Spinal manipulation force and duration affect vertebral movement and neuromuscular responses

Clin Biomech (Bristol, Avon). 2006 Mar;21(3):254-62. doi: 10.1016/j.clinbiomech.2005.10.006. Epub 2005 Dec 27.


Background: Previous study in human subjects has documented biomechanical and neurophysiological responses to impulsive spinal manipulative thrusts, but very little is known about the neuromechanical effects of varying thrust force-time profiles.

Methods: Ten adolescent Merino sheep were anesthetized and posteroanterior mechanical thrusts were applied to the L3 spinous process using a computer-controlled, mechanical testing apparatus. Three variable pulse durations (10, 100, 200 ms, force = 80 N) and three variable force amplitudes (20, 40, 60 N, pulse duration = 100 ms) were examined for their effect on lumbar motion response (L3 displacement, L1, L2 acceleration) and normalized multifidus electromyographic response (L3, L4) using a repeated measures analysis of variance.

Findings: Increasing L3 posteroanterior force amplitude resulted in a fourfold linear increase in L3 posteroanterior vertebral displacement (p < 0.001) and adjacent segment (L1, L2) posteroanterior acceleration response (p < 0.001). L3 displacement was linearly correlated (p < 0.001) to the acceleration response over the 20-80 N force range (100 ms). At constant force, 10 ms thrusts resulted in nearly fivefold lower L3 displacements and significantly increased segmental (L2) acceleration responses compared to the 100 ms (19%, p = 0.005) and 200 ms (16%, p = 0.023) thrusts. Normalized electromyographic responses increased linearly with increasing force amplitude at higher amplitudes and were appreciably affected by mechanical excitation pulse duration.

Interpretation: Changes in the biomechanical and neuromuscular response of the ovine lumbar spine were observed in response to changes in the force-time characteristics of the spinal manipulative thrusts and may be an underlying mechanism in related clinical outcomes.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Elasticity
  • Lumbar Vertebrae / physiology*
  • Manipulation, Spinal / methods*
  • Movement / physiology*
  • Muscle Contraction / physiology
  • Muscle, Skeletal / physiology*
  • Physical Stimulation / methods*
  • Range of Motion, Articular / physiology*
  • Reflex / physiology
  • Sheep
  • Stress, Mechanical
  • Weight-Bearing / physiology*