Hypergravity exercise against bed rest induced changes in cardiac autonomic control

An intermittent exposure to artificial hypergravity with physical exercise by a human centrifuge may provide a countermeasure against various physiological problems after space flight. To test the effects of hypergravity with ergometric exercise on dynamic regulation of heart rate during weightlessness, we quantified autonomic cardiovascular control before and after head-down-tilt bed rest (HDBR) with and without the countermeasure. Twelve male subjects underwent a 14-day period of HDBR. Six of them were exposed to a hypergravity (+1.2 Gz acceleration at heart level) for 30 min with ergometric exercise (60 W, n=4; 40 W, n=2) as a countermeasure on day 1, 2, 3, 5, 7, 9, 11, 12, 13 and 14, during HDBR (CM group). The remaining six were not exposed to a hypergravity exercise during HDBR (control group). Blood pressure and ECG were recorded at a supine position before and after HDBR. The high frequency power of R–R interval (HFRR; 1,008±238 to 353±56 ms² P<0.05) as an index of cardiac parasympathetic activity, and transfer function gain between BP and R–R interval in the high frequency range (GainHF; 21.9±5.4 to 14.5±4.2 ms/mmHg, P<0.01) as an index of vagally mediated arterial-cardiac baroreflex, decreased significantly after HDBR in the control group. However, these changes were not statistically significant in the CM group (HFRR, 1,150±344 to 768±385 ms²; GainHF, 21.5±3.3 to 18.6±3.4 ms/mmHg). Moreover, baroreflex gain by sequence analysis showed similar results. This observation suggests that the intermittent exposure to hypergravity with ergometric exercise may attenuate the decreases in the parasympathetic activity and the spontaneous arterial-cardiac baroreflex function after weightlessness.     

Relationship between indices of adiposity obtained by peripheral quantitative computed tomography and dual-energy X-ray absorptiometry in pre-pubertal children

Background/Aim: The study investigated the relationship between indices of adiposity measured by peripheral quantitative computed tomography (pQCT) and dual-energy X-ray absorptiometry (DXA) in pre-pubertal children.

Subjects and methods: DXA-derived per cent body fat (%BF) was measured in 284 boys and 288 girls, aged 7–10 years. Cross-sections of the forearm (n=427) and lower leg (n=560) were obtained by pQCT to measure total cross-sectional area of the limb (Total CSA), Muscle CSA, Fat CSA, %Fat CSA (Fat CSA/Total CSA×100) and muscle density.

Results: Peripheral QCT-derived %Fat CSA in the forearm and lower leg correlated strongly with DXA-derived %BF (r=0.83–0.89, p<0.01) in both boys and girls. However, forearm and lower leg %Fat CSA were higher than whole body %BF by 5% and 10%, respectively. A better prediction of whole-body %BF was achieved by including %Fat CSA, muscle density and height into a hierarchical regression model. Using sex-specific regression equations, 87.7% of the boys and 83.7% of the girls had a predicted %BF within 3% units of the %BF obtained by DXA.

Conclusion: In pre-pubertal children, pQCT measures of adiposity are strongly associated with whole-body per cent body fat. This reproducible method could be an alternative technique to estimate body composition in this population.     

Sensitivity and specificity of the body mass index to assess low percent body fat in African women

The objective of this study was to evaluate the ability of the body mass index (BMI, kg/m²) to reflect low percent body fat (%BF) in a population with a rather mild but widespread prevalence of low BMI. A sample of 586 women was studied in the Plateau Koukouya, a rural area of the Republic of Congo, Central Africa. Percent BF was estimated from bioelectrical impedance (BIA). BIA parameters were assumed to reflect lean body mass. The correlation between %BF and BMI was high (r = 0.84; P < 0.001). Low %BF or low BIA parameters were defined as the first quartile of the distribution. Sensitivity, specificity, positive and negative predictive value of BMI <18.5, an accepted international cutoff for thinness, in relation to %BF was 58.5%, 93.6%, 75.4%, and 87.1%, respectively. A continuous sensitivity/specificity analysis (receiver operator characteristic [ROC] curves) for characterizing low %BF or low BIA parameters was done for a large range of BMI values. ROC curve analysis for %BF suggested that an acceptable trade-off between sensitivity (89.8%) and specificity (77.9%) occurred at a BMI of 19.7 kg/m². However, the positive predictive value was low (57.6%). For the prediction of low BIA parameters, results were similar, showing moderate sensitivity and high specificity for BMI <18.5, a cutoff point of BMI = 19.6, and low positive predictive values (<48%). The data suggest that BMI was not a good predictor of low %BF. This is consistent with the assumption of a decrease in both fat and fat free body mass in cases of low BMI. Am. J. Hum. Biol. 12:25–31, 2000. © 2000 Wiley-Liss, Inc.     

Influence of head-down bed rest on the circadian rhythms of hormones and electrolytes involved in hydroelectrolytic regulation

We investigated in six men the impact of a 17-day head-down bed rest (HDBR) on the circadian rhythms of the hormones and electrolytes involved in hydroelectrolytic regulation. This HDBR study was designed to mimic an actual spaceflight. Urine samples were collected at each voiding before, during and after HDBR. Urinary excretion of aldosterone, arginine vasopressin (AVP), cyclic guanosine monophosphate (cGMP), cortisol, electrolytes (Na⁺ and K⁺) and creatinine were determined. HDBR resulted in a significant reduction of body mass (P<0.01) and of caloric intake [mean (SEM) 2,778 (37) kcal·24 h^–1 to 2,450 (36) kcal·24 h^–1, where 1 kcal·h^–1=1.163 J·s^–1; P<0.01]. There was a significant increase in diastolic blood pressure [71.8 (0.7) mmHg vs 75.6 (0.91) mmHg], with no significant changes in either systolic blood pressure or heart rate. The nocturnal hormonal decrease of aldosterone was clearly evident only before and after HDBR, but the day/night difference did not appear during HDBR. The rhythm of K⁺ excretion was unchanged during HDBR, whereas for Na⁺ excretion, a large decrease was shown during the night as compared to the day. The circadian rhythm of cortisol persisted. These data suggest that exposure to a 17-day HDBR could induce an exaggeration of the amplitude of the Na⁺ rhythm and abolition of the aldosterone rhythm. Electronic Publication     

Body fat and skinfold thicknesses: A dimensional analytic approach

Background: Body fat may be estimated from skinfold thickness measurements (Skfs), but current prediction equations are dimensionally inconsistent and do not properly allow for the influence of body size on fat mass.

Aim: To find a dimensionally correct formula relating fat content to Skfs and body size.

Subjects and methods: 285 African children aged 9–11 years, with fat content measured by dual-energy X-ray absorptiometry, were studied. Because least-squares regression parameters can be a misleading guide to true functional relationships, the real data were compared with simulated data sets conforming to a dimensionally correct statistical model.

Results: The data are consistent with functional relationships such that fat mass is proportional to Skf×height². The mean ratio (fat mass)/(Skf×height²) is 6% higher in the girls than in the boys.

Discussion: Appropriately, Skf×height² has the dimensions of fat mass/density. Height² has no obvious physical significance and a more meaningful expression might be ‘height×X', where X corresponds to some measure of body width or girth.

Conclusion: In formulae for predicting fat mass, multiplying Skfs by height² gives better estimates, especially for the tallest and shortest individuals. Fat mass, rather than percentage body fat (%BF), is best taken as the variable initially predicted.     

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(√BM_kg/Ht_m). 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.     

Association of FTO and IRX3 genetic variants to obesity risk in north India

Abstract

Objective: Validation of body adiposity index (BAI) in a paediatrics sample; and to develop, if necessary, a valid BAI for paediatrics (i.e. BAI_p).

Methods: A total of 1615 children (52% boys) aged 5–12 years underwent anthropometry. Their body composition was assessed using a foot-to-foot bioimpedance. The validity of BAI?=?(Hip circumference/Height^1.5)???18 was tested by combining correlation and agreement statistics. Then, the sample was split into two sub-samples for the construction of BAI_p. A regression was used to compute the prediction equation for BAI_p-based percentage of body fat (%BF).

Results: The initial BAI over-estimated the %BF of children by 49% (29.6?±?4.2% versus 19.8?±?6.8%; p?<?0.0001). The original methodology led to a BAI_p?=?(Hip circumference/Height^0.8) ? 38 in children. When compared to BAI, BAI_p showed both better correlation (r?=?0.57; p?<?0.01 versus r?=?0.74; p?<?0.0001) and agreement (ICC?=?0.34; [95% CI?=??0.19–0.65] versus ICC?=?0.83; [95% CI?=?0.81–0.84]). However, there were some systematic biases between the two values of %BF as exemplified by the large 95% limit of agreement [?9.1%; 8.8%] obtained.

Conclusion: BAI over-estimates the %BF in children. In contrast, BAI_p appears as a new index for children’s body fatness, with acceptable accuracy. In its current form, this index is valid only for large-scale studies.     

Proximal electrode placement improves the estimation of body composition in obese and lean elderly during segmental bioelectrical impedance analysis

Bioelectrical impedance analysis (BIA) is an affordable, non-invasive, easy-to-operate, and fast alternative method to assess body composition. However, BIA tends to overestimate the percent body fat (%BF) in lean elderly and underestimate %BF in obese elderly people. This study examined whether proximal electrode placement eliminates this problem. Forty-two elderly men and women (64–96 years) who had a wide range of BMI [22.4 ± 3.3 kg/m² (mean ± SD), range 16.8–33.9 kg/m²] and %BF (11.3–44.8%) participated in this study. Using ²H and ¹⁸O dilutions as the criterion for measuring total body water (TBW), we compared various BIA electrode placements; wrist-to-ankle, arm-to-arm, leg-to-leg, elbow-to-knee, five- and nine-segment models, and the combination of distal (wrists or ankles) and proximal (elbows or knees) electrodes. TBW was most strongly correlated with the square height divided by the impedance between the knees and elbows (H ²/Z _proximal; r = 0.965, P < 0.001). In the wrist-to-ankle, arm-to-arm, leg-to-leg, and five-segment models, we observed systematic errors associated with %BF (P < 0.05). After including the impedance ratio of the proximal to distal segments (P/D) as an independent variable, none of the BIA methods examined showed any systematic bias against %BF. In addition, all methods were able to estimate TBW more accurately (e.g., in the wrist-to-ankle model, from R ² = 0.90, SEE = 1.69 kg to R ² = 0.94, SEE = 1.30 kg). The results suggest that BIA using distal electrodes alone tends to overestimate TBW in obese and underestimate TBW in lean subjects, while proximal electrodes improve the accuracy of body composition measurements.     

Body measurement variability,fatness, and fat‐free mass in children 8, 11, and 14 years of age: Project HeartBeat!

Project HeartBeat! is a four year mixed‐longitudinal study of the development of cardiovascular risk factors in White and African American children who at baseline comprised three age cohorts 8, 11, and 14 years. This paper focuses on the anthropometric variables which were chosen to reflect body fat and fat‐free mass. Selected anthropometric dimensions are compared with those of samples from the combined National Health and Nutrition Examination Surveys I and II to explore the similarities of the samples in terms of central tendencies and variances. The measurements were then explored in terms of their ability to estimate the two compartment model of body composition: fat‐free mass (FFM) and body fat (BF) from bioelectrical impedance (BIA). Project HeartBeat! children are slightly larger than NHANES children and have variances that are generally comparable to the national surveys. Over seven percent (7.7%) of children were overweight (BMI) and 25% had ‘mild obesity’ by %BF. Three different factor analytic methods (incomplete principal components, alpha and maximum likelihood) produced two latent variables from 17 anthropometric dimensions which together accounted for 76–83% of the variation: (1) A body mass factor (F1) which was weighted highly on six circumferences, weight and six skinfolds, and (2) a linear growth factor (F2) which was strongly associated with height, arm length, and sitting height. Triceps, subscapular and midaxillary skinfolds were consistently highly loaded on the body mass factor and their sum was highly correlated to %BF and fat mass (0.90–0.99). This suggests that this sum could be used to estimate fatness in children in studies where the BIA or other body composition techniques are unavailable. FFM and %BF were predicted from the anthropometric factors. Both factors contributed to the estimate of FFM (R² = 0.81–0.93), although F2 contributed proportionately more. The ‘body mass’ factor (F1) was the main predictor of %BF (R² = 0.86–0.93), though at some ages the linear factor (F2) was significantly and negatively related to %BF. This set of anthropometric dimensions, taken for the purpose of estimating body composition and summarized as two latent vectors by factor analysis, strongly reflects body fat and FFM in children and adolescents. Am. J. Hum. Biol. 11:69–78, 1999. © 1999 Wiley‐Liss, Inc.     

Criterion methods of body composition analysis for children and adolescents

The lack of chemical maturity, subsequent to normal growth and maturation, complicates the assessment of body composition in children. Even though known to overpredict percent body fat (%BF), the use of adult prediction equations is widespread in the pediatric literature. Many sex- and age-specific modified equations have been proposed. This study reports a cross-validation analysis of selected laboratory-based criterion methods in an attempt to identify the most appropriate reference which could be used in future validation studies of the more practical field/clinical testing methods. Subjects were 48 (24 boys and 24 girls) peripubertal children evenly distributed according to stage of maturation. Criterion measurements included body density (Db) by hydrostatic weighing, total body water (TBW) by deuterium oxide dilution, and total body mineral content (TMC) by dual energy x-ray absorptiometry. Five different prediction models were evaluated. Test-retest reliabilty was high (ICC = .970 to .999). Of the prediction models tested, the four-component model was considered the most accurate laboratory-based criterion model since it involves measurement of the primary constituents of fat-free mass. Based on high r² (≥.942) values, low standard errors of estimate (SEE = 1.8 %BF males, 1.1 %BF females); and low total prediction errors (TE = 1.9 %BF males, 2.0 %BF females), the Lohman age-adjusted prediction equation showed the best agreement with the four component model. If multiple testing facilities are unavailable, the Lohman two-component (Db) model would be the criterion method of choice. © 1993 Wiley-Liss, Inc.     

The relationship between body composition and onset of menarche

Background: A late age of menarche in elite adolescent athletes is frequently attributed to low body fat/weight. If a critical body weight/fat is necessary for menarche, a reduction in the variability of these parameters would be observed at menarche compared to times before and after this event.

Aim: The study determined the variability in body mass (BM), per cent body fat (%BF) and total body fat (TBF) of girls between ?2 and +2 years from menarche.

Methods: Participants were part of the Saskatchewan Pediatric Bone Mineral Accrual Study (1991–1998). Body composition was assessed using dual X-ray absorptiometry (DXA). An individual's data was retained for analysis if they had at least four DXA scans between ?3 and +3 years from menarche. Values were interpolated from the cubic spline at whole years between ?2 and +2 years from menarche. Coefficient of variation (CV) was used to assess variability.

Results/Conclusion: Data on 61 girls were retained for analysis. The range in BM, TBF and %BF at menarche was 50.10 kg, 35050.06 g and 31.61%, respectively. Reductions in variability of body fat and weight were not apparent at menarche, which does not provide support for the hypothesis that a critical body weight/fat is required for menarche.     

Association between different attributes of physical activity and fat mass in untrained, endurance- and resistance-trained men

The objective of this cross-sectional study was to assess different attributes of physical activity and fitness and their relationship to nutritional state in endurance- and resistance-trained, compared to untrained men. The subjects were 42 men matched for age, of which 13 were untrained [UT, mean age 30.2 years, mean height 180.7 cm, mean body mass 83.6 kg, mean body mass index (BMI) 25.6 kg·m^–2], 14 were endurance-trained athletes (ET, mean age 29.6 years, mean height 178.4 cm, mean body mass 74.0 kg, mean BMI 23.2 kg·m^–2) and 15 were resistance-trained athletes (RT, mean age 28.4 years, mean height 183.4 cm, mean body mass 94.1 kg, mean BMI 27.4 kg·m^–2). Fat mass (FM), fat free mass (FFM), muscle mass (MM) and total body water (TBW) were assessed using anthropometry and bioelectrical impedance analysis. Resting energy expenditure was measured by indirect calorimetry (IC) and total energy expenditure (TEE) by a combination of IC and individually calibrated 24-h heart-rate monitoring. The activity related energy expenditure (AEE) and the physical activity level were calculated. Movements were assessed using pedometry. Aerobic fitness was determined using ergometry, muscle strength [quadriceps muscle (Fa_max), ischiocruralis muscle (Fb_max), biceps muscle (Fc_max), triceps muscle (Fd_max)] by computer tensiometry. Different time domain indexes of heart rate variability (HRV) were examined during sleep, rest and the whole day as an index of sympathetic nervous system (SNS) activity. When compared with UT and RT, ET had reduced body masses and FM, but increased percentage TBW (P<0.05 and P<0.01, respectively). FFM and MM were increased in RT, when compared with UT and ET (P<0.01). ET had higher TEE, AEE, pedometry derived activities, oxygen consumption and power during vigorous exercise than RT and UT (P<0.05 and P<0.01, respectively). Respiratory exchange ratio at moderate exercise intensities was increased in RT (P<0.05). In the 12 time domain indexes of HRV 6 and 10 were higher in ET than in RT and UT respectively (P<0.05 or P<0.01, respectively) suggesting an increased SNS activity in ET. By contrast, Fa_max, Fc_max and Fd_max were elevated in RT (P<0.01). FM was negatively associated with aerobic fitness, but not with muscle strength. We concluded that the physiological and metabolic adaptations to exercise and nutritional state differ between ET and RT subjects. Participation in RT results predominantly in changes in body composition and strength but not in energy expenditure, movements and SNS activity. The opposite was the case for ET. Aerobic fitness, physical activity, movements and activity of SNS were all increased but body mass and FM were decreased. The latter finding may support the idea that, with regard to possible health benefits, ET is more effective than RT. Electronic Publication     

Allometric scaling of strength measurements to body size

For comparative purposes, normalisation of strength measures to body size using allometric scaling is recommended. A wide range of scaling exponents have been suggested, typically utilising body mass, although a comprehensive evaluation of different body size variables has not been documented. Differences between force (F) and torque (T) measurements of strength, and the velocity of measurement might also explain some of the variability in the scaling exponents proposed. Knee extensor strength of 86 young men was assessed with measurement of torque at four velocities (0–4.19 rad s⁻¹) and force measured isometrically. Body size variables included body mass, height and fat-free mass. Scaling exponents for torque were consistently higher than for force, but the velocity of torque measurement had no influence. As the confounding effects of fat mass were restricted, scaling exponents and the strength of the power-function relationships progressively increased. Fat-free mass determined a surprisingly high proportion of the variance in measured strength (F, 31%; T, 52–58%). Absolute force and torque measurements, and even torque normalised for body mass, were significantly influenced by height, although strength measures normalised to fat-free mass were not. To normalise strength measurements to body mass, for relatively homogenous lean populations (body fat <20%), exponents of 0.66 (F) and 1.0 (T) are appropriate. For more adipose populations (body fat >20%) lower body mass exponents appear more suitable (F, 0.45; T, 0.68). Nevertheless, fat-free mass is the recommended index for scaling strength to body size, and higher exponents (F, 0.76; T, 1.12) are advocated in this case.     

The utility of generalized girth and skinfold equations to predict body composition in women runners

Although generalized equations to predict body composition exist, the validity of these equations when applied to a homogeneous group of athletic women is uncertain. Sixty-five women runners (age = 28.3 ± 6.4 yrs; ht = 166.8 ± 6.2 cm; wt = 58.9 ± 6.6 kg; body density (D_b) = 1.047 ± 0.009 g · cc^?1; percentage body fat (%BF) = 22.1 ± 3.7%; V?O₂max = 56.0 ± 5.3 ml/kg · min^?1; training volume = 45.8 ± 16.0 km · wk^?1) were used to cross-validate the Jackson, Pollock, and Ward (1980) generalized quadratic skinfold equations (JPW) and the Tran and Weltman (1989) generalized girth equation (TW). Additionally, the average of TW and the JPW quadratic skinfold equations were calculated and compared to hydrostatic weighing (HW). None of the JPW equations nor the TW equation accurately predicted D_b (P <0.05). All JPW equations underpredicted %BF with values ranging from 16.3–19.7%. Correlations ranged from r = 0.73 to r = 0.79. Standard errors (SE = [∑(Y ? Y′)²/N]^1/2) for predicting %BF ranged from 6.6% to 3.9%. The TW equation underestimated body density (1.041 ± 0.008) with a correlation of r = 0.54 and a SE of 4.2%. When the results of the JPW sum of 4 skinfolds (or the sum of 7 skinfolds) was averaged with TW, no significant mean differences in D_b or %BF were observed and the standard errors were 2.7%. Additionally, a population specific equation was derived using skinfolds and girths (n = 40) and was shown to accurately predict body density in a cross-validation sample of women runners (n = 25). This equation yielded a correlation of r = 0.72 and a SE = 2.7%. It was concluded that the combination of skinfold and girth techniques is superior to either method alone when predicting body composition in women runners. © 1993 Wiley-Liss, Inc.     

Alu insertions versus blood group plus protein genetic variability in four Amerindian populations

Background: Various charts based on body mass index (BMI) and per cent body fat (%BF) are used to classify childhood body composition but outcomes may vary.

Aim: The study investigated variation in incidences of childhood obesity as depicted by four classification charts.

Subjects and methods: BMI and DXA-derived %BF were assessed in 741 children. Incidences of overweight and obesity were compared between two BMI charts and two bioelectrical impedance (BIA)-based %BF charts.

Results: The International Obesity Task Force (IOTF)-adopted BMI chart designated 21%, 6% (boys), and 26%, 9% (girls) as overweight and obese, respectively. Corresponding figures using the USA CDC BMI chart were 27%, 11% (boys) and 27%, 12% (girls). Using a USA-derived %BF chart incidences were 17%, 2% (boys) and 21%, 8% (girls) and using a UK-derived %BF chart 51%, 24% (boys) and 53%, 36% (girls). Sensitivity of BMI varied according to the %BF reference chart.

Conclusions: In contrast to the BMI-based charts, there were considerable variations in depicted incidences of obesity between the %BF-based charts. These discordances were considered to result from previously reported variation within and between BIA and DXA %BF assessments underlying the charts. The present study highlights the need for valid, reliable, unchanging BIA and DXA procedures.     

Relevance of Physical Activities,Sedentary Behaviors,and Genetic Predisposition in Body Fatness: Population-Based Study on Chinese Adults

IntroductionLittle attention has been paid to the interacting effect of specific intensities of physical activities (PAs) and sedentary lifestyle, like television watching, and genetic predisposition on body composition indices among Chinese adults. Herein, we aimed to examine whether specific types of PAs and sedentary behaviors (SBs) were associated with body composition indices among Chinese adults and to further explore whether these associations interacted with the genetic predisposition to high BMI.MethodsCross-sectional data regarding PAs and time spent on SBs and dietary intake of 3,976 Chinese adults (54.9% women) aged 25–65 years in Southwest China were obtained via questionnaires in 2013–2015. Weight, height, and waist circumference (WC) were measured, and BMI, percentage of body fat (%BF), fat mass index (FMI), and fat-free mass index (FFMI) of the participants were calculated. Genetic risk score (GRS) was calculated on 9 established BMI-associated SNPs among Chinese adults.ResultsWhen the participants were stratified by GRS for BMI, significant associations were only found for adults with high GRS for BMI: moderate-to-vigorous physical activity (MVPA) was negatively associated with WC and %BF and positively related to FFMI. The adjusted positive relationship of time spent watching television with BMI, WC, %BF, and FMI were also just found between adults with high weighted GRS for high BMI: for every 1 h increment in television watching, the BMI, WC, %BF, and FMI of the participants increased by 0.2 kg/m², 0.9 cm, 0.3%, and 0.1 kg/m², respectively (p < 0.02).ConclusionMVPA may be a protective factor against obesity, and prolonged television watching may accentuate adiposity. These putative effects may be more pronounced among individuals with a high genetic risk of a high BMI.     

Body composition estimation using skinfolds in children with and without health conditions affecting growth and body composition

Background: Body composition prediction equations using skinfolds are useful alternatives to advanced techniques, but their utility across diverse paediatric populations is unknown.

Aim: To evaluate published and new prediction equations across diverse samples of children with health conditions affecting growth and body composition.

Subjects and methods: Anthropometric and dual-energy X-ray absorptiometry (DXA) body composition measures were obtained in children with Down syndrome (n?=?59), Crohn disease (n?=?128), steroid-sensitive nephrotic syndrome (n?=?67) and a healthy reference group (n?=?835). Published body composition equations were evaluated. New equations were developed for ages 3–21 years using the healthy reference sample and validated in other groups and national survey data.

Results: Fat mass (FM), fat-free mass (FFM) and percentage body fat (%BF) from published equations were highly correlated with DXA-derived measures (r?=?0.71–0.98), but with poor agreement (mean difference = 2.4?kg, ?1.9?kg and 6.3% for FM, FFM and %BF). New equations produced similar correlations (r?=?0.85–1.0) with improved agreement for the reference group (0.2?kg, 0.4?kg and 0.0% for FM, FFM and %BF, respectively) and in sub-groups.

Conclusions: New body composition prediction equations show excellent agreement with DXA and improve body composition estimation in healthy children and those with selected conditions affecting growth.     

Skeletal differences between black and white men and their relevance to body composition estimates

Skeletal differences exist between closely matched Black and White women, although it is unknown if similar differences also exist between Black and White men after controlling for age, body weight, and stature. The aim of this study was twofold: to test the hypothesis that Black men have greater bone mass, higher bone mineral density, and longer limbs compared to White men of similar age, weight, and height; and second, to establish if ethnic variation in skeletal characteristics has an impact on the models upon which three widely used methods for estimating total body fat are based. Twenty-four healthy Black men were matched by age (±5 years), height (±3 cm), and weight (±2 kg) to 24 healthy White men. Skeletal characteristics and body composition were studied using anatomical and compartment estimates derived by anthropometry, ³H₂O dilution, hydrodensitometry, whole-body ⁴⁰K counting, and dual photon systems. Black men had greater bone mineral mass (P = 0.007), higher bone density (P = 0.054), longer femurs (P = 0.002), longer anthropometric arm and thigh lengths (P = 0.001 and P = 0.002, respectively), lower spine to femur ratio (P = 0.004), and similar spine length (P = 0.271) compared to White men. Total body fat and fat-free body mass (FFM) were estimated in the men using a four-compartment model. Black and White men had similar total body fat, K (TBK), water (TBW), and FFM. Density of FFM and TBK/FFM were also similar between Black and White men, suggesting that current two-compartment hydrodensitometry and TBK models for estimating fat may not require adjustments for ethnicity. The TBW/FFM ratio, which is the main assumed steady-state relation for the two-compartment TBW method of estimating fat, was modestly increased (P = 0.05) in Black men (x? ± SD, 0.744 ± 0.018) compared to White men (0.732 ± 0.021). These results confirm that Black and White men differ significantly in some skeletal characteristics and these differences have implications in the study of both osteoporosis and human body composition. © 1994 Wiley-Liss, Inc.     

Multicompartment model of body composition assessment in Chinese-American adults

Using hydrodensitometry, dual energy x-ray absorptiometry, and deuterium dilution techniques, multiple compartment body composition assessment was performed on 29 adult Chinese-American men (n = 11) and women (n = 18). The purpose of the investigation was to determine if significant differences exist in the estimation of percentage of body fat (%BF) and fat-free mass (FFM), based on 2-, 3-, and 4-compartment models of body composition. Height, weight, and the body mass index (BMI) for the men were 170 cm, 63 kg, and 22 kg/m²; for the women, values were 161 cm, 59 kg, and 23 kg/m², respectively. Estimated values for %BF from density alone and density adjusted for TBW were not significantly different for either the men or women (20.5% vs. 18.8%) and (28.2% vs. 27.4%). However, %BF estimated from the 4-compartment model of density, TBW and BMC resulted in significantly lower values for both groups, 17.5% for men and 26.8% for women. The lack of a significant difference in %BF between density only and density adjusted for TBW indicates that TBW was within the accepted constancy value associated with hydrodensitometry. When density was adjusted for variation in both TBW and BMC, a significant decline occurred in the estimate of %BF for men, but not for women. The average TBW to FFM ratio was 0.75., 0.74, and 0.73 when using FFM values from 2-, 3-, and 4-compartment models, respectively. The average BMC to FFM ratio from two-, three-, and four-compartment estimates of FFM were 0.054, 0.053, and 0.052 for the men and 0.060, 0.059, and 0.059 for the women. The results suggest that Chinese-American men and women have similar TBW/FFM ratios, but the BMC/FFM ratio is higher in women than men. Am. J. Hum. Biol. 9:21–27 © 1997 Wiley-Liss, Inc.

1 This article is a US Government work and, as such, is in the public domain in the United States of America.

     

Importance of proper scaling of aerobic power when relating to cardiometabolic risk factors in children

Background: The relationship between cardiometabolic risk factors (CMRF) and aerobic power (VO_2max) scaled as mL O₂ per kilogram body mass is controversial because mass includes both fat and fat-free mass, and fat mass is independently associated with the CMRF.

Aim: To examine common units used to scale VO_2max and their relationships to mean blood pressure (MBP), total cholesterol (TC), HDL cholesterol, triglycerides (TG), insulin resistance (HOMA-IR) and cumulative risk score (z-score).

Subjects: 1784, 8–18 year-old youths, 938 girls and 886 boys.

Methods: Fasting blood samples were obtained. VO_2max was estimated in mL/min from cycle ergometry and scaled to body mass (kg), fat free mass (kg_FFM), body surface area (m²), height (cm) and allometric (mL/kg^0.67/min).

Results: Unadjusted correlations between CMRF and many of the scaled VO_2max units were significant (p < 0.0001), especially for MBP, HOMA-IR, HDL and z-score, with lower correlations for TC and TG. After adjusting for ancestry, sex, height and body fat associations were greatly weakened (r < 0.09), except for MBP.

Conclusions: On a population basis, the physical characteristics of the child, especially body fat, are more related to CMRF than any scaled units of VO_2max; thus care is needed when relating fitness and health issues.