DXA Body Fat Analysis

Here in my town, there is a diagnostic center that will do this scan for $75.00. It’s not covered by insurance.  It was another bodybuilder who told me about it.  The techs there have told me several bodybuilders use this tool.  I have had six of these scans done since June 2011.  It is pretty cool.  You get a lot info.  It doesn’t just tell you how much body fat you have, but also where it is – just in case you couldn’t tell.  You also get information about bone density, which is good to know.  Since June 2011, I’ve increased my bone mass by almost 100 grams (.2 lbs).  Doesn’t seem like much, but I’m 50 years old and a couple years beyond menopause, so bone mass going up is a very good thing.  Building pretty muscles is just the fun part.  Fixing damage from physical neglect of this one and only body God blessed me with – that’s the most important thing I’m doing.

Had the scan done again this morning. I’m not discouraged or anything, but I’m not sure if it’s giving me useful data anymore.  Sometimes the data doesn’t make sense. Like how when today’s results are compared to last March’s results, it appears that I’ve maintained overall muscle, but I lost almost 13 pounds of fat.  Not a bad thing, I know.  But I weigh only 2 pounds less than I did in March. WTH??? Don’t need a math degree (which I happen to have) to see that those numbers don’t add up. Also, my last scan in July calculated my body fat percentage to be 19%. “Stage ready” for women’s physique would be below 15% for sure – probably closer to 10%.  I competed on August 25th and I think I looked lean enough to be on stage.  So did I lose almost 10% body fat from July 12th to Aug 25th?  No.  I lost a lot of water.  Water.  That’s been the variable I’ve asked about several times.

DEXA Sources of Error

Like all other body fat estimation techniques, DEXA has numerous sources of error. There can be inconsistent results between different machines from different manufacturers, and even different results between machines from the same manufacturer. Software upgrades can change the algorithms that the device uses to calculate body composition. Different hardware and software configurations can result in different interpolations of soft tissue over bone, and different treatment of pixels of which a small portion is bone. The type of X-ray beam (fan beam or pencil beam) can also be a source of error; DEXA machines with fan beams can suffer from beam magnification (also known as parallax error). A final source of error is the same error that all 2-compartment models also have: the hydration of fat-free mass. In fact, a 5% variation in fat-free mass hydration can change your DEXA-determined body fat percentage by nearly 3%. This can be a problem when comparing different ethnicities or body types where fat-free mass hydration can vary. It can also be a problem when trying to measure change over time.

from “The Pitfalls of Body Fat “Measurement”, Part 6: Dual-Energy X-Ray Absorptiometry (DEXA)

Ah hah! There it is… “hydration of fat-free mass”!  Water in the muscle…creatine.  I’m getting different results based on when I’m on/off creatine.   From summer 2011 to late fall 2011, I thought I lost something like 9 pounds of muscle.  After a few weeks of freaking out, I realized that for the summer scan I was on creatine and for the fall one, I wasn’t.  Duh.

I think I like the “mirror” body fat test a lot more. I’m going to stick with that one now.

Honestly – I couldn’t really use the “mirror” test until lately. It wasn’t until I did the Peak Week depletes and reloads that I really started to see the results of my work for the last three years. 75 pounds ago, progress was very hard to see. Those scans were helpful to me then. During that first year, I had a couple plateaus, but not too many. I started in June 2009. The first plateau I remember was in December that year. Then again in March. I learned how to bust through them. The second year, my weight loss slowed down, but I was gaining muscle and losing fat. That’s when I started the DXA scans and they were useful.

Oh – and just in case you’re a new follower – I did get a hydrostatic weighing test last June. I decided to do it mostly to face the fear of doing it.  If nothing else, it would be a nice blog post.  I’m not a swimmer, so blowing all my air out and sitting on the bottom of a pool is NOT in my skill set.  I literally sucked water at it and it was a fun blog to write.  I titled it “How I Didn’t Drown Today.”

I really do like all the pretty numbers I get with these scans, though. Totally nerdy.

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3 Comments

Filed under Bodybuilding Journal

3 responses to “DXA Body Fat Analysis

  1. I love that you’re a math teacher; I wanted to be a mathematician in 8th grade.. haha. Now I spend my days crunching numbers in accounting. Bleh.
    I would be terrified of the water one!
    Is this screening like the Body Pod that I hear people talk about?

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  2. Very interesting! Thank you for sharing. I’ll have to see if I can set one of those up around here.

    Like

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