Framework for modulating ambulatory load in the context of in vivo mechanosensitivity of articular cartilage

OBJECTIVE: Different stress modalities have been used to provoke a load induced mechanoresponse in blood markers of articular cartilages. The challenge in in vivo experiments is to alter specific loading characteristics. Here, we aimed to develop a load modification framework that changes ambulatory load magnitude without changing load frequency or joint kinematics. DESIGN: Spatiotemporal parameters, sagittal joint kinematics and vertical ground reaction force (vGRF) of 24 healthy participants were recorded while walking with reduced (80%), normal (100%) and increased (120%) bodyweight (BW) on three separate test days in a block randomized cross-over design. The reduced and increased load conditions were compared to the normal load condition using paired sample t-tests for spatiotemporal parameters and statistical parametric mapping for vGRF and joint kinematics. RESULTS: Load modification resulted in measured vGRF differences of −19.5%BW (reduced) and +16.8%BW (increased). Spatiotemporal parameters with reduced and increased load did not differ from normal load except of a shorter stance time under reduced load (−21 ms). Joint kinematics for both conditions did not differ from normal load except of decreased ankle dorsiflexion (maximum −5.9°) and increased knee flexion (maximum +6.5°) for the reduced load condition during pre-swing when the support limb is already unloaded. CONCLUSION: Overall, we did not observe relevant differences in spatiotemporal parameters or joint kinematics between loading conditions. Mean absolute joint angle deviations below 4.1° demonstrate that the proposed load modification framework changes ambulatory load magnitude without changing load frequency or joint kinematics.