title: Spinal reflex attenuation associated with spinal manipulation.
abstract: METHODS
  This study evaluated the effect of lumbosacral spinal manipulation with thrust and spinal mobilization without thrust on the excitability of the alpha motoneuronal pool in human subjects without low back pain.
  
  
  OBJECTIVE
  To investigate the effect of high velocity, low amplitude thrust, or mobilization without thrust on the excitability of the alpha motoneuron pool, and to elucidate potential mechanisms in which manual procedures may affect back muscle activity.
  
  
  BACKGROUND
  The physiologic mechanisms of spinal manipulation are largely unknown. It has been proposed that spinal manipulation may reduce back muscle electromyographic activity in patients with low back pain. Although positive outcomes of spinal manipulation intervention for low back pain have been reported in clinical trials, the mechanisms involved in the amelioration of symptoms are unknown.
  
  
  METHODS
  In this study, 17 nonpatient human subjects were used to investigate the effect of spinal manipulation and mobilization on the amplitude of the tibial nerve Hoffmann reflex recorded from the gastrocnemius muscle. Reflexes were recorded before and after manual spinal procedures.
  
  
  RESULTS
  Both spinal manipulation with thrust and mobilization without thrust significantly attenuated alpha motoneuronal activity, as measured by the amplitude of the gastrocnemius Hoffmann reflex. This suppression of motoneuronal activity was significant (P < 0.05) but transient, with a return to baseline values exhibited 30 seconds after intervention.
  
  
  CONCLUSIONS
  Both spinal manipulation with thrust and mobilization without thrust procedures produce a profound but transient attenuation of alpha motoneuronal excitability. These findings substantiate the theory that manual spinal therapy procedures may lead to short-term inhibitory effects on the human motor system.
authors.affiliation: Department of Anatomy, New York Chiropractic College, Seneca Falls, New York 13148, USA. ddishman@nycc.edu.
authors.forename: J D
authors.initials: JD
authors.lastname: Dishman
authors.forename: R
authors.initials: R
authors.lastname: Bulbulian
mesh_terms: D000328:Adult; D004576:Electromyography; D005260:Female; D006801:Humans; D017116:Low Back Pain / Q000503:physiopathology / Q000534:rehabilitation; D008161:Lumbosacral Region; D008297:Male; D020393:Manipulation, Spinal; D009046:Motor Neurons / Q000502:physiology; D009119:Muscle Contraction; D018482:Muscle, Skeletal / Q000294:innervation* / Q000502:physiology; D012016:Reference Values; D012018:Reflex / Q000502:physiology*; D013116:Spinal Cord / Q000502:physiology*