Lean mass predicts soldier performance where BMI falls short

Militaries have long leaned on body mass index and simple body measurements to judge whether personnel are ready for duty, yet BMI cannot distinguish a kilogram of muscle from a kilogram of fat. Whether body composition genuinely predicts strength, endurance, load carriage and injury risk, and how consistently, has been described unevenly across military populations, settings and assessment methods. The answer matters well beyond the armed forces, because military personnel offer a demanding real-world test of how body composition relates to physical performance. This review set out to pull the scattered evidence together.

Following PRISMA 2020 guidance and a protocol registered in advance, the authors searched PubMed/MEDLINE, Web of Science, LILACS/BVS, Scopus and Embase for experimental and observational studies of adult military personnel of either sex that linked anthropometric or body composition variables to physical performance, operational capacity or musculoskeletal injury risk. From 3,320 records identified, 17 studies met the criteria. Methodological quality was assessed with National Heart, Lung, and Blood Institute tools. Because the studies disagreed with each other in design, body composition measures and performance outcomes, the findings were synthesised qualitatively rather than pooled statistically.

Greater total lean mass and a favourable distribution of muscle across body segments were generally associated with better strength, power, load carriage and cardiorespiratory performance. In the other direction, higher body fat percentage, elevated BMI, visceral fat and larger waist circumference were generally associated with poorer cardiorespiratory and functional performance, and in some studies with greater musculoskeletal injury risk. Across the included studies, direct measures of body composition consistently provided more meaningful performance-related information than BMI alone.

The direction of these findings fits the wider literature linking lean mass to strength and endurance and excess fat to poorer function, but this review consolidates it specifically in military populations across varied operational settings. Because the underlying studies could not be pooled, the strength of each relationship cannot be sized precisely, and the links reported are associations rather than demonstrations of cause. The authors call for more methodological consistency, more studies including women, and outcomes that better reflect real operational demands.

The practical thread here is about measurement: BMI treats muscle and fat identically, and these studies suggest that distinction is exactly where the useful information lives. Greater lean mass tracked with better performance across strength, power, carrying load and endurance, while markers of fatness, especially visceral fat and waist circumference, tracked the other way. This is a reason to judge fitness by body composition rather than scale weight or BMI alone, while remembering that these are associations in a specific population, not proof of cause.