BIA and measuring Body Composition

BIA is becoming a very popular way to measure Body Composition easily and accurately, however it can be difficult to decide what sort of machine to buy. The technical language can sometimes seem quite baffling.


Here we try to explain the differences between some of the available options.

BIA stands for Bio-electrical Impedance Analysis. It involves passing a small, safe electrical current around the body and looking at the flow of that current through the body’s tissues.

Water conducts electricity so the resistance to the current is low, fat acts as an insulator so the resistance measured is high and muscle is in between as the current needs to be higher to get into the muscle cell, but once in the cell resistance is low. This allows the device to build up a picture of what your body is made up of.


Some machines use only 1 frequency of current so these machine can only measure outside of body cells (extra cellular space ) whereas those machine with multiple frequencies can measure inside & outside the body’s cells. This is a more accurate method of measuring body composition.

Another factor is where the machine measures. Some take a partial measurement such as the across the arms, or across the legs, or down one side of the body. These methods assume that the body tissue distribution is equal or similar in all parts of the body or symmetrical in terms of fat and muscle mass. Of course that is often not the case.


Machines that measure all parts of the body are much better at assessing body make up.

Even better are those that measure each segment (4 limbs and trunk) separately at multiply frequencies – this is called Direct Segmental Multi-frequency measurement


So please don’t try and compare Apples with Pears when you look at investing in a Body Composition Tracker