T Nation

Determining BF%

I have a Tanita Body Fat scale which uses bioelectrical impedence to determine BF% , and it has different settings for gender, age, etc. It even has a different setting for athletes. I actually fit into their “athlete” category because I train at least ten hours per week, at the gym and on the tennis courts. For experimentations’sake, I measured my BF at several different settings (female, male, athlete, non-athlete) and got VERY different results. I have three questions:

  1. Does anybody know what the various settings “tell” the machine in order to alter the results?

  2. Are these machines accurate and/or to be believed at all? (I’ve also read that bodybuilders and hardcore athletes will not get accurate readings from such devices.)

  3. Is there an accessible method out there that IS accurate?

[quote]

  1. Does anybody know what the various settings “tell” the machine in order to alter the results?[/quote]

They use different equations for the various settings (i.e. athlete vs. adult, male vs. female, etc.). Unfortunately, they don’t give you these equations or on what they are based.

They’re not accurate at all. Reliable, they may be, but that only refers to consistency. For validity (i.e. accuracy), they do not compare well to the gold standard methods (i.e. underwater weighing, DXA), particularly for athletes with low levels of bodyfat.

Skinfolds would probably be your most accessible method that could be considered valid (read Jason Norcross’ two Body Composition for Beginers articles). As mentioned, underwater weighing and DXA (i.e. Dual-Energy X-Ray Absorptiometry) would be the absolute gold standards for accuracy.

These settings tell the machine with regression equation to plug your impedance into. All these machines are measuring is your weight and impedance. Then they take these values along with the data you input and base your %BF on a regression equation derived from comparison studies between bioimpedance and the reference method (I’d assume this would be a multi-compartment model using hydrostatic weighing, total body water analysis and a DXA scan for bone mineral content)

[quote]2. Are these machines accurate and/or to be believed at all? (I’ve also read that bodybuilders and hardcore athletes will not get accurate readings from such devices.)

  1. Is there an accessible method out there that IS accurate? [/quote]

They can be used quite well to track relative changes and for some people bioimpedance correlates very well with other reference methods.

Check out these articles at T-Mag to find out all you might want to know about how to measure body composition:


  1. Not sure, but I use the male athlete setting.

  2. They seem to be accurate as far as changes. In other words, if it read 15% and a few weeks later it read 12%, you probally did have a 3% change.

There are a few things that I have noticed that can effect the reading: hydration level and constipation level. So, try to take your readings on the same day of the week, at the same time of day, at the same hydration level, and after visiting the toilet.

  1. You could get a caliper test done. See if they can doo it for free at your gym. You could then go home and try the scale and then you can see how close it is. My scale tends to understimate my bf level by about 2%.

Do a search on T-Mag, they reviewed the scale in a previous “Things We Like.”

Jester, I would recommend skinfold calipers, tested preferably by a competent trainer.

I have a set of the Lange medical calipers that I love, but they aren’t cheap ($200 at the time I got them). For a cost-effective route, try the Slim Guide calipers. I think they’re around $30-40 and are pretty close to the Lange model. Somewhere I have an old article by Lyle McDonald (or maybe it was Will Brink…can’t remember for sure) where he tested with both the SlimGuide and the Lange on a few people and figured out that if you add so much to the Slim Guide measurements, you can get them to come out exact with the Lange model.

If you get a set, let me know and I’ll see if I can find that article.

I read that article the other day. It was written by Lyle Macdonald. The variance was very small. He found that with the three site Jackson-Pollack method the slim guide measurements were about 2mm higher than the Lange and because the Jackson-Pollack equation was developed using a Lange caliper, you would have to deduct 2mm from the total to get the correct values. This is so because the spring tension on the slim guide caliper is tighter.

That’s not accuracy, that’s consistency. Accuracy refers to validity, relative to a gold-standard method. Consistency refers to reliability, which means repeatability of test results.

Sorry to be so anal, but terminology is very important.

are incedental changes all that important? Use the tantia to measure changes, like every other week, and judge how your clothes feel, how you look nekkid and your training journal. If you are able to do more work with a greater intensity, or work longer at the same intensity, then you will have a higher quality of life. Worring whether the .0325468% change was really 100% fat or 97.235 fat to 2.765 muscle is a bit like chasing the end of a rainbow.

I think these things suck and are only good to fuck with poor dieted down ultra lean body builders.
Last year i jumped on and it said i was 12% (i was about 14% with callipers) which aint too far off. Stan “the man” Mr Musclemania Australasia" was however 17% 2 weeks out from the show.
Awesome!! I was bigger AND leaner than one of the best natural bodybuilders in the world!!
He hadnt even started restricting water, you should have seen his face, hilarity on a stick!!!