A PCA Approach to Quantifying Foot Clearance and Foot Clearance Variability.

Low foot clearance and high variability may be related to falls risk. Foot clearance is often defined as the local minimum in toe height during swing; however, not all strides have this local minimum. The primary purpose of this study was to identify a non-discrete measure of foot clearance during all strides, and compare discrete and non-discrete measures in ability to rank individuals on foot clearance and variability. Thirty-five participants (young adults (n=10), older fallers (n=10), older non-fallers (n=10), and stroke survivors (n=5)) walked overground while lower-extremity 3D kinematics were recorded. Principal Components Analysis (PCA) of the toe height waveform yielded representation of toe height when it was closest to the ground. Spearman rank-order correlation assessed the association of foot clearance and variability between PCA and discrete variables, including the local minimum. PCA had significant (P<0.05) moderate or strong associations with discrete measures of foot clearance and variability. An approximation of the discrete local minimum had a weak association with PCA and other discrete measures of foot clearance. A PCA approach to quantifying foot clearance can be used to identify the behavioral components of toe height when it is closest to the ground, even for strides without a local minimum.