Pressure pain threshold mapping of the trapezius muscle reveals heterogeneity in the distribution of muscular hyperalgesia after eccentric exercise

This study aimed at investigating in details the spatial characteristics of muscular hyperalgesia after development of delayed onset muscle soreness (DOMS) in the trapezius muscle. High density pressure pain mapping consisting of 36 pain pressure threshold (PPT) recording points were assessed over the trapezius muscle from 20 subjects. PPT were recorded before, immediately after and 24 h after eccentric exercise/rest for the exercise group (N = 10) and the control group (N = 10). A 36 points geometric grid was used on both the exercise and control groups. The eccentric exercise used to elicit DOMS consisted of 50 contractions against a downward pressing force at 100% maximum voluntary contraction in bouts of 10 contractions followed by 2 min break. For the exercise group, PPT values decreased significantly over time for all points (P < 0.001) but not for the control group. At baseline, both muscle belly sites and upper part of the trapezius were more sensitive than muscle belly sites and middle and lower parts (P < 0.001 for both). The hyperalgesia was also mostly developed in the muscle belly sites (P < 0.001), further enhancing its position as the most sensitive part of the muscle. The present results showed the topographical distribution of pressure pain sensitivity over the trapezius muscle and also that hyperalgesia developed in a heterogeneous manner over the trapezius muscle in response to eccentric exercise underlining sensory partitioning of the muscle. The technique of high density pressure pain topographical mappings can be helpful in characterizing muscle hyperalgesia and its heterogeneity.