*Article* **A Wireless Body Sensor Network for Clinical Assessment of the Flexion-Relaxation Phenomenon**

**Michele Paoletti 1 , Alberto Belli 1 , Lorenzo Palma 1 , Massimo Vallasciani 2 and Paola Pierleoni 1,\***


Received: 27 May 2020; Accepted: 20 June 2020; Published: 24 June 2020

**Abstract:** An accurate clinical assessment of the flexion-relaxation phenomenon on back muscles requires objective tools for the analysis of surface electromyography signals correlated with the real movement performed by the subject during the flexion-relaxation test. This paper deepens the evaluation of the flexion-relaxation phenomenon using a wireless body sensor network consisting of sEMG sensors in association with a wearable device that integrates accelerometer, gyroscope, and magnetometer. The raw data collected from the sensors during the flexion relaxation test are processed by an algorithm able to identify the phases of which the test is composed, provide an evaluation of the myoelectric activity and automatically detect the phenomenon presence/absence. The developed algorithm was used to process the data collected in an acquisition campaign conducted to evaluate the flexion-relaxation phenomenon on back muscles of subjects with and without Low Back Pain. The results have shown that the proposed method is significant for myoelectric silence detection and for clinical assessment of electromyography activity patterns.

**Keywords:** flexion-relaxation phenomenon; surface electromyography; wearable device; WBSN; automatic detection of the FRP
