Kinematic patterns while walking on a slope at different speeds

During walking, the elevation angles of the thigh, shank and foot (i.e. the angle between the segment and the vertical) co-vary along a characteristic loop constrained on a plane. Here we investigate how the shape of the loop and the orientation of the plane, which reflects the intersegmental coordination, change with the slope of the terrain and the speed of progression. Ten subjects walked on an inclined treadmill at different slopes (between -9degree sign and +9degree sign) and speeds (from 0.56 to 2.22 m s-1). A principal component analysis was performed on the co-variance matrix of the thigh, shank and foot elevation angles. At each slope and speed, the variance accounted for by the two principal components was >99% indicating that the planar covariation is maintained. The two principal components can be associated to the limb orientation (PC1*) and the limb length (PC2*). At low walking speeds, changes in the intersegmental coordination across slopes are characterized mainly by a change in the orientation of the covariation plane and in PC2*; and to a lesser extent by a change in PC1*. As speed increases, changes in the intersegmental coordination across slopes are more related to a change in PC1*, with limited changes in the orientation of the plane and in PC2*. Our results show that the kinematic patterns highly depend on both slope and speed.