# Use of Wearable Sensor Technology in Gait, Balance, and Range of Motion Analysis
###### Abstract  
More than 8.6 million people suffer from neurological disorders that affect their gait and balance. Physical therapists provide interventions to improve patient's functional outcomes, yet balance and gait are often evaluated in a subjective and observational manner. The use of quantitative methods allows for assessment and tracking of patient progress during and after rehabilitation or for early diagnosis of movement disorders. This paper surveys the state-of-the-art in wearable sensor technology in gait, balance, and range of motion research. It serves as a point of reference for future research, describing current solutions and challenges in the field. A two-level taxonomy of rehabilitation assessment is introduced with evaluation metrics and common algorithms utilized in wearable sensor systems. wearable sensors; gait analysis; balance; range of motion; rehabilitation; healthcare +
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Floor-based sensors and force platform systems are used in research labs or clinically to provide very detailed spatiotemporal gait variables and postural stability measurements, respectively. The main drawbacks of these systems are their cost and lack of portability; they are primarily confined to research labs and rarely available for use in clinical settings. Additionally, camera-based systems are unable to track the subject outside of the camera's visibility, leading to purchasing additional sensors to increase the system's range of visibility, while increasing the cost of the overall system [7,9]. In addition, camera-based systems are computationally expensive to obtain accurate results and may raise privacy concerns. Camera-based systems have been used primarily to conduct motion analysis in research labs, but recently, camera systems have been deployed in people's homes to track their daily activities or assess their fall risk [10,11]. Unlike external sensors, wearable sensors are cheaper and mounted to the subject's body, eliminating cost and portability limitations set by external sensors [9]. The high level of portability allows physical therapists and researchers to analyze gait and balance not only in research laboratories but also in clinic, in patient's home or out the community. The accuracy of a wearable sensor system will depend on how many sensors are used, where and how are the sensors located, and other challenges that will be further discussed. There are many types of wearable sensors that are used in applications ranging from monitoring subject's physiologic responses like heart rate, ECG, or blood glucose [11], to measuring gait, balance, and RoM during movements like walking, turning, sit to stand or postural sway. Wearable sensors have been utilized in conjunction with tests and measures, like the Timed Up and Go, to provide more detailed and objective balance data [12]. Wearable sensors have also been used to study changes in gait and balance over time in people with neurodegenerative diseases and to investigate improvements post interventions [13]. This review paper will not cover external sensors, but will focus on the use of wearable sensors in gait, balance, and RoM analysis. Other papers have reviewed the use of wearable sensors in gait or balance, however, none have reviewed the literature on gait, balance, and lower extremity and trunk RoM [12,14,15]. It is important to review the literature in gait, balance, and RoM collectively since researchers and clinicians often evaluate the interplay between gait, balance, and lower extremity and trunk RoM. Therefore, this review surveys the wearable sensor system methodologies currently used to examine gait, balance, and RoM. Additionally, current reviews do not discuss the technical aspects in wearable sensor technologies that can affect the outcomes of gait, balance, and RoM measurements. This review discusses common design issues when using wearable sensors and describes how quantitative parameters are extracted from wearable sensors in gait, balance, and RoM research.