Foot injury is often associated with abnormal pronation. The position of the foot during touchdown has been observed to influence pronation during gait. Because there is a wide variance of foot landing positions (FLP) during gait among individuals, it is important to understand how FLP affect the foot mechanics which may be related to foot injuries. The purpose of this study was to determine if different FLP during gait would affect the angular mechanics of the foot-ankle complex. Thirty female participants who had no history of lower extremity dysfunction were selected and assigned to three groups (5.69° ± 1.03°, -3.83° ± 1.98° and 14.30° ± 2.72° for neutral, toe-in and toe-out FLP, respectively) based on their FLP during natural gait. Four CCD-TV (100 fps) cameras and an AMTI force platform (1000 Hz) connected to a BTS™ system were used for the testing. A single factor (FLP) design was used for the study. Each participant performed ten trials of natural barefoot walking. Angular displacements and velocities, net muscle moments (NMM) about the foot clinical axes and center of pressure (COP) paths were generated, as well as ground reaction forces (GRF) expressed relative to both the room coordinate system (GRFrm) and the foot coordinate system (GRFp-r). Several differences among the FLP groups were evident. Compared to the neutral FLP performers, the toe-out participants demonstrated the following: greater inversion displacements occurred during the contact and propulsion periods; the GRFpr that were laterally applied during the contact period increased; and peak abduction and inversion NMMs occurring during the contact period and peak adduction and eversion NMMs occurring during the propulsion period were increased. Conversely, the toe-in performers demonstrated decreased values for these variables. The results indicated that the differences for the NMM values exhibited for the three FLP groups were due partially to the differences in GRF moments acting on the foot. The COP path, an indicator of the GRF moment arms, moved from the lateral to the medial side of the foot's long axis for the toe-out FLP group, but for the toe-in FLP group, the COP path moved from the medial to the lateral side of the foot's long axis. The magnitudes of the GRF, another determinant of the GRF moments, were different among the FLP groups for the GRF^ variables. Based on the GRFpj. coordinate system, the lateral GRFn increased during the contact period, but decreased and even became medially applied at the end of the stance phase for the toe-out FLP group. Because the FLP affected the mechanics of the foot segment, the FLP should always be considered as a factor for gait analysis.
Keywords:
Angular Kinematics; Center of Pressure; Foot-Ankle Complex; Foot Landing Position; Gait; Ground Reaction Force; Injury; Net Muscle Moment; Pronation