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 pa- rameters and statistical parametric mapping for vGRF and joint kinematics. Results: Load modification resulted in measured vGRF differences of 19.5%BW (reduced) and þ16.8%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 þ6.5) 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.