This study will use microdialysis to investigate myofascial pain. This pain is characterized by "trigger points" (exquisitely tender spots) in a group of tense muscle fibers that extend from the trigger point to the muscle attachments. Trigger points in the trapezius, a large muscle lying between the neck and shoulder, are typically caused by emotional stress, postures such as hunching shoulders, certain activities like using a telephone receiver without elbow support, or by wearing certain articles such as a heavy coat or heavy purse. Microdialysis uses a very thin needle probe (about the size and shape of an acupuncture needle) to collect and measure chemicals directly from soft tissue. Analysis of these chemicals will show whether changes in the tissue around a muscle with trigger points are confined to that muscle, or if these changes also occur in more distant muscles.