Abstract
Fat-free mass index (FFMI) is a heightadjusted assessment of fat-free mass (FFM), with previous research suggesting a natural upper limit of 25 kg. m(-2) in resistance trained male athletes. The current study evaluated upper limits for FFMI in collegiate American football players (n = 235) and evaluated differences between positions, divisions, and age groups. The sample consisted of 2 National Collegiate Athletic Association Division I teams (n = 78, n = 69) and 1 Division II team (n = 88). Body composition was assessed via dual-energy x-ray absorptiometry and used to calculate FFMI; linear regression was used to normalize values to a height of 180 cm. Sixty-two participants (26.4%) had height-adjusted FFMI values above 25 kg.m(-2) (mean = 23.7 +/- 2.1 kg.m(-2); 97.5th percentile = 28.1 kg.m(-2)). Differences were observed among position groups (p < 0.001; eta(2) = 0.25), with highest values observed in offensive linemen (OL) and defensive linemen (DL) and lowest values observed in offensive and defensive backs. Fat-free mass index was higher in Division I teams than Division II team (24.3 +/- 1.8 kg.m(-2) vs. 23.4 +/- 1.8 kg.m(-2); p, 0.001; d = 0.49). Fat-free mass index did not differ between age groups. Upper limit estimations for FFMI seem to vary by position; although the 97.5th percentile (28.1 kg.m(-2)) may represent a more suitable upper limit for the college football population as a whole, this value was ex-ceeded by 6 linemen (3 OL and 3 DL), with a maximal observed value of 31.7 kg.m(-2). Football practitioners may use FFMI to evaluate an individual's capacity for additional FFM accretion, suitability for a specific position, potential for switching positions, and overall recruiting assessment.
