The effect of delayed onset of muscle soreness on habitual trapezius activity.

The aim of the study was to investigate the effect of acute trapezius pain, induced by delayed onset of muscle soreness (DOMS), on habitual trapezius activity. Long-term (5 h) surface electromyographic (sEMG) activity was recorded bilaterally from the clavicular, descending, transverse, and ascending trapezius on two consecutive weekdays in eleven female subjects (mean age 22 years, range 20-24 years). Body and arm posture were recorded by inclinometers. Immediately after the first long-term recording, the subjects performed eccentric depression exercise of the left shoulder to induce DOMS. From day 1 to day 2, pressure pain threshold (PPT) decreased and pain scores on visual analog scale (VAS) increased for the left upper trapezius (P<.004 for all comparisons). Habitual sEMG activity (median sEMG level, μV) of the clavicular and descending part of the exercised left trapezius increased from first to second long-term recording during periods with seated posture (P<.05 for both comparisons). In contrast, trapezius sEMG activity remained unchanged for all other trapezius parts and postures. This study indicates that acute trapezius pain induces elevated habitual trapezius activity during periods with low biomechanical loading of the shoulder/neck muscles with the elevated sEMG activity being restricted to the painful part of the muscle. In contrast to the pain-adaption model, the current study indicates a relation between acute muscle pain and elevated low-level muscle activity; however, it remains unknown if development of chronic muscle pain can be preceded by an initial stage with elevated muscle activity.