Body-borne Loads Increase Knee Joint Contact Force During Run-to-stop Task

Abstract

Running with body-borne load can cause abnormal knee joint loads, such as increased tibio-femoral compressive forces. These elevated compressive forces (i.e. knee joint contact force) may lead to knee pain, injury or disease (e.g. osteoarthritis). A sudden stop during running (i.e. run-to-stop) may exacerbate these compressive forces, particularly when impaired with body-borne load, further increasing risk of injury. Currently it is not understood if body-borne load impacts knee joint contact force during a sudden stop. PURPOSE: The purpose of this study was to determine how body-borne load impacts knee joint contact force during a run-to-stop task. METHODS: Five males (23.4 ± 3.7 yrs; 1.8 ± 0.1 m; 71.8 ± 8.1 kg) had lower limb biomechanics recorded during a run-to-stop task with three military-relevant load conditions: unloaded (UL; 6.2 kg), fighting load (FL; 20.0 kg) and approach load (AL; 40.0 kg). During the run-to-stop, participants ran 3.5 m/s ± 5% down a walkway, planted their dominant limb on an embedded force platform and stopped in a low-ready position. Kinematic and kinetic data were processed in Visual 3D during the stopping phase, from initial heel strike of the dominant limb to heel strike of non-dominant limb. Knee joint contact force, defined as the force acting on the tibial plateau parallel to the longitudinal tibial axis, was estimated using OpenSim and normalized to bodyweight. Peak knee joint contact force was quantified from the normalized data, and then subject-based means calculated and submitted to a one-way ANOVA with alpha level P<0.05 to compare the load conditions. RESULTS: Peak knee joint contact forces increased significantly with the addition of body-borne load (p = 0.025), where UL was 2.42*BW (±0.51), FL was 3.10*BW (±0.54) and AL was 3.77*BW (±0.89). Specifically, peak knee joint contact force was significantly greater during AL compared to the UL (p=0.019), but not compared to the FL load (p=0.291) or between the UL and FL loads (p=0.276). CONCLUSION: When stopping, body-borne load increases knee joint contact force, potentially causing tibio-femoral compressive forces that can lead to pain and injury. Future work is necessary to determine the specific mechanical traits needed to reduce elevated knee joint contact forces evident, particularly with heavy (40.0 kg) approach loads.