DXA Body Composition

There are a many ways to measure basic body composition, and I have used a few over the years.  Calipers are quite simple, accurate, and often free.  I was calipered once at 24 hour fitness as part of a free analysis / sales pitch.  In Boulder, the Rec Center will do them for free if there is someone on duty in the weight room.  If you’re on a budget, this is probably your best bet.

Next is the body fat scales which work by electrical impedance.  In general, these are not very accurate.  They can track your body’s changes with some precision, but expect the percent to be off by 3-5%.  I had to set mine at home for someone four inches taller than I am to get results consistent with other, more accurate methods.  Some scales are better than others (you get what your pay for), but expect the number to vary a lot daily, primarily due to hydration.  Try using a weekly average of body fat % to get a good number.

The scientific standard is the .  It uses two types of X-rays and measures the absorption of each to measure body mass, body fat, lean mass, and bone density.  The radiation exposure is minimal (about a month of sun exposure at 5000′ altitude), and the scan takes only six minutes.  The primary drawback is cost, and will set you back $125 at the .

The Study

I have a limited budget, and was lucky enough to have the opportunity to volunteer for an academic study.  The study provided four DXA scans at no cost.  I was also provided with ‘chews’ which may or may not contain additional calcium.  When I signed up I was living closer to University Hospital, but even the 45 minute drive from Boulder was not too far considering the benefit I received.

Low bone density in cyclists has been for some time.  The investigator’s was the first to follow cyclists for an entire season.  It’s my understanding that the study I was part of was trying to find out if they could do anything to effect the bone loss.  I made four visits for DXA Scans, blood tests, VO2 Max test, and a couple high resolution tibia CT Scans.

My 2010 Body Composition

Body Composition Chart

It should be noted the second scan was done after an intense, indoor time trial without fluid intake, and I think the weight and lean mass are about 2 lbs low.  Otherwise, I found a few things interesting about these results.  Firstly, my body fat percent was not as low as I would have thought, only 11.2% at its lowest.  I was also happy to see that despite my off season weight gain, I am not as heavy as last season (yet).  I know some is to be expected, but I did lose a little muscle over the course of the season as well.

Body Comosition by Region

Most interesting from this data set is that despite my overall mass being lower at the end of the season, my muscle mass is currently identical to the start of the season when I was ~5 lbs heavier. I am carrying a touch more fat in my arms, but again my lean mass there is the same. By percentage of my overall mass, my trunk is by far the largest, and also saw the largest swings in mass over the season, but again, by year’s end: same muscle, less fat.

This only adds evidence to my goal of racing in 2011 at 155 lbs.  I briefly saw 158 this season, but for most of the racing I was at 160.  I should be at about 8% body fat at 155, which I believe to be attainable without significant muscle loss, or the need for a nutritionist.

Bone Mass

Hip & Spine Bone Density Chart

This is the most troubling of all the data.  On the chart above, zero is average for my age group.  Below -1.0 is classified “Osteopenia”, the lowest grade of abnormal low bone density.  When I was most fit, at my lowest weight, and after my hardest racing, I fell to -1.1 in my spine.  Additionally, while my already low spinal bone density fell to abnormal levels, my hip density fell dramatically and continued to trend downward.

This information gave me new evidence for some of my new 2011 goals.  I will spend more time on my feet cross training this off-season, including running, hiking, and snowshoeing.  Last year I had planned to add weight training, but eventually I never went to the gym.  This year I am making it a specific goal to do so, not only for my strength, but my overall well being.


I hope this gives you some perspective on the benefits of advanced testing.  I’m sure you can see why PROs use frequent tests of their physiology to make sure they’re on track and staying healthy.  For the rest of us, we need to take what we can get and use approximations and cheaper alternatives.  Personally I can see with clarity that these tests have helped me make specific changes for next year’s training regime.

About Russell

I have been racing bicycles for a decade. This blog will chronicle my efforts as a Category 1 road racer lining up with the pros.
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