Effect of foot progression angle alteration on medial–lateral center of pressure position during single-leg standing

[Purpose] This study aimed to investigate the effect of altering the foot progression angle (FPA) on the center of pressure (COP) position during single-leg standing. [Participants and Methods] Fifteen healthy adult males participated. The participants performed single-leg standing on the left leg in three different FPA conditions, namely toe-in, neutral, and toe-out, in which the FPA was set to 0°, 10°, and 20°, respectively. The COP positions and pelvis angles were measured using a 3D motion analysis system, and each measurement value among the three conditions was compared. [Results] The medial–lateral COP position differed among conditions in the coordinate system based on the laboratory condition but did not differ in the coordinate system based on the longitudinal axis of the foot segment. Moreover, no changes were observed in pelvis angles that would affect COP position. [Conclusion] Altering the FPA does not change the medial–lateral position of the COP during single-leg standing. Here we show that COP displacement based on the laboratory coordinate system is involved in the mechanism-linking alteration of FPA and changes in knee adduction moment.