RESUMEN
BACKGROUND: Recent studies have shown that a transcutaneous electrical nerve stimulation (TENS) and interferential current (IFC) application reduces pain in subjects with musculoskeletal disorders. However there are no clinical trials evaluating or comparing the muscle relaxation generated for these devices. PURPOSE: To compare the muscle relaxation of the upper trapezius induced by the application of TENS and IFC in females with chronic nonspecific neck discomfort. METHODS: Sixty-four females between 18 and 40 years of age and a history of nonspecific neck discomfort were randomly assigned to a TENS or an IFC group. The women in the TENS (N = 32; mean age 22 years) and IFC (N = 32, mean age 23 years) group were submitted to current application during 3 consecutive days and were assessed by electromyography (EMG) in different times aiming to quantify the muscular tension of the upper trapezius. A visual analogue scale (VAS) was used as pain measure at baseline (before TENS or IFC application) and at the end of the study. RESULTS: At baseline, demographic, pain, and EMG assessment data were similar between groups. Those in the IFC group had a significant trapezius relaxation after 3 IFC applications when compared to baseline and intermediate evaluations (P < 0.05). In contrast, the same analysis showed no significant difference between all assessments in the TENS group (P >0.05). In relation to pain relief, both groups showed an improvement at the end of the study when compared to baseline (both,P <0.05). The between-group analysis showed no difference for the subjects who received such IFC as TENS application (P <0.05). CONCLUSION: IFC induced the upper trapezius relaxation after 3 sessions in females with neck discomfort, but the TENS application did not change the muscular tension. However, these results should be carefully interpreted due to the lack of differences between groups. A significant pain decrease was found in the subjects of both groups, however, only the IFC application presented a clinically important improvement.