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Activator Methods International Ltd.
2950 N. Seventh Street, Suite 200
Phoenix, AZ 85014
ofc 602-224-0220
fax 602-224-0230
toll free 1-800-598-0224
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Subject: Spinal Stiffness |
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| Title: In Vivo Transient Vibration Assessment of the Normal Human Thoracolumbar Spine |
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| Reference: Tony S. Keller, Ph.D., Christopher J. Colloca, D.C., Arlan W. Fuhr, D.C. : in press |
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Abstract: Objective: The objective of this study was to quantify the mobility (dynamic stiffness & mechanical impedance) characteristics of the normal human thoracolumbar spine using a transient vibration analysis technique.
Design: This study is a prospective clinical investigation to obtain normative biomechanical data from the human male and female spine in vivo.
Setting: Musculoskeletal research laboratory, University setting.
Subjects: Twenty asymptomatic subjects (age range 20 – 60 yrs.) with no recent history of musculoskeletal complaints.
Main Outcome Measures: Mechanical impedance, effective stiffness, and resonant frequency analyses were used to quantify the dynamic stiffness of the thoracolumbar spine in this subject population. Data was obtained from posteroanterior (PA) mechanical thrusts delivered with an ActivatorÒ Adjusting Instrument (AAI) equipped with a load cell and accelerometer by means of a portable computer.
Results: In response to the AAI thrusts, the thoracolumbar spine typically exhibited an impedance minimum at frequencies ranging between 30-50 Hz. The maximum PA impedance and corresponding maximum effective stiffness of the thoracolumbar spine and sacrum was roughly two to eight times greater than the magnitude of the impedance minimum. Statistically significant differences in mobility between males and females were noted, particularly for frequencies corresponding to the maximum mobility (» 40 Hz) and minimum mobility (10-20 Hz, 70-80 Hz). For most subjects (both males and females) the lumbar region exhibited a higher impedance and stiffness (less mobility) when compared to the thoracic region.
Conclusions: The PA mechanical behavior of the human thoracolumbar spine was found to be sensitive to mechanical stimulus frequency and showed significant region specific and gender differences. In the frequency range of 30-50 Hz, the lumbar spine of this subject population is the least stiff and therefore has the greatest mobility. From a biomechanical point-of-view, the results of this study indicate that dynamic spinal manipulative therapy (SMT) procedures will produce more spinal motion for a given force, particularly when the PA manipulative thrust is delivered in frequency ranges at or near the resonant frequency. In this regard, SMT procedures designed to target the resonant frequency of the spine require less force application. Both magnitude and frequency content of manual and mechanical thrusting manipulations may be critical elements therapeutic outcome.
Support for this study was from the National Institute of Chiropractic Research |
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