Relationship of Lower Extremity Kinematics in the Sagittal Plane with Free Moment during Walking

Torsional stress is observed in the lower extremity during walking. The feet tend to rotate even though they are in contact with the ground, causing friction. Lower extremity kinematics in the sagittal plane during walking is an important clinical outcome, and few reports exist on the torsional stress of the lower limbs during walking. This study aimed to clarify the relationship between lower extremity kinematics (hip extension, knee extension, and ankle dorsiflexion), which peak in the sagittal plane during the late stance phase of walking, and free moment (FM), serving as an index of torsional stress of the lower extremity. This study included 21 healthy male participants. The peak extension angles of the hip and knee, peak dorsiflexion angle, and FM during the stance phase were measured using a motion capture system. The correlation coefficient between each variable, including walking speed, peak FM (PFM), and impulse of absolute FM (FMimp) were calculated. To clarify the coefficient of determination, a regression analysis was performed on joint kinematics that correlated with FM. In addition, the partial correlation coefficient between the kinematics and FM, excluding the influence of walking speed, was also examined. A regression analysis was performed on joint kinematics that were correlated with FM to determine the determination coefficient. Walking speed and peak dorsiflexion angle showed a positive correlation with PFM (r=0.49, and 0.44, respectively). However, the determination coefficients were low (R-2=0.24, and 0.19, respectively). A significant partial correlation coefficient with PFM was found only for the peak hip extension angle (r=0.52). No joints were correlated with FMimp. Regardless of walking speed, there was a positive correlation between FM and sagittal lower limb kinematics. However, since the correlation coefficient was small, it was necessary to consider individual factors such as bone morphology, joint laxity, and walking strategies.