Burning Runner: No Missed Measurements

If measurement the key to fat loss, the first stop is the gold standard of body fat analysis: the DEXA body composition scan.

The Fit Scan’s DEXA technician, Tara O’Connell, prepares the DEXA report. The entire procedure took 20 minutes tops.

If measurement the key to fat loss, the first stop is the gold standard of body fat analysis: the DEXA body composition scan.

Written by: T.J. Murphy

“What gets measured gets improved,” is a mantra when it comes to training, and perhaps just about any other endeavor. Based on conversations with Crossfit Endurance founder, Brian MacKenzie, and recent reading I’ve been doing I’ve decided to put my diet through a microscope to see where the holes are in my nutrition.

The first thing MacKenzie asked me to do was to get a proper body fat measurement test. I did this Tuesday afternoon with a quick visit to The Fit Scan in Encinitas, Calif. ( — a licensed DEXA body fat scanning center. I first came across DEXA scanning in reading Tim Ferriss’s new book, “The 4-Hour Body,” where Ferriss ranks DEXA as his favorite, most precise method of calculating body fat. DEXA is indeed largely referred to as the gold standard of body measuring technologies, and measures the three primary components of the human body—muscle, fat and bone. Not only does the DEXA scan tell you how much but also tells you where—professional sports athletes can refer to a DEXA scan to let them know how much lean muscle tissue is in the right arm versus the left. I asked Gavin Zaid of the Fitness Scan if this could give the client a general idea of a strength imbalance in the works. “Not just a general one—you’ll get a very specific idea of any imbalances.”

In addition to whatever other practical values the DEXA offers, I was happy to know that I wouldn’t have to be dunked in a tank of water. One of the previous gold standards, Hydrodensitometry Weighing—aka underwater weighing—can require the subject to have to be dunked multiple times to gain an average percentage, and part of the equation is how much residual air is in your lungs at the time of being dunked, as you’re required to expel as much as possible before you go underneath.

The DEXA scan is easier than being measured with body fat calipers. You just lie on a cushioned platform and hold relatively still for a few minutes while the platform slowly glides underneath the scanner above.  The DEXA composition analysis is  non-invasive and exposes you to a low-dose of X-ray radiation. There’s no sensation to the procedure—and the only rule I was asked to follow in what I was wearing was to use clothes without metal zippers. So I went in my running stuff.

The scanning took four minutes or so, and the DEXA technician,  Tara O’Connell, came in and went straight to a nearby computer. She took a few minutes to align the scan into a software program and then wham, the computer printed up a four-page report that included a summary page of my results, a page that helps you determine the analysis report, a bone density analysis, and the DEXA results summary, the told me, for example, in grams, precisely how much muscle, fat and bone existed in my arms, trunk, legs and head. My left arm had 96.4 grams more fat than my right arm, a fact that seemed weird to me until Zaid told me “this is because you’re right-handed. It’s common.”

My overall body fat percentage was 16.8%, the key number I was looking to dial in for MacKenzie as I embrace an additional measuring tool—weighing and measuring everything I eat. I’ll be reporting on that tomorrow.


T.J. Murphy is the Editorial Director of Competitor Magazine. A 2:38 marathoner and five-time Ironman finisher, he is the former editorial director of Triathlete Magazine and Inside Triathlon. His writing has also appeared in Outside Magazine and Runner’s World.