Comparison of Supine and Vertical Bioimpedance Measurements in Young Adults

Topics in Exercise Science and Kinesiology Volume 3: Issue 1, Article 11, 2022. Bioelectrical impedance analysis (BIA) methods estimate health parameters such as phase angle (PhA) and body fat percentage (%BF) from various positional and electrode configurations. PhA and %BF are known biological markers of cellular and physical health, respectively, and can be used to predict various health-related conditions and therefore require accurate assessment. The purpose of this study was to evaluate the effect of body position during BIA by investigating the difference and agreement between PhA and %BF using RJL (supine) and InBody (vertical) analyzers. Thirty-eight young adults (23.4±4.1 yrs.) volunteered and underwent body composition assessments by both analyzers. Difference and agreement in assessments of PhA and %BF between analyzers were assessed using paired samples t-tests and Lin’s concordance correlation coefficient (rc), respectively. RJL’s PhA (7.15±0.84°) exceeded InBody’s (6.11±0.74°), p\u3c0.001, and had poor agreement (rc =0.47). RJL’s %BF (23.0±6.8%) was similar to InBody’s (23.1±7.4%), p=0.813, and had substantial agreement (rc =0.95). Both analyzers estimated %BF similarly and may be interchangeable for this purpose, thus demonstrating no effect of body position on the estimation of %BF with these BIA devices. An individual\u27s PhA may be underestimated if measured in the vertical position and compared to supine reference values. Current reference values for PhA are based on measurements in the supine position, so until vertical reference values of PhA are available, caution is urged when interpreting PhA from vertical BIA assessments

Time Course of Supine Assessment of Bioelectrical Variables: An Evaluation of Resistance, Reactance, and Phase Angle

To minimize the effect of shifts in bodily water compartments, assessments of resistance (R) and reactance (Xc) via bioelectrical impedance analysis (BIA) is recommended to occur after the individual has been supine for 15 minutes. While changes in bodily water compartments within 15 minutes of laying in the supine position may affect values for R and Xc, it’s unknown how these body water shifts affect phase angle (PhA). PURPOSE: Investigate the effect of time for stabilization of supine measurements of R, Xc, and PhA obtained via the RJL Quantum Legacy BIA analyzer. METHODS: Thirty-eight men (n=16) and women (n=22) were deemed hydrated (urine specific gravity ≤1.020) and were prepped for standard tetrapolar electrode placement. In the supine position, R, Xc, and PhA at 50kHz were measured on the right side of the body immediately after laying down (baseline) and every 5 minutes for 15 minutes. Participants remained motionless throughout the duration of the test. Separate one-way repeated measures ANOVA were used to assess the effect of time on R, Xc, and PhA. For repeated measures ANOVA comparisons, generalized eta squared (η2G)was reported to quantify the observed effect size, where small = .01; medium = .06; large = .14. An alpha of .05 was used to determine statistical significance. RESULTS: There was a small but significant effect of time on R, F(1.76, 65.16) = 74.091, p \u3c .001, η2G \u3c .001. Average values for R increased from 553.2 ± 90.1Ω at baseline to 560.4 ± 93.3Ω post-15 minutes. A small but significant effect for time on Xc was also observed, F(1.34, 46.01) = 20.958, p \u3c .001 η2G = .004. Average values for Xc increased from 68.2 ± 7.8Ω at baseline to 69.6 ± 8.1Ω post-15 minutes. Laying in the supine position for 15 minutes had no significant effect on PhA, F(1.2, 44.51) = 3.401, p = .065, η2G \u3c .001. Average PhA values went from 7.13 ± .90° at baseline to 7.18 ± .86° post-15 minutes. CONCLUSION: While time to allow for bodily water compartment stabilization has a small but significant effect on R and Xc, this study demonstrates that PhA is likely unaffected. PhA can be accurately assessed immediately upon assuming the supine position without allowing for bodily water compartment stabilization via the RJL Quantum Legacy

A Comparison of Multiple Body Composition Measurement Methods to the Department of Defense’s Physical Fitness and Body Fat Program Procedures

INTRODUCTION: The Department of Defense (DoD) developed body composition standards that require service personnel to meet sex- and branch-specific body mass index criteria. Failing to meet these criteria leads to body fat percentage (%BF) estimation via the DoD’s circumference method. Service members exceeding these standards face administrative action and a possible premature discharge, thus emphasizing the importance of accurately estimating %BF with this method. PURPOSE: To compare the predictive accuracy of the DoD’s circumference-based equation to estimate %BF compared to hydrostatic weighting (HW); segmental and whole-body bioelectrical impedance analyses (BIA), and sex-specific skinfold thickness assessments. METHODS: Physically active men (n = 35, 25 ± 4.7 yrs, 79.6 ± 21 kg, 176.3 ± 6.7 cm) and women (n = 34, 24.7 ± 5.1 yrs, 63.6 ± 8.6 kg, 166.0 ± 7.3 cm) participated. Population-specific equations were used to compute body density (Db) from ΣSKF and HW and to convert Db to %BF. Sex-specific repeated measures ANOVAs with Bonferroni’s multiple comparisons tests were applied. Agreement between the DoD and the other %BF results were quantified via Bland-Altman 95% limits-of-agreement plots. Statistical significance was set at p\u3c.05. RESULTS: The DoD method predicted a significantly (p\u3c.05) higher %BF (27.1 ± 6.3%) compared to upper body BIA (23.1 ± 4.9%) and SKF (21.9 ± 4.8%) for the women only. For men, the DoD method estimated a significantly lower (p\u3c.05) %BF (12.9 ± 5.5%) compared to lower body BIA (17.5 ± 5.7%). Wide limits-of-agreement (\u3e ±3.5 %BF) for mean differences in %BF were observed between the DoD method and all assessments for both men and women. CONCLUSION: Our findings suggest that at the group level, the DoD’s current method of assessing %BF produces similar values compared to whole-body vertical BIA and HW. However, DoD estimates of %BF at the individual level lack predictive accuracy given the wide limits-of-agreement. Since the DoD method is applied at the individual level, caution is needed when determining if administrative action is necessary

Comparison of Whole-Body Phase Angle Assessed by Supine and Vertical Bioelectrical Impedance Analyzers

Several bioelectrical impedance analysis (BIA) analyzers such as the RJL Quantum Legacy and the InBody 770 measure phase angle (PhA, marker of cellular health) in addition to estimating body fat percentage (%BF). These analyzers require the participant to be supine or vertical, respectively, during the assessment and use different electrode configurations, both of which may affect the measurement of PhA and %BF. PURPOSE: Investigate the difference and agreement between PhA and %BF assessed by the RJL and InBody analyzers. METHODS: Thirty-eight young (18-38 yrs.), hydrated (urine specific gravity ≤1.020) adults (16 men; 22 women) stood for 15 minutes to allow for body water compartment stabilization prior to undergoing PhA and %BF assessment by the InBody. Participants then laid in the supine position for 15 minutes prior to having resistance, reactance, and PhA assessed on the right side of their body via the RJL analyzer. Resistance and reactance values were used in prediction equations provided by the RJL’s BC4 software to estimate %BF. Paired samples t-tests were used to determine differences in PhA and %BF between the two analyzers. Agreement between the analyzers for assessing PhA and %BF was quantified via Bland-Altman 95% limits-of-agreement (LoA) plots. Acceptable LoA for %BF and PhA were determined to be less than ±3.5% and ±1.0°, respectively. Cohen’s d was used to represent effect size, where small = .2; medium = .5; large = .8. Statistical significance was set at α \u3c .05. RESULTS: PhA was significantly greater using the RJL (7.15 ± 0.84°) compared to the InBody (6.11 ± 0.74°), p ≤ .001; d = 2.47. The LoA for bias in PhA between devices (RJL - InBody) was 1.04 ± .42°, indicating poor agreement at the individual level. No significant difference was observed for %BF estimated between the RJL (23.0 ± 6.8%) and the InBody (23.1 ± 7.4%), p = .813; d = .04. The LoA for bias in %BF between devices (RJL - InBody) was -.09 ± 2.5%, indicating good agreement at the individual level. CONCLUSION: Both analyzers estimated %BF similarly, suggesting they are interchangeable for this purpose. An individual’s PhA may be misclassified if measured in the vertical position and compared to supine reference values. Until vertical reference values of PhA are available, caution is urged when interpreting PhA from vertical BIA assessments

Evaluating the Effect of Electrode Placement on Phase Angle and Body Fat Percentage via the RJL Quantum Legacy Device

To obtain the highest values for resistance (R) and reactance (Xc) during bioelectrical impedance analysis (BIA) it’s recommended to measure on the right side of the body. Less is known if this relationship is true for phase angle (PhA) or when these variables are measured with the RJL Quantum Legacy device. PURPOSE: Evaluate the reliability, difference, and bias between bioelectrical impedance variables assessed on the left and right side of the body by the RJL Quantum Legacy device. METHODS: Thirty-eight young (18-38 yrs.), hydrated (urine specific gravity ≤1.020), men (n=16) and women (n=22) laid in the supine position for 15 minutes to allow for bodily water compartment stabilization prior to having three measurements of R, Xc, and PhA at 50 kHz on the left and right sides of their body. Paired samples t-tests were used to determine side differences in R, Xc, and PhA on both sides of the body. Cronbach’s alpha reliability coefficient was used to evaluate the internal consistency of the device. Systematic bias between sides for PhA was quantified via Bland-Altman plots with linear regression analysis. Alpha of .05 was used to determine statistical significance. RESULTS: No significant differences were observed for R (564.7 ± 94.5Ω, 562.1 ± 92.3Ω; p=.407), Xc (68.9 ± 7.4Ω, 69.4 ± 8.0Ω; p=.143), or PhA (7.09 ± .94°, 7.15 ± .84°; p=.083) when measured on the left and right sides, respectively. Cronbach’s alpha showed that the RJL device had excellent internal consistency across the three assessments on both sides for the measurement of R (.999), Xc (.998), and PhA (.998). A systematic bias between sides for PhA was identified so that values on the right side was significantly lower than on the left when PhA was greater than 6.50° (p=.006). CONCLUSION: It’s recommended that R, Xc, and PhA are measured on the right side of the body, but we observed no difference and excellent reliability between these variables when assessed on either side. Only measuring PhA on the right side may underestimate and ultimately misclassify individuals with greater PhA values. We recommend measuring on the left side to confirm that the highest PhA is being represented for individuals with a PhA ≥6.50°. While we observed a statistically significant bias, more research is warranted to determine whether this relationship is of clinical importance

Worth the wait? Time course of supine shifts in body water compartments on variables of bioelectrical impedance analysis

Bioelectrical impedance analysis (BIA) reference values are based on supine assessments. Little is known regarding the effects of time course shifts in body water compartments after assuming a supine position. The aim of this study was to characterize these effects and provide recommendations regarding the optimal waiting time to perform BIA. Thirty-eight healthy adults underwent BIA via the RJL Quantum Legacy analyzer immediately upon lying down and every 5 minutes for 15 minutes. Differences in resistance (R), reactance (Xc), intracellular (ICW), extracellular (ECW), total body water (TBW), body fat percentage (%BF), and phase angle (PhA) were assessed. There were small but significant increases in R, Xc, and %BF (all p<0.001), as well as small but significant decreases in ICW, ECW, and TBW (all p<0.001) over 15 minutes. No difference was observed for PhA (p=0.065). Average values changed over 15 minutes by +7.14Ω, +1.36Ω, -0.2L, -0.2L, -0.4L, +0.05° and +0.1% for R, Xc, ICW, ECW, TBW, PhA and %BF, respectively. BIA measurements are affected by shifts in body water compartments after assuming a supine position, but these differences lack clinical significance in healthy adults. Technicians working with healthy adults can perform BIA within 15 minutes after participants assume a supine position