Estimation Of Total Body Water Research Articles

Accuracy of quantitative magnetic resonance and eight-electrode bioelectrical impedance analysis in normal weight and obese women

Quantitative magnetic resonance (QMR) has previously been shown to both overestimate and underestimate average fat mass (FM) in humans. Eight-electrode bioelectrical impedance analysis (BIA) has previously been found biased as well as successfully validated. We report cross-sectional accuracy of QMR and eight-electrode BIA evaluated with air displacement plethysmography (ADP) as reference method. Fat mass and fat free mass (FFM) by QMR and eight-electrode BIA were evaluated against ADP as reference in 38 normal weight and 30 obese women. Total body water estimates by QMR and eight-electrode BIA were compared. Fat mass was overestimated by QMR (1 ± 2 kg, p < 0.001) and was underestimated by eight-electrode BIA (1 ± 3 kg, p = 0.03, Bonferroni adjusted p = 0.29) in normal weight women. Fat mass was underestimated by both QMR (2 ± 2 kg, p < 0.001) and eight-electrode BIA (9 ± 3 kg, p < 0.001) in obese women. Fat free mass biases were of similar magnitude but in opposite direction to FM biases. Total body water estimates were larger by eight-electrode BIA compared to QMR (1-10 kg). Fat mass and FFM by QMR were both biased but in opposite directions in both normal weight and obese women. Eight-electrode BIA FM and FFM estimates were imprecise and biased in obese women. Thus, QMR is more precise and more accurate than eight-electrode BIA for estimating body composition in women, but is not accurate enough to be used for individual single assessment of body composition.

Response to Letter to the Editor from Dr. Safer et al. regarding the article “Age-related changes in body composition in a sample of Czech women aged 18–89 years: a cross-sectional study,” published in European Journal of Nutrition

We appreciate that Dr. Umut Safer and his colleagues considered our study [1] interesting and recommended it to readers of the European Journal of Nutrition. With regards to the letter from Safer et al. about our recent publication, our responses to the letter are as follows. In the Letter to the Editor, Safer et al. argued that pretesting preparation is necessary to maximize the accuracy of the direct segmental multi-frequency bioelectrical impedance analysis (BIA). We agree with this statement and guarantee that all participants were asked to fast for 2 h, to avoid any vigorous physical activity for at least 48 h before the procedure, and to urinate or defecate before the measurements were taken. To comply with the standard conditions of measurement, we excluded those who use diuretics or are undergoing diuretic therapy. Safer et al. have noted in their letter that we calculated fat-free mass (FFM) by an equation based on total body water (TBW) measurement, but this was not referenced. We would like to respond to this comment. In ‘‘Methods,’’ we described the principles for estimate body composition via BIA. According to Thibault et al. [2], the measurement of total body impedance allows estimation of TBW, and, by assuming that TBW is constant, FFM which contains body water. InBody 720 (Biospace Co., Ltd.; Seoul, Korea) estimates FFM by dividing TBW by constant. TBW was estimated from area, volume, length, impedance, and a constant proportion. In contrast to single-frequency devices, InBody 720 uses multiple-frequency technology which improves the estimation of FFM, and, hence, body fat, by determining intracellular and extracellular water. Finally, Safer et al. highlighted that validity of segmental multi-frequency BIA was referenced by the study of Ling et al. [3] that describes Korean middle-aged adult population. We dare to disagree with this statement because the study sample of the study mentioned above includes participants from Leiden Longevity Study (Netherlands). Although Mally et al. [4] reported that actual BIA equations should be revised, we have to point out that the authors of the study used single-frequency device (Tanita BC-418 MA) and the study participants were over 60 years old. And hence, this conclusion should not be generalized for all BIA devices and all age groups.

Bioelectrical Impedance Analysis

It is 50 years since Thomasett demonstrated the application of the measurement of the impedance of the human body to the estimation of total body water...

Water-deficit equation: systematic analysis and improvement

The water-deficit equation {WD(1) = 0.6 × B(m) × [1 - (140 ÷ Na(+))]; B(m) denotes body mass} is used in medicine and nutrition to estimate the volume (L) of water required to correct dehydration during the initial stages of fluid-replacement therapy. Several equation assumptions may limit its accuracy, but none have been systematically tested. We quantified the potential error in WD(1) for the estimation of free water (FW) and total body water (TBW) losses and systematically evaluated its assumptions. Thirty-six euhydrated volunteers were dehydrated (2.2-5.8% B(m)) via thermoregulatory sweating. Assumptions within WD(1) were tested by substituting measured euhydrated values for assumed or unknown values. These included the known (premorbid) B(m) (WD(2)), a proposed correction for unknown B(m) (WD(3)), the TBW estimated from body composition (WD(4)), the actual plasma sodium (WD(5)), the substitution of plasma osmolality (Posm) for sodium (WD(6)), and actual Posm (WD(7)). Dehydration reduced TBW by 3.49 ± 0.91 L, 57% of which (2.02 ± 0.96 L) was FW loss, and increased plasma sodium from 139 (range: 135-143 mmol/L) to 143 (range: 141-148 mmol/L) mmol/L. Calculations for WD(1) through WD(7) all underestimated TBW loss by 1.5-2.5 L (P < 0.05). WD(1) through WD(5) underestimated FW by 0.5 L to 1.0 L (P < 0.05), but WD(6) and WD(7) estimated FW loss to within 0.06-0.16 L (P > 0.05). WD(1) grossly underestimates TBW and FW losses. Corrections for unknowns and assumptions (WD(2) through WD(5)) improved estimates little. The use of WD(6) = 0.6 × B(m) × [1 - (290 ÷ Posm)] accurately estimates FW but still underestimates TBW losses by >40%.

Bioimpedance prediction of fat-free mass from dual-energy X-ray absorptiometry in a multi-ethnic group of 2-year-old children

Bioimpedance analysis (BIA) is a simple, convenient and widely used tool for the measurement of body composition in population surveys and surveillance. Prediction equations based on BIA applicable to preschool children are available but are based on total body water estimation and have not been developed across multiple ethnic groups. Our aim was to develop a BIA-based equation in a multi-ethnic sample of 2-year old using fat-free mass (FFM) from dual-energy X-ray absorptiometry (DXA) as criterion measure. Single-frequency hand-to-foot BIA (model BIM4, Impedimed) and whole-body DXA measurements were carried out in 77 (35 boys, 42 girls; 27 European, 20 Polynesian, 30 Asian and other) healthy preschool children (age range 22-38 months). Body mass index s.d. scores were 0.41 ± 1.23 for boys and 0.61 ± 1.09 for girls. The performance of published equations applicable to this age group was assessed. The predicted residual sum of squares method was used to develop and cross-validate a multiple regression equation relating FFM to BIA measures. Published equations performed poorly for estimating FFM in this group of children. The prediction equation developed in all 77 children was: FFM (kg)=0.367 height(cm)(2)/resistance+0.188 weight (kg)+0.077 height (cm)+0.273 sex (male=1, female=0)-2.490, R(2)=0.89, standard error of estimate=0.50 kg. Ethnicity and age did not add significantly to the model. We have developed an equation that may have application for prediction of FFM in 2-3-year-old children, which does not require determination of hydration factors. Further work should be carried out using DXA scanning to extend the applicable age range.

Body composition of Bangladeshi children: comparison and development of leg-to-leg bioelectrical impedance equation.

The aim of this study was to investigate the validity of the Tanita TBF 300A leg-to-leg bioimpedance analyzer for estimating fat-free mass (FFM) in Bangladeshi children aged 4-10 years and to develop novel prediction equations for use in this population, using deuterium dilution as the reference method. Two hundred Bangladeshi children were enrolled. The isotope dilution technique with deuterium oxide was used for estimation of total body water (TBW). FFM estimated by Tanita was compared with results of deuterium oxide dilution technique. Novel prediction equations were created for estimating FFM, using linear regression models, fitting child's height and impedance as predictors. There was a significant difference in FFM and percentage of body fat (BF%) between methods (p<0.01), Tanita underestimating TBW in boys (p=0.001) and underestimating BF% in girls (p<0.001). A basic linear regression model with height and impedance explained 83% of the variance in FFM estimated by deuterium oxide dilution technique. The best-fit equation to predict FFM from linear regression modelling was achieved by adding weight, sex, and age to the basic model, bringing the adjusted R² to 89% (standard error=0.90, p<0.001). These data suggest Tanita analyzer may be a valid field-assessment technique in Bangladeshi children when using population-specific prediction equations, such as the ones developed here.

A Clinical Approach to the Treatment of Chronic Hypernatremia

Hypernatremia is a commonly encountered electrolyte disorder occurring in both the inpatient and outpatient settings. Community-acquired hypernatremia typically occurs at the extremes of age, whereas hospital-acquired hypernatremia affects patients of all age groups. Serum sodium concentration is linked to water homeostasis, which is dependent on the thirst mechanism, arginine vasopressin, and kidney function. Because both hypernatremia and the rate of correction of hypernatremia are associated with significant morbidity and mortality, prompt effective treatment is crucial. Chronic hypernatremia can be classified into 3 broad categories, hypovolemic, euvolemic, and hypervolemic forms, with each form having unique treatment considerations. In this teaching case, we provide a clinically based quantitative approach to the treatment of both hypervolemic and hypovolemic hypernatremia, which occurred in the same patient during the course of a prolonged illness.

Development of bioelectrical impedance analysis-based equations for estimation of body composition in postpartum rural Bangladeshi women

Equations for predicting body composition from bioelectrical impedance analysis (BIA) parameters are age-, sex- and population-specific. Currently there are no equations applicable to women of reproductive age in rural South Asia. Hence, we developed equations for estimating total body water (TBW), fat-free mass (FFM) and fat mass in rural Bangladeshi women using BIA, with ²H₂O dilution as the criterion method. Women of reproductive age, participating in a community-based placebo-controlled trial of vitamin A or β-carotene supplementation, were enrolled at 19·7 (SD 9·3) weeks postpartum in a study to measure body composition by ²H₂O dilution and impedance at 50 kHz using multi-frequency BIA (n 147), and resistance at 50 kHz using single-frequency BIA (n 82). TBW (kg) by ²H2O dilution was used to derive prediction equations for body composition from BIA measures. The prediction equation was applied to resistance measures obtained at 13 weeks postpartum in a larger population of postpartum women (n 1020). TBW, FFM and fat were 22·6 (SD 2·7), 30·9 (SD 3·7) and 10·2 (SD 3·8) kg by ²H₂O dilution. Height²/impedance or height²/resistance and weight provided the best estimate of TBW, with adjusted R² 0·78 and 0·76, and with paired absolute differences in TBW of 0·02 (SD 1·33) and 0·00 (SD 1·28) kg, respectively, between BIA and ²H₂O. In the larger sample, values for TBW, FFM and fat were 23·8, 32·5 and 10·3 kg, respectively. BIA can be an important tool for assessing body composition in women of reproductive age in rural South Asia where poor maternal nutrition is common.

In vivo measurement of body composition of chickens using quantitative magnetic resonance

Quantitative magnetic resonance (QMR) is a nuclear magnetic resonance-based method for measuring the fat, lean, and water content of the total body of the live animal. The purpose of this study was to evaluate the use of QMR for measuring the body composition of chickens while comparing QMR results to those obtained by dual x-ray absorptiometry (DXA) and chemical analysis (CA). A total of 191 birds were scanned live (nonanesthetized) by QMR, killed, and then scanned by DXA. The birds were Ross 708 broiler chickens and ranged in weight from 786 to 3,130 g. In addition, 48 of the carcasses were chemically analyzed for total body lipid, water, and ash content. Compared with CA, QMR underestimated the percentage of total body fat by 34% whereas DXA overestimated the percentage of fat by 50% (10.35 ± 3.35 by CA vs. 6.73 ± 3.90 by QMR and 15.55 ± 4.01 by DXA; P < 0.05). Both QMR and DXA measurements of percentage total body fat were highly correlated with the CA measurement (R(2) = 0.94 and 0.68, respectively). Both QMR and DXA estimates of total body water were close to the CA measurement (1,166 ± 277 g by CA vs. 1,214 ± 279 g by QMR and 1,217 ± 255 g by DXA; P > 0.05), with R(2) values of 0.90 and 0.91, respectively. Based on regression analysis, when prediction equations were applied to the entire group of birds, the QMR and DXA measurements of total body water and total body lean mass were in good agreement, with no significant difference (1,125 ± 244 g vs. 1,135 ± 246 g and 1,377 ± 311 g vs. 1,403 ± 309 g, respectively; P > 0.05) and highly correlated (R(2) = 0.97 for both). Likewise, the QMR measurement of total body fat agreed closely with that measured by DXA (164 ± 48 g and 167 ± 47 g, respectively) and was highly correlated (R(2) = 0.72). The results of this study demonstrate that with proper calibration, both QMR and DXA can provide accurate measurements of the body composition of chickens. The major advantage of the QMR method is that no anesthesia is required, thus facilitating the ease of measurement and repeated measurements.

Validation of bioelectrical impedance analysis for total body water assessment against the deuterium dilution technique in Asian children

To develop and cross-validate bioelectrical impedance analysis (BIA) prediction equations of total body water (TBW) and fat-free mass (FFM) for Asian pre-pubertal children from China, Lebanon, Malaysia, Philippines and Thailand. Height, weight, age, gender, resistance and reactance measured by BIA were collected from 948 Asian children (492 boys and 456 girls) aged 8-10 years from the five countries. The deuterium dilution technique was used as the criterion method for the estimation of TBW and FFM. The BIA equations were developed using stepwise multiple regression analysis and cross-validated using the Bland-Altman approach. The BIA prediction equation for the estimation of TBW was as follows: TBW=0.231 × height(2)/resistance+0.066 × height+0.188 × weight+0.128 × age+0.500 × sex-0.316 × Thais-4.574 (R (2)=88.0%, root mean square error (RMSE)=1.3 kg), and for the estimation of FFM was as follows: FFM=0.299 × height(2)/resistance+0.086 × height+0.245 × weight+0.260 × age+0.901 × sex-0.415 × ethnicity (Thai ethnicity =1, others = 0)-6.952 (R (2)=88.3%, RMSE=1.7 kg). No significant difference between measured and predicted values for the whole cross-validation sample was found. However, the prediction equation for estimation of TBW/FFM tended to overestimate TBW/FFM at lower levels whereas underestimate at higher levels of TBW/FFM. Accuracy of the general equation for TBW and FFM was also valid at each body mass index category. Ethnicity influences the relationship between BIA and body composition in Asian pre-pubertal children. The newly developed BIA prediction equations are valid for use in Asian pre-pubertal children.

Comparison of bioimpedance methods for estimating total body water and intracellular water changes during hemodialysis

The accurate assessment of body fluid volume is important in many clinical situations. Hannan et al. proposed a single-frequency bioimpedance equation (HE) to calculate extracellular water (ECW) and total body water (TBW). There are two equations based on the bioimpedance spectroscopy (BIS) method for the evaluation of body fluid volume: Xitron equations (XE) and body composition spectroscopy equations (BCSE). The aim of the study was to compare the accuracy of these three equations in body fluid volume point estimation in maintenance hemodialysis (MHD) patients. The BIS method was performed in MHD patients before and after a hemodialysis (HD) session. TBW, ECW and intracellular water (ICW) were calculated by XE, BCSE and HE, respectively. Hydration status (HS) was calculated using inputs of XE, BCSE and HE. ICW before dialysis was compared to ICW after dialysis. The change of TBW and HS using different equations was compared to actual ultrafiltration volume (AUV) that was calculated as weight difference of pre- to postdialysis. Fifty MHD patients (27 females) were included in the study. Significant changes in ICW were observed using the XE and HE method with ultrafiltration (XE: 15.51 ± 5.07 versus 16.17 ± 5.34 L, P < 0.01; HE: 17.40 ± 5.13 versus 16.55 ± 4.71 L, P < 0.01). However, no significant ICW change was observed using BCSE (17.47 ± 4.35 versus 17.54 ± 4.36 L, P > 0.05). ΔTBW_XE and ΔTBW_HE were significantly different from AUV (XE 1.76 ± 0.89 versus 2.46 ± 0.89 L, P < 0.01; HE 4.16 ± 1.36 versus 2.46 ± 0.89 L, P < 0.01); however, ΔTBW_BCSE was much closer to AUV (2.27 ± 0.90 versus 2.46 ± 0.89 L, P = 0.129). The change of HS using inputs of BCSE was also closer to AUV (2.41 ± 0.86 versus 2.46 ± 0.89 L, P = 1.0). Our study indicated that BCSE provided a better point estimation of ICW and TBW.

Assessment of body fat in the pony: Part II. Validation of the deuterium oxide dilution technique for the measurement of body fat

Excessive accumulations or depletions of body fat have been associated with increased morbidity and mortality in horses and ponies. An objective, minimally-invasive method to accurately quantify body fat in living animals is required to aid nutritional management and define welfare/performance limits. To compare deuterium oxide (D(2) O) dilution-derived estimates of total body water (TBW) and body fat with values obtained by 'gold standard' proximate analysis and cadaver dissection. D(2) O dilution offers a valid method for the determination of TBW and body fat in equids. Seven mature (mean ± s.e. 13 ± 3 years, 212 ± 14 kg, body condition scores 1.25-7/9), healthy, Welsh Mountain pony mares, destined for euthanasia (for nonresearch purposes) were used. Blood samples were collected before and 4 h after D(2) O (0.11-0.13 g/kg bwt, 99.8 atom percent excess) administration. Plasma was analysed by gas isotope ratio mass spectrometry following filtration and zinc reduction. After euthanasia, white adipose tissue (WAT) mass was recorded before all body tissues were analysed by proximate chemical analyses. D(2) O-derived estimates of TBW and body fat were strongly associated with proximate analysis- and dissection-derived values (all r(2) >0.97, P≤0.0001). Bland-Altman analyses demonstrated good agreements between methods. D(2) O dilution slightly overestimated TBW (0.79%, limits of agreement (LoA) -3.75-2.17%) and underestimated total body lipid (1.78%, LoA -0.59-4.15%) and dissected WAT (0.72%, LoA -2.77-4.21%). This study provides the first validation of the D(2) O dilution method for the minimally-invasive, accurate, repeatable and objective measurement of body water and fat in living equids.

Volaemic assessment of the elderly hyponatraemic patient: reliability of clinical assessment and validation of bioelectrical impedance analysis

Hyponatraemia is the commonest electrolyte disturbance of hospital inpatients. Assessment of volaemic status is an important part of diagnosis and management. To determine reliability of clinical assessment of volaemic state by assessing inter-observer variability of clinical measures of volaemic state. To assess validity of bioelectrical impedance analysis as a tool to measure total body water in elderly hyponatraemic patients. Observational study conducted in a Department of Medicine for the Elderly. Hospital inpatients >65 years old (n=22) with serum sodium concentration <130 mmol/l were included. Two assessors determined volaemic state on two occasions 72 h apart. Level of agreement between observers was determined on each occasion. Total body water estimation was undertaken with bioelectrical impedance analysis and measurement of dilution of deuterium oxide. Correlation between these two measures was then analysed. Cohen's κ for agreement between two observers for overall assessment of volaemic state was 0.59 (P<0.01). Values for agreement between individual clinical markers of volaemic state ranged between 0.16 and 0.45. Pearson correlation coefficient (r) for correlation between estimation of total body water undertaken by bioelectrical impedance analysis and by measurement of dilution of deuterium oxide was 0.69 (P<0.001). There was moderate inter-observer agreement of overall clinical volaemic assessment of elderly hyponatraemic patients. Total body water estimation by bioelectrical impedance analysis correlates well with estimation by measurement of dilution of deuterium oxide, providing a potentially useful tool to improve the management of the elderly hyponatraemic patient.

Reproducibility and validity of bioimpedance spectroscopy for tracking changes in total body water: implications for repeated measurements

Bioimpedance spectroscopy (BIS) has been used to track changes in total body water (TBW). Accurate TBW estimations can be influenced by both methodological and biological factors. One methodological variation that contributes to BIS TBW errors is the electrode placement. The purpose of the present study was to compare the reproducibility and validity of fixed-distance electrode placements (5cm) with the standard single-site electrode placements. Twenty-nine subjects (fifteen men and fourteen women) participated in the reproducibility study, while sixty-nine subjects (thirty-three men and thirty-six women) participated in the validity study. The reproducibility study included two measurements that were taken 24h apart, while the validity study consisted of a 12-week exercise intervention with measurements taken at weeks 1 and 12. TBW was estimated using BIS and 2H techniques. Reproducibility results indicated that fixed-distance electrodes reduced the day-to-day standard error of the measurement in men (from 1·13 to 0·81litres) but not in women (0·47litres). sem values were lower for women than for men, suggesting that BIS TBW estimates are sex dependent. Validity results produced similar accurate findings (mean difference<0·21litres). However, fixed-distance electrodes improved delta TBW errors (mean difference improvements>0·04litres in men, women, and men and women combined). When tracking changes in TBW, fixed-distance electrodes may reduce reproducibility errors and allow for smaller changes to be detected. However, the reduction of reproducibility errors may be greater for men than for women. Therefore, reproducibility calculations should be based on the sex of the sample population.

Estimates of Body Composition in Drug Naïve Asymptomatic HIV‐infected Rural Kenyan Women

ObjectiveBioelectrical impedance analysis (BIA), as a method to estimate fat free mass (FFM) and % body fat (%BF), is compared to the anthropometric (Anthro) method using skinfold (SF) and body circumference (BC) measures in HIV‐infected women in rural Kenya.MethodsIn 138 women, (WHO Stage 1 or 2; CD4 &gt; 250 cells/uL), height, weight, SF, BC and BIA were obtained with standardized procedures. Fat area of the arm (MAFA), muscle area of the arm (MAMA), thigh (MTMA), calf (MCMA) and sum of SF were calculated from standard equations using BC and SF. Estimates of FFM, %BF and total body water (TBW) from BIA measures of resistance were calculated with standard equations.ResultsThe mean (SD) for age, BMI and CD4 was 36.4(7.5) yrs, 22.3(3.6); 11% &lt; 18.5, and 492(191) cells/uL, respectively. Anthro compared to BIA for estimates of lean and fat mass Anthro MAMA MTMA MCMA MAMA MAFA Sum SF BIA FFM FFM FFM TBW %BF %BF __ r 0.61 0.70 0.71 0.65 0.84 0.87 __ All correlations p&lt;0.001 ConclusionsBIA, when compared to the method using anthropometry measures, has a strong relationship to fat and lean mass, at baseline, in drug naïve asymptomatic HIV‐infected rural Kenyan women enrolled in an 18 month randomized controlled field trial that measures the impact of added protein and energy on body composition. Supported in part by USAID Grant No. PCE‐G‐00‐98‐00036‐00 and 1R01HD57646‐01A1 (CFDA #93.865)

Increased fluid intake does not augment capacity to lay down new collagen in nursing home residents at risk for pressure ulcers: A randomized, controlled clinical trial

Prevention of pressure ulcers is fundamental to safe care of nursing home residents yet the role of hydration in pressure ulcer prevention has not been systematically examined. This randomized clinical trial was undertaken to determine whether administration of supplemental fluid to nursing home residents at risk for pressure ulcers would enhance collagen deposition, increase estimated total body water, augment subcutaneous tissue oxygenation, and was safe. After a baseline period, 64 subjects were randomized to receive the fluid volume prescribed or additional fluid (prescribed plus 10 mL/kg) for 5 days. Participants' potential to heal as measured with hydroxyproline was low at baseline and did not increase significantly during treatment when additional fluid was systematically provided. Fluid intake increased significantly during treatment. Estimates of total body water and subcutaneous oxygen did not increase, indicating hydration was not improved. Supplemental fluid did not result in overhydration as measured by clinical parameters. Further work is needed to examine the relationship between fluid intake and hydration in nursing home residents as well as the role of hydration in pressure ulcer prevention.

Total Body Water Measurements in Adolescent Athletes: A Comparison of Six Field Methods With Deuterium Dilution

-Assessing hydration, that is, total body water (TBW) in adolescent athletes should be part of a comprehensive training program. However, there are no specific methods to assess TBW in young athletes. Moreover, the use of traditional techniques developed in healthy youths, based on a 2-compartment model, may yield inaccurate TBW estimates in young athletes. Therefore, the purpose of this study was to assess the accuracy of TBW non-reference field methods with a criterion method (i.e., deuterium dilution) in 118 adolescent athletes. Body volume was assessed by air displacement plethysmography, bone mineral was measured by dual-energy X-ray absorptiometry, and TBW by deuterium dilution. Non-reference TBW methods included 2 bioelectrical impedance analysis techniques (Tanita Body Composition Analyzer, model TBF-310) and bioelectrical impedance spectroscopy (BIS) (model 4000B); the Lohman's hydration constants of fat-free mass (FFM); and 3 derived anthropometric equations developed, respectively, by Kushner et al., Wells et al., and Morgenstern et al. The highest accuracy between TBW estimates and the reference model in both girls and boys was observed using the Lohman's constants (r2= 0.94, SEE = 1.56 kg; r2 = 0.92, SEE = 2.42 kg, respectively; p < 0.001), followed by both foot-to-foot Tanita (r2 = 0.88, SEE = 2.15 kg; r2 = 0.87, SEE = 3.01 kg, respectively; p < 0.001) and BIS (r2 = 0.92, SEE = 1.70 kg; r2 = 0.87, SEE = 3.04 kg, respectively; p < 0.001) with slopes and intercepts not significantly different from the line of identity. The regressions between anthropometric equations and the criterion method deviated from the line of identity (p < 0.05). The practical application of this study is that the specific constants of FFM hydration developed by Lohman seem to accurately estimate TBW in adolescent athletes. Foot-to-foot Tanita and BIS were also found to be valid and non-biased tools for predicting TBW. It would appear that the 3 anthropometric equations used are not appropriate for young athletes.

Total body water changes after an exercise intervention tracked using bioimpedance spectroscopy: A deuterium oxide comparison

Bioimpedance spectroscopy (BIS) for the estimation of total body water (TBW) has advantages over isotope dilution techniques, including cost, portability, and ease of use. The aim of the current study was to determine the validity of a BIS device (Imp SFB7) for tracking changes in overfat and obese individuals. Sixty overfat and obese men and women (27+/-8 yr, 33.41+/-3.81%fat) participated in the study. TBW was estimated using BIS and deuterium oxide (D(2)O) before and after the ten-week intervention. Pre-and post-intervention BIS TBW estimations errors increased as body mass index (BMI), fat mass (FM), and fat-free mass (FFM) increased (p<0.05). Delta values were more accurate than pre- and post-TBW estimations (total error=1.45 L). Age significantly influenced pre- and post-TBW errors (p<0.05). Therefore, a regression equation was developed to correct for the pre- and post-BIS-estimated TBW errors: D(2)O TBW=11.478+0.743(BIS TBW)-2.429(Gender), (Men=1, Women=2). BIS can be considered an accurate tool for tracking changes in TBW regardless of variations in BMI, FM, FFM, or age in both overfat and obese men and women (BMI>24). Employing a BIS TBW equation is suggested over the development of resistivity coefficients based on BMI, FM, FFM or age.

Cardiac Interbeat Intervals To Assess Combat Readiness.

PURPOSE: Chronic fatigue/physical exhaustion (FPE) impacts combat readiness but is difficult to identify. We tested the hypothesis that resting cardiac interbeat intervals, including both time- and frequency-domain assessments of heart rate variability (HRV), would correlate with hydration status and aerobic capacity in military recruit-age men and women with varying fitness levels. METHODS: Cardiac interbeat intervals were recorded using a Polar R-R monitor during 20 minutes of quiet, supine rest with paced breathing (0.25 Hz). HRV metrics included: R-R intervals (RRI); R-R interval standard deviation (RRISD); the percentage of adjacent R-R intervals varying by ≥ 50 ms (pNN50); and integrated areas of R-R interval spectral power at the high (0.15 - 0.4 Hz; RRIHF) and low (0.04 - 0.15 Hz; RRILF) frequencies. Treadmill VO2 peak; segmental bioimpedance estimates of total body water (TBW); and urine specific gravity (USG) were also assessed. RESULTS: All dependent variables of interest were within expected ranges, although absolute ranges of individual values were considerable. RRI correlated with VO2 peak (r = 0.49; p < 0.001), TBW (r = 0.38; p < 0.001) and inversely with USG (r = -0.23; p = 0.02). RRISD correlated with VO2 peak (r = 0.21; p = 0.03), but not with TBW or USG. pNN50 correlated inversely with urine specific gravity (r = -0.21; p = 0.03) but not VO2 peak or TBW. R-R interval spectral power at the high and low frequencies correlated poorly with VO2 peak, TBW, and USG. CONCLUSIONS: These results provide direction as to how fitness level and hydration status may affect cardiac function via changes in autonomic tone, highlighting the potential utility of applying field-based assessment of various interbeat interval metrics to identify FPE and other aspects of combat readiness.

Heart Rate Variability to Assess Combat Readiness

Chronic fatigue/physical exhaustion (FPE) impacts combat readiness but is difficult to identify. We tested the hypothesis that resting heart rate variability (HRV), including both time- and frequency-domain assessments, would correlate with hydration status and aerobic capacity in military recruit-age men and women with varying fitness levels. Cardiac interbeat intervals were recorded using a heart R-R monitor during 20 minutes of quiet, supine rest with paced breathing (0.25 Hz). HRV metrics included average R-R interval (RRIavg), R-R interval standard deviation (RRISD), the percentage of adjacent R-R intervals varying by > or = 50 ms (pNN50), and integrated areas of R-R interval spectral power at the high (0.15-0.4 Hz) (RRIHF) and low (0.04-0.15 Hz) (RRILF) frequencies. Treadmill maximal oxygen uptake (VO2 max), segmental bioimpedance estimates of total body water (TBW), and urine specific gravity (USG) were also assessed. All dependent variables of interest were within expected ranges, although absolute ranges of individual values were considerable. RRI correlated with VO2 max (r = 0.49; p < 0.001), with TBW (r = 0.38; p < 0.001), and inversely with USG (r = -0.23; p = 0.02). RRISD correlated with VO2 max (r = 0.21; p = 0.03), but not with TBW or USG. pNN50 correlated inversely with USG (r = -0.21; p = 0.03) but not with VO2 max or TBW. R-R interval spectral power at the high and low frequencies did not correlate with VO2 max, TBW, or USG. We have demonstrated that fitness level and hydration status may affect cardiac function via changes in autonomic tone, highlighting the potential of field-based assessment of heart rate variability metrics to identify FPE and other aspects of combat readiness.