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Polymer optical fiber for in-shoe monitoring of ground reaction forces during the gait

LEAL-JUNIOR, A. ; Frizera-Neto, A. Frizera-Neto ; Avellar, L. ; Marques, C. ; Pontes, M. J.

IEEE Sensors Journal Vol. 18, Nº 6, pp. 2362 - 2368, March, 2018.

ISSN (print): 1530-437X
ISSN (online):

Journal Impact Factor: 1,762 (in 2014)

Digital Object Identifier: 10.1109/JSEN.2018.2797363

Ground reaction force (GRF) measurement is usually made by means of force platforms, which can lead to errors when the foot is not precisely placed inside the platform boundaries. Although electronic in-shoe plantar pressure sensors solve this problem, they lack in stability, robustness to impact loads and also can present some errors and inconsistencies. Polymer optical fibers (POF) present high elastic strain limits,
fracture toughness, flexibility in bend, relative low cost and are not influenced by electromagnetic fields, which enable their
application for in-shoe plantar pressure measurements. This paper presents an in-shoe system to measure the vertical GRF
during the gait cycle. The system comprises of four POF sensors in an insole. Since the polymer does not have a constant response
with stress or strain due to its viscoelasticity, a compensation technique for this effect is also proposed. The proposed insole is
compared with a commercial force platform and a root mean squared error of 5.30 N was obtained. Results also show the
feasibility of the system to measure the GRF during the gait and the identification of all subdivisions of the stance phase with the
additional advantages of full portability, lower cost and higher flexibility than the one presented by commercial force platforms and fiber Bragg gratings-based insoles.