Relationship between knee adduction moment and knee contact forces during walking and running with modified foot progression angles.

Knee osteoarthritis (KOA) is a leading cause of disability, influenced by both systemic and mechanical factors. Gait modifications, such as toe-in (TIN) and toe-out (TOUT) foot progression angles, can alter knee adduction moment (KAM) and knee contact forces (KCF), but the task-specific relationship between these measures in walking and running remains unclear. Twenty healthy adults (age 18-35 years) were randomly assigned to walking or running groups. Participants completed natural and modified gait trials: TIN for walking and TOUT for running. KAM was calculated using a clinically feasible inverse-dynamics workflow in Visual3D, while musculoskeletal modelling in OpenSim estimated KCF. Correlations between KAM and medial KCF were assessed, and paired t-tests or linear mixed models examined the effects of gait modifications. During natural walking, early stance KAM was moderately correlated with medial KCF (r = 0.484; p = 0.011), but this relationship disappeared during TIN walking. Both KAM and medial KCF decreased with TIN walking (p < 0.040). In natural running, peak KAM did not correlate with medial KCF, whereas a strong correlation emerged during TOUT running (r = 0.619; p < 0.001). TOUT running increased medial KCF (p = 0.041) without altering KAM. The relationship between KAM and medial KCF is task- and modification-dependent. KAM is a reasonable surrogate for medial loading during natural walking but not during modified gait or running. Toe-in walking reduces both KAM and KCF, supporting its use in gait interventions for knee OA. Conversely, toe-out running can increase medial KCF despite unchanged KAM, highlighting gait modifications beneficial during walking may not translate to running.