Dose-dependent and Ceiling Effects of Therapeutic Laser on Myofascial Trigger Spots in Rabbit Skeletal Muscles

Objective: To evaluate the effect of low-level laser treatment with different dosages on the irritability of myofascial trigger spots [MTrS] in rabbit skeletal muscles. Methods: Twenty rabbits were equally divided into a low dose group and a high dose group. In each rabbit, the MTrS on the experimental side was irradiated with 660-nm continuous-wave gallium-aluminum-arsenate laser daily for six sessions. The energy per session was 27 J/cm(2) [low dose group] and 72 J/cm(2) [high dose group]. The MTrS on the other side received sham treatment. The MTrS irritability was assessed with the prevalence of endplate noise [EPN] at baseline after the first and after the last treatments. Results: After the first laser treatment, the EPN prevalence was significantly decreased in both groups. The percentage change in the high dose group was greater than that in the low dose group. The EPN prevalence after the last laser treatment was lower than that after the first laser treatment in the low dose group, but not in the high dose group. Conclusions: In the present study, a dose-dependent effect of laser treatment on the MTrS irritability was demonstrated. A cumulative effect was only observed in low dose treatments. It appears that a ceiling effect may have occurred in relatively high dose laser treatment.