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What is BIA?

What is BIA?

Bioelectrical Impedance Analysis (BIA) is a commonly used method for calculating body composition. This metric is used to assess health and nutrition by measuring body fat, lean muscle mass and hydration levels.

In the long term, excess body fat can be damaging to your health and can actually increase your risks for cardiovascular disease, diabetes, and more. By using BIA, users can assess their health and make decisions to balance their body fat levels.

How Does BIA Work?

BIA is one of the quickest and most reliable ways to measure body composition; it works by sending a safe, weak electric current through the body. During its travels through your body, it will encounter different types of masses, all of which have a different resistance to electricity. For example, as fat-free masses are mainly made up of water, this means they are good conductors, so will have less resistance than body fat mass. So, they will provide less resistance.

Upon leaving the body and finishing its journey, the voltage will be reduced, allowing impedance to be determined.

It’s important to remember that actual results are based on a calculation and that algorithms for different brands will be different. Choosing a scale that is close to DEXA is something that should be taken into consideration when choosing a BIA scale.

In order to provide more accurate results, some body composition scales now test multiple frequencies, rather than only a single frequency. This also means that they can calculate extracellular water, intracellular water and total body water levels.

But with so many BIA scales on the market, how do they compare?

BIA Floor Scales

What many people do not realise is that BIA Floor Scales are not as accurate as they may originally appear. Due to the lack of handheld electrodes, these scales only send a current up through one leg and down through the other. It does not reach your upper body. Because of this, all measured results are coming from the legs, and the upper body results are just estimates. If a user does a lot of cardio, but not much upper body, this scale could disproportionately calculate the upper body fat mass by assuming it will correspond to the lower body.

Handheld BIA devices

Much like BIA Floor Scales, handheld BIA devices only measure part of your body and use a formula to calculate the rest of your body’s results. Where a current from BIA Floor Scales tends to travel through the legs only, handheld scales typically only journey up one arm and down another. Similarly, if a gym goer prefers rowing or weight training, their upper body may be disproportionately healthier than their lower body, which this device will not reflect.

Direct Segmental Multi-Frequency Bioelectrical Impedance Analysis (DSM-BIA)

The benefit of DSM-BIA scales, such as the Marsden MA601 is that they actually do a complete body analysis. The body is divided into 5 segments and the impedance for each section is recorded. This allows the scale to accurately calculate the measurements for each body segment and provide a thorough analysis of body fat.


For the reasons listed above, BIA is the preferred way to see a body's breakdown by segment. It is also useful to help users know which areas to focus on during training. This is significantly more accurate than using BMI or a standard weighing scale.

Further Reading

If you think that body composition scales have a lot of measurements and can be difficult to understand, try reading our free guide.

In this blog post, we discussed why you should use a body composition scale.

Can you really trust the results you get from your body composition scale? In this blog post we discuss how accurate body composition scales are, and what they're used for.