Foot Angle Affects Rotation of the Lower Extremity during Stair Descent

[Purpose] The purpose of this study was to examine the effect of foot angle on rotation of the lower extremity while descending stairs. [Subjects and Methods] Fifteen subjects participated in this study. Subjects stepped down from a 20-cm platform under 5 foot angle conditions with contact of their right leg: neutral, toe-out of 5 and 10°, and toe-in of 5 and 10°. Rotation of the lower extremity was measured with triaxial accelerometers from the start of ankle dorsiflexion to maximum dorsiflexion. [Results] No significant differences were found among the conditions in knee angle. However, the external rotation angles of the thigh under the toe-in condition were significantly smaller than that of toe-out of 10°, and internal rotation of the knee was also smaller. [Conclusion] In descent of stairs with toe-out, rotation of the thigh is restricted, and this becomes a factor affecting overloading of the knee, suggesting that not only the activity of the foot, but also thigh rotation and knee function are important.