Accurate foot clearance estimation during level and uneven ground walking using inertial sensors

Abstract

Foot clearance during walking is considered as a key indicator for assessing fall risk, obstacle negotiation strategies and energy expenditure. Foot clearance estimation using inertial measurement units (IMUs) has the advantages of small size, low cost and user-friendliness. However, its application is still limited due to issues with accuracy and reliability. In this paper, we aimed at understanding the limiting factors in foot clearance estimation using low-cost IMUs and proposed a foot clearance estimation method with millimeter-level accuracy. We first analyzed each component in conventional double-integration-based foot clearance estimation, and then proposed a set of new procedures for foot trajectory estimation, including a gait-adaptive complementary filter for orientation estimation, a two-IMU configuration and a shock absorber. Finally, we extracted the foot clearance from the estimated foot trajectory. In the experiments, we recruited eight healthy subjects and instructed them to walk under level and uneven ground conditions; moreover, to validate the applicability of the proposed method, we also instructed the subjects to mimic pathological gaits, including ataxic gait (zigzag walking), waddling gait and Parkinsonian gait. A total of 2640 gait cycles were collected and the extracted foot clearances were benchmarked with the optical motion capture system. With the proposed method, the average mean and standard deviation of the extracted maximal heel clearance and minimal toe clearance in all the gait cycles were −0.34 ± 0.24 cm and 0.02 ± 0.26 cm. The results are more accurate than in previous studies. Most importantly, the proposed method does not require any post correction and flat-floor assumption. The presented foot clearance estimation method provides an applicable and practical clinical solution not only for heel and toe clearance estimation but also for foot trajectory estimation.