The Dose-dependent Effect of an 830-nm, 450-mW Low-Level Laser Therapy on the Myofacial Trigger Point of the Upper Trapezius Muscle: A Randomized, Double-Blinded, Clinical Trial

[Purpose] The purpose of this study was to evaluate the dose-dependent effect of treatment with an 830-nm, 450-mW GaAlAs laser on changes of the pressure-pain threshold (PPT) of the myofascial trigger point (MTrP) of the upper trapezius (UT) muscles of seated workers, in comparison with a placebo GaAlAs laser. [Subjects] Twenty-four seated workers (10 males, 14 females) with UT pain agreed to participate in this study. [Methods] The subjects were given treatment either with a placebo GaAlAs laser or an active GaAlAs laser according to a double-blinded, randomized procedure. [Results] The placebo group did not show significant changes in PPT after 1 min, 2 min and 5 min of low-level laser therapy (LLLT). The active group did not show significant changes in pressure-pain threshold (PPT) after 1 min and 2 min of LILT. However, significant changes in PPT were apparent after 5 min of LLLT. [Conclusion] We suggest that a higher energy, such as 1929 J/cm(2), may be necessary to produce an immediate effect on PPT when treating the MTrP of the UT with an 830-nm, 450-mW GaAlAs laser.