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Body Fat scales


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The scales measure your bioelectric impedence and is based on the principle that body fat is an insulator and muscle is a conductor. The low level charge is sent from one hand to the other (or one foot to the other depending on if you're standing on it or holding it) and it measures the amount of resistance it experiences. The problem is the current follows the shortest path: hand-arm-chest-arm-hand. Depending on your genetic pre-disposition, you may store most of your fat in your legs giving an inaccurate reading. A clinical bio-electric impedence device will actually measure from your ankle to your wrist to prevent this. As long as you know this limitation, along with inaccuracies related to hydration levels and gender issues, the Tanita scales are good for measuring a fitness program over time because of their test-retest reliability.

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Just to add to Eddie's reply: since fat is low-impedance and muscle and water are high impedance, the scale determines what percentage of your body mass is fat versus muscle. BIA (bioelectrical impedance analysis) seems to be one of the more accurate and certainly inexpensive measurements of body fat available, though if you have someone thoroughly trained in assessing body fat by taking skinfold caliper measurements, or if you can find someplace to do densitometry (underwater weighing, rather unpleasant), these can be more reliable. If you compare all sets of numbers there will probably be some disparity.

Also, for any women who might happen to be lurking out there, remember that women tend to retain more water at certain times in their cycle, and the Tanita scale (in general) tends to overestimate bodyfat by about 7% (based on personal observation, disparities noted between Tanita scale measurements and clients' skinfold caliper measurements at various times throughout the month).

That having been said, it is still a pretty good way to assess RELATIVE changes over several months, as Eddie points out. Other ways to assess progress, of course, include how you feel in your clothes (body measurements), overall energy levels, performance...

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Come on Courtenay, underwater weighing is the best. "Keep blowing, keep blowing!" Just 'cause the poor victims think they're going to drown and don't do the test properly, don't let that throw you off. I did the tests for a lab class one quarter, we had one person who floated even after they blew all of their air out. What are you supposed to tell them? "Sorry, we can't accurately measure you because you're too fat." Brutal.

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I've heard of a guy who ate an entire salami and brick of cheese one night and then tested his fat percentage using the electric impedence method. He said according to that he had lost like 10 lbs of fat! (it was because of the high sodium content of the salami improved electrical conductivity).

A much more accurate method of measuring body fat is the simple skin fold calipers (by someone who is skilled in using them).

And you can buy a pair for about $15-20.

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