Using an Optical Proximity Sensor to Measure Foot Clearance During Gait: Agreement With Motion Analysis

Abstract

Foot clearance is an important measurement variable in understanding trip falls. Current methods for measuring foot clearance are limited by their inability to capture multiple steps and confinement to a laboratory. Given that variation in this parameter is considered a factor in trip falling, it’s measurement in the field over multiple steps would be valuable. The development of an optical proximity sensor (OPS) has created the opportunity to collect this type of data. This study aimed to test the validity of an OPS through comparison with a motion capture system. Twenty subjects aged 33(+/−10) years, with a height of 174(+/−6) cm and a weight of 75(+/−12) kg, walked at three self selected velocities (preferred, slow, and fast). The OPS was mounted on the shoe of each subject. The motion of the shoe was recorded with a motion analysis system which tracked three markers attached to the shoe and outer casing of the OPS. Both systems were sampled at 50 Hz. The lowest point of the foot during the swing phase was recorded from each system and compared using intraclass correlation coefficients (ICCs). There was excellent agreement between the two systems. ICCs of 0.925 (all speeds), 0.931 (preferred), 0.966 (slow), and 0.889 (fast) were recorded. These results represent a strong agreement between the two systems in measuring the lowest point during swing. The OPS could thus be used instead of a camera system to record foot clearance, opening up opportunities for data collection over long periods of time, in natural settings. These results should be interpreted in context of the young healthy sample.

A Scoping Review on Minimum Foot Clearance Measurement: Sensing Modalities

“…Another difference that made it difficult to compare results of different studies was that not all studies used the same metrics to report the performance of their device. While many used accuracy± precision [19,22,23,29,32], some measured the performance of their device with RMSE [18,20], or correlation [30].…”

Design of a Novel Wearable System for Foot Clearance Estimation

“…These sensors provide a direct method to measure the foot clearance without performing intermediate calculations that can introduce errors [ 7 ]. In [ 14 ], Kerr et al proposed a system that used an optical proximity sensor located at the first metatarsal to measure foot clearance. The system demonstrated excellent agreement compared to the motion capture system with intraclass correlation coefficients of 0.93 for all speeds, 0.93 for normal speed, 0.97 for slow speed, and 0.89 for fast speed [ 14 ].…”

“…In [ 14 ], Kerr et al proposed a system that used an optical proximity sensor located at the first metatarsal to measure foot clearance. The system demonstrated excellent agreement compared to the motion capture system with intraclass correlation coefficients of 0.93 for all speeds, 0.93 for normal speed, 0.97 for slow speed, and 0.89 for fast speed [ 14 ]. It is worth noting that these correlation values are estimated based on the signals for each step and not for the whole trial.…”

Estimation of Continous Heel and Toe Clearances Using Foot-Worn Inertial Sensors

“…The most accurate measuring system is optical motion capture system, but it is costly and can only be used within the laboratory. Andy Kerr et al used an optical proximity sensor attached to the shoe to measure foot clearance during gait [2]. Yongbin Qi et al used wearable wireless ultrasonic sensor network to measure 3-dimentional foot displacement [3].…”