A Novel Wearable Imu-Based Assessment of Postural Stability.

다국어 초록 (Multilingual Abstract)

Balance and postural stability has been studied for decades, and recently these efforts have incorporated small-size, lightweight, and inexpensive devices that may be worn on the body inside or outside the laboratory. Generally speaking, these inertial measurement units (IMUs) contain three-direction accelerometers, gyroscopic sensors for sensing angular velocity, and magnetometers for measuring orientation. IMUs have been widely used in balance studies of the high fall-risk populations, such as the elderly, people who have chronic disease, and people with impaired balance. Pregnant women constitute another population with high fall risk, but their balance has not been studied substantially using IMUs. Instead, studies of balance in pregnant women have mostly been performed in the laboratory environment with force plate. However, there are more complicated and dynamic tasks of daily living that are best studied outside the laboratory. If balance were to be studied in pregnant women using IMUs, the location of the sensor may be a problem; the IMU sensor is usually placed on a belt, near the body's center of mass. Wearing a sensor on a waist belt, however, may cause discomfort for pregnant women. Thus, the main purpose of this dissertation is to explore an alternative way of using an IMU by placing it a case worn around the neck as a pendant and to test whether a pendant IMU is as sensitive to postural instability as one work on a belt.In the first study, the design of the pendant case was investigated by testing three different novel pendant cases that could contain an IMU. The three designs differed in their curvature and included: a flat case with curvature only at the edges, a slightly curved case, and a deeply curved case. We investigated the possibility that a free-swinging pendant would magnify postural instability and potentially be more sensitive to postural instability than a sensor attached to the body. In order to test this sensitivity, we had research participants perform three standing tasks: double-leg stance, tandem stance, and single-leg stance. Each standing task involved two vision conditions: eyes open and eyes closed. We assumed that in the double-leg stance with eyes open induced the least postural instability, while the single-leg stance with eyes closed induced the most. In the exploration phase of the pilot study, we found out that the pendant sensor with the slightly curved base was most sensitive to differences in stability across the different standing tasks.In the second study, we tested the sensitivity of the pendant sensor design identified in the first study to postural instability. We recruited 26 young healthy adults who wore the pendant sensor and an IMU placed on a waist belt during experiments. In order to induce instability, three types of standing tasks were considered: double-leg stance, tandem stance, and single-leg stance. Two vision conditions were also involved: eyes open and eyes closed in each standing task. We assumed that the tandem and single-leg standing would induce postural instability, and in the eyes closed condition the instability was more obvious. Thus, our hypothesis was that the pendant sensor would be more sensitive to postural instability.