Agreement and reproducibility of a portable electrical impedance myography device for body fat percentage estimation in normal weight men and women

Concordância e reprodutibilidade de um dispositivo portátil de miografia por impedância elétrica para estimativa do percentual de gordura corporal em homens e mulheres com peso normal

Abstract

The aim of this study was to investigate the agreement and reproducibility of a portable electrical impedance myography device (EIM - SKULPT^®) for body fat percentage (BF%) estimation in young adults. Sixty young adults volunteered for the study (women, n=30, 25.0±7.7 years; 21.5±1.9 kg/m²; and men, n=30, 21.6±6.3 years; 22.5±1.8 kg/m²). Participants underwent air displacement plethysmography (ADP) and EIM measurements for agreement analysis. EIM was performed three times on the same day for the within-day reproducibility analysis. Seven days later, 37 participants repeated the EIM measurements for the between-days reproducibility analysis. Comparisons of EIM and ADP methods, and EIM repeated measurements were performed with the paired T-test or one-way ANOVA repeated measures, the Bland-Altman plot, and simple linear regressions. BF% was higher (p<0.05) when estimated by EIM (19.91 ± 5.70 for men, and 30.77 ± 5.89 for women) compared to ADP (15.28 ± 5.66 for men, and 27.31 ± 5.98 for women). The Bland-Altman analysis presented a bias of 4.4% (95%CI=-3.4–12.2) and linear regression presented an R²=0.78. For between-days reproducibility, EIM means did not differ (25.33±7.69 and 24.94±8.30, p=0.890). Thus, while the EIM device exhibited high reproducibility of BF% estimates, caution should be exercised when comparing the results with other techniques for measuring BF%. The EIM device overestimated BF% compared to ADP. However, the EIM measurements presented very good within-day and between-days reproducibility and, thus, the EIM device can be used for longitudinal monitoring of BF%.

Key words:
Body composition; Electric impedance; Physical examination

Resumo

O objetivo deste estudo foi investigar a concordância e a reprodutibilidade de um aparelho portátil de miografia por impedância elétrica (EIM - SKULPT®) para estimativa do percentual de gordura corporal (GC%) em adultos jovens. Sessenta adultos jovens foram voluntários para o estudo (mulheres, n=30, 25,0±7,7 anos; 21,5±1,9 kg/m2; e homens, n=30, 21,6±6,3 anos; 22,5±1,8 kg/m2). Os participantes fizeram medições de pletismografia de deslocamento de ar (ADP) e EIM para análise de concordância. A EIM foi realizada três vezes no mesmo dia para a análise de reprodutibilidade dentro do dia. Sete dias depois, 37 participantes repetiram as medições do EIM para a análise de reprodutibilidade entre dias. As comparações dos métodos EIM e ADP e medições repetidas do EIM foram realizadas com o teste T pareado ou medidas repetidas ANOVA de uma via, o gráfico de Bland-Altman e regressões lineares simples. O %GC foi maior (p<0,05) quando estimado pelo EIM (19,91 ± 5,70 para homens e 30,77 ± 5,89 para mulheres) em relação ao ADP (15,28 ± 5,66 para homens e 27,31 ± 5,98 para mulheres). A análise de Bland-Altman apresentou viés de 4,4% (IC95%=-3,4–12,2) e a regressão linear apresentou R2=0,78. Para a reprodutibilidade entre dias, as médias do EIM não diferiram (25,33±7,69 e 24,94±8,30, p=0,890). Assim, enquanto o dispositivo EIM exibiu alta reprodutibilidade das estimativas de %GC, deve-se ter cautela ao comparar os resultados com outras técnicas para medir %GC. O dispositivo EIM superestimou %GC em comparação com ADP. No entanto, as medidas de EIM apresentaram reprodutibilidade intradia e entre dias muito boa e, portanto, o dispositivo de EIM pode ser usado para monitoramento longitudinal de %GC.

Palavras-chave:
Composição corporal; Impedância elétrica; Exame físico

INTRODUCTION

According to the World Health Organization¹, obesity has tripled since 1975 in medium and high income countries. Among the obesity-related diseases, type 2 diabetes, cardiovascular diseases, stroke, and some types of cancer can be highlighted². Because of the increase in the population with obesity, public health expenses have increased year by year, causing a burden to health systems all over the world³. The proper treatment or prevention of overweight or obesity requires an early diagnosis. In this sense, there is an evident need for low cost and portable methods, that provide accurate and reliable measurements for body fat estimation, which could be adopted in clinical practice⁴.

Body fat percentage is typically estimated using different methods, among them, hydrostatic weighing, air displacement plethysmography (ADP), dual energy X-ray absorptiometry (DXA), computed tomography, and magnetic resonance imaging⁵. Regarding the precise and reliable indirect methods for analyzing body composition, ADP stands out for being a quick and easy technique that uses the inverse relationship between pressure (p) and volume (v), based on Boyle's Law (P1V1 = P2V2) to determine body volume⁶. However, although these methods can provide valid estimates of body fat for different populations⁷, they are usually high cost and present low portability, which can limit their application in clinical practice.

In recent years, many clinical practice methods have been developed based on indirect techniques, denominated doubly indirect evaluations. Among these techniques, bioelectrical impedance (BIA) stands out, for being a safe, low-cost, fast, and non-invasive method that provides body composition, nutritional status, health, and cell integrity estimates(8). In addition, BIA has been shown to be useful in clinical practice for body fat percentage (BF%) estimation. BIA provides raw parameters such as impedance (Z), resistance (R), and reactance (Xc) and parameters derived from the relationship between R and Xc, such as phase angle (PA) and bioimpedance vector analysis (BIVA), in addition to presenting estimates of BF% through regression equations⁸. Associated with BIA, another method of analyzing body composition is electrical impedance myography (EIM), which is a non-invasive and highly reproducible emerging electrophysiological technique that objectively characterizes body structure and composition, measured through bioimpedance⁹. In this technique, the relationship and normalization of voltage and current amplitudes and phase delays provide a simple approach to measuring impedance magnitude and phase angle¹⁰.

Currently, there are several types of BIA and EIM devices available on the commercial market, classified according to the number of electrodes, the position in which they are placed, the region of the body submitted to the examination, and the type of frequency used¹¹. A relatively new EIM device, the SKULPT CHISEL® scanner (Skulpt Inc., San Francisco, CA), is a portable electrical impedance myography (EIM) device that works in a similar way to bioimpedance analysis (BIA). Both EIM and BIA use impedance, which is derived from resistance and reactance¹² .The SKULPT® was developed as a portable EIM device, to assess total and regional body fat percentages, in addition to muscle quality (i.e., measurement of muscle in relation to its size). According to the manufacturer, the device has 12 electrodes and demonstrates some important characteristics (electric current can be applied in a range of frequencies and it also flows more easily along muscle fibers than through them)¹³.

Previous studies that compared body fat obtained by BIA and other reference methods, such as ADP, showed that despite the small differences between methods, BIA seems to be a valid method to estimate body fat¹⁴,¹⁵. Although the manufacturer reports that EIM has an accuracy of 1 - 2% for body fat when compared with DXA, its accuracy and reliability were recently tested, and the authors reported no differences for BF% estimates between DXA and EIM in healthy young individuals, concluding that EIM could be an acceptable method for use in adult men and women¹². In addition, another study showed that although DXA and ADP estimates demonstrated strong agreement with the four-component model, the ADP estimates showed a smaller error than the DXA estimates¹⁶. In this sense, comparing the estimates of BF% from a new BIA device (i.e., EIM) with the ADP method could be useful for providing health professionals with information on the degree of agreement of these techniques. Thus, the current study aimed to compare the BF% estimates obtained by EIM and ADP in men and women. As a secondary outcome, we tested the within- and between-days reliability of the EIM device. It was hypothesized that EIM would present good agreement and reproducibility for BF% compared to the ADP method.

METHODS

Experimental approach to the problem

The body composition of 60 young adults with a normal body mass index was assessed using electrical impedance myography (EIM) and ADP. The% BF values verified by the EIM were compared against the ADP reference method. Furthermore, the within and between days reliability of the EIM device were tested, and these data were used to verify if there is good agreement and reproducibility between the EIM and ADP methods.

Participants

Sixty healthy young adults were included in the present study (Women, n = 30, 25.0±7.7 years, 57.8±6.4 kg, 1.62±5 m, 21.5±1.9 kg/m2; and Men, n = 30, 21.6±6.3 years, 69.1±8.0 kg, 1.73±6 m, 22.5±1.8 kg/m2); a mean of three measures was adopted for height (ICC=0.97). All participants (n = 60) were included in the agreement and within-day reproducibility, and 37 in the between-days reproducibility procedures (men=18, 23.7±6.5 years, 62.7±10.1 kg, 1.66±8.3 m, 22.3±1.9 kg/m2). To be included, participants were required to be aged between 18 and 45 years and have a BMI between 18 and 24.9 kg/m2, classified as normal weight¹. Participants with physical impairment, claustrophobia, or any diagnosed disease that would prevent the correct testing procedures were excluded.

Procedures

Participants reported to the laboratory for two visits, in the morning (between 8 a.m. and 12 a.m.), seven days apart. On both visits, body mass was assessed with a digital scale (Tanita Inc., Arlington Heights, IL, USA), height with a stadiometer (SECA^®, São Paulo, Brazil), and body fat percentage with Air Displacement Plethysmography (BODPOD, Body Composition System; Life Measurement Instruments, Concord, CA, USA). This measurement was considered the reference value for the agreement analysis, and was taken with a portable electrical impedance myography device (EIM - SKULPT^®, San Francisco, USA). Participants were requested to avoid food and water consumption for two hours before the body composition measurements, as recommended in the Bod Pod Operator’s manual, and avoid smoking, drinking alcohol, using body-hydrating lotion on the skin, and practicing physical exercise for 24 h before the measurements.

Electrical impedance myography

The EIM device provides limited information about the electrical current frequency and respective algorithms adopted to calculate the body fat percentage. According to the manufacturer, the device emits an electrical current with different frequencies, directions, and depths. Thereafter, an application on a smartphone, connected to the device, provides information regarding the body fat percentage. A quick start option within the application suggests a single measure on the arm, trunk, and thigh, as presented in Figure 1. To address reproducibility, three measurements were conducted on the respective body regions, with a 3 min interval between them. The participant remained in a sitting position during the between-measurements interval. The mean value of the 3 measurements was adopted for the agreement and between-days reproducibility statistics.

Figure 1
Electrical impedance myography positioning. (A) Arm; (B) Trunk; and (C) Thigh.

Air displacement plethysmograph

All participants were evaluated for body fat percentage by ADP. The evaluation was performed according to the manufacturer’s instructions. The ADP device was calibrated through the computation of the ratio of the pressure for an empty chamber and a known volume (56.056 l). The scale attached to the device was also calibrated using a known reference (20kg). After receiving an explanation about the procedures, the participants entered the ADP wearing minimal clothing. A swimming cap was used to decrease hair volume and metal objects on the body were prohibited (for example, earrings, rings, piercings, and so on). The participants remained seated inside the device and at each step of the ADP evaluation the door was opened. The test lasted an average of 4 min. During this phase, the participant’s raw body volume was determined according to Boyle’s law. Because of the difficulty in assessing the pulmonary volume of the participants’, predicted values were used. This procedure did not affect the estimation of body composition¹⁷. The body density was determined by range of pressure and volume. Finally, BF% was calculated using the Siri equation¹⁸. The Siri equation is based on the two-compartment model (fat mass and fat-free mass) and ADP is a densitometry method that is also based on the two- compartment model. In addition, when compared to other equations, the Siri equation presents similar estimates¹⁹.

Statistical analyses

All descriptive results are presented as mean ± standard deviation. The Shapiro Wilk and Levene tests were conducted for normality and homogeneity testing, respectively. For agreement assessment, the following tests were conducted: a) paired T-test between body fat percentage obtained by ADP and EIM on the same day; b) Bland-Altman plot for agreement analysis between ADP and BIA results; c) simple linear regressions to verify how much the result of the dependent variable (ADP) was explained by the independent variable (EIM); and d) intraclass correlation coefficients (ICC) and typical error, as a percentage of the coefficient of variation (%CV), were calculated between methods²⁰. For the between-days reproducibility assessment, the paired t-test, ICC, and % CV were adopted between the repeated measurements for the EIM. For the within-day reproducibility assessment, one-way ANOVA repeated measures, ICC, and % CV were adopted between the three repeated measurements for the EIM performed on the same day. The SPSS Statistical Software package (version 25.0) and Graph Pad Prism (version 6.0) were used to analyze all data.

RESULTS

Agreement

Body fat (%) results measured by EIM were higher than the ADP results for all participants (p<0.001), women (p<0.004), and men (p<0.001) (Table 1). The Bland-Altman plot confirmed that EIM overestimated body fat (%) compared to ADP for all participants (4.4%), women (4.1%), and men (4.6%) (Figure 2). The linear regression indicated that EIM explained 78%, 52%, and 62% of the variance in the ADP results, for all participants, women, and men, respectively (Figure 2).

Table 1
Body fat (%) comparison between electrical impedance myography and air displacement plethysmography (validity), between electrical impedance myography in day 1 and 2 (between-days reproducibility), and between electrical impedance myography measures 1, 2, and 3 at day 1.

Agreement
	All (n = 60)	Men (n = 30)	Women (n = 30)
EIM (%)	25.34 ± 7.94	19.91 ± 5.70	30.77 ± 5.89
ADP (%)	21.30 ± 8.38	15.28 ± 5.66	27.31 ± 5.98
T-Test p-value	<0.001	<0.001	0.004
Between-days reproducibility
	All (n = 37)	Men (n = 18)	Women (n = 19)
EIM day 1 (%)	25.33 ± 7.69	19.97 ± 6.05	30.40 ± 5.62
EIM day 2 (%)	24.94 ± 8.30	18.86 ± 5.99	30.69 ± 5.64
T-Test p-value	0.54	0.33	0.64
ICC	0.890	0.716	0.887
TE as CV (%)	6.8	6.7	6.9
Within-day reproducibility
	All (n = 60)	Men (n = 30)	Women (n = 30)
EIM1	25.26 ± 8.24	19.99 ± 5.66	30.53 ± 6.93
EIM2	25.49 ± 8.05	20.16 ± 5.79	30.82 ± 6.25
EIM3	25.28 ± 8.05	19.59 ± 5.90	30.98 ± 5.45
One-way ANOVA p-value	0.845	0.452	0.830
ICC	0.926	0.923	0.824
TE as CV (%)	8.9	6.9	10.7

• Note. Descriptive statistics are presented as mean and standard deviation. EIM: electrical impedance myography; ADP: air displacement plethysmography; ICC: Intraclass correlation coefficient; TE as CV: typical error as coefficient of variation.

Figure 2
Bland-Altman plots and simple linear regression between ADP and EIM measurements of body fat (%), for all participants (A and B), women (C and D), and men (E and F). Dotted lines in the colored area of the Bland-Altman plots depict mean bias and 95% confidence interval. EIM: electrical impedance myography; ADP: air displacement plethysmography.

Within and between-days reproducibility

There was no difference in body fat (%) for EIM measured on days 1 and 2 (between-days reproducibility). A good ICC for all participants (n = 37) and women (n = 19), and a moderate ICC for men (n = 18) were presented. The typical error remained between 6.7 and 6.9%. There were no differences in body fat (%) for EIM when performing 3 measures on the same day (within-day reproducibility). An excellent ICC²¹ was found for all participants (n = 60) and men (n = 30), and a good ICC for women (n = 30). The typical error remained between 6.9 and 10.7% (Table 1).

DISCUSSION

The present study aimed to compare the body fat percentage estimated by the EIM and ADP devices, and to test the reproducibility of the EIM device in men and women. The main findings suggest that % body fat estimated by EIM is overestimated for women (4.1%) and men (4.6%), when compared with ADP. It should be noted that for 23 women (76.6%) and 28 men (93.3%), the EIM results were higher than the ADP results. In addition, the device did not present significantly different values for body fat percentage when tested on the same day or on different days, for both men and women.

To the best of our knowledge, this is the first study to compare the accuracy and reproducibility of fat percentage measurements obtained using ADP and EIM. A similar study was developed¹², in which the authors assessed the accuracy of the fat percentage results obtained by EIM with the values obtained by DXA and BIA. The reproducibility of EIM was evaluated on 3 different days. The results did not show significant differences between the methods and the authors also reported correlations above 0.93 between EIM and DXA. In addition, the authors reported high reproducibility of the measurements performed by EIM¹². In the findings of the current study the fat percentage data obtained by EIM demonstrated a high correlation with the reference measure (ADP), in addition to presenting good reproducibility between days.

Studies that compared body fat percentage values obtained through ADP and BIA indicate that there are no significant differences in the percentage of fat between the methods, and that they present high correlation¹⁴,²²,²³. The body fat percentage is estimated based on the Siri equation¹⁸, considering the body density (body mass/ body volume) measured by the ADP device²⁴. Conversely, the EIM manufacturer does not provide details about the algorithm used to estimate body fat percentage, only mentioning that it uses electrical currents with different frequencies, directions, and depths. We believe that the overestimation of the results observed for the EIM, of 4.1% for women and 4.6% for men, is because we only used 3 measures (Figure 1), one of which was evaluated in the abdominal region. In this way, body composition analysis could be performed differently between men and women, possibly adding measures concentering more on the lower trunk and lower limbs in women, and with the addition of an upper limb region in men.

Studies that evaluate the agreement and reproducibility of low-cost and portable devices that assess body composition are important because they allow the equipment to be used in public health services to monitor acute and chronic changes in body composition. It was found that patients with acute/critical illness are particularly vulnerable to muscle loss and alterations in body fluids, negatively impacting clinical outcomes²⁵. The evaluation of these parameters in hospital environments is often subjective and imprecise, which creates discrepancies in identity and difficulty in assessing longitudinal changes. In this sense, BIA seems to be a good strategy to use in these contexts, since it provides information on both body composition and hydration status²⁶. In addition, we presented high interclass correlation coefficients within and between days for MIE, and this characteristic is important for a clinical scenario, because it guarantees feasibility during treatment to control overweight.

It is important to acknowledge limitations in the study design; we included only individuals with a normal BMI, and the absence of information on the algorithm used from the manufacturer of the EIM, which limited our understanding of the findings during the agreement analysis between EIM and ADP. Some strong positive points should also be mentioned; we adopted seven days for between-days reproducibility analysis, which, in our opinion, reflects a more specific clinical scenario during overweight treatment. In addition, ADP was shown to be a more specific method to analyze body fat, and this was the first study to compare EIM and ADP.

CONCLUSION

In conclusion, EIM presents good within- and between-days reliability, however, it can overestimate the body fat percentage compared to ADP for both men and women. Health and fitness professionals could be encouraged to use EIM for longitudinal body fat monitoring.

• How to cite this articleRibeiro JG, Rossato M, Orssatto LBR, Picanço LAA, Silva DAS, Bezerra ES. Agreement and reproducibility of a portable electrical impedance myography device for body fat percentage estimation in normal weight men and women. Rev Bras Cineantropom Desempenho Hum 2023, 25:e92458. DOI: https://doi.org/10.1590/1980-0037.2023v25e92458

• Funding

  The study was supported by the National Council for Scientific and Technological Development and the Coordination for the Improvement of Higher Education Personnel. This work was carried out within the framework of the Health Sciences research program at the Federal University of Amazonas. The authors would like to thank the Fundação de Amparo à Pesquisa do Estado do Amazonas (FAPEAM) for the master’s scholarship granted to JGR.

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  » http://dx.doi.org/10.1038/s41430-018-0360-2
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  Mundi MS, Patel JJ, Martindale R. Body composition technology: implications for the ICU. Nutr Clin Pract. 2019;34(1):48-58. http://dx.doi.org/10.1002/ncp.10230 PMid:30586471.
  » http://dx.doi.org/10.1002/ncp.10230

Publication Dates

• Publication in this collection
  27 Nov 2023
• Date of issue
  2023

History

• Received
  18 Jan 2023
• Accepted
  21 Aug 2023