Effect of topical heat on electromyographic power density spectrum in subjects with myofascial pain and normal controls - A pilot study

Objective: To investigate the influence of superficial heat on the fatigue cascade of the upper trapezius muscle in subjects with myofascial pain and matched normal controls. Design: In a prospective randomized block crossover pilot study, eight fema le subjects, ages 20-35 yr, with upper trapezius muscle trigger points and eight matched female control subjects without pain were studied. Subjects p erformed six 100-sec shoulder shrug contractions to fatigue, with subjects randomly chosen to receive heat during the first three or last three trials . The initial median frequency and the slope of the median frequency declin e were calculated from the data. Results: In the subjects with pain, the slope of the median frequency was e levated in ambient room temperature as compared with controls. There was no difference in slope of the median frequency under heated conditions. Heat application in controls before fatiguing exercise caused an increase in ini tial median frequency, whereas exercise before heat treatment resulted in a significantly lower initial median frequency. Subjects with myofascial pai n had no significant change in initial median frequency. Conclusions: Heat seems to have a positive effect on muscle function in nor mal individuals when applied before exercise. Subjects with myofascial pain respond differently to exercise and heat challenge, which suggests a diffe rence in their muscle physiology.