{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,15]],"date-time":"2026-01-15T04:24:22Z","timestamp":1768451062245,"version":"3.49.0"},"reference-count":42,"publisher":"MDPI AG","issue":"5","license":[{"start":{"date-parts":[[2015,4,23]],"date-time":"2015-04-23T00:00:00Z","timestamp":1429747200000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>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\u00b0 \u00b1 0.57\u00b0 with the reference system. Statistical analysis indicated great agreements between these two systems with a Pearson\u2019s correlation coefficient (PCC) value larger than 0.99 for all joint angles\u2019 estimation. These results show that the proposed ultrasonic measurement system is useful for applications, such as rehabilitation and sports.<\/jats:p>","DOI":"10.3390\/s150509610","type":"journal-article","created":{"date-parts":[[2015,4,23]],"date-time":"2015-04-23T11:40:29Z","timestamp":1429789229000},"page":"9610-9627","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":15,"title":["Lower Extremity Joint Angle Tracking with Wireless Ultrasonic Sensors during a Squat Exercise"],"prefix":"10.3390","volume":"15","author":[{"given":"Yongbin","family":"Qi","sequence":"first","affiliation":[{"name":"School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Cheong","family":"Soh","sequence":"additional","affiliation":[{"name":"School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Erry","family":"Gunawan","sequence":"additional","affiliation":[{"name":"School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Kay-Soon","family":"Low","sequence":"additional","affiliation":[{"name":"School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore"}],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Rijil","family":"Thomas","sequence":"additional","affiliation":[{"name":"School of Electrical and Electronic Engineering, Nanyang Technological University, 50 Nanyang Avenue, 639798 Singapore"}],"role":[{"role":"author","vocabulary":"crossref"}]}],"member":"1968","published-online":{"date-parts":[[2015,4,23]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","first-page":"1920","DOI":"10.1109\/TBME.2013.2245131","article-title":"Real-Time Estimate of Body Kinematics during a Planar Squat Task Using a Single Inertial Measurement Unit","volume":"60","author":"Bonnet","year":"2013","journal-title":"IEEE Trans. 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