title: The relationship of the audible pop to hypoalgesia associated with high-velocity, low-amplitude thrust manipulation: a secondary analysis of an experimental study in pain-free participants.
abstract: OBJECTIVE
  High-velocity, low-amplitude (HVLA) manipulation is an effective treatment of low back pain (LBP); however, the corresponding mechanisms are undetermined. Hypoalgesia is associated with HVLA manipulation and suggests specific mechanisms of action. An audible pop (AP) is also associated with HVLA manipulation; however, the influence of the AP on the hypoalgesia associated with HVLA manipulation is not established. The purpose of the current study was to observe the influence of the AP on hypoalgesia associated with HVLA manipulation.
  
  
  METHODS
  The current study represents a secondary analysis of 40 participants. All participants underwent thermal pain sensitivity testing to their leg and low back using protocols specific to A delta fiber-mediated pain and temporal summation. Next, participants received HVLA manipulation to their low back, and the examiner recorded whether an AP was perceived. Finally, participants underwent immediate follow-up thermal pain sensitivity testing using the same protocols. Separate repeated-measure analyses of variance (ANOVAs) were used to observe changes in pain sensitivity before and immediately after HVLA manipulation.
  
  
  RESULTS
  Hypoalgesia of A delta fiber-mediated pain was observed in the low back after HVLA (P < .05), and this was independent of whether an AP was perceived (P > .05). Hypoalgesia of temporal summation was observed in the lower extremity after HVLA (P < .05), and this was independent of whether an AP was perceived (P = .08). However, a moderate effect size for temporal summation was observed favoring participants in whom an AP was perceived.
  
  
  CONCLUSIONS
  The current study suggests hypoalgesia is associated with HVLA manipulation and occurs independently of a perceived AP. Inhibition of lower extremity temporal summation may be larger in individuals in whom an AP is perceived, but further study is necessary to confirm this finding.
authors.affiliation: University of Florida Department of Physical Therapy, Gainesville, FL 32610, USA. bialosky@phhp.ufl.edu
authors.forename: Joel E
authors.initials: JE
authors.lastname: Bialosky
authors.forename: Mark D
authors.initials: MD
authors.lastname: Bishop
authors.forename: Michael E
authors.initials: ME
authors.lastname: Robinson
authors.forename: Steven Z
authors.initials: SZ
authors.lastname: George
mesh_terms: D000328:Adult; D005260:Female; D006358:Hot Temperature; D006801:Humans; D007866:Leg; D017116:Low Back Pain / Q000209:etiology / Q000503:physiopathology; D008297:Male; D020393:Manipulation, Spinal / Q000379:methods*; D009412:Nerve Fibers; D010146:Pain / Q000209:etiology / Q000503:physiopathology; D017288:Pain Threshold; D010812:Physical Stimulation / Q000379:methods; D013016:Sound; D013997:Time Factors; D055815:Young Adult