Objective
The aim of the present study was to investigate the pain intensity, quality, and pattern in experimental muscle pain.

Method
Eleven healthy adults and eleven myofascial pain syndrome (MPS) patients participated in this study. Hypertonic saline (5%) was injected into upper trapezius, infraspinatus and tibialis anterior muscles of 11 healthy adults. A continuous recording of ongoing pain intensities of the local pain and referred pain was measured. After pain had subsided, the subjects completed a Korean version of the McGill Pain Questionnaire (MPQ). This study included 11 patients who have trigger point on upper trapezius muscle. Pain pressure thresholds (PPTs) and pain intensity ratings of different pressure stimuli in upper trapezius muscles were compared with experimental group.

Results
In experimental group, local pain became maximal after one minute and referred pain after one and a half minutes. At that time, Visual analogue scale (VAS) score was 3.8 and 1.9 each other. The referred pain of upper trapezius muscle primarily radiated to the posterolateral side of neck. The one of infraspinatus muscle radiated to the shoulder joint and anterolateral side of upper arm area and the one of tibialis anterior muscle radiated to the shin and dorsum of ankle joint. The PPTs were found to be significantly lower in upper trapezius muscle of patients with myofascial pain syndrome (MPS) than in those of experimental group. The slope of VAS to different stimuli showed the linear relationship at both group, and in that of patient groups was found to be significantly steeper than in that of experimental group. The experimental muscle pain group had no difference in pain quality compared with MPS patients except affective subscale.

Conclusion
The present results suggest that intramuscular injection of hypertonic saline can be used a experimental pain model of MPS, and PPTs and pain intensity ratings of different pressure stimulus are valuable tools for quantitative description of chronic and experimental muscle pain.