Immediate effects of low-level laser therapy on the electromyographic activity of the upper trapezius muscles and pain intensity among patients with non-specific neck pain: a randomised, double-blind, sham-controlled, crossover study

Background/Aims Low-level laser therapy can be considered an important resource in non-specific neck pain treatment, given that it has been shown to relieve pain and regenerate tissue in different clinical conditions. However, the optimum dose of low-level laser therapy for the treatment of non-specific neck pain remains unclear in literature. The aim of this study was to assess the immediate effect of photobiomodulation with low-level laser therapy on electromyographic activity of the upper trapezius muscles and pain intensity in patients with non-specific neck pain. Methods A total of 20 individuals with non-specific neck pain received two forms of treatment in random order: a single session of active low-level laser therapy (wavelength of 820 nanometers, 30 miliwatts, energy total of 18 Joules) and placebo low-level laser therapy over the upper trapezius muscle. The primary outcome of the study was the electromyographic activity of the upper trapezius muscles after a single session of low-level laser therapy. The secondary outcome for the study was pain intensity, as measured by the Numeric Rating Scale score for pain, and the area of pain. Results A significant decrease in electromyographic amplitude was found in the placebo group (P<0.01; Wilcoxon test). A significant difference between groups was found for muscle fibre conduction velocity (F=9.46; P=0.003; ηp 2 =0.07; analysis of variance test). No significant difference between groups was found for pain intensity (F=0.002, P=096; ηp 2 <0.001; analysis of variance test) or area of pain (F=0.24, P=0.62, ηp 2 =0.007; analysis of variance test). Conclusions This study demonstrated that a single session of photobiomodulation with low-level laser therapy did not provide analgesia to individuals with non-specific neck pain. However, the decrease in the amplitude of the electromyography signal and the increase in muscle fibre conduction velocity found in the placebo low-level laser therapy group suggests an ergogenic effect of the treatment applied. Implications for practice Rehabilitation clinicians have long recognised the importance of optimising neuromuscular function in individuals with neck pain. Findings from this study may assist in structuring rehabilitation programmes by supporting the use of low-level laser therapy as a preparatory intervention to enhance muscle performance before active exercise.