third National Health and Nutrition Examination Survey. The optimal combination of BMI and WC was developed using logistic regression models with BMI and WC as predictors and CVD risk factors as outcomes. The combined measure of BMI and WC using current cutoff points was also examined. Sensitivity, specificity, and receiver operating characteristics curves were compared between the combined measures and BMI alone. Results: For white men, the optimal combination of BMI and WC for identifying CVD risk factors was 0.68 ϫ BMI ϩ 0.32 ϫ WC. This combination generated a score that better estimated the odds of having CVD risk factors than either alone. For white women, WC alone largely determined the likelihood of having CVD risks. The combination of BMI and WC using current cutoff points may provide an improved measure of CVD risk. Combined measures showed a higher sensitivity or a shorter distance in receiver operating characteristic curves in the identification of CVD risk factors. Discussion: Combined measures of BMI and WC may provide a higher overall test performance for CVD risk factors and may be useful in some ethnic groups as an improved means of screening subjects for further evaluation in the clinical setting.
American journal of physiology. Endocrinology and metabolism, 2001
Potassium is an essential element of living organisms that is found almost exclusively in the int... more Potassium is an essential element of living organisms that is found almost exclusively in the intracellular fluid compartment. The assumed constant ratio of total body potassium (TBK) to fat-free mass (FFM) is a cornerstone of the TBK method of estimating total body fat. Although the TBK-to-FFM (TBK/FFM) ratio has been assumed constant, a large range of individual and group values is recognized. The purpose of the present study was to undertake a comprehensive analysis of biological factors that cause variation in the TBK/FFM ratio. A theoretical TBK/FFM model was developed on the cellular body composition level. This physiological model includes six factors that combine to produce the observed TBK/FFM ratio. The ratio magnitude and range, as well as the differences in the TBK/FFM ratio between men and women and variation with growth, were examined with the proposed model. The ratio of extracellular water to intracellular water (E/I) is the major factor leading to between-individual...
Although magnetic resonance imaging (MRI) can accurately measure lower limb skeletal muscle (SM) ... more Although magnetic resonance imaging (MRI) can accurately measure lower limb skeletal muscle (SM) mass, this method is complex and costly. A potential practical alternative is to estimate lower limb SM with dual-energy X-ray absorptiometry (DXA). The aim of the present study was to develop and validate DXA-SM prediction equations. Identical landmarks (i.e., inferior border of the ischial tuberosity) were selected for separating lower limb from trunk. Lower limb SM was measured by MRI, and lower limb fat-free soft tissue was measured by DXA. A total of 207 adults (104 men and 103 women) were evaluated [age 43 Ϯ 16 (SD) yr, body mass index (BMI) 24.6 Ϯ 3.7 kg/m 2 ]. Strong correlations were observed between lower limb SM and lower limb fat-free soft tissue (R 2 ϭ 0.89, P Ͻ 0.001); age and BMI were small but significant SM predictor variables. In the cross-validation sample, the differences between MRI-measured and DXApredicted SM mass were small (Ϫ0.006 Ϯ 1.07 and Ϫ0.016 Ϯ 1.05 kg) for two different proposed prediction equations, one with fat-free soft tissue and the other with added age and BMI as predictor variables. DXA-measured lower limb fatfree soft tissue, along with other easily acquired measures, can be used to reliably predict lower limb skeletal muscle mass.
We employed a whole body magnetic resonance imaging protocol to examine the influence of age, gen... more We employed a whole body magnetic resonance imaging protocol to examine the influence of age, gender, body weight, and height on skeletal muscle (SM) mass and distribution in a large and heterogeneous sample of 468 men and women. Men had significantly ( P < 0.001) more SM in comparison to women in both absolute terms (33.0 vs. 21.0 kg) and relative to body mass (38.4 vs. 30.6%). The gender differences were greater in the upper (40%) than lower (33%) body ( P < 0.01). We observed a reduction in relative SM mass starting in the third decade; however, a noticeable decrease in absolute SM mass was not observed until the end of the fifth decade. This decrease was primarily attributed to a decrease in lower body SM. Weight and height explained ∼50% of the variance in SM mass in men and women. Although a linear relationship existed between SM and height, the relationship between SM and body weight was curvilinear because the contribution of SM to weight gain decreased with increasing...
The American Journal of Clinical Nutrition, Sep 1, 2000
Background: Skeletal muscle (SM) is a large body compartment of biological importance, but it rem... more Background: Skeletal muscle (SM) is a large body compartment of biological importance, but it remains difficult to quantify SM with affordable and practical methods that can be applied in clinical and field settings. Objective: The objective of this study was to develop and cross-validate anthropometric SM mass prediction models in healthy adults. Design: SM mass, measured by using whole-body multislice magnetic resonance imaging, was set as the dependent variable in prediction models. Independent variables were organized into 2 separate formulas. One formula included mainly limb circumferences and skinfold thicknesses [model 1: height (in m) and skinfold-corrected upperarm, thigh, and calf girths (CAG, CTG, and CCG, respectively; in cm)]. The other formula included mainly body weight (in kg) and height (model 2). The models were developed and cross-validated in nonobese adults [body mass index (in kg/m 2) < 30]. Results: Two SM (in kg) models for nonobese subjects (n = 244) were developed as follows: SM = Ht ϫ (0.00744 ϫ CAG 2 + 0.00088 ϫ CTG 2 + 0.00441 ϫ CCG 2) + 2.4 ϫ sex Ϫ 0.048 ϫ age + race + 7.8, where R 2 = 0.91, P < 0.0001, and SEE = 2.2 kg; sex = 0 for female and 1 for male, race = Ϫ2.0 for Asian, 1.1 for African American, and 0 for white and Hispanic, and SM = 0.244 ϫ BW + 7.80 ϫ Ht + 6.6 ϫ sex Ϫ 0.098 ϫ age + race Ϫ 3.3, where R 2 = 0.86, P < 0.0001, and SEE = 2.8 kg; sex = 0 for female and 1 for male, race = Ϫ1.2 for Asian, 1.4 for African American, and 0 for white and Hispanic. Conclusion: These 2 anthropometric prediction models, the first developed in vivo by using state-of-the-art body-composition methods, are likely to prove useful in clinical evaluations and field studies of SM mass in nonobese adults.
Limited research has been done to explore differences between ethnic groups, including Hispanic A... more Limited research has been done to explore differences between ethnic groups, including Hispanic Americans (HAs), in the association between percentage body fat (PBF) and body mass index (BMI; in kg/m(2)); the numbers of HAs are increasing in the US population. We investigated whether the relation between PBF and BMI in adult HAs differed from that of African Americans (AAs) and European Americans (EAs). We used a multiple regression model in which PBF measured with dual energy X-ray absorptiometry was predicted by the reciprocal of BMI (1/BMI; in m(2)/kg) in a sample of 487 men (n(EA) = 192, n(AA) = 148, and n(HA) = 147) and 933 women (n(EA) = 448, n(AA) = 304, and n(HA) = 181). For men, our results showed no significant differences between HAs and EAs, AAs and EAs, or HAs and AAs in the slope of the line relating 1/BMI to PBF. In women, there were significant differences in PBF as predicted by BMI between HAs and EAs (P < 0.002) and AAs and HAs (P = 0.020), but not between AAs a...
The study objective was to compare the accuracy of portable and hospital or laboratory-based body... more The study objective was to compare the accuracy of portable and hospital or laboratory-based body composition methods, as well as to evaluate reference methods that may be necessary for the development of population-specific phenotyping equations in field-study settings. Subjects were healthy adults of mixed ethnicity from the greater New York metropolitan area. Adiposity was evaluated by whole-body magnetic resonance imaging (MRI), dual energy x-ray absorptiometry (DXA), underwater weighing (UWW), air displacement plethysmography (ADP), isotope dilution (ID), bioimpedance analysis (BIA), and anthropometry (ANTH). Anthopometric measurements included height, weight, and skinfolds. MRI was selected as the reference for assessing total body adiposity. Pearson correlation coefficients with MRI-derived adipose tissue mass and fat mass measured by the other methods were: DXA (r=0.98, n=251), ADP (r=0.98, n=73), UWW (r=0.96, n=216), ID (r=0.95, n=248), ANTH (r=0.94, n=235), and BIA (r=0.92...
Journal of applied physiology (Bethesda, Md. : 1985), 1999
Although there is growing interest in studying muscle distribution, regional skeletal muscle (SM)... more Although there is growing interest in studying muscle distribution, regional skeletal muscle (SM) mass measurement methods remain limited. The aim of the present study was to develop a new dual-energy X-ray absorptiometry (DEXA) model for estimating regional adipose tissue-free skeletal muscle mass (AT-free SM). Relationships were derived from Reference Man data between tissue-system- level components (i.e., AT-free SM, AT, skeleton, and skin) and molecular-level components including fat-free soft tissue, fat, and bone mineral. The proposed DEXA-SM model was evaluated by multiscan computerized axial tomography (CT). Twenty-seven male subjects [age, 36 +/- 12 (SD) yr; body mass, 73.2 +/- 12.4 kg; 20 were healthy, and 7 had acquired immunodeficiency syndrome] completed DEXA and CT studies. Identical landmarks for DEXA and CT measurements were selected in three regions, including calves, thighs, and forearms. There was a strong correlation for AT-free SM estimates between the new DEXA ...
Aging is associated with the onset of chronic diseases that lead to pathological expansion of the... more Aging is associated with the onset of chronic diseases that lead to pathological expansion of the extracellular water (ECW) compartment. Healthy aging, in the absence of disease, is also reportedly accompanied by a relative expansion of the ECW compartment, although the studies on which this observation is based are few in number, applied different ECW measurement methods, included small ethnically homogeneous subject samples, and failed to adjust ECW for non-age-related influencing factors. The aim of the current study was to examine, in a large ( n = 1,538) ethnically diverse [African American (AA), Asian, Caucasian, Hispanic] subject group the cross-sectional relationships between ECW and age after controlling first for other potential factors that may influence fluid distribution. ECW and intracellular water (ICW) were derived from measured total body water (isotope dilution) and potassium (40K whole body counting). The cross-sectional relationships between ECW, ICW, and ECW/ICW...
Despite research and clinical significance, limited information is available on the relations bet... more Despite research and clinical significance, limited information is available on the relations between skeletal muscle (SM) and age in adults, specifically among Hispanics, African Americans (AA), and Asians. The aim was to investigate possible sex and ethnic SM differences in adults over an age range of 60 years. Subjects were 468 male and 1280 female adults (≥18 years). SM was estimated based on DXA-measured appendicular lean-soft tissue using a previously reported prediction equation. Locally weighted regression smoothing lines were fit to examine SM trends and to localize age cutoffs; piecewise multiple linear regression models were then applied, controlling for weight and height, to identify age cutoffs for sex-specific changes in SM among the ethnic groups. The age of 27 years was identified for women and men as the cutoff after which SM starts to show a negative association with age. Both sexes had a similar ethnic pattern for expected mean SM at the age cutoff, with AA presenting the highest SM values, followed by Whites, Hispanics, and Asians. After the age cutoffs, the lowering of SM differed by ethnicity and sex: AA women showed the greatest SM lowering whereas Hispanic women had the least. Hispanic men tended to show a higher negative association of SM with age followed by AA and Whites. To conclude, significant sex and ethnic differences exist in the magnitude of negative associations of SM with age >27 years. Further studies using a longitudinal design are needed to explore the associations of ethnicity-related decline of SM with health risks. Skeletal muscle (SM), the largest component of adipose tissue-free body mass in humans, is central to the study of nutritional, physiologic, and metabolic processes (Janssen et al., 2000; Lukaski, 2005; Malina, 1996). Total-body and regional SM mass can now be accurately quantified with imaging methods, including computed axial tomography (CT) and magnetic resonance imaging (MRI) (Heymsfield et al., 1997; Lee et al., 2001). However, CT and MRI are costly methods and instrument access is limited. An alternative approach for measuring total-body SM is dual energy X-ray absorptiometry (DXA), because DXA instruments are widely available and are relatively inexpensive; and radiation exposure is also minimal (Lukaski, 2005; Pietrobelli et al., 1996; Wang et al., 1999). DXA systems provide a measure of appendicular lean soft tissue (ALST), a fat-and
A whole body skeletal muscle [(SM); kg] mass estimation model, based on total body potassium [(TB... more A whole body skeletal muscle [(SM); kg] mass estimation model, based on total body potassium [(TBK); mmol] measured by whole body (40)K counting (WBC) was developed (SM = 0.0082.TBK) and validated in adults in a previous study. It is unknown whether the adult TBK SM prediction model is applicable for pediatric use. The aim of this study was to derive and validate a pediatric TBK SM prediction equation. SM measured by MRI was used as the criterion and TBK was measured by WBC. The protocol was completed in 116 healthy children, 66 males and 50 females, 11.7 +/- 3.5 y (mean +/- SD, range = 5-17 y). A strong linear correlation was observed between TBK and SM (r = 0.984; P < 0.001). The SM:TBK ratio was 0.0071 +/- 0.0008 kg/mmol in the children studied, much lower than the corresponding value of 0.0082 kg/mmol in adults. An empirical SM prediction equation was developed using TBK alone: SM = 0.0085.TBK - 2.83, r(2) = 0.97, SEE = 1.39 kg. Bland-Altman analysis did not disclose a signif...
ABSTRACT Traditional techniques to measure whole-body composition divide the body into five level... more ABSTRACT Traditional techniques to measure whole-body composition divide the body into five levels – atomic, molecular, cellular, tissue and organ. Adiposity within the whole body is usually estimated via the body mass index or anthropometrically by measurement of body weight, stature, skinfolds and circumference. Visceral adipose tissue is an independent predictor of obesity health-related risk. All major tissues and organs can now be measured in vivo using computerized axial tomography or magnetic resonance imaging. At the cellular level, fat cell mass cannot be quantified in vivo; it is usually estimated by combining total body adipose tissue mass with biopsy-derived adipose tissue cell mass concentration. The concentration of molecular fat, or triglyceride, in the body is measured by either body volume analysis, labelled water dilution and dual-energy X-ray absorptiometry. Studies at the atomic level assess total body potassium or total body nitrogen and carbon. The most suitable method depends on the intended use of the data and the required degree of accuracy.
The study of human body composition is a branch of human biology which focuses on the in vivo qua... more The study of human body composition is a branch of human biology which focuses on the in vivo quantification of body components, the quantitative relationships between components, and the quantitative changes in these components related to various influencing factors. Accordingly, the study of human body composition is composed of three interrelated research areas, body composition rules, body composition methodology, and body composition alterations. This thesis describes the authors recent investigations related to the first two of the three research areas. In the rules area, this thesis begins with a comprehensive five-level model of body composition. The approximate 40 body components are systematically organized into five levels with increasing complexity: 1, atomic; 11, molecular; III, cellular; IV, tissue-system; and V 1 whole-body. Although each level and its multiple components are distinct, interconnections exist such that the model is consistent and functions as a whole. ...
The assumed "constancy" of fat-free body mass hydration is a cornerstone in the body-co... more The assumed "constancy" of fat-free body mass hydration is a cornerstone in the body-composition research field. Hydration, the observed ratio of total body water to fat-free body mass, is stable at approximately 0.73 in mammals and this constancy provides a means of estimating total body fat in vivo. This review examines both in vitro and in vivo data that support the hydration constancy hypothesis and provides a critique of applied methodology. Biological topics of interest are then examined and critical areas in need of future research are identified. These are important issues because water dilution is the only method currently available for estimating body fat in all mammals, which range in body mass by a factor of 10(4).
Objective: BMI (kilograms per meters squared) and waist circumference (WC) (measured in centimete... more Objective: BMI (kilograms per meters squared) and waist circumference (WC) (measured in centimeters) are each associated with the risk of developing cardiovascular disease (CVD). Therefore, a combination of the two may be more effective in identifying subjects at risk than either alone. The present study sought to identify the combination of BMI and WC that has the strongest association with CVD risk factors in whites. Research Methods and Procedures: Subjects were 8712 white men and women from the Third National Health and Nutrition Examination Survey. The optimal combination of BMI and WC was developed using logistic regression models with BMI and WC as predictors and CVD risk factors as outcomes. The combined measure of BMI and WC using current cutoff points was also examined. Sensitivity, specificity, and receiver operating characteristics curves were compared between the combined measures and BMI alone. Results: For white men, the optimal combination of BMI and WC for identifying CVD risk factors was 0.68 ϫ BMI ϩ 0.32 ϫ WC. This combination generated a score that better estimated the odds of having CVD risk factors than either alone. For white women, WC alone largely determined the likelihood of having CVD risks. The combination of BMI and WC using current cutoff points may provide an improved measure of CVD risk. Combined measures showed a higher sensitivity or a shorter distance in receiver operating characteristic curves in the identification of CVD risk factors. Discussion: Combined measures of BMI and WC may provide a higher overall test performance for CVD risk factors and may be useful in some ethnic groups as an improved means of screening subjects for further evaluation in the clinical setting.
American journal of physiology. Endocrinology and metabolism, 2001
Potassium is an essential element of living organisms that is found almost exclusively in the int... more Potassium is an essential element of living organisms that is found almost exclusively in the intracellular fluid compartment. The assumed constant ratio of total body potassium (TBK) to fat-free mass (FFM) is a cornerstone of the TBK method of estimating total body fat. Although the TBK-to-FFM (TBK/FFM) ratio has been assumed constant, a large range of individual and group values is recognized. The purpose of the present study was to undertake a comprehensive analysis of biological factors that cause variation in the TBK/FFM ratio. A theoretical TBK/FFM model was developed on the cellular body composition level. This physiological model includes six factors that combine to produce the observed TBK/FFM ratio. The ratio magnitude and range, as well as the differences in the TBK/FFM ratio between men and women and variation with growth, were examined with the proposed model. The ratio of extracellular water to intracellular water (E/I) is the major factor leading to between-individual...
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Papers by Zimian Wang