(E-175) Design and Prototyping of Reusable Wearable Sensor System for Monitoring Motion of the Lower Back During Daily Activities

Introduction:: Lower back pain is the most disabling condition in the world but is unfortunately difficult to treat. There has long been a connection between improper motion / posture and back pain, hence various systems have been applied to the tracking of spinal motion. However, such devices generally require application and monitoring in a clinical environment. This leaves a distinct gap in our current set of knowledge since our knowledge of spinal biomechanics comes from a relatively constrained environment, in terms of human activity and time. A system is required that can monitor how spinal motion during daily activities, potentially revealing trends in how lower back pain and associated biomechanical characteristics evolve. This work focuses on the design and preliminary testing of a user-friendly wearable sensor device meant for the monitoring of lower back motion during daily activities over significant periods of time.

Materials and Methods:: It was assumed that the proposed sensing system would be roughly based upon an available garment design, for easy of application by the user. Furthermore, it was hypothesized, based upon previous experience with skin-mounted sensors, that the optimal garment configuration would be one that most closely followed skin motion. Multiple rounds of testing conducted with several different garments, including a compression shirt, a camisole, and multiple types of waist belt. A 12-camera Vicon motion capture system was used to record motion data for each of the garment types. The data sets were compared to skin motion data collected in the same manner. The same subject performed a fixed set of exercises for all garment types to minimize variability. Eight marker positions were tracked, and six exercises were performed that encompass all of the axes of motion of the human spine.

Results, Conclusions, and Discussions:: From the analysis, it was determined that the waist belt most closely followed the skin’s natural movement for extension/flexion and lateral motion, but the camisole initially performed the best during the rotation exercises. The motion of each garment used in the first round of testing is shown in Figure 1. A second round of testing was performed with a waist belt made of a four-way stretch material like the camisole—with this change in material, the waist belt performed notably better during rotation tests than in the pervious round of testing. The addition of silicone patches in the marker locations increased the skin adherence even further due to the Van der Waals bonds between the silicone and the skin. The subject reported little to no discomfort while wearing the garment and that it was easy to don and remove independently.
Optical motion capture was used to measure how well different kinds of garments conformed to skin motion in the lower back. It was determined that, of the garments tested, the waist belt made of four-way stretch material with silicone patches most closely adhered to skin motion. Optimal location of high-elongation nano-composite strain gauges is currently being determined from the data, and a prototype system for tracking lower back biomechanics during every day activities will then be constructed, tested and reported on at BMES.


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