Monday, June 23, 2014

Should the Waist Measurement be Part of the USAF PT Test?

(This post was actually adapted from a paper I wrote for an English class that I thought would be an interesting topic for this blog. Just keep in mind that this my personal opinion and does not reflect the opinions of the USAF in any way, shape, or form.)

Every year, the US Air Force (USAF) spends billions of dollars both training and retaining its military members. (1) To make sure that these well-trained members are physically fit enough to accomplish their jobs, it also created a bi-annual physical fitness test. This test includes two strength components (the push-up and sit-up), an aerobic component (the 1.5-mile run), and a body fatness component (the waist measurement). 

If someone fails this PT test too many times, they are seen as unfit and are very likely to get kicked out of the military. So, obviously, if you want to stay in the Air Force, you must consistently pass your PT test.

But there's something strange in the USAF PT test: The waist measurement. The strength and aerobic components seem like a valid way to measure physical fitness, but the body fat component seems a bit out of place. What does the size of my waist have to do with my ability to be "fit-to-fight"?

How the Waist Measurement got Its Start
The requirement for an annual military fitness test actually got its start in 1981 when Jimmy Carter commented that too many military members looked unfit in their uniforms. (2) His use of the word “unfit” referred to excess body fatness, not physical fitness. This comment prompted the Department of Defense (DoD) to mandate all military services to evaluate the fitness of its members annually later that year. In addition to measuring strength and aerobic capacity, this updated definition of fitness also included the measurement of body fatness. (3)

You can thank US President Jimmy Carter for today's annual PT test (as well as the waist requirement).

Initially, the DoD allowed each service to identify body fatness in their own way. But, in 2002, the DoD mandated that all services use the body mass index (BMI), which uses a formula to divine a person’s general body fatness by looking at their body weight relative to their height. (4) The DoD’s new policy limited military members’ BMI to a maximum of between 25 and 27.5. Members whose BMI exceeded these maximums would be in jeopardy of separation from the military.

Unlike the other services, the Air Force didn't like the BMI and successfully argued that the waist circumference was a better predictor of body fatness and poor health than BMI. (5) It then included this waist measurement in its fitness test, limiting the waist size of men to no larger than 39 inches and women to no larger than 35 inches. BMI would only be measured if a person’s waist was too big.  

BMI and Waist Size do not Predict Body Fatness
Unfortunately, there is a big problem with using BMI or the waist measurement to determine overall body fatness: These measurements can’t identify exactly how much body fat a person actually has. 

Let's start with BMI. The formula for determining BMI is:

As you can see, this number can only measure a person’s body weight relative to their height. At no time is fat or lean mass determined, just relative body weight. This is a big reason why BMI is such a terrible measure of body fat.

Both of these people have the same BMI, but one has much more fat than the other.
Assumptions are often made by health professionals that if a person is overweight by BMI then they will likely have excess body fat. (6) These assumptions are usually correct, except when it comes to athletes, elite soldiers, and fitness enthusiasts, who are notorious for having a high BMI from extra muscle, not extra fat. (7

Then there is the waist measurement, which is no better than BMI at approximating a person's overall body fat percentage. It largely measures visceral fat, which is one of the two main types of fat found in the human body. (8

It is entirely possible for a person to have very low subcutaneous fat (the fat directly under the skin) while also having excessive visceral fat (the fat directly behind the abdominal wall). This causes a condition affectionately known as "pot belly" or "beer belly."

The only way to tell if someone is too fat is to directly measure their body fat. Unfortunately, this is really hard to do (especially measuring visceral fat). Most of the current methods measure body fat indirectly using proxy measurements (e.g., hydro-static weighingair-displacement plethysmographybioelectrical impedanceX-RAYskin folds), with each method exhibiting its own degree of inaccuracy. 

BMI and Waist Size do not Predict Fitness Performance
So BMI and waist size aren't the best way to measure body fatness, but what about fitness? Can either of them predict fitness performance? Not always.

Again, starting with BMI, if you have a job that is very physically demanding (e.g., combat controllers, PJs), then a high BMI does not predict poor fitness, likely because most of the extra weight is lean mass, not fat mass. (9) This would also apply to military members who are heavily into strength and cardio fitness. These technically overweight individuals will likely never struggle with passing the PT test (assuming that these individuals can run well).

On the other hand, odds are good that individuals who have a high BMI because of excess body fat will not be fit. These individuals will likely struggle to pass their PT test (or barely pass). (10

But that's not to say that someone who has a low BMI and a thin waist is guaranteed to pass their PT test. As a PTL, I've seen many normal weight and skinny members who struggle with both the strength and aerobic components. 

And I've yet to come across studies that looked at how waist size correlates with poor fitness, but I've seen many blisteringly fast runners who have a noticeable belly (although not a failing waist size). But it is possible that if someone's waist gets too big (a PT-failing size) then they could have a difficult time passing their 1.5-mile run.

BMI and Waist Size do not Predict Work Performance
As important as health and fitness performance are, what seems most important to the mission is how BMI and waist size affects work performance. Is there a connection? Maybe.

When it comes to learning, there has been some evidence that good physical fitness--but not high BMI or waist size--is positively associated with academic performance, but this evidence isn't very strong. (11,12,13) Work performance also seems to be enhanced by good physical fitness, but high BMI and waist size don't really show themselves to be problematic in this respect either. (14)  

In fact, based on one study, there are many Air Force members who successfully support their assigned missions while being technically overweight or obese by BMI or waist size. (15) And using demographics from the general American population, there is also evidence that many military members are reliably supported by thousands of contracted civilians, many of whom are also considered overweight or obese by BMI or waist size. (16)

A Large Waist Size is Associated with Poor Health 
As far as predictors of body fat, fitness, and work performance are concerned, neither BMI nor waist circumference are very useful. But what about predicting poor health? 

Here the Air Force is spot on: Waist size is a good predictor of poor health. This was demonstrated in to a study conducted in 2004 by The American Journal of American Nutrition, which concluded that when taken on their own, waist circumference had a stronger association with overall health than BMI. (17

Another good indicator of disease risk is Metabolic Syndrome X (MSX), which describes a "group of risk factors that occur together and increase the risk for coronary artery disease, stroke, and type 2 diabetes." These risk factors include:
  • Large waist size 
  • Elevated fasting blood sugar (a.k.a., insulin resistance)
  • Elevated blood pressure
  • Elevated blood triglycerides
  • Decreased blood HDL cholesterol.
  • Excess uric acid in the blood.

Since these risk factors tend to appear together, those who have a PT-failing waist size are likely to also suffer from some or all of the other symptoms of MSX. (18,19,20,21)

The good news is that as you improve your health, your waist size is likely to automatically decrease as well. This decrease in waist size will also likely be followed by improvements in blood sugar, pressure, cholesterol, and uric acid, as well as a much better PT test score.

Should the PT Test Contain the Waist Measurement?
So now that we're at the end of this post, I can answer my original question: Does the waist measurement belong on the PT test?

As I understand it, the point of the PT test is to determine who is fit-to-fight. And I understand "fit" to mean physically fit and able to perform satisfactorily while in garrison and deployed. Looking at the PT test through this lens, I would agree that the strength and aerobic components will do a good job of making sure that all military members are fit enough to perform their duties. However, since the waist measurement isn't very good at predicting fitness or work performance, then it should be removed from the test.

Or, if it is kept in the PT test, maybe the waist measurement could be changed to only be pass/fail. This would allow more points to be awarded to the strength components, giving them the same weight as the aerobic component.

There is another option. Despite the fact that the waist measurement can't determine specific body fatness, it is still an excellent indicator of overall health. Because of that, I think that the waist measurement's proper place is in the Periodic Health Assessment (PHA). Since the PHA is done every year, doing this satisfies the DoD's requirement for "measuring" body fatness annually. More importantly, moving the waist measurement over to the PHA means that an excessive waist size can be treated as the medical problem it is (just like high blood pressure, high cholesterol, insulin resistance, etc.). 

Personally, I really like this third option, especially in light of the recent changes in Air Force PT policy where too many failures within a 24 month period will likely result in separation from the military. By treating a big waist as a health problem--instead of a fitness problem--the USAF keeps from unnecessarily removing too many of its expensively-trained experts (on average, the Air Force invests six months of instruction and spends almost $26,500 to train a single military member (22)). And that helps us all get the mission done.

Am I off base? Let me know what you think!


  1. Bryan--thank you for your post! I am a SMSgt in the Air Force Reserves, and a Health Services Management technician. I am working towards a master's degree in Human Resources Management and I am currently working on a research project about the Air Force Fitness test. I completely agree with your assessment that the waist measurement should be a part of the PHA instead of the Fit to Fight test. I don't know if anyone has actually thought of that solution! It never crossed my mind! Thanks again Dawn Romano

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