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Monday, November 7, 2011

Body Fat Assessment #3: Bioelectrical Impedence

Bioelectrical Impedance or BIA is an indirect method of determining body fat percentage by measuring the amount of resistance the body provides when a current of electricity is passed through the body.  A high or low resistance corresponds to a high or low body fat percentagE, respectively.

Compared to other methods, this is the least invasive and most comfortable way to assess body fat.  Unlike other methods where they are only effective if the individual wears short running shorts with no shirt, the only body parts that need to be exposed with BIA are the hands and the feet.  The BIA machine I used involved only two pairs of electrodes which needed to be placed on my right hand and foot; afterwards, all I needed to do was lie down supine (on my back) and relax while the machine did all of the work.  Very easy and less painful than the deep folds that need to be pinched for skinfold measurements.  While I'm on the subject of pain, it's also worth mentioning that BIA doesn't hurt and is in fact, the electrical current is so weak that it is unnoticeable- only the machine itself can detect the current.  The only thing I found painful was removing the electrodes and some of my hair at the same time.  This is still less painful than the pinching and pulling required for skinfold measurements.

In terms of comfort, invasiveness, convenience and ease of execution, BIA is a great assessment to use.  Its only flaw involves a few conditions where its accuracy may become questionable.
  • Limitation #1 - Hydration Affects BIA:  Because electrical currents may become affected by water and electrolyte levels, the individual's hydration and nutritional status must be kept within normal limits to get more accurate results.  Too much water would theoretically decrease resistance and the body fat percentage; although studies have also found the opposite to occur in two conditions: During exercise and after consuming a large quantity of sport drinks (3).  I'm not sure why anyone would do either during a BIA test though...
    • SOLUTION:  To get around this problem, it is recommended that the BIA be done three to four hours after a meal or an exercise session (3).
  • Limitation #2 - Ambient and Skin Temperatures Affects Resistance: When the temperature of the testing area is cool, resistance will be higher- the opposite is true for hot temperatures (2,4).  This same relationship also holds true for hot and cold skin temperatures (2,4).
    • SOLUTION:  If you're going to take a BIA measurement, make sure the room has a neutral temperature of 27-29 degrees Celcius or 80-84 degrees Fahrenheit (3).  Also make sure that you are neither overheated or chilly.  Get to the assessment on time so that you won't have to literally run or speed walk to make it in on time- even a quick sprint will cause skin temperatures to rise quickly.  If it is cold outside, dress appropriately so that your skin temperatures adjust more quickly to the temperature of the room.
  • Limitation #3 - BIA Equations Vary By Make/ Model of Machine: Don't get angry if the measurement taken at your first assessment does not agree with the measurements you received at new place.  Because there isn't a universal equation available for BIA, the manufacturer must "tailor-fit" their equation to match their machine.
    • SOLUTION:  There really isn't a way to get around this but to try to find a new place that uses the same BIA equipment.
  • Limitation #4 - Inaccurate on Individuals with Normal %BF:  Due to a combination of the above limitations, BIA cannot accurately measure individuals who are not at the extreme of leanness or obesity.
    • SOLUTION:  According to a study, although BIA is accurate under standard conditions, BIA is probably no better than skinfolds (1).  So if accuracy is top priority, it might be wise to stick with skinfolds from the start to avoid headaches in the future.  This is the final limit of BIA where it is basically useless as a way to track progression.  The best method at this point is to use skinfold measurements to track where fat is being stored at specific sites in the body.
  1. Baumgartner, R.N., W.C. Chaunlea, & A.F. Roche: Bioelectrical impedance for body composition. In K.B. Pandolf (ed.), Exercise and Sport Sciences Reviews. Baltimore, MD: Williams & Wilkins, 18: 193-224 (1990).
  2. Caton, J.R., P.A. Mole, W.C. Adams, & D.S. Heustis: Body composition analysis by bioelectrical impedance: Effect of skin temperature. Medicine and Science in Sports and Exercise. 20(5):489-491 (1988).
  3. Plowman, Sharon A., and Denise L. Smith. Exercise physiology for health, fitness, and performance. 3rd ed. Philadelphia: Wolters Kluwer Health/Lippincott Williams & Wilkins, 2011. Print.
  4. Stump, C.S., L.B. Hourkooper, M.H. Hewein, S.B. Going, & T.G. Lohman: Bioelectrical impedance varability with dehydration and exercise. Medicine and Science in Sports and Exercise. 20(2):S82 (1988).