Normative fat-free mass index values based on body composition method in Army personnel

Abstract: Background: Normative fat-free mass index (FFMI) values with proposed upper and lower thresholds have been established in sport. However, FFMI has not been widely reported in military personnel. Given the importance of FFM as a predictor of military performance and physical readiness, the purpose of this study was to provide normative FFMI values in Army personnel and propose initial FFMI classification ranges in male and female Army personnel based on various body composition methods. Methods: A sample of 504 Army personnel (n=351 male [age 27.3±6.8 years; height 177.6±8.6 cm; body mass 86.4±14.8 kg]); n=153 female [age 28.4±7.8 years; height 164.1±8.0 cm; body mass 67.6±11.4 kg]) participated. Body mass and height were measured via digital scale with a stadiometer. Fat-free mass was assessed by multiple body composition methods (Army tape test [ATT], bioelectrical impedance analysis [BIA], and dual-energy x-ray absorptiometry [DXA]). Mean, range, and percentile ranks of FFMI were calculated for all soldiers based on body composition method. Univariate ANOVA evaluated differences in FFMI between MOS category, occupational type, and body composition methods (p<.05). Results: A majority of our sample were enlisted (75.2%) and those with a combat support specialty (46.6%). Among females, FFMI was 17.5±1.9, 17.9±1.6, 16.9±1.6 kg·m−2, for ATT, BIA, and DXA, respectively. For males, FFMI was 21.6±2.2, 21.6±2.5, and 20.4±2.2 kg·m−2, for ATT, BIA, and DXA, respectively. DXA-derived FFMI was significantly lower than BIA (p<.001) in females and BIA (p<.001) or ATT (p=.004) in males. Depending on body composition method, the 15–85th percentile was 15.5–18.3 kg·m−2 and 18.1–23.0 kg·m−2 for females and males, respectively. Low FFMI status was classified as ≤ 14.5–15.5 kg·m−2 and ≤ 17.7–18.3 kg·m−2 in female and male soldiers, respectively. Conclusion: This is the first investigation to report normative FFMI values and propose classification ranges in Army personnel. The FFMI values presented may provide a more comprehensive and modernized body composition analysis, such that accession and retention standards include a minimum FFMI threshold.