Two-megahertz impedance index prediction equation for appendicular lean mass in Korean older people.

BACKGROUND: Whole-body bioelectrical impedance analysis (BIA) has been accepted as an indirect method to estimate appendicular lean mass (ALM) comparable to dual-energy X-ray absorptiometry (DXA). However, single or limited frequencies currently used for these estimates may over or under-estimate ALM. Accordingly, there is a need to measure the impedance parameter with appendicular lean-specific across multiple frequencies to more accurately estimate ALM. We aimed to validate muscle-specific frequency BIA equation for ALM using multifrequency BIA (MF-BIA) with DXA as the reference. METHODS: 195 community-dwelling Korean older people (94 men and 101 women) aged 70 ~ 92y participated in this study. ALM was measured by DXA and bioimpedance measures at frequencies of 5 kHz ~ 3 MHz were assessed for independent predictive variables. Regression analyses were used to find limb-specific frequencies of bioimpedance, to develop the ALM equations and to conduct the internal cross-validation. The six published equations and the final equation of MF-BIA were externally cross-validated. RESULTS: 195 participants completed the measurements of MF-BIA and DXA. Using bivariate regression analysis, the 2 MHz impedance index explained R2 = 91.5% of variability (P < 0.001) in ALM and predictive accuracy of standard error of estimate (SEE) was 1.0822 kg ALM (P < 0.001). Multiple stepwise regression analysis obtained in the development group had an adjusted R2 of 9.28% (P < 0.001) and a SEE of 0.97 kg ALM. The cross-validation group had no significant difference between the measured ALM and the predicted ALM (17.8 ± 3.9 kg vs. 17.7 ± 3.8 kg, P = .486) with 93.1% of R2 (P < 0.001) and 1.00 kg ALM of total error. The final regression equation was as follows: ALM = 0.247ZI@2 MHz + 1.254SEXM1F0 + 0.067Xc@5 kHz + 1.739 with 93% of R2 (P < 0.001), 0.97 kg ALM of SEE (Subjective Rating as "excellent" for men and "very good" for women). In the analysis of the diagnostic level for sarcopenia of the final regression, the overall agreement was 94.9% (k = 0.779, P < 0.001) with 71.4% of sensitivity, 98.8% of specificity, 91.3 of positive prediction value and 95.3% of negative prediction value. CONCLUSION: The newly developed appendicular lean-specific high-frequency BIA prediction equation has a high predictive accuracy, sensitivity, specificity, and agreement for both individual and group measurements. Thus, the high-frequency BIA prediction equation is suitable not only for epidemiological studies, but also for the diagnosis of sarcopenia in clinical settings.

Accuracy of Estimated Bioimpedance Parameters with Octapolar Segmental Bioimpedance Analysis.

The validity of the impedance parameters of the five body segments estimated using octapolar segmental bioelectrical impedance analysis (OS-BIA) has not been confirmed. This study aimed to verify the accuracy of the resistance (R), reactance (Xc), and phase angle of each five-body segment. The accuracy of the OS-BIA at 50 kHz was measured based on the direct tetrapolar segmental BIA. The differences in the estimated impedance parameters of the five body segments were compared to those measured from the OS-BIA in elderly men (N = 73) and women (N = 63). The estimated 50 kHz-R (Ω) was significantly higher than the measured 50 kHz-R in the right and left arms, and lower than the measured 50 kHz-R of the trunk, right leg, and left leg (all, p < 0.05). The estimated 50 kHz-phase angles in all the five body segments were significantly lower than the measured ones (all, p < 0.05). The findings suggest that the estimated impedance parameters, R, Xc, and phase angle of the trunk, were remarkedly underestimated, limiting the assessment of the physiological state of the organs in the body. Therefore, further intensive research is needed in the field of estimated segmental BIA in the future.

Reference values of body composition indices: the Korean National Health and Nutrition Examination Surveys.

PURPOSE: An increase in the prevalence of obesity has been observed in children and adolescents. As remarkable changes in body composition occur with growth during the adolescent period, it is important that changes in body composition be monitored. The purpose of this study was to propose reference percentile values for body composition indices including body mass index (BMI) in children and adolescents in Korea. MATERIALS AND METHODS: This study was performed using data from the Fourth and Fifth Korea National Health and Nutrition Examination Surveys. Body composition data were obtained using dual-energy X-ray absorptiometry. The percentile curves of body composition indices were constructed by the LMS method. RESULTS: A total of 2123 children and adolescents between the ages of 10 and 19 years were included in this study. We obtained the percentile curves for BMI and body composition indices. CONCLUSION: The reference values for body composition from this study could help with assessing body composition in Korean adolescents.

The ACTN3 R577X variant in sprint and strength performance.

PURPOSE: The aim of this study is to examine the association between the distribution of ACTN3 genotypes and alleles in power, speed, and strength-oriented athletics. METHODS: ACTN3 genotyping was carried out for a total of 975 Korean participants: top-level sprinters (n = 58), top-level strength athletes (n = 63), and healthy controls (n = 854). RESULTS: Genetic associations were evaluated by chi-squire test or Fisher's exact test. In the power-oriented group composed of sprinters and strength athletes, the frequency of the XX genotype was significantly underrepresented (11.6%) in comparison to its representation in the control group (11.6% versus 19.1%, P < 0.05). When the power-oriented group was divided into strength-oriented and speed-oriented groups, no significant difference in the ACTN3 XX genotype was found between the strength-oriented athletes and the controls (15.9% versus 19.1%, P < 0.262). Only the speed-oriented athletes showed significant differences in the frequency distributions of the ACTN3 XX genotype (6.9% versus 19.1%, P < 0.05) from that of the controls. CONCLUSION: The ACTN3 genotype seems to mainly affect sports performance and especially speed.

External cross-validation of bioelectrical impedance analysis for the assessment of body composition in Korean adults.

Bioelectrical impedance analysis (BIA) models must be validated against a reference method in a representative population sample before they can be accepted as accurate and applicable. The purpose of this study was to compare the eight-electrode BIA method with DEXA as a reference method in the assessment of body composition in Korean adults and to investigate the predictive accuracy and applicability of the eight-electrode BIA model. A total of 174 apparently healthy adults participated. The study was designed as a cross-sectional study. FM, %fat, and FFM were estimated by an eight-electrode BIA model and were measured by DEXA. Correlations between BIA_%fat and DEXA_%fat were 0.956 for men and 0.960 for women with a total error of 2.1%fat in men and 2.3%fat in women. The mean difference between BIA_%fat and DEXA_%fat was small but significant (P < 0.05), which resulted in an overestimation of 1.2 ± 2.2%fat (95% CI: -3.2-6.2%fat) in men and an underestimation of -2.0 ± 2.4%fat (95% CI: -2.3-7.1%fat) in women. In the Bland-Altman analysis, the %fat of 86.3% of men was accurately estimated and the %fat of 66.0% of women was accurately estimated to within 3.5%fat. The BIA had good agreement for prediction of %fat in Korean adults. However, the eight-electrode BIA had small, but systemic, errors of %fat in the predictive accuracy for individual estimation. The total errors led to an overestimation of %fat in lean men and an underestimation of %fat in obese women.

Optimal cutoffs of percentage body fat for predicting obesity-related cardiovascular disease risk factors in Korean adults.

BACKGROUND: Obesity is a major health problem. It is associated with cardiovascular disease. The diagnosis of obesity is crucial to treating and preventing obesity-related medical problems. OBJECTIVE: The objective was to determine optimal percentage body fat cutoffs in Korean adults for predicting obesity-related cardiovascular disease risk factors. DESIGN: We evaluated the body composition and prevalence of obesity-related cardiovascular risk factors, such as hypertension, diabetes mellitus, and dyslipidemia, in 41,088 Korean adults aged 18-92 y. The optimal percentage body fat cutoffs for Korean adults were determined. Multivariable-adjusted odds ratios (ORs) of overweight and obesity were estimated by logistic regression. RESULTS: The first cutoffs in men and women were 17% and 32% body fat, respectively; the second cutoffs were 21% and 37% body fat, respectively. The percentages of obese men and women were 41.8% and 15.9%, respectively. The adjusted OR of at least one risk factor for overweight or obesity in men was 2.22 (95% CI: 2.07, 2.38) or 4.05 (95% CI: 3.78, 4.33). The adjusted OR for women was 1.95 (95% CI: 1.79, 2.07; P < 0.0001) or 3.21 (95% CI: 2.87, 3.57). CONCLUSIONS: Only one-fourth of Korean men had a normal body composition, whereas most of the Korean women had a normal body composition. We conclude that susceptibility to cardiovascular disease and its risk factors is higher in Korean men than in Korean women. The cutoffs are useful for providing adequate guidelines for treating and preventing cardiovascular disease. This was the first study to determine cutoffs of percentage body fat for Korean adults.

Norm references of fat-free mass index and fat mass index and subtypes of obesity based on the combined FFMI-%BF indices in the Korean adults aged 18-89 yr.

OBJECTIVE: To establish reference values for fat-free mass index (FFMI), fat mass index (FMI), and percent body fat (%BF) in a large Korean adult group of apparently healthy subjects, and to analyze the characteristics of body composition indices among the subtypes of obesity in Korean adults. SUBJECTS AND METHODS: A multicenter, cross-sectional study was conducted on a sample of 1275 community-dwelling healthy Koreans, 504 men and 771 women, aged 18-89 years. Body composition parameters were measured by dual-energy X-ray absorptiometry. FFMI (FFM/height squared) and FMI (FM/height squared) were calculated, and then three subtypes of obesity were divided by FFMI; underlean (or sarcopenic), proportional, and heavy (or muscular) obesity. RESULTS: The reference values (5th-95th percentile) of the reference group (18-59 yr) for the FFMI was 16.3-22.3 kg/m(2) in men and 13.3-17.8 kg/m(2) in women. The %BF increased with age because of the reduction of FFM. Due to lower FFMI in the oldest men, they had the lowest BMI while FMI and BMI of Korean women increased with age like Caucasian women. The %BF among three subtypes of obesity was similar while FMI and BMI were increased as FFMI increased. The prevalence of underlean obesity in men was more than double in women. CONCLUSION: It is essential to analyze FFMI as well as %BF because %BF alone cannot explain the effects of ageing on FFM and the characteristics of subtypes of obesity. This is the first study to present DXA-determined age- and sex-specific percentiles for body composition indices in Korean adults. These reference values may be useful for clinical evaluation of body composition and nutritional status for Korean adults.

Modeling the human body shape in bioimpedance vector measurements.

Human body shape, called somatotype, has described physique of humans in health and sports applications, relating anthropometric measurements to fatness, muscularity and linearity in a structured way. Here we propose a new method based on bioelectric impedance vector analysis (BIVA) of R/H and Xc/H to represent the cross-sectional area and the body cell mass in a given surface area (m(2)) respectively. Data from six gymnasts, ten dancers, and five fashion models, groups whose physiques and BMI ranges were distinct from one another, were measured for somatotype and BIVA. The models had highest values of the R/H and gymnasts the lowest. Xc/H was lower in models than in the dancers and gymnasts (p < 0.05). Phase angle was lowest in the models and highest in gymnasts significantly (p < 0.05). Pattern analysis from BIVA corresponded to the calculated anthropometric somatotype supporting the hypothesis that BIA's resistance (R) and reactance (Xc) are meaningful discriminates of body size and function which relate to physique in a purposive way.