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.

This study aimed to determine mechanisms involved in the decrease of knee adduction moment (KAM) when waking with a contralateral cane without any constraint. Ten young subjects performed walking under two conditions: unassisted (no cane) or with a cane. After collecting data from the stance phase of the left foot, kinematic and kinetic data at early and late peaks of KAM were extracted for further analyses. When using a cane, early and late peaks of KAM decreased (p < 0.05) by 20.5% and 29.6%, respectively. Stepwise multiple regression analysis showed that the moment arm accounted for 59% and 95% of the variance of early and late KAM peaks, respectively. This reduction in moment arm occurred primarily due to lateral rotation of the GRF. Regarding the mechanism behind this, it could be due to the following: 1) by using a cane, the synthetic center of pressure shifted medially, which caused synthetic GRF to become more vertical than that of an unassisted walking and accordingly, and 2) the decrease of horizontal component of synthetic GRF reduced horizontal component of foot GRF, leading to lateral rotation of foot GRF. Understanding these mechanisms might help us improve effective use of canes.

In the rehabilitation of upper limb function impaired by stroke, facilitating the coordinated activation of multiple muscles is desirable. This study aims to analyze the coordination patterns of the tonic and phasic components of EMG during a reaching task and to investigate how the phasic component changes in relation to reaching speed. The analysis focused on the shoulder and elbow joints. EMG was recorded at five different speeds, with the slowest speed selected to represent the tonic component. The tonic component was then removed from the total EMG at the other four speeds to extract the phasic component. Correlation coefficients were calculated between the tonic component and joint angles, as well as between the phasic component and joint angular accelerations. For the tonic component, as joint angle increased during reaching, muscle activation also increased to counteract gravitational moments and enhance joint stiffness. For the phasic component, as reaching speed increased, the correlation between acceleration-deceleration patterns and muscle activation also increased. This suggests a greater synergistic contraction for enhanced acceleration and deceleration, as well as increased antagonistic contraction to ensure dynamic stability during faster movements