Body composition changes over a 4-year span in American college football players.

American collegiate football players (13 lineman; 14 non-lineman) underwent total body composition assessment using dual energy x-ray absorptiometry during August football camp in 2019 (Year 1/baseline); 2021 (Year 3); and 2022 (Year 4). Data were not collected in 2020 (Year 2) due to COVID. Main outcome measures included: total mass (TM); lean mass (LM); fat mass (FM); and bone mass, assessed as bone mineral density/BMD). Lineman had significantly more TM (124 ± 15 vs. 89 ± 15 kg; p < 0.001), LM (90 ± 6 vs.72 ± 10 kg; p < 0.001), and FM (31 ± 9 vs. 15 ± 5 kg; p < 0.001) versus non-lineman. 2-way ANOVA demonstrated no difference between Groups (linemen vs. non-linemen) but significant (p < 0.001) increases in LM (3.3 kg ± 2.4/4.1%) and BMD (0.04 ± 0.04 g/cm/3%) across Time. Correlations between LM vs. TM were significant (p < 0.0001) for linemen (r 2 = 0.80) and non-linemen (r 2 = 0.98), with the regression slopes intersecting at a TM "breakpoint" of 104 kg. A positive correlation was noted between the 4-year change (Δ) in LM Δ vs. FM Δ for linemen only (r 2 = 0.54; p = 0.004), with slope equations predicting a 1.8 kg increase in FM for every 1 kg increase in LM. In conclusion, longitudinal body composition gains are modest (3-4%) with linemen gaining more FM (2:1) than LM, above a 104 kg TM threshold. Our modest sample size requires confirmation in larger cohorts.