## 2 Materials and Methods  
The presented study was conducted in two stages. In the first stage, people were classified into the study and control groups based on a two-axis Research Diagnostic Criteria for Temporomandibular Disorders (RDC/TMD) and the MTrPs diagnostic criteria presented by [PERSON] et al. [6]. In the second stage, the electromyographic examination and the compression technique within the study group were carried out. This study was carried out at the Department of Functional Masticatory Disorders, Medical University of Lublin, by experienced researchers, dentists, and physiotherapists, in the period between December 2017 and November 2018. The tests were carried out according to the recommendations of the Helsinki Declaration and with the consent of the Bioethics Committee of the Medical University of Lublin (KE-0254/73/2017). All participants were informed about the aim of the study and have given written consent for the research. During qualifying for the research, all participants were clinically examined based on a two-axis Research Diagnostic Criteria for TemporomandibularDisorders (RDC/TMD) form by an experienced dentist with a specialization in dental prosthetics (the author M.B. ([PERSON])). The inclusion criteria used in the study were: female gender, age range 18-23 years, and good or very good general health status according to the RDC/TMD questionnaire, the presence of bilateral active MTrPs in the MM muscles according to diagnostic criteria presented by [PERSON] et al. (study group), and absence of active and/or latent MTrPs in the MM muscles (controls) [6]. The following exclusion criteria were used: the occurrence of headache and cervical spine pain within the month preceding the examination; head and neck injuries within the last six months before the examination; previous head and neck surgical treatment within the last six months before the examination; pregnancy; craniofacial trauma; class II and III of the bite according to [PERSON]'s classification; open bite; lack of four support zones in dental arches; lack of more than four teeth within both dental arches; any form of TMDs found according to the RDC/TMD (excluding MM pain in the study group); condition during orthodontic treatment; possession of dental prostheses (regardless of type); mental and neurological disorders. After applying the above criteria, the study group comprised 26 women (mean age \(22\pm 2\)) with bilateral active MTrPs in the MM muscles. The control group comprised 26 healthy women (mean age \(22\pm 1\)) without the presence of MTrPs in the MM. The diagnosis of MTrPs was performed by an experienced physiotherapist skilled in the diagnosis of MTrPs (the author M.G.). Firstly, sEMG of the MM and TA muscles was performed by using the 8-channel electromyograph BioEMG III, compatible with BioPAK Measurement System (BioResearch Associates, Inc. Milwaukee, WI, USA). The sEMG examinations were conducted between 8 and 12 a.m., to minimize the influence of daily fluctuations of muscle activity. During sEMG measurement, the examined person was instructed to sit upright on a dental chair with the head supported, the trunk perpendicular to the floor, the lower limbs straightened, and hands resting on the lap. Before electrode placement, the skin was cleansed with a 90% ethyl alcohol solution to reduce electrode-skin impedance. The arrangement of surface electrodes was carried out by the same physiotherapist (the author M.G. ), following the guidelines of the SENIAM (surface EMG for a non-invasive assessment of muscles) standards [15]. Surface electrodes Ag/AgCl with a diameter of 30 mm and a conductive surface of 16 mm (SORIMEX, Torun, Poland) were placed in accordance with the course of the muscle fibers of MM and TA muscles, according to the placement technique described by [PERSON] and [PERSON] [16]. The reference electrode was placed on the forehead.