Knee And Hip Joint Reaction Force Dampening During Running In Heavier American Style Football Players

American style football players (ASF) encounter osteoarthritis (OA) risk factors, including excessive body weight and high joint loads. Further, retired ASF over 50 years old are 10 times more likely to require hip or knee arthroplasty compared to other retired professional athletes, with linemen being at greater risk. These factors highlight the need for early career joint kinetics assessments. PURPOSE: To compare normalized hip and knee joint kinetics associated with OA risk between lighter and heavier ASF during high-speed running. METHODS: One-hundred twenty-five ASF from a professional draft preparation camp were categorized into lighter (n1 = 64, mass = 86.8 ± 6.7 kg) and heavier (n2 = 61, mass = 116.6 ± 16.1 kg) groups based on a median mass of 94.5 kg. ASF performed a 5-sec run at 5.5-6.5 m/s on an instrumented treadmill synchronized with 10-camera motion capture system. Data were processed in Vicon Nexus (version 2.16) and MATLAB. Group differences in normalized peak compression (-Z) net joint reaction forces (JRF) and adduction moments and normalized average vertical ground reaction forces (vGRF) were determined using independent t-tests (p < .05). RESULTS: The heavier group exhibited significantly lower bilateral hip and knee net JRF (p < 0.001), knee adduction moments (KAM) (p < 0.05), and vGRF (p < 0.05), but no significant difference in left (3.09 ± 0.91 vs. 3.13 ± 0.83 Nm/kg) and right (3.05 ± 0.72 vs. 3.16 ± 0.85 Nm/kg) hip adduction moments (p > 0.05). Left and right hip JRF were 24.3 ± 2.6 vs. 25.8 ± 1.9 N/kg and 24.2 ± 2.4 vs. 25.7 ± 1.9 N/kg, respectively. Knee JRF for the left was 24.4 ± 2.0 vs. 25.7 ± 2.1 N/kg and for the right was 24.6 ± 2.4 vs. 25.9 ± 2.1 N/kg. KAM for the left was 2.13 ± 0.47 vs. 2.34 ± 0.46 Nm/kg and for the right was 2.06 ± 0.45 vs. 2.27 ± 0.49 Nm/kg. Left and right vGRF were 17.6 ± 1.3 vs. 18.9 ± 1.2 N/kg and 17.6 ± 1.5 vs. 18.9 ± 1.1 N/kg, respectively. CONCLUSION: Heavier ASF exhibited reduced hip and knee joint compressive forces and knee adduction moments during running, potentially due to increased muscle mitigating loads. Despite this dampening effect, the high incidence of OA in retired ASF suggests that this reduction does not confer long-term protection against OA risk. Longitudinal and more comprehensive monitoring are necessary to better understand OA risk in this population.