Jack Stensland

Background/Objectives: National Football League (NFL) American football players are exposed to osteoarthritis risk factors of obesity and high joint loads. We sought to examine the association between total body mass (TBM), lean body mass (LBM), body fat percentage (BF%), and normalized compressive knee joint reaction forces (JRFcomp), peak knee adductor moments (KAM), and vertical ground reaction forces (vGRF) in NFL draft-eligible players during a high-speed run. Methods: A total of 125 participants ran a single trial at 5.5–6.5 m/s for 5 s on an instrumented treadmill. Bilateral vGRF and knee joint kinetics were calculated using inverse dynamics. Body composition was assessed using bioelectrical impedance. Results: LBM demonstrated significant moderate associations with vGRF (left, r(123) = −0.56, p < 0.001; right, r(123) = −0.60, p < 0.001) and low-to-negligible associations with KAM (left, r(123) = −0.20, p = 0.026; right, r(123) = −0.30, p < 0.001) and JRFcomp (left, r(123) = −0.39, p = 0.020; right, r(123) = −0.38, p = 0.015), respectively. TBM showed significant moderate negative associations with vGRF (left, r(123) = −0.56, p < 0.001; right, r(123) = −0.61, p < 0.001) and low-to-negligible associations with KAM (left, r(123) = −0.21, p = 0.021; right, r(123) = −0.28, p = 0.002) and JRFcomp (left, r(123) = −0.39, p < 0.001; right, r(123) = −0.37, p < 0.001), respectively. BF% showed significant low-to-negligible negative associations with JRFcomp (left, r(123) = −0.21, p < 0.001; right, r(123) = −0.22, p < 0.001) and vGRF (left, r(123) = −0.39, p < 0.001; right, r(123) = −0.41, p < 0.001), respectively, and no significant associations with KAM, p > 0.05. The heavier group exhibited significantly lower normalized JRFcomp, and vGRF, p < 0.05. Conclusions: Heavier, but not fatter, players attenuate knee loads. Dampening may be a short-term protective strategy for joints of heavier players.

Background/Objectives: Using advanced methodologies may enhance athlete profiling. This study profiled morphological and laboratory-derived performance biomechanics by position of American-style football players training for the draft. Methods: Fifty-five players were categorized into three groups: Big (e.g., lineman; n = 17), Big–skill (e.g., tight end; n = 11), and Skill (e.g., receiver; n = 27). Body fat (BF%), lean body mass (LBM), and total body mass were measured using a bioelectrical impedance device. Running ground reaction force (GRF) and ground contact time (GCT) were obtained using an instrumented treadmill synchronized with a motion capture system. Dual uniaxial force plates captured countermovement jump height (CMJ-JH), normalized peak power (CMJ-NPP), and reactive strength. Asymmetry was calculated for running force, GCT, and CMJ eccentric and concentric impulse (IMP). MANOVA determined between-group differences, and radar plots for morphological and performance characteristics were created using Z-scores. Results: There was a between-group difference (F(26,80) = 5.70, p < 0.001; Wilk’s Λ = 0.123, partial η² = 0.649). Fisher’s least squares difference post hoc analyses showed that participants in the Skill group had greater JH, CMJ-NPP, reactive strength, and running GRF values versus Big players but not Big–skill players (p < 0.05). Big athletes had greater BF%, LBM, total body mass, and GCT values than Skill and Big–skill athletes (p < 0.05). Big–skill players had greater GCT asymmetry than Skill and Big players (p < 0.05). Asymmetries in running forces, CMJ eccentric, and concentric IMP were not different (p > 0.05). Morphological and performance biomechanics differences are pronounced between Skill and Big players. Big–skill players possess characteristics from both groups. Laboratory-derived metrics offer precise values of running and jumping force strategies and body composition that can aid sports science researchers and practitioners in refining draft trainee profiles.