I once explained to a client of mine, who is a brilliant astronomer, why I prefer using old school skinfold calipers over my $2000 ultrasound machine—or a $20,000 DEXA machine, for that matter. He said, “You know, NASA spent thousands of dollars developing a pen that would write in space. The Russians? They used pencil.” This is exactly how I feel about methods for measuring body composition.
Every now and then I get into a bit of a scuffle with trainers over this. I’ve seen thousands of clients in my practice and come across many methods of measuring composition, and at the end of the day I stand by the claim that Old School, as with many things—hollow body guitars, tube amps, stick shifts, film cameras, and pencils in space—is still the best way to go.
It’s also important to remember that all methods of body composition have inherent flaws and different methods yield very different results. DEXA and ultrasound tend to be consistent with each other but will spit out much higher body fat percentage numbers than hydrostatic weighing, the BodPod, or calipers. The most important thing is that a method is consistent with itself. From there we look for trends. Remember in science class when they explained accuracy vs. precision?
In this case, accuracy can only truly be known if we were to examine you as a cadaver. Since this isn’t terribly convenient (and probably not desired), we settle for precision. If methods are consistent and performed precisely, then trends in measurements should tell us whether or not a treatment plan is heading in the right direction. And never, ever discount how you feel in your clothes or appearance. You’d be surprised how many people have told me how great they feel and how many clothing sizes they’ve lost, and yet, they still run into my office crying (literally) when the machine tells them otherwise! Never let a machine override your common sense or the glaringly obvious.
An Overview of Methods for Measuring Body Composition
- While DEXA (dual energy x-ray absorptiometry) may be our new gold standard, the problem lies in human error. Well, more like human laziness. I’ve had many clients go for a DEXA scan, lose 3 or 4 pant or dress sizes, only to re-measure a year later and be told they’re fatter—considerably fatter—than they were before they lost the sizes. This is impossible. So where did the doctor’s office go wrong? Apparently, the machine needs to be recalibrated daily but most offices don’t do this. They can let the machine go uncalibrated for weeks or even months! If you do a DEXA scan make sure your facility has calibrated the machine the day of your test and get proof! Human laziness aside, DEXA is also not particularly practical for the size of the machine, cost, and exposure to radiation.
- Bio Impedance Analysis is my least favorite of all body composition methods. While some scales are better than others—and certainly better than handhelds—I’ve never seen this method achieve satisfactory consistency with itself. I used to work at a fitness club where we had a $4000 BIA machine. I can’t tell you how many clients cried in my office over the numbers they got from that machine when they had, in fact, significantly improved their composition. The machine was so finicky, if you breathed on it or shifted your weight or, most important, popped on it at anything less than fully hydrated, you would get a crazily inflated number. Essentially, BIA measures the resistance to an electrical signal from one hand and/or foot on a sensor to the other hand/foot. Since water is a conductor of electricity, if you are dehydrated even in the slightest, you will end up with an inflated number.
- Hydrostatic weighing used to be our gold standard and while it has always been consistent with the BodPod and caliper numbers, it’s not particularly convenient to have a water tank or even a tub in the office. Nor is it fun for the subject to frequently slip into their bathing suit exhale all air from their lungs and then dunk themselves underwater…over and over again until they can maintain the required stillness. Unless you’re experienced at drowning, most find it particularly unpleasant.
- The BodPod results are consistently consistent with hydrostatic weighing and calipers, and, even more important, it’s consistent with itself. But like hydrostatic weighing, the Pod takes up considerable space, is not portable, and is wildly expensive. It also doesn’t measure specific areas of the body so you cannot pinpoint problem spots or determine how fat is distributed.
- Ultrasound is my second favorite method. It’s a convenient handheld device that is non-invasive, portable, and fairly consistent with itself. It’s great for assessing visceral fat which lies under a layer of muscle. Skinfold measurements can’t get to visceral fat. This seems to be the preferred method of Tim Ferris. But as someone who measures clients weekly, it is not as sensitive to small increments of change as the calipers. And like the calipers it is subject to more error depending on the pressure applied by the wand to the site being measured. The margin of error for precision because of this is actually much greater than it is with the calipers. It’s easier to find a consistent measurement site and let the caliper spring do the work than it is to apply the exact same wand pressure to a site. And while your main objective may be to measure only body fat, I find the calipers are actually pretty handy for assessing other things as well. But like the calipers, ultrasound does enable you to see how fat is distributed throughout the body.
- Which brings us to good ol’ skinfold calipers. Yes, they’re primitive but they’re still my go-to. And I’m not the only one. My friend who works with a fifth of the NFL, various college teams, and a huge Rolodex of professional athletes uses the same retro-green Lange calipers that I do. He’s the only person I know who’s gone through more pairs than I have. Yes, caliper numbers are subject to inaccuracies but I’ve found them to be more reliable than any other method in the hands of an experienced professional pincher.
Troubleshooting Caliper Measurements
- Site consistency. The measurer needs to have reliable landmarks to measure and hit them every time.
- Separation of fat from muscle. Most sites require some kind of flexing and relaxation of the muscles in the area to help separate fat from muscle. Too often—almost always—I see trainers just grab people and measure. This happens at the highest levels of professional athletics, by the way. I’ve had NBA players report back to me with horror at the lack of technique often involved in team measurements.
- Multiple measurements Most trainers will only take one measurement. I take at least three for every site. All should be within a millimeter of each other and if there are outliers, take more measurements until they are consistent!
Next week, we’ll discuss an even more important function of calipers as a tool for measuring inflammation.