title: The refractory period of the audible "crack" after lumbar manipulation: a preliminary study.
abstract: OBJECTIVE
  This study evaluates if side posture lumbar manipulation is associated with a refractory period of the audible "crack" and if so, to quantify this refractory period across subjects.
  
  
  METHODS
  Three subjects were exposed to multiple "baseline" side posture manipulations until no further audible cracks were recorded. "Test-refractory period" manipulations were administered after a set time (ie, potential refractory period) at which point the number of audible cracks was recorded. The refractory period was declared when a minimum of 50% of the baseline audible "cracks" had recovered during the test manipulations. The study design included 2 clinicians who performed side posture lumbar manipulation on asymptomatic subjects ranging from 38 to 49 years of age.
  
  
  RESULTS
  The refractory period was 40 minutes for subject A, 70 minutes for subject B, and 95 minutes for subject C. The average refractory period across subjects was 68.33 minutes. The audible "crack" recovery was maintained for the remaining test days once the refractory period had been met.
  
  
  CONCLUSIONS
  The audible "crack" heard during side posture lumbar manipulation is believed to originate from the zygapophyseal joints. This is supported by the presence of a refractory period and by the number of audible "cracks" found per manipulation.
authors.affiliation: Department of Applied Chiropractic, Canadian Memorial Chiropractic College, Toronto, Ontario, Canada.
authors.forename: David E
authors.initials: DE
authors.lastname: Bereznick
authors.forename: Cosma G
authors.initials: CG
authors.lastname: Pecora
authors.forename: J Kim
authors.initials: JK
authors.lastname: Ross
authors.forename: Stuart M
authors.initials: SM
authors.lastname: McGill
mesh_terms: D000328:Adult; D005260:Female; D006801:Humans; D008159:Lumbar Vertebrae / Q000502:physiology*; D008297:Male; D020393:Manipulation, Spinal / Q000379:methods*; D008875:Middle Aged; D011187:Posture; D016059:Range of Motion, Articular; D013016:Sound; D013997:Time Factors; D021801:Zygapophyseal Joint / Q000502:physiology*