What are the differences between standing and supine BIA devices?

Short Answer: Convenience

 

Each type of device has its advantages and disadvantages. Standing BIA devices are faster and more convenient to use, compared to supine (lying down) BIA devices. Most professional BIA devices use a standing design nowadays.

 

Conversely, for clients that are unable to stand, prone BIA devices may be the only available measurement option. When BIA was first invented back in the 1980s, there were only prone models, but after standing models were invented in the 1990s, prone models have generally become reserved for more specialized usage, for those unable to use standing BIA devices.

 

In terms of measurement principle, both standing and prone type BIA devices use the same principle; both measure bioelectrical impedance and use this to calculate body composition results.

 

However, it is important to note that impedance (and related bioelectrical indicators such as resistance and reactance)  measured in each position is naturally different, so impedance results should not be directly compared between positions. Algorithms should be developed for different body positions to ensure level of accuracy for body composition results regardless of position.

 

To illustrate, let's go over a research paper published in the International Journal of Environmental Research and Public Health that observed differences in bioelectrical impedance and body composition results between prone and standing, as well as sitting and standing positions. This observation is not particularly surprising, given an expected difference in distribution of body fluids between different positions.

 

Calculated parameters such as Intracellular and Extracellular Water differed significantly between supine vs standing positions, as well as sitting vs standing posture. Directly measured parameters such as Phase Angle also differed between posture.

 

However, body position did not significantly affect the percentages and absolute values of overall fat and fat-free mass. In other words, while we would not recommend comparing the results of "Supine Body Composition Measurement" against "Standing Body Composition Measurement", it is safe to say that if you consistently use the same type of device, change in body composition indicators can still be tracked accurately.

 

Despite being easier-to-use and more convenient, standing body composition analyzers are not inherently more or less accurate compared to older supine-position analyzers. Results between different types should not be directly compared, but otherwise, the decision to utilize standing vs supine is largely based upon what position is most practical for the patient.