Increased Impact Loads In Marine Special Operations Forces Personnel With A Previous Knee Injury

United States Marine Forces Special Operations Command (MARSOC) personnel undergo rigorous training resulting in cumulative mechanical loads on the musculoskeletal (MSK) system and subsequent increased risk of MSK injury. It is important to understand if those who sustained a previous injury exhibit altered loading patterns that affect performance or risk of future injury. PURPOSE: To evaluate running performance and impact loads of MARSOC personnel who sustained a knee injury compared to those without a recent injury. METHODS: 14 MARSOC personnel who reported a knee injury within 18 months of testing but were currently cleared for unrestricted duty were matched to those who reported no lower extremity injuries in the same span. Participants performed a maximal effort 5-minute run on a non-motorized treadmill. Inertial measurement units placed on the anteromedial portion of each tibia measured impacts. Student’s t-tests (α = 0.05) with η2 effect sizes were used to compare group means. RESULTS: The No Injury group had less Total Impact Load (p < 0.001, η2 = 0.425) and Average Intensity (p < 0.001, η2 = 0.215) with greater low intensity steps (p = 0.013, η2 = 0.232) and fewer medium intensity steps (p = 0.009, η2 = 0.085). All other variables yielded no significant differences, including Total Distance (p = 0.617). Table 1. Descriptive statistics of performance and impact variables. * = significant difference, p < 0.05 - Total Distance (yd) *Total Impact Load (L + R) *Average Intensity (L + R) Impact Asymmetry Step Count Total (L + R) *Step Count Total by Intensity - Low 1 g-5 g (L + R) *Step Count Total by Intensity - Medium 6 g-20 g (L + R) Step Count Total by Intensity - High 21 g-200 g + (L + R) No Injury (n = 14) 857.96 ± 88.17 6283.20 ± 1072.78 7.57 ± 1.21 7.03 ± 4.61 829.57 ± 38.47 269.57 ± 174.84 558.36 ± 174.30 1.64 ± 2.44 Knee Injury (n = 14) 841.48 ± 84.71 8698.87 ± 1763.06 10.30 ± 2.02 7.85 ± 5.09 843.79 ± 30.96 108.43 ± 143.26 728.71 ± 146.02 6.64 ± 10.70 CONCLUSION: Following a knee injury, MARSOC personnel exhibit greater impact loads to achieve similar performance as uninjured personnel. This pattern suggests that residual effects of the injury persist, increasing risk of subsequent injury. Incorporating strategies to improve movement and shock attenuation into current rehabilitation programs and performance training may reduce risk of future injury and optimize physical preparedness. Supported by the Office of Naval Research N00014-18-C-2025. DISCLAIMER: The content is solely the responsibility of the authors and does not necessarily represent the official views of the Office of Naval Research or the US Navy.