c o m p u t e r m e t h o d s a n d p r o g r a m s i n b i o m e d i c i n e 1 1 3 ( 2 0 1 4 ) 314–322 j o ur na l ho me pag e: www.intl.elsevierhealth.com/journals/cmpb Simulation of surface EMG for the analysis of muscle activity during whole body vibratory stimulation Antonio Fratini a,∗ , Paolo Bifulco a , Maria Romano a , Fabrizio Clemente b , Mario Cesarelli a a Department of Electrical Engineering and Information Technologies, University “Federico II” of Naples, Via Claudio, 21, 80125 Naples, Italy b Institute of Biomedical Engineering – CNR, Via Salaria Km 29,300, 00016 Monterotondo S., Italy a r t i c l e i n f o Article history: Received 8 March 2013 Received in revised form 7 October 2013 Accepted 8 October 2013 Keywords: Whole body vibration Motor unit synchronization EMG Motion artifact a b s t r a c t This study aims to reproduce the effect of motor-unit synchronization on surface EMG recor- dings during vibratory stimulation to highlight vibration evoked muscle activity. The authors intended to evaluate, through numerical simulations, the changes in surface EMG spectrum in muscles undergoing whole body vibration stimulation. In some specific bands, in fact, vibration induced motion artifacts are also typically present. In addition, authors meant to compare the simulated EMGs with respect to real recor- dings in order to discriminate the effect of synchronization of motor units discharges with vibration frequencies from motion artifacts. Computations were performed using a model derived from previous studies and modi- fied to consider the effect of vibratory stimulus, the motor unit synchronization and the endplates-electrodes relative position on the EMG signal. Results revealed that, in particular conditions, synchronization of MUs’ discharge gen- erates visible peaks at stimulation frequency and its harmonics. However, only a part of the total power of surface EMGs might be enclosed within artifacts related bands (±1 Hz centered at the stimulation frequency and its superior harmonics) even in case of strong synchronization of motor units discharges with the vibratory stimulus. © 2013 Elsevier Ireland Ltd. All rights reserved. 1. Introduction The analysis of surface electromyographic signal (EMG) and its concise parameters (i.e. root mean square – RMS) is a com- mon method of analysis of muscle activity [1–10]. However, in some situations such as vibratory stimulation, the presence of artifacts can severely affect the reliability of data [11–14]. ∗ Corresponding author. Tel.: +39 0817683786. E-mail address: a.fratini@unina.it (A. Fratini). Direct application of mechanical vibration to a muscle belly or a tendon produces a reflex muscle contraction known as Tonic Vibration Reflex (TVR) [15–18]. It also induces a rhythmic movement of electrodes and skin that is responsible for the occurrence of pseudo-sinusoidal artifacts, sometimes referred to as mechanograms [11,19]. Due to its capacity to generate muscles responses, vibra- tory stimulation has been extended to the entire body (the 0169-2607/$ – see front matter © 2013 Elsevier Ireland Ltd. All rights reserved. http://dx.doi.org/10.1016/j.cmpb.2013.10.009