Research Review: BMI Doesn’t Reflect Strength or Readiness in Tactical Testing

BLUF (Bottom Line Up Front)

This study looked at how body composition—muscle mass, fat mass, body fat percentage, and body weight—relates to performance on two different military fitness assessments. For bodyweight-based events like push-ups and running, candidates with lower body fat and less mass generally performed better. For strength and load-bearing tasks like deadlifts and weighted carries, more muscle mass helped performance. Importantly, a higher body mass index (BMI) was not a negative factor in this population—higher BMI often meant more muscle, not fat. The results suggest training to increase lean muscle while managing body fat is key for improving military fitness outcomes.

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Purpose of the Study

To examine how body composition affects performance on two different fitness assessments used for United States Air Force Special Warfare candidates:

1. A calisthenic-based fitness test (push-ups, sit-ups, pull-ups, running, and swimming)
2. A task-based fitness test (deadlifts, ruck marches, weighted carries, shuttle runs, and swimming)

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Subjects and Methods

• The study included 1,337 male candidates assessed between 2018 and 2021
• Body composition was measured using a bioelectrical impedance device (InBody 770)
• The assessments included:
  • Pull-ups, push-ups, sit-ups, 1.5-mile run, and 500-meter swim
  • Deadlift (three-rep max), standing broad jump, agility shuttle, 3-mile ruck march, weighted farmer’s carry, and 1,500-meter swim
• Researchers analyzed how body mass, muscle mass, fat mass, body fat percentage, and BMI related to performance in each event

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Key Findings

1. Bodyweight Fitness Favored Leaner Builds

• Candidates with lower body fat and lower overall mass performed better in pull-ups, push-ups, and sit-ups – as expected
• Faster run times were associated with lower body fat and BMI
• Swim performance in the shorter distance (500 meters) was weakly associated with higher muscle mass and overall body mass

2. Strength and Tactical Tasks Favored Muscle Mass

• Performance in the occupational-style assessment—deadlifts, rucking, and carries—was strongly linked to higher muscle mass
• The deadlift was positively correlated with higher body mass, BMI, and muscle mass
• Candidates with more muscle mass performed better in the weighted carry and 3-mile ruck march
• More fat mass and higher body fat percentage were associated with worse performance in the shuttle, agility test, and ruck march

3. Body Fat Percentage Hurt Performance Across Tests

• Higher body fat percentage consistently correlated with poorer outcomes in endurance, agility, and strength events
• Candidates with more fat mass were slower in running and rucking and performed worse in agility and shuttle events

4. Body Mass Index Misrepresents Readiness in Tactical Athletes

• BMI was positively associated with performance in several strength-based tasks
• In this fit, high-performance population, a higher BMI usually indicated more muscle—not excess fat
• The authors recommend caution when using BMI to evaluate military candidates, as it may misclassify muscular individuals as overweight

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Conclusion

Candidates with more muscle mass and lower body fat performed better on both traditional and tactical fitness tests. Calisthenic and endurance-based tasks favored leaner athletes. Strength and load-bearing tasks favored heavier, more muscular builds. Across the board, excess fat mass hurt performance. While BMI is often used as a general fitness measure, it failed to distinguish between fat and muscle in this population. For tactical performance, the best approach is to increase lean muscle while keeping body fat in check.

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Bibliography

Feeney, K.A., Melton, B.F., Ryan, G.A., Bland, H.W., & Butler, C.R. (2025). The Association Between Body Composition and Performance on Military Fitness Tests. Journal of Strength and Conditioning Research, 39(1), 94–98. https://www.nsca.com