Evaluation of skin resistivity for upper trapezius trigger points in healthy humans

Forty two healthy volunteers with unilateral latent TrPs within the upper trapezius muscle will be recruited to the study. Each of the participants will be re-diagnosed towards unilateral TrPs confirmation within the upper trapezius muscle. Additionally, the presence of confirmatory signs, namely referred pain and twitch response, will be examined. Then, the localization of TrPs defined by Travell and Simons as x1 and x2 will be marked and the same will be done for the area corresponding to the region common for TrPs (control). Then, the examiner will look for 4 pain-free points on each side (not tender; without any features of TrPs) in the closest area to the previously marked crosses. When the four points will be found, they will be marked and named norm. Next, the skin resistance measurement will be performed. The participants will be evaluated towards skin resistance in the marked area by an expert without any knowledge about TrPs examination results. During tests, a Keithley electrometer 610B will be used for measuring skin resistance (Ag/AgCl self-adhesive, disposable ground electrode; 30 mm diameter). The electrodes will be placed on the specific points of the skin. Two electrodes will be put on the points defined as x1 and x2 within the upper trapezius (TrPs-positive and control), four – on other points which will show no evidence of pathology (norm). One of the norm points (positioned centrally in relation to the other) will function as a reference point. Skin resistance (in ohms) will be measured once in every marked point. The electrometer will be rezeroed before every measurement. Input parameters will be turned off, and the electrometer will be corrected for internal noise to recalibrate as the participants change. All test will be completed in a climate controlled room. The duration of the procedure for each participant will be around 30 minutes and it will be conducted on a single occasion only. Data analysis Previously obtained resistance values from each of the marked points (TrPs-positive, control and norm) will be used to calculate the resistivity using the formula: resistivity =RS/x ; resistivity [Ohm*m]; R – resistance [Ohm]; S – electrode surface [m2]; x – distance between electrodes (reference and others) [m]. The mean value obtained from the calculations made for three norm points will be determined in order to calculate the so-called personal norm for the pain-free area (without any TrPs features). Additionally, TrPs skin resistivity value will be analyzed as regards the gender and the presence of confirmatory signs (referred pain and twitch response).