Research Review: The Association Between Body Composition and Performance on Military Fitness Tests

A USAF Special Tactics tactical air control party candidate leads his teammates in pushups during assessment and selection at Hurlburt Field, Florida, Sept. 24, 2020. (U.S. Air Force photo by Tech. Sgt. Rose Gudex)

By Rob Shaul

BLUF

A study on Air Force Special Warfare candidates found that while traditional calisthenic tests (like pull-ups and running) favor leaner athletes, modern occupational tests —like rucking and farmer’s carries—having more muscle mass and even a higher BMI correlates with better performance.

Study Details

The study was completed on 1,337 US Air Force Airmen attempting to qualify for the USAF Special Tacticals training pipeline from 2018 to 2021. The majority (1,250) were enlisted and only 48 had prior service.

Special Warfare candidates must take and pass two fitness assessments to qualify for the training pipeline, the calisthenic-based Initial Fitness Test (IFT) and the the occupational-based Candidate Fitness Test. Below are the test events for both:

Initial Fitness Test (IFT)

• Max Rep Pull Ups in 2 Minutes
• Max rep Sit Ups in 2 Minutes
• Max Rep Push Ups in 2 Minutes
• 1.5 Mile Run for Time
• 500m Swim for Time

Candidate Fitness Test

• 3-Mile Ruck for Time @ 60lbs
• Broad Jump
• Pro Agility Drill for time (left)
• Pro Agility Drill for time (right)
• 3RM Max Dead Lift
• Max Rep Pull Ups
• 100-yard Farmer’s Carry for time @ 2x 24kg kettlebells
• 300-Yard Shuttle for time
• 1,500m Swim for Time – with fins

Anthropometric and body composition measurements were completed at the beginning of the developmental course. Body mass and body composition were measued by trained staff using an InBody 770 machine. Recorded body composition components include body mass, fat mass, skeletal muscle mass (SMM), BMI, and % bodyfat.

Correlation analyses were performed by running Pearson correlations between each relevant body composition measurement and fitness test result. For body composition, this included body mass, BMI, SMM, fat mass and % bodyfat. For fitness testing, this included the raw score on each component of the IFT and CFT, and the composit CFT Score.

Results

When it came to the traditional calisthenic test  (pull-ups, sit-ups, and a 1.5-mile run), candidates with lower body mass and lower body fat generally performed better. If you have to pull your chin over a bar repeatedly, being lighter helps.

However, the CFT results flipped the script. This test included a 3-mile ruck, a heavy farmer’s carry, and a 3-rep max deadlift⁴. Here, higher skeletal muscle mass and even a higher BMI were linked to better performance..

For example, the farmer’s carry showed a large negative association with skeletal muscle mass, meaning those with more muscle completed the carry significantly faster. Similarly, the deadlift favored candidates with higher overall body mass and BMI. When you add external loads—like heavy kettlebells or a ruck—mass moves mass. It makes intuitive sense that a 250 pound airman doing a 100-yard farmer’s carry for time @ 2x 24kg kettlebells would move faster than a 150 pound airman completing the same event. The smaller airman is carrying over half his bodyweight.

In the general public, a high BMI often indicates poor health. But in this group of fit candidates, a higher BMI (often pushing into the “overweight” category) was actually beneficial for strength-heavy tasks. The authors noted that the “overweight” range (BMI 25-30) might actually be ideal for completing military obstacle courses or heavy lifting tasks, provided that weight comes from muscle, not fat.

Swimming was an outlier. Body composition didn’t seem to matter much for swim performance. Neither low body fat nor muscle mass strongly correlated with swim times. The authors suggest this might be because higher body fat provides buoyancy, which could offset the drag that usually slows swimmers down.

Source: 
The Association Between Body Composition and Performance on Military Fitness Tests, Feeney et al. Journal of Strength and Conditioning Research 2025; 39(1):94-98.