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Sensors 2015, 15(5), 9610-9627; doi:10.3390/s150509610

Lower Extremity Joint Angle Tracking with Wireless Ultrasonic Sensors during a Squat Exercise

School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore
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Author to whom correspondence should be addressed.
Academic Editor: Xiaoning Jiang
Received: 12 December 2014 / Revised: 6 April 2015 / Accepted: 16 April 2015 / Published: 23 April 2015
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Abstract

This paper presents an unrestrained measurement system based on a wearable wireless ultrasonic sensor network to track the lower extremity joint and trunk kinematics during a squat exercise with only one ultrasonic sensor attached to the trunk. The system consists of an ultrasound transmitter (mobile) and multiple receivers (anchors) whose positions are known. The proposed system measures the horizontal and vertical displacement, together with known joint constraints, to estimate joint flexion/extension angles using an inverse kinematic model based on the damped least-squares technique. The performance of the proposed ultrasonic measurement system was validated against a camera-based tracking system on eight healthy subjects performing a planar squat exercise. Joint angles estimated from the ultrasonic system showed a root mean square error (RMSE) of 2.85° ± 0.57° with the reference system. Statistical analysis indicated great agreements between these two systems with a Pearson’s correlation coefficient (PCC) value larger than 0.99 for all joint angles’ estimation. These results show that the proposed ultrasonic measurement system is useful for applications, such as rehabilitation and sports. View Full-Text
Keywords: ultrasound; wireless sensor network; joint angles; squat; rehabilitation; inverse kinematics ultrasound; wireless sensor network; joint angles; squat; rehabilitation; inverse kinematics
This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. (CC BY 4.0).

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MDPI and ACS Style

Qi, Y.; Soh, C.B.; Gunawan, E.; Low, K.-S.; Thomas, R. Lower Extremity Joint Angle Tracking with Wireless Ultrasonic Sensors during a Squat Exercise. Sensors 2015, 15, 9610-9627.

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