The purpose of this assessment is to provide a minimally invasive body composition analyses procedure for determining body fat levels. This type of test involves the placement of an electrode on the top upper portion of the biceps where it emits a low level electrical current. The impedance is determined based off the electrical impulse and is based upon the conduction of lean tissue over fat mass, which is a poorer conductor.
In general this testing method has a large margin of error, which should be taken into account when interpreting the results of this type of assessment. The hydration status of the individual is one of the guidelines that needs to be followed with this type of test. Therefore the consumption of certain types of medications, stimulants, caffeine, alcohol, diuretics, and overall not drinking enough water prior the exam can greatly affect the results. In addition to this, users should not eat within 4 hours of taking the exam, exercise, or perform strenuous activity within 12hours. Age, gender, fitness levels, and for women, menstrual cycles, are additional considerations which can affect results as well. If all of the above guidelines are met, the individual can proceed to perform the assessment.
Strengths of bioelectrical impedance testing include quickness, cheap, practicality, non-invasive, no water weighing, no weight restriction, and no height restriction (Shafer, Siders, Johnson, & Lukaski, 2009; Aandstand, Holtberget, Hageberg, Holme, & Anderssen, 2014). Weaknesses lie in how many electrode frequencies are able to be produced. Single frequencies do not have the capability to accurately measure the trunk of a person, making it difficult to diagnose obesity or over weight individuals (Shafer et al., 2009). Segmental frequencies better allow for the shape complexity of a person (Shafer et al., 2009).
A study published in Nutrition estimated body fat percentage using an eight-electrode, multiple frequency (segmented) bioelectrical impedance analysis (Shafer et al., 2009). The researchers performed the testing on normal, overweight, and obese participants. The conclusions of this study were that with increasing adiposity of both men and women, the test becomes less accurate and has significant ranges of error in obese measurements (Shafer et. al., 2009). Segmented bioelectrical impedance was found to be valid for both normal and overweight individuals because the results were within reference method ranges of the dual-energy x-ray absorption test (Shafer et al., 2009).
Reliability of this test can be explained using a study published in Military Medicine (2014). The test-retest method was used to measure body fat percentage by bioelectrical impedance and it was found that in both men and women this method had the lowest limits of agreement, giving notion that of the other methods tested (skinfold and dual-energy x-ray absorption), bioelectrical impedance was the most reliable (Aandstad et al., 2014).
Sources:
Aandstad, A., Holtberget, K., Hageberg, R., Holme, I., Anderssen, S.A. (2014). Validity and reliability of bioelectrical impedance analysis and skinfold thickness in predicting body fat in military personnel. Military Medicine, 179(2), 208-217. Retrieved from https://academic.oup.com/milmed/article/179/2/208/4160693
Shafer, K.J., Siders, W.A., Johnson, L.K., & Lukaski, H.C. (2009). Validity of segmental multiple-frequency bioelectrical impedance analysis to estimate body composition of adults across a range of body mass indexes. Nutrition, 25, 25-32. Retrieved from https://pubag.nal.usda.gov/pubag/downloadPDF.xhtml?id=22872&content=PDF
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