Body Fat and PT test performance

  • Published
  • By Guy Leahy
  • Health Promotion Flight

With the Air Force physical fitness assessment on hold until October 2020, and the abdominal circumference (AC) component delayed until 2021, there may be a temptation for some Airmen to exercise less and eat more, assuming they can still pass. That’s not a good idea as 99.7% of Airmen who fail the AC test also fail at least one other component (run, push-ups, sit-ups). This indicates that excess body fat is the overwhelming contributor to PT test failure, regardless of the component. 

Too much body fat is dead weight and it slows Airmen down on the run test and makes push-ups/sit-ups more difficult. I and colleagues of mine recently posted online research on this subject as part of a virtual strength and conditioning conference. Our research focused on the effect of fat mass and fat free mass on 1.5 mile run times. 

For fat free mass (FFM), which is everything but fat, we found no significant relationship between FFM and run times. For fat mass (FM) and run times, however, there was a significant relationship; higher body fat (FM) = slower run times. 

For example, an Airman with an average body weight of 176 lbs and 26% body fat would result in a run time of 12:20. By contrast, an Airman with a weight of 154 lbs and 15.5% body fat would record a run time of 11:11, over one minute faster. 

The effect of body fat was so strong that we were able to estimate how much slower an Airman would run based on how much excess body fat they had. For every extra 2.2 pounds of body fat, the run time would be 5.5 seconds slower. Therefore, 11 pounds of body fat would slow run times by 27.5 seconds, and 2 pounds of body fat would slow run times by 55 seconds; almost a minute. 

This ‘fat drag’ effect on run times can be substantial. I recently conducted a Bod Pod test on an Airman, and calculated that if he reduced his body fat to 20%, (which is the upper limit for healthy body fat in males) his run time would improve by 75 seconds! 

Let’s take two hypothetical Airmen. Both Airmen have the same amount of FFM. Airman A has 20 pounds more body fat than Airman B. Airman B, however, is wearing a ruck which weighs 20 pounds.

If both Airmen run 1.5 miles, the 20 pound ruck will degrade Airman B’s run time TO THE SECOND the exact same amount as the 20 pounds of body fat degrades the run time of  Airman A; there’s no difference at all.

A similar effect has been observed with push-ups. When you perform a push-up, the primary resistance is gravity, which is the same for everyone. How much added mass you have to move against a constant resistance matters. Excess body fat for a push-up test is like wearing a ruck, except that every Airman’s ‘ruck’ is a different weight, depending on how much body fat they have. 

In fact, research has shown that if everyone who took a run test or push-up test wore a 30 pound ruck, the added mass would result in a test in which the outcome is independent of body size. That 30 pounds will be a larger percent increase in weight for smaller Airmen relative to bigger Airmen, so it cancels out the advantage that a smaller Airman would normally have. 

The take-home message is that spending time in the weight room gaining muscle won’t slow down your run time (it may actually improve run times) but excess body fat WILL slow down your run times, and make push-ups/sit-ups more difficult. For information on how to reduce your ‘fat drag,’ contact the Health Promotion Flight at 846-1186.