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Wang, B. Gutin, R. Pierson and T. Weststrate and J. Lukaski, W. Bolonchuk, W. Body fat adipose tissue causes greater resistance impedance than lean mass and slows the rate at which the current travels. BIA scales estimate body fat percentage using bioelectrical impedance analysis.

You may have seen body fat scales on store shelves or online that use bioelectrical impedance analysis. Because the scales can be expensive, you have probably wondered what bioelectrical impedance analysis is and if it is worth paying for.

Below is more to help you decide. While "bioelectrical impedance analysis" sounds technical, BIA devices use straightforward technology. They measure the rate at which a painless low-level electrical current travels through your body. Different tissues in your body allow the electrical current to travel at individual speeds.

Fat is more resistant than muscle or water, so the higher the resistance, the higher the body fat percentage calculation is likely to be. Most scales measure an estimate of your total fat, muscle, water, and bone in weight and percentage.

Based on that rate, a calculation is used to estimate fat-free mass. The device then uses other data such as your height, gender, and weight measurements to determine your body fat percentage. There are different types of BIA devices, but each requires two contact points. On a handheld device, the two points are your two hands called hand-hand BIA.

The two contact points on a typical BIA scale are your two feet called foot-foot bioelectrical impedance analysis.

This means that when you use the device, you place each foot on a pad, and the current travels through your body between your feet. There are also hand-to-foot BIA devices, as well.

Many of the newer models of BIA scales link with a smartphone app so you can track your progress over time. The price of your BIA scale will depend on how sophisticated the product is. Some scales use more than one frequency and more advanced algorithms to provide a result.

And some offer segmental fat analysis, meaning you can get body fat measurements for each leg, arm, and belly. Some experts say that segmental fat analysis using hand-foot BIA is more accurate because hand-hand devices primarily measure the upper body, while foot-foot scales primarily measure the lower body.

Bioelectrical impedance analysis devices are considered safe for most people. However, BIA should not be used by anyone with an electronic medical implant, such as a heart pacemaker or an implantable cardioverter defibrillator ICD.

Also, most device makers recommend that pregnant people not use the products. Some studies showed that bioelectrical impedance analysis is a reasonably accurate method for estimating body fat. But these research studies generally do not test the scales you find in the store. Experts generally agree that the accuracy of the measurement depends, in part, on the quality of the device.

In addition, other factors may affect a reading when you use a BIA scale. Some researchers also say that ethnicity can affect the accuracy of BIA measurements. Overall, studies show that this method is not very accurate although it may be able to track change over time, your results are unlikely to reflect your actual body composition.

Even if you get an accurate reading on a bioimpedance scale, the number represents an estimate of your total body fat percentage. Bioelectrical impedance analysis does not accurately measure your total body fat.

Most scales also cannot tell you where fat is located on your body. Even though many factors can affect your reading accuracy, a regular BIA scale can show you changes in your body fat over time. Discrete resistors were used to model body impedance and contact resistance.

The resistance value of the model for body impedance Z body was fixed at Ω. Figure 3 c shows the variation of measured impedance values before and after contact resistance compensation when the contact resistance varied from 0 to 3 k Ω.

A novel wrist-wearable bioelectrical impedance analyzer with contact resistance compensation function was developed. Figure 4 a shows the block diagram of the developed BIA device.

a Hardware block diagram of the overall system, b current path for 4-point measurement mode, and c current path for 2-point measurement mode. Z body measured impedance, Z i input impedance of the voltmeter, R s output impedance of the current source, R c contact resistance, I current, V M measured voltage, SW switch, α the size ratio of voltage to current electrode, β the size ratio of finger to wrist electrode.

The electrodes part is composed of two current-driving electrodes and two voltage-sensing electrodes. The total area of finger electrodes a pair of one current electrode and one voltage electrode on the top side of the device was 68 mm 2 and that of wrist electrodes another pair of one current electrode and one voltage electrode on the bottom side of the device was mm 2.

The AFE S3FBP5A, BioProcessor2, Samsung Electronics delivers 30 μA sinusoidal alternating current with 50 kHz frequency to the two current electrodes and measures voltage drop between the two voltage electrodes.

Acquired voltage values were converted to digital signal by analog-to-digital converter ADC , and this digital code was converted to impedance value with a calibration curve which had been made by calibration process.

The internal micro controller unit of BioProcessor2 calculated body fat, lean body mass, and body water volume using impedance data and user profile information such as height, age, weight, and gender. The measured data was displayed on liquid crystal display.

Bluetooth was used for data transfer between body fat analyzer and a personal computer, and external flash memory was used for user data storage.

Contact resistance compensation function was adapted to our bioelectrical impedance analyzer. The contact resistance compensation circuit included two analog switches. One analog switch was connected between the current and voltage path of the finger electrodes, and the other was connected between the current and voltage path of the wrist electrodes.

For the 4-point measurement mode, analog switches were turned off, and for the 2-point measurement mode, analog switches were turned on for electrical connection of each voltage and current electrode pair.

This very simple and small compensation circuit had a flexibility that allowed easy adaptation to variable AFEs. The dynamic range the range of measureable impedance was configured to cover the range of body impedance and contact resistance.

TX dynamic range the range of impedance that current source can drive and RX dynamic range the range of impedance that voltmeter can measure should satisfy the overall system dynamic range required. Figure 4 b,c show the current paths for the 4-point and 2-point measurement modes, respectively.

Based on our user data from volunteers in , TX and RX dynamic range were set as 15 kΩ and 10 kΩ, respectively, by adjusting the driving current level To improve measurement accuracy along the wide dynamic range stated above, a calibration algorithm that adopts 4-point coordinate conversion is proposed, in which four high-precision reference resistors are used to reduce the errors in three resistance sections.

The ADC output code was converted to impedance by calibration process. The ADC output code and body impedance Z body have a nonlinear relationship due to the finite input impedance of the voltmeter Z i and the finite output impedance of the current source R s , since the equivalent impedance detected by the voltmeter is the parallel combination impedance of body impedance Z body , Z i , and R s as in Eq.

Note that contact resistance R c is zero during the calibration process. In the calibration curve, the measurement on the x-axis is changed from reference impedance to parallel combination impedance of reference impedance, Z i , and R s.

This change enhances the linearity of the calibration curve and the accuracy of measurement. The dashed lines are ideal calibration curves, and the solid lines are extracted calibration curves derived by calibration process.

It is easily seen from Fig. Calibration algorithm was developed using C code and loaded as firmware of the device. Whenever the device is turned on, self-calibration is conducted using 4 reference resistance values as shown in Fig. Calibration curve and measurement error at midpoint between two reference points for a 2-point calibration, b 4-point calibration, and c 4-point coordinate conversion calibration.

ADC analog-to-digital converter, Z i input impedance of the voltmeter, R s output impedance of the current source. Figure 6 shows the measurement procedure and corresponding graphical user interface of our wrist-wearable device.

On the home screen, a user can register information gender, age, height, and weight by touching the [CHG INFO] icon. If the user is already registered on the device, registration process can be skipped by touching [USER] icon. The measurement is initiated by touching the [START] icon. When the proper posture is maintained, BIA measurement begins automatically.

It takes about 7 s to complete the test: 3 s for 4-point measurement, 1 s for measurement mode change, and 3 s for 2-point measurement. When the measurement is completed, percentage body fat, lean mass, and basal metabolic rate are shown on the screen.

Measurement procedure and corresponding graphical user interface of the wrist-wearable bioelectrical impedance analyzer. To evaluate the accuracy of our bioelectrical impedance analyzer, a clinical test was conducted on volunteers who were recruited at Seoul St.

Participants were recruited to have as uniform distributions as possible on the bases of gender, age, and body mass index BMI. The BIA pretesting client guidelines 20 in Table 2 were explained to all volunteers before the clinical test. Four different devices were used in the clinical test: our wrist-wearable device, a whole-body composition analyzer InBody , an upper-body portable body fat analyzer Omron HBF , and a DEXA instrument GE Lunar Prodigy.

The study was approved by the Institutional Review Board of Seoul St. For the approval of the review board, our bioelectrical impedance analyzer was registered as a broadcasting and communication equipment MSIP-REM-SEC-SAIT-MyLean by the Ministry of Science, ICT and Future Planning MSIP , Republic of Korea.

Written informed consent was obtained from each volunteer before the clinical test. To undergo the test, participants changed into a light gown in order to control the weight of clothes.

All metal items were removed from the participants to ensure accuracy of measurement. Then anthropometric measurement was conducted by a skilled nurse.

After anthropometric measurement, body impedance and body composition data were measured using the whole-body composition analyzer and the upper-body portable body fat analyzer.

Next, the DEXA instrument was used to measure the reference body composition. Finally, our wrist-wearable device was used to measure body impedance. Statistical analysis was performed after data acquisition. The accuracy of each device was compared to that of others. Our study explored a novel method that uses considerably small electrodes that can be adapted into small devices, such as a wristwatch.

Figure 7 shows the calculated contact resistance distribution of the study participants. While the average value was Ω, it is notable that the maximum value was as high as Ω. Figure 8 a shows the impedance correlation between our device and the whole-body composition analyzer.

The coefficient of determination R 2 of impedance was 0. This result shows that there is a strong correlation for impedance measurements between the wrist-wearable bioelectrical impedance analyzer and the whole-body bioelectrical impedance analyzer, and the proposed contact resistance compensation method improves the correlation coefficient effectively.

a Impedance correlation with contact resistance compensation blue dots and without contact resistance compensation orange dots. DEXA dual-energy X-ray absorptiometry.

Figure 8 b shows the correlation of percentage body fat measurement between our wrist-wearable bioelectrical impedance analyzer and the reference instrument DEXA , from which it can be seen that R is 0. The SEE was estimated to be 3. It can be seen that the errors between the two instruments are randomly distributed without any skewed tendency and Table 3 shows the comparison of accuracy in measurement of percentage body fat by the whole-body composition analyzer, the upper-body portable body fat analyzer, and our wrist-wearable bioelectrical impedance analyzer.

We developed a novel wrist-wearable bioelectrical impedance analyzer with a contact resistance compensation function such that bioelectrical impedance can be accurately estimated even with considerably small sizes of electrodes outer electrodes: 68 mm 2 ; inner electrodes: mm 2.

The correlation coefficient and the SEE of percentage body fat relative to the DEXA instrument were estimated to be 0.

Considering that the measurement time of our wrist-wearable BIA device was only 7 s and could be reduced further, this sensor technology provides a new possibility for a wearable bioelectrical impedance analyzer with more miniature electrodes toward daily obesity management. Kyle, U.

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