title: Nociceptive and non-nociceptive hypersensitivity at latent myofascial trigger points.
abstract: OBJECTIVE
  The aim of the study was to evaluate whether or not there exists nociceptive and non-nociceptive hypersensitivity at latent myofascial trigger points (MTrPs).
  
  
  METHODS
  Eleven healthy volunteers participated in this study, which consisted of 3 sessions of electromyography-guided intramuscular injection with a minimum of a week interval in between. In each session, a bolus of either hypertonic saline (6%, 0.1 mL, each), glutamate (0.1 mL, 0.5 M, each), or isotonic saline (0.9%, 0.1 mL, each) was randomly injected into a latent MTrP and a non-MTrP located in the right or left gastrocnemius medialis muscles. After each injection, participants were asked to rate the perceived pain intensity on an electronic visual analog scale (VAS) and to mark the pain areas on pain drawings. Maximal pain intensity (VAS(peak)), the area under the curve (VAS(auc)), and local and referred pain areas were extracted.
  
  
  RESULTS
  Injections of either hypertonic saline, glutamate, or isotonic saline into the latent MTrPs induced a higher VAS(peak) and larger VAS(auc) than the non-MTrPs (all, P<0.05). Furthermore, the MTrPs with referred pain after painful injections were found to show higher VAS(peak) and larger VAS(auc) than those without referred pain (both, P<0.001).
  
  
  CONCLUSIONS
  These results confirm the existence of nociceptive hypersensitivity at latent MTrPs and provide the first evidence that there exists non-nociceptive hypersensitivity (allodynia) at latent MTrPs. Finally, the occurrence of referred muscle pain is associated with higher pain sensitivity at latent MTrPs.
authors.affiliation: Department of Rehabilitation, Qi-Lu Hospital of Shandong University, Jinan, China.
authors.forename: Lian-Tao
authors.initials: LT
authors.lastname: Li
authors.forename: Hong-You
authors.initials: HY
authors.lastname: Ge
authors.forename: Shou-Wei
authors.initials: SW
authors.lastname: Yue
authors.forename: Lars
authors.initials: L
authors.lastname: Arendt-Nielsen