Goals: We have recently introduced a new class of wearable loop sensors for joint flexion monitoring that overcomes limitations in the state-of-the-art.Our previous studies reported a proof-of-concept on a cylindrical phantom limb, under static scenarios and with a rigid sensor.In this work, we evaluate our sensors, for the first time, on human subjects, under dynamic scenarios, using a flexible textile-based prototype tethered to a network analyzer.An untethered version is also presented and validated on phantoms, aiming towards a fully Conditioner wearable design.Methods: Three dynamic activities (walking, brisk walking, and full flexion/extension, all performed in place) are used to validate the tethered sensor on ten (10) adults.
The untethered sensor is validated upon a cylindrical phantom that is bent manually at random speed.A calibration mechanism is developed to derive the sensor-measured angles.These angles are then compared to gold-standard angles simultaneously captured by a light detection and ranging (LiDAR) depth camera using root mean square error (RMSE) and Pearson's correlation coefficient as metrics.Results: We find excellent correlation (≥ 0.981) to gold-standard angles.
The sensor achieves an RMSE of 4.463° ± 1.266° for walking, 5.541° ± 2.082° for brisk walking, 3.
657° ± 1.815° for full flexion/extension activities, and 0.670° ± 0.366° for the phantom bending test.Conclusion: The tethered sensor achieves similar to slightly higher RMSE as compared to other wearable flexion sensors on human subjects, while the untethered version achieves excellent RMSE Pre-Rolled on the phantom model.
Concurrently, our sensors are reliable over time and injury-safe, and do not obstruct natural movement.Our results set the ground for future improvements in angular resolution and for realizing fully wearable designs, while maintaining the abovementioned advantages over the state-of-the-art.