Smart Sensing System for Combined Activity Classification and Estimation of Knee Range of Motion

Abstract

This paper proposes a novel wearable system and assesses its reliability in monitoring sagittal knee movement, and discriminating between activities of daily living. The system consists of a flexible conductive polymer unit, embedded into a pair of leggings at the level of the knee, interfaced with a customized sensing node for wireless data acquisition. Design constraints included the need for the system to be unobtrusive, low cost, low power, and simple to use. The wearable system was evaluated through a series of trials conducted on healthy participants, tested on two different occasions, while walking, running, and going up and down a set of stairs. The waveforms of the sensor output resemble typical knee kinematics curves. An intraclass correlation coefficient greater than 0.8 was obtained for the output signal of the sensor from which, knee movement is derived for each of the different activities. Time and frequency domain features of the signal were used to discriminate between activities. Results show good discriminative capacity of selected parameters to an accuracy of 93% when employing a random forest analytical approach. These results suggest that the system can be used accurately to monitor both knee movement and activity performed in unconstrained environments, and thus suggesting its potential use to support knee rehabilitation.Index Terms-Activity discrimination, flexible sensor, knee rehabilitation, median frequency, power spectral density, random forest, range of motion.

A flexible wearable sensor for knee flexion assessment during gait

“…This makes our system advantageous to use for unobtrusive and discreet measurements in everyday life settings. Moreover, in addition to a similar sensor [ 16 ], our system has been previously validated to identify activities of daily living and exercise performance [ [7] , [8] ]; this combined with its ability to measure peak flexion angles, makes our sensor capable of providing a more comprehensive description of subjects’ movement capabilities for clinical use. One limitation of the sensor is that requires a subject-specific calibration requiring a motion capture system.…”

“…The sensor system consists of a flexible sensor unit and a sensing node for wireless data acquisition operated by 2 AA batteries [ [6] , [7] , [8] ]. The sensor unit (0.02 × 50 × 100 mm) is made by graphitized carbon black nanopowder (20%) embedded in a polyurethane substrate (80%).…”

“…We previously developed a flexible conductive polymer sensor as knee sensing modality and used it in controlled knee movement condition to measure angles [ 6 ], to characterise exercises performance [ 7 ], classify activities of daily living and measure knee range of motion as surrogate of the sensor signal amplitude range in uncontrolled environments [ 8 ]. The aim of this study is to further validate the new sensor for measuring peak knee joint sagittal angles during gait.…”

Impact of wearable technology on psychosocial factors of osteoarthritis management: a qualitative study

“…At this point, before starting the debate, participants were shown the knee-monitoring device developed, although still at a prototype stage. 22 This consisted of a sensor unit, a thin (0.2 mm) rectangular (50×10 mm) strip of flexible conductive material with two connectors at each end. The connectors were soldered via flexible cables to a small box (35×50×40 mm) which contains the circuits to allow sensor unit data capturing and Bluetooth data transmission to a proprietary device application.…”

Detection of Talking in Respiratory Signals: A Feasibility Study Using Machine Learning and Wearable Textile-Based Sensors

“…Similarly, Mattman et al [ 16 ] integrated sensors into tight-fitting clothing to classify between various body postures. Papi et al [ 17 ] explored the feasibility to discriminate between daily activities (i.e., walking, running, stair climbing) by using a stretch sensor attached to the knee. These studies suggest the preliminary feasibility of textile-based stretch sensors to monitor human motions.…”