Citation

Firmani F, Robinovitch S, Park EJ. J. Biomech. Eng. 2014; ePub(ePub): ePub.

Copyright

(Copyright © 2014, American Society of Mechanical Engineers)

DOI

10.1115/1.4027469

PMID

24756467

Abstract

This paper presents a methodology that quantifies gait and fall characteristics from video of real-life fall events. The method consists in selecting on-screen the points on the ground where the feet are in contact with the ground. The essence of the method lies in establishing a transformation from the video frames to the "real world". In projected images, geometric properties such as lengths, angles and parallelism are not preserved, thus concepts of projective geometry are applied, namely homography. Since the ground is an invariant plane, using this plane for homography results in a constant transformation. The homographic transformation relies on the accuracy in the selection of on-screen points. An optimization algorithm that minimizes the errors caused by inaccurate on-screen point selection improves the results of the homographic transformation. The methodology is compared with the GAITRite system at three walking velocities (slow, preferred and fast). The results indicate that step lengths (0.85 < R2 < 0.99), stride lengths (0.96 < R2 < 0.99) and stride velocities (0.69 < R2 < 0.89), are not significantly different from each other in any speed condition (p > 0.1 in all cases). Temporal parameters are less confident due to the existence of dropped frames in the video footage. This method is then used to analyze two real fall events as demonstrative cases. First, the gait characteristics are analyzed prior to imbalance and subsequently the characteristics of stepping are analyzed during the fall. In particular, we are interested in studying the relationship of the first step after imbalance and the direction of the fall.

Language: en