The knee adduction moment (KAM) is widely used as a surrogate measure of medial knee loading and is a primary target of gait modification. Toe-in and toe-out modifications of the foot progression angle are commonly assumed to reduce KAM peaks by displacing the center of pressure (COP), but this mechanism has not been firmly established. This study therefore aimed to clarify the mechanism underlying KAM reduction during these modifications. Healthy adults walked under normal, toe-out, and toe-in conditions. KAM, the moment arm of the ground reaction force (GRF), GRF magnitude, GRF angle, and COP were analyzed at the first and second KAM peaks. Toe-in and toe-out walking predominantly reduced the first and second KAM peaks, respectively. The moment arm was the primary determinant of both peaks (R2 > 0.90). Contrary to conventional assumptions, the reduction in moment arm depended largely on changes in GRF angle, whereas the contribution of COP was minimal or even opposed the change in moment arm. These findings provide a mechanistic basis for foot progression modification strategies and should help improve their clinical effectiveness.
The knee adduction moment (KAM) is commonly used as a surrogate measure of medial compartment loading in individuals with medial knee osteoarthritis. This study investigated the effects of four gait modification strategies—toe-in, toeout, trunk lean, and knee thrust—on KAM peak and impulse using a within-subject design. Fourteen healthy adults performed normal walking and each modified gait condition. All gait modifications significantly reduced KAM peak compared to normal gait (p<0.05). However, a significant reduction in KAM impulse was observed only during the toe-out gait (p<0.01). Multiple regression analysis revealed that the moment arm accounted for 89–92% of the variance in KAM peak, while the combined effects of moment arm and stance time explained 87% of the variance in KAM impulse (p<0.001). The decrease in impulse during toe-out gait was primarily driven by a lower KAM peak without a significant increase in stance time. In contrast, for the other gait modifications, reductions in KAM peak were counterbalanced by prolonged stance time, resulting in no overall reduction in impulse. These findings suggest that both KAM peak and impulse should be considered when selecting gait modification strategies, with toe-out gait appearing to offer the most favorable biomechanical response in healthy adults.
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