**Influence of Posture and Frequency Modes in Total Body Water Estimation Using Bioelectrical Impedance Spectroscopy in Boys and Adult Males**

**Masaharu Kagawa 1,2,3,4,\*, Connie Wishart 4 and Andrew P. Hills <sup>5</sup>**


*Received: 21 February 2014; in revised form: 16 April 2014 / Accepted: 26 April 2014 / Published: 5 May 2014* 

**Abstract:** The aim of the study was to examine differences in total body water (TBW) measured using single-frequency (SF) and multi-frequency (MF) modes of bioelectrical impedance spectroscopy (BIS) in children and adults measured in different postures using the deuterium (2 H) dilution technique as the reference. Twenty-three boys and 26 adult males underwent assessment of TBW using the dilution technique and BIS measured in supine and standing positions using two frequencies of the SF mode (50 kHz and 100 kHz) and the MF mode. While TBW estimated from the MF mode was comparable, extra-cellular fluid (ECF) and intra-cellular fluid (ICF) values differed significantly (*p* < 0.01) between the different postures in both groups. In addition, while estimated TBW in adult males using the MF mode was significantly (*p* < 0.01) greater than the result from the dilution technique, TBW estimated using the SF mode and prediction equation was significantly (*p* < 0.01) lower in boys. Measurement posture may not affect estimation of TBW in boys and adult males, however, body fluid shifts may still occur. In addition, technical factors, including selection of prediction equation, may be important when TBW is estimated from measured impedance.

**Keywords:** body fluid; deuterium; dilution technique; impedance technique; prediction equation; accuracy; technical error

#### **1. Introduction**

Body composition, including fat mass (FM) and fat-free mass (FFM), is an important variable in the assessment of health status. Obesity has been defined as a state of excessive fat deposition [1,2] and the assessment of body composition assists in identifying individuals with metabolic risks. In addition, while body mass index (BMI: kg/m<sup>2</sup> ) and other simple anthropometric indices have been utilized as convenient screening tools for obesity, assessment of body composition reduces misclassification of individuals at risk.

Body composition can be determined using a wide range of techniques. Each technique varies not only in its accuracy and precision, but also in cost, portability, convenience, and requirements for accredited operators. Bioelectrical impedance analysis (BIA) is one of the most commonly utilized techniques as it is simple, portable and cost- and time-efficient. The technique assesses differences in the electrical conductivity between tissues. Tissues that contain water and electrolytes have higher conductivity compared to those with less body fluid. From the measurement of electrical conductivity, resistance (R) and reactance (Xc) can be determined. These components can be utilized to calculate impedance (Z) based on their association Z2 = R<sup>2</sup> + Xc2 and also a phase angle based on a ratio of Xc to R [3]. In addition, together with information on the length (L) or height (Ht), a total volume of body water (TBW) can be determined [4,5]. Furthermore, while R has been used most frequently, R, Xc, and Z have been used to estimate TBW, intra-cellular fluid (ICF) and extra-cellular fluid (ECF) as well as percentage body fat (%BF) of individuals [4].

Existing BIA devices can be divided into single-frequency BIA (SFBIA), multi-frequency BIA (MFBIA) and bioelectrical impedance spectroscopy (BIS). SFBIA devices generally use a frequency of 50 kHz that passes through both ECF and ICF [4]. In comparison, MFBIA uses multiple frequencies in the range of 1 to 1000 kHz and enables one to distinguish between ICF and ECF. A previous study reported that a low frequency, generally below 20 kHz, is used to predict ECF whereas a higher frequency (above 50 kHz) is used to estimate TBW in MFBIA [6]. As a result, ICF can be determined from the difference of the two. Although it has been suggested that MFBIA may overestimate %BF of lean individuals and underestimate that of obese individuals [7], error in estimation of %BF may be minimized compared with SFBIA [8]. BIS is a more sophisticated model that uses a wide range of frequencies and non-linear mathematical algorithm to assess relationships between R and body fluid. This allows estimation of R extrapolated to zero (R0) and infinite (R) frequencies and development of empirically-derived prediction equations [4,5,9]. Although both accuracy and precision of results may vary depending on the characteristics of the study population [9], past studies have reported that BIS provides better estimation of ECF than SFBIA [4,5,10,11] and also has an acceptable accuracy and precision using an animal model [12]. In addition, a technique known as "segmental BIA" is available which determines information

on total body composition through measurements of each segment (*i.e.*, upper and lower limbs and the trunk). A previous review has described a number of advantages and considerations [13], and another study reported that segmental BIA can provide valid information on body composition compared with the four-compartment model [14]. However, most studies have been undertaken on adults and studies of children are relatively scarce. Consequently, little knowledge is available on any differences in TBW estimation between adults and children and the effects of using different frequencies.

In addition, wide variations in measurement posture are commonplace using the impedance technique depending on the device used. Many hand-to-foot models measure in a supine position, the posture recommended in the European Society for Parenteral and Enteral Nutrition (ESPEN) guidelines [10]. However, modern segmental BIAs that are in a scale type are designed to measure in a standing position [13]. A previous study on the influence of posture during measurements reported 2%–5% changes in ECF and 1.8%–8.0% changes in ICF depending on body position [15]. Another study reported no significant differences in %BF using a hand-to-foot device but a significant increase in %BF using a hand-to-hand device [8]. These results suggest that body posture may influence estimation of body fluid status and therefore estimation of %BF using the impedance technique. However, these studies were conducted on adults and no previous research has reported differences between adults and children.

Therefore, the present study aimed to examine influences of frequency modes and measurement posture in estimation of TBW in adult males and boys. The estimated TBW was compared with the result obtained from the reference deuterium (2 H) dilution technique.

#### **2. Experimental Section**

The study was approved by the Human Research Ethics Committee of Queensland University of Technology and adhered to the principles of medical research established by the National Health and Medical Research Council [16]. Boys aged below 15 years or adult males aged above 20 years with no medical conditions or under medication were included in the study. Participants were recruited through flyers. All participants were given an information package and all signed a consent form prior to their participation. For participants below 18 years of age, parents or legal guardians also signed the consent form. All participants were provided with a \$20 gift voucher after their full participation in the study. In total, 49 participants including 23 boys aged between 6 and 14 years and 26 adult males aged between 23 and 82 years, completed all assessments and were included in the study. All participants were instructed to fast overnight and void their bladders in the morning, prior to measurements being conducted. All assessments on children were conducted by the primary investigator.
