Using an optical proximity sensor to measure foot clearance during gait : agreement with motion analysis

Kerr, Andrew and Rafferty, D and Dall, P.M. and Smit, Philip and Barrie, Peter (2010) Using an optical proximity sensor to measure foot clearance during gait : agreement with motion analysis. Journal of Medical Devices, 4 (3). 031004. (

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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.