Upper and lower thresholds of fat-free mass index in a large cohort of female collegiate athletes

Fat-free mass index (FFMI) is a height-adjusted metric of fat-free mass which has been suggested as a useful method of body composition assessment in athletic populations. The purpose of this study was to determine sport-specific FFMI values and the natural upper threshold of FFMI in female athletes. 372 female collegiate athletes (Mean±SD; 20.03±1.55 years, 167.55±7.50 cm, 69.46±13.04 kg, 24.18±5.48% bodyfat) underwent body composition assessment via dual-energy x-ray absorptiometry. FFMI was adjusted to height via linear regression and sport-specific reference values were determined. Between-sport differences were identified using one-way ANOVA with Tukey post-hoc tests. Average FFMI was 18.82±2.08 kg/m2; height-adjusted values were not significantly different (p<0.05) than unadjusted values. FFMI in rugby athletes (20.09±2.23 kg/m2) was found to be significantly higher (p<0.05) than in gymnastics (18.62±1.12 kg/m2), ice hockey (17.96±1.04 kg/m2), lacrosse (18.58±1.84 kg/m2), swim & dive (18.16±1.67 kg/m2), and volleyball (18.04±1.13 kg/m2). FFMI in cross country (16.56±1.14 kg/m2) and synchronized swimming (17.27±1.47 kg/m2) was significantly lower (p<0.05) than in Olympic weightlifting (19.69±1.98 kg/m2), wrestling (19.15±2.47 kg/m2), and rugby. The upper threshold for FFMI in female athletes (97.5th percentile) was 23.90 kg/m2. These results can be used to guide personnel decisions and assist with long-term body composition, training, and nutritional goals.