Electrical impedance myography (EIM), used in Skulpt Aim, is not standard bioelectrical impedance analysis (BIA), used in the “Smart Scales” to measure body fat percentage.
While standard bioimpedance analysis (BIA) has given electrical impedance techniques in general a bit of a bad rap, there is nothing inherently poor or low quality about these techniques. In fact, electrical impedance is used in all sorts of highly scientific and measurement endeavors that require incredible accuracy, from evaluating the purity of metals to measuring contaminants in drinking water, and ensuring the quality of food that we eat.
However, standard BIA, in which current is passed through the entire body, usually between the hands and feet or between the feet only, is highly inaccurate. With such an approach, electrical current can flow anywhere and can be affected by a variety of factors that have little or nothing to do with body composition—it is very indiscriminate. Essentially, the current will choose the path of least resistance and thus any factors that distort the current’s path will alter the data.
For example, your level of hydration will play a huge role in the results. Deep veins expand with increased hydration or even upon standing, and this will provide a low-resistance path for the current to travel. Additionally, the contents in your abdominal area can vary dramatically after eating or drinking, and expectedly, this will highly alter your data. Furthermore, even your body position can have a huge effect, as joint positioning contributes to variations in the data. , The size and length of the limbs also impact data — a taller person will simply have a greater resistance because they are taller! Finally, the presence of metal implants, such as hip or knee replacements or spinal implants, will make the data virtually meaningless.
In electrical impedance myography (EIM) an entirely different approach is taken. Electrical current is not applied in an inelegant and unsophisticated fashion between the hands and feet. Instead, the sensors are strategically positioned with optimized configurations and frequencies, so the electrode geometry is kept constant and consistent. Moreover, the array is placed over a small, discrete region of tissue. Thus, many of the factors that lead to the major inconsistencies in standard BIA are entirely removed. For example, the position between the electrodes is unchanging, as there are no large veins in the muscles, there is no digestive tract to interfere with the measurement, and the current is not flowing across joints. In short, unlike bioimpedance analysis (BIA), EIM testing is both precise and very stable.
Now, no biological test is completely perfect. Changes in skin condition, temperature, and subcutaneous blood flow will produce some alterations in the data, but these are relatively modest compared to the very large effects that occur in standard BIA. Studies have shown that EIM is capable of remarkably good consistency and test-reproducibility.
As a final example, in one study evaluating EIM to track progression of muscle deterioration in amyotrophic lateral sclerosis (ALS or Lou Gehrig’s disease), also studied BIA. The standard BIA data, even though acquired by medical professionals, was both highly inconsistent and insensitive to disease status. Using a statistical analysis, we realized that you would need literally thousands of subjects to study if you wanted to use BIA as an outcome measure in ALS; with EIM, you would need less than 100, far fewer than with any technology or method currently available.
While both EIM and BIA belong to the same larger technological category of impedance techniques, they are very distinct.