Brad S. Currier1, Patrick S. Harty1, Jessica M. Moon1, Shane A. Ponder1, Richard A. Stecker1, Hannah A. Zabriskie1, Andrew R. Jagim1, Chad M. Kerksick1, FACSM

1Lindenwood University, St. Charles, Missouri

Fat-free mass index (FFMI) is a body composition metric that has been employed to assess relative muscularity, with a 28.1 kg/m2 upper limit reported in male athletes. FFMI is calculated by dividing fat-free mass by squared height, though further height corrections via linear regression may be required to normalize FFMI in taller individuals. To date, only two investigations have reported height-adjusted FFMI (FFMIAdj) in males. PURPOSE: The purpose of this study was to report height-adjusted FFMI data and natural upper limits of FFMI in male collegiate athletes. METHODS: The body composition of 209 male collegiate athletes from 10 sports (Mean ± SD; Age: 20.7 ± 1.9 years, Height: 182.9 ± 6.7 cm, Weight: 90.8 ± 16.8 kg, Percent Body Fat: 15.6 ± 5.3 %) was measured using dual-energy x-ray absorptiometry. The height adjustment was calculated by regressing unadjusted FFMI against height in all athletes above the median unadjusted FFMI. The slope of this line was used to adjust all FFMI values. The natural upper limit for FFMIAdj in this sample was determined by calculating the 97.5th percentile of all values. FFMIAdj data were assessed for normality using the Shapiro-Wilks test. One-way ANOVAs with Tukey post-hoc comparisons were used to determine between-sport differences. RESULTS: The slope of the line used in height adjustment was -0.014 (p = 0.631). A paired-samples t-test revealed a significant difference (0.041 kg/m2, p < 0.001) between unadjusted and adjusted mean FFMI values. The overall mean FFMIAdj was 22.8 ± 2.8 kg/m2. FFMIAdj was not normally distributed and was log transformed prior to analysis. Significant between-sport differences (p < 0.001) in FFMIAdj were identified. Upper limits (97.5th percentile) for FFMIAdj were found to be 28.32 kg/m2 for the entire cohort while upper limits for rugby and baseball were found to be 29.1 kg/m2 and 25.5 kg/m2, respectively. CONCLUSION: This study reported FFMIAdj values in a diverse cohort of male collegiate athletes, providing data for the first-time in several sports. These values can be used to guide nutritional and exercise interventions and provide coaches with standardized information regarding the potential for further fat-free mass accretion in male athletes.

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