Bioelectrical impedance analysis is the study of the electrical properties of biological material and its change over time. This includes humans, animals, fish, plants, vegetables, fruits and anything living. Even human circulation and breathing can be quantified with a real-time BIA instrument that has enough sensitivity and a short sampling interval[1].
The most popular application for BIA is predicting human body composition as a total body measurement from hand to foot where resistance and reactance is evident from a biological circuit that conducts alternating current. The source electrodes introduce an alternating current (50 Khz) at the base of the toes and fingers. The detecting electrodes measure the voltage drop due to this circuit at the anatomical land marks of the ankle and wrist bones. This is a four electrode or tetrapolar measurement, which is essential to eliminate electrode and field distribution problems associated with two electrode measurements. The conducting media has a resistive and capacitive electrical path. These two values are independently measured and resolve the cellular and ionic components of the material. The cellular volume is measured as capacitive reactance and the resistive volume is ionic resistance, both are expressed in ohms. Modeling these two values as their series or parallel equivalent circuits is important when comparing them to criterion methods.
1. Nyboer, J.: Electrical Impedance Plethysmography. Second Edition. Charles C. Thomas, Springfield, IL, 1970.
Why is Body Composition Important ?
Scale weight is not an indicator of an individual's body fat or health. Body composition is the amount of lean tissue compared to fat. Body composition data can form the basis for a wide variety of therapeutic health and fitness prescriptions. In clinical applications, body composition analysis along with nonpharmacologic nutrition and exercise prescriptions provide the foundation upon which further treatment is based. Only body composition analysis can determine how much muscle and fat are lost or gained as the result of any nutrition, exercise, or pharmaceutical prescription.
How is Abnormal Body Composition Managed ?
When there is an imbalance between calorie intake and calorie burn, we change our body composition. The quantitative management of abnormal body composition, i.e. obesity, anorexia, disease, etc. must be associated with daily calorie intake and expenditure. The successful application of body composition analysis must have a three compartment assessment. These compartments are:
What are the Long-Term Benefits of a Good Body Composition Prescription ?
The ability to (1) analyze body composition data interactively, (2) create prescriptions for change and (3) visualize the effectiveness of those prescriptions with projected and historical graphs helps increase motivation for positive change.
The ultimate outcome is improved health and increased longevity!
Body Cell Mass is the functional mass of the body where work is done. All oxygen consumption, carbon dioxide production, glucose oxidation, protein synthesis and other metabolic work takes place within the body cell mass. The body cell mass is, in effect, the total mass of all the cellular elements in the body, and therefore, represents the metabolically active component of the body. In the normally nourished individual, muscle tissue accounts for approximately 60% of the body cell mass, organ tissue for 20% of body cell mass, with the remaining 20% made up of red cells and tissue cells. It also contains the majority of the body's potassium, (98 - 99%).
The support compartment, Extracellular Cell Mass
Extracellular Cell Mass is the support mass of the body and is metabolically inactive, consumes no oxygen, produces no carbon dioxide and performs no work. The extracellular mass consists of extracellular fluids and solids, such as bone and cartilage, with its primary function that of support and transport. ECM is located outside of the cellular compartment or outside of the body cell mass. Lean body mass is the sum of body cell mass and extracellular mass.
The energy storage compartment, Fat Mass
Fat Mass Body fat is the storage of potential energy that you consume when doing work or exercise. Fat has 3500 calories per pound of body fat. It is the total lipid mass (triglycerides) with a density of .9 g/ml. Fat is equal to actual weight minus fat free mass
What is Phase Health and Activity Number (formerly called Phase Angle)?
Your health and activity number is based on total body resistance and reactance and is independent of height, weight and body fat. Lower phase angles appear to be consistent with either cell death or a breakdown of the cell membrane. Higher phase angles appear to be consistent large quantities of intact cell membranes and body cell mass. All living substances have a health and activity number, in fresh uncooked vegetables health and activity numbers can exceed 45 degrees. In cooked vegetables health and activity numbers is zero because they are dead.
Why is The Health and Activity Number Important?
The health and activity number is a predictor of outcome and indicates the course of disease or increases as the result of optimal health based on good nutrition and consistent exercise.
As we get older our health and activity number will decrease and will be approximately 4 or less when we die. Fit adolescents may have a health and activity number greater than 10. This effect is a result of cell integrity due to age. Low health and activity numbers are consistent with:
Good fitness and life style is the key to maintaining a healthy health and activity number.
Health and Activity Number Conclusion The Health and activity number is good indicator of disease progression although it is not used to diagnose a specific disease. It may be thought of as a thermometer with a broad range of normal. It may also be used to monitor the practice of good health, which would include healthy diets, the use nutritional supplements and exercise.
References:
M. Ott, H. Fisher, H. Polat, E. B. Helm, M. Frenz, W. F. Caspary B. Lembcke "Bioelectrical Impedance Analysis as a Predictor of Survival in Patient with HIV Infection" J. of Acquired Immune Deficiency Syndromes and Human Retrovirology 9:20-25 1995.
R. Liedtke "Principles of Bioelectrical Impedance" http://rjlsystems.com
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