Normalized Cross-Correlation of Subsequent Strides for Evaluation of Walking Stability

Evaluation of walking stability is essential for the elderly population to prevent possible falls due to degradation of their walking stability caused by aging. Previous studies mainly focused on center of pressure (COP) and center of body mass (COM) and their relationship during walking. However COM can not be directly measured and existing COP parameters are mainly investigated within one stride and their effectiveness is not conclusive. In this study, new parameters are proposed based on normalized cross-correlation of subsequent strides (NCSS), derived from comparison of subsequent strides of foot plantar pressure. The mean and standard deviation of NCSS are calculated for three walking conditions that are progressively less stable (1 - normal walking, 2 - walking with eyes closed, and 3 - walking with eyes closed after being spun around) for six healthy subjects. Results show that the NCSS can effectively distinguish normal walking (1) and the less stable walking with eyes closed after being spun around (3). The mean of NCSS decreases from stable to less stable walking conditions, whereas the corresponding standard deviation of NCSS increases. For each subject the value of NCSS of walking with eyes closed (2) is between those of the other two walking conditions (1 and 3), although the value varies somewhat, depending on the controllability and adaptability of the subject.