The Impact of Localized Muscle Mass on Sprint Mechanics During the Swing and Stance Phases of Division I Collegiate American Football Players.

Abstract: Metoyer, CJ, Lever, JR, McGinty, M, Landow, L, Hunt, R, Hauenstein, JD, Huebner, A, Stone, MH, and Wagle, JP. The impact of localized muscle mass on sprint mechanics during the swing and stance phases of Division I collegiate American football players. J Strength Cond Res XX(X): 000-000, 2025-This study evaluates the impact of localized muscle volume on sprint mechanics among Division-I collegiate American football players across 3 position groups: Skills (Defensive Backs, Wide Receivers), Mids (Linebackers, Running Backs, Tight Ends), and Bigs (Offensive, Defensive Linemen). A total of 108 male athletes (age: 21.4 ± 1.9 years, BMI: 29.6 ± 4.3) were assessed. Lower extremity muscle volumes were measured using magnetic resonance imaging, and sprint kinematics were captured using an inertial motor unit system during maximal effort sprints. Stepwise multiple linear regressions were conducted to evaluate the relationship between muscle volumes, stance, and swing times for each position group. In the Skills group, increased volumes in the vastus intermedius (β = -0.15, p < 0.01) and sartorius (β = -0.17, p = 0.01) were associated with reduced swing time, while those in the vastus medialis (β = 0.18, p < 0.01) increased swing time. For stance time, the gluteus maximus (β = -0.02, p = 0.03) was associated with reduced stance time, and the tibialis posterior (β = 0.28, p < 0.01) increased it. In the Mids group, the biceps femoris long head (β = -0.15, p < 0.01) was associated with reduced stance time, while the vastus medialis (β = 0.09, p < 0.01) increased it. In the Bigs group, the rectus femoris and sartorius were associated with reduced stance time, while the tensor fasciae latae and tibialis anterior increased stance time. These findings highlight the role of localized muscle volume in influencing sprint mechanics and emphasize the potential need for position-specific physical development programs tailored to the biomechanical demands of running mechanics in American football players.