Archive for category Activator I

Activator as a theraputic instrument: Survey of usage and opinions amongst members of the British Chiropractic Association

June 1, 2006 Activator I, Activator Methods Chiropractic Technique: General Articles, Research,

Summary

This paper provides an account of a survey of chiropractors registered with the British Chiropractic Association that was designed to examine use of the Activator as a therapeutic instrument, and opinions related to its use. The survey was mailed to a sample population of 300 chiropractors and achieved a response rate of 82%. Of the chiropractors who responded to the survey and were included in data analysis, 82% reported that they used an Activator adjusting instrument, but only 2% of these stated that they typically used it as their primary method of treatment. The survey suggested that Activator I was the most frequently used form of the instrument. Cervical pain was the most frequently identified condition for whIch the activator was used. The vast majority of responders believed that the Activator was a useful therapeutic instrument in chiropractic practice (81%), and that it offered a safe treatment option (84%). Viewed in the context of other surveys of activator usage, this work adds to a body of literature which suggests an increase In Activator usage among chiropractors practicing in the United Kingdom since the early 1990’s. This being the case, it is appropriate that issues of effectiveness and safety in relation to Activator therapy are given due consideration in future research.

 

Clinical Chiropractic Volume 9, Issue 2, June 2006, Pages 70–75.
Author information: Dicken T. Reada, Francis J.H. Wilsonb, Hugh A. Gemmell. Anglo-European College of Chiropractic, 13-15 Parkwood Road, Bournemouth, Dorset, BH5 2DF, UK.

 

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A Randomized Clinical Trial of the Relative Effectiveness of Manual Versus Mechanical Force Chiropractic Adjustments in the Management of Sacroiliac Joint Syndrome

September 1, 2005 Activator I, Clinical Trials, Research, Sacroiliac Joint,

Abstract

OBJECTIVE:

To investigate the effect of instrument-delivered compared with traditional manual-delivered thrust chiropractic adjustments in the treatment of sacroiliac joint syndrome.

METHODS:

Prospective, randomized, comparative clinical trial. Sixty patients with sacroiliac syndrome were randomized into two groups of 30 subjects. Each subject received 4 chiropractic adjustments over a 2-week period and was evaluated at 1-week follow-up. One group received side-posture, high-velocity, low-amplitude chiropractic adjustments; the other group received mechanical-force, manually-assisted chiropractic adjustments using an Activator Adjusting Instrument (Activator Methods International, Ltd, Phoenix, Ariz).

RESULTS:

No significant differences between groups were noted at the initial consultation for any of the outcome variables. Statistically significant improvements were observed in both groups from the first to third, third to fifth, and first to fifth consultations for improvements (P < .001) in mean numerical pain rating scale 101 (group 1, 49.1-23.4; group 2, 48.9-22.5), revised Oswestry Low Back Pain Disability Questionnaire (group 1, 37.4-18.5; group 2, 36.6-15.1), orthopedic rating score (group 1, 7.6-0.6; group 2, 7.5-0.8), and algometry measures (group 1, 4.8-6.5; group 2, 5.0-6.8) for first to last visit for both groups.

CONCLUSIONS:

The results indicate that a short regimen of either mechanical-force, manually-assisted or high-velocity, low-amplitude chiropractic adjustments were associated with a beneficial effect of a reduction in pain and disability in patients diagnosed with sacroiliac joint syndrome. Neither mechanical-force, manually-assisted nor high-velocity, low-amplitude adjustments were found to be more effective than the other in the treatment of this patient population.

J Manipulative Physiol Ther. 2005 Sep;28(7):493-501. [PMID:16182023]

Author information: Shearar KA, Colloca CJ, White HL. Chiropractic Department, Durban Institute of Technology, Durban, South Africa.

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Active Trunk Extensor Contributions to Dynamic Posteroanterior Lumbar Spinal Stiffness

May 1, 2004 Activator I, Lumbar Spine, Neurophysiological, Research,

Abstract

BACKGROUND:

Assessments of posteroanterior (PA) spinal stiffness using mobilization apparatuses have demonstrated an increase in PA spine stiffness during voluntary contraction of the lumbar extensor muscles; yet, little work has been done to this degree in symptomatic subjects.

OBJECTIVE:

To use a previously validated dynamic mechanical impedance procedure to quantify changes in PA dynamic spinal stiffness at rest and during lumbar isotonic extension tasks in patients with low back pain (LBP).

METHODS:

Thirteen patients with LBP underwent a dynamic spinal stiffness assessment in the prone-resting position and again during lumbar extensor efforts. Stiffness assessments were obtained using a handheld impulsive mechanical device equipped with an impedance head (load cell and accelerometer). PA manipulative thrusts (approximately 150 N, <5 milliseconds) were delivered to skin overlying the L3 left and right transverse processes (TPs) and to the L3 spinous process (SP) in a predefined order (left TP, SP, right TP) while patients were at rest and again during prone-lying lumbar isotonic extension tasks. Dynamic spinal stiffness characteristics were determined from force and acceleration measurements using the apparent mass (peak force/peak acceleration, kg). Apparent mass measurements for the resting and active lumbar isotonic task trials of each patient were compared using a 2-tailed, paired t test.

RESULTS:

A significant increase in the PA dynamic spinal stiffness was noted for thrusts over the SP (apparent mass [17.0%], P=.0004) during isotonic trunk extension tasks compared with prone resting, but no statistically significant changes in apparent mass were noted for the same measures over the TPs.

CONCLUSIONS:

These findings add support to the significance of the trunk musculature and spinal posture in providing increased spinal stability.

J Manipulative Physiol Ther. 2004 May;27(4):229-37. [PMID:15148461]

Author information: Colloca CJ, Keller TS. Department of Kinesiology, Atizona State University, Tempe, AZ, USA.

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Force-deformation response of the lumbar spine: a sagittal plane model of posteroanterior manipulation and mobilization

March 1, 2002 Activator I, Lumbar Spine, Research,

Abstract

OBJECTIVE:

To develop a mathematical model capable of describing the static and dynamic motion response of the lumbar spine to posteroanterior forces.

DESIGN:

Static, impulsive and oscillatory forces with varying thrust angles and offsets were applied to the model, and the resulting motion responses were compared to experimental data published for spinal mobilization and manipulation of prone-lying subjects.

BACKGROUND:

Methods are sought to improve understanding of the dynamic force-induced displacement response of the lumbar spine during spinal mobilization and manipulation treatment.

METHODS:

The thorax, pelvis and five lumbar vertebrae were represented as seven rigid structures and eight flexible joint structures. Flexible joint structures were modeled using spring and damper elements with three displacement degrees-of-freedom (posterior-anterior and axial displacement, and flexion-extension rotation). The resulting 21 degrees-of-freedom lumped parameter model was solved in modal space.

RESULTS:

The fundamental natural frequency of vibration was 5.24 Hz. Simulations performed using 100 N static and dynamic posteroanterior forces applied to the L3 vertebrae indicated that peak L3 segmental displacements were up to 2.40 mm (impulsive) and 8.23 mm (oscillatory at 2 Hz). Appreciable axial displacements (0.41 mm) and flexion-extension rotations (1.49 degrees ) were also observed for oscillatory forces at L3. The posteroanterior motion response of the lumbar vertebrae was relatively insensitive to both the thrust force angle and thrust force offset, but axial displacements and flexion-extension rotations showed a large change (2-fold or greater) for thrust angles greater than -5 degrees (caudal) in comparison to vertical thrusts. Intersegmental motion responses for static, impulsive and oscillatory loads were more comparable than their segmental counterparts.

CONCLUSIONS:

The model predicts lumbar segmental and inter-segmental motion responses to manipulative forces that are otherwise difficult to obtain experimentally.

RELEVANCE:

This study assists clinicians to understand the biomechanics of posteroanterior forces applied to the lumbar spine of prone-lying subjects. Of particular clinical relevance is the finding that greater spinal mobility is possible by targeting specific load-time histories.

Clin Biomech (Bristol, Avon). 2002 Mar;17(3):185-96. [PMID:11937256]

Author information: Keller TS, Colloca CJ, Béliveau JG. Department of Mechanical Engineering, University of Vermont, 119C Votey Building, Burlington VT 05405-0156, USA.

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Stiffness and Neuromuscular Reflex Response of the Human Spine to Posteroanterior Manipulative Thrusts In Patients With Low Back Pain

October 1, 2001 Activator I, Neurophysiological, Research,

Abstract

BACKGROUND:

Studies investigating posteroanterior (PA) forces in spinal stiffness assessment have shown relationships to spinal level, body type, and lumbar extensor muscle activity. Such measures may be important determinants in discriminating between patients who are asymptomatic and those who have low back pain. However, little objective evidence is available concerning variations in PA stiffness and their clinical significance. Moreover, although several studies have assessed only load input in relation to stiffness, a more complete assessment based on dynamic stiffness measurements (force/velocity) and concomitant neuromuscular response may offer more information concerning mechanical properties of the low back.

OBJECTIVE:

To determine the stiffness and neuromuscular characteristics of the symptomatic low back.

STUDY DESIGN:

This study is a prospective clinical study investigating the in vivo mechanical and muscular behavior of human lumbar spinal segments to high loading rate PA manipulative thrusts in research subjects with low back pain (LBP).

METHODS:

Twelve men and 10 women, aged 15 to 73 years (mean age of 42.8 +/- 17.5 years) underwent physical examination and completed outcome assessment instruments, including Visual Analog Scale, Oswestry Low Back Disability Index, and SF-36 health status questionnaires. Clinical categorization was made on the basis of symptom frequency and LBP history. A hand-held spinal manipulation device, equipped with a preload control frame and impedance head, was used to deliver high-rate (<0.1 millisecond) PA manipulative thrusts (190 N) to several common spinal landmarks, including the ilium, sacral base, and L5, L4, L2, T12, and T8 spinous and transverse processes. Surface, linear-enveloped, electromyographic (sEMG) recordings were obtained from electrodes (8 leads) located over the L3 and L5 paraspinal musculature to monitor the bilateral neuromuscular activity of the erector spinae group during the PA thrusts. Maximal-effort isometric trunk extensions were performed by the research subjects before and immediately after the testing protocol to normalize sEMG data. The accelerance or stiffness index (peak acceleration/peak force, kg-1) and composite sEMG neuromuscular reflex response were calculated for each of the thrusts.

RESULTS:

Posteroanterior stiffness obtained at the sacroiliac joints, transverse processes, or spinous processes was not different for subjects grouped according to LBP chronicity. However, in those with frequent or constant LBP symptoms, there was a significantly increased spinous process (SP) stiffness index (7.0 kg-1) (P <.05) in comparison with SP stiffness index (6.5 kg-1) of subjects with only occasional or no LBP symptoms. Subjects with frequent or constant LBP symptoms also reported significantly greater scores on the visual analog scale (P =.001), Oswestry (P =.001), and perceived health status (P =.03) assessments. The average SP stiffness index was 6.6% greater (P <.05) and 19.1% greater (P <.001) than the average sacroiliac stiffness index and average transverse process stiffness index, respectively.

CONCLUSIONS:

This study is the first to assess erector spinae neuromuscular reflex responses simultaneously during spinal stiffness examination. This study demonstrated increased spinal stiffness index and positive neuromuscular reflex responses in subjects with frequent or constant LBP as compared with those reporting intermittent or no LBP.

J Manipulative Physiol Ther. 2001 Oct;24(8):489-500. [PMID:11677547]

Author information: Colloca CJ, Keller TS.Postdoctoral and Related Professional Education Department, Logan College of Chiropractic, St. Louis, MO, USA.

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A Pilot Randomized Clinical Trial on the Relative Effect of Instrumental Versus Manual Thrust Manipulation in the Treatment of Cervical Spine Dysfunction.

May 1, 2001 Activator I, Cervical Spine, Clinical Trials, Research,

Abstract

OBJECTIVE:

To determine the relative effect of instrument-delivered thrust cervical manipulations in comparison with traditional manual-delivered thrust cervical manipulations in the treatment of cervical spine dysfunction.

DESIGN:

Prospective, randomized, comparative clinical trial.

SETTING:

Outpatient chiropractic clinic, Technikon Natal, South Africa.

PATIENTS:

Thirty patients diagnosed with neck pain and restricted cervical spine range of motion without complicating pathosis for at least 1 month were included in the study.

INTERVENTIONS:

The patients were randomized into 2 groups. Those in one group received mechanical force, manually assisted (MFMA) manipulation to the cervical spine, delivered by means of a hand-held instrument (Activator II Adjusting Instrument). Those in the other group received specific contact high-velocity, low-amplitude (HVLA) manipulation consisting of standard Diversified rotary/lateral break techniques to the cervical spine. Each group received only the specific therapeutic intervention, no other treatment modalities or interventions (including medication) being used, until asymptomatic status was achieved or a maximum of 8 treatments had been received.

MAIN OUTCOME MEASURES:

Both treatment groups were assessed through use of subjective (Numerical Pain Rating Scale 101, McGill Short-Form Pain Questionnaire, and Neck Disability Index) and objective (goniometer cervical range of motion) measurement parameters at specific intervals during the treatment period and at 1-month follow-up. The data were assessed through use of 2-tailed nonparametric paired and unpaired analysis, descriptive statistics, and power analysis of the data.

RESULTS:

The results indicate that both treatment methods had a positive effect on the subjective and objective clinical outcome measures, no significant difference being observed between the 2 groups (P < .025). The subjective data from all 3 questionnaires showed statistically significant changes from initial to final consultations as well as from initial consultation to 1-month follow-up (P < .025). The objective range of motion measures showed statistically significant changes in the MFMA group for left and right rotation and left and right lateral flexion from initial consultation to final consultations and for right rotation and right lateral flexion from initial consultation to 1-month follow-up. The HVLA group showed only the change in left rotation from initial to final consultations and from initial consultation to 1-month follow-up to be statistically significant.

CONCLUSIONS:

The results of this clinical trial indicate that both instrumental (MFMA) manipulation and manual (HVLA) manipulation have beneficial effects associated with reducing pain and disability and improving cervical range of motion in this patient population. A randomized, controlled clinical trial in a similar patient base with a larger sample size is necessary to verify the clinical relevance of these findings.

J Manipulative Physiol Ther. 2001 May;24(4):260-71. [PMID:11353937]

Author information:Wood TG, Colloca CJ, Matthews R. Department of Chiropractic, Technikon Natal, South Africa.

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In Vivo Transient Vibration Assessment of the Normal Human Thoracolumbar Spine

October 1, 2000 Activator I, Biomechanical, Research,

Abstract

OBJECTIVE:

The objective of this study was to quantify the mobility characteristics (dynamic stiffness and mechanical impedance) of the normal human thoracolumbar spine with 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 years) 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 were obtained from posteroanterior mechanical thrusts delivered with an activator adjusting instrument equipped with a load cell and accelerometer by means of a portable computer.

RESULTS:

In response to the activator adjusting instrument thrusts, the thoracolumbar spine typically exhibited an impedance minimum at frequencies ranging between 30 and 50 Hz. The maximum posteroanterior impedance and corresponding maximum effective stiffness of the thoracolumbar spine and sacrum was roughly 2 to 8 times greater than the magnitude of the impedance minimum. Statistically significant differences in mobility between male and female subjects 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 male and female), the lumbar region exhibited a higher impedance and stiffness (less mobility) when compared with the thoracic region.

CONCLUSIONS:

The posteroanterior 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 to 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 procedures will produce more spinal motion for a given force, particularly when the posteroanterior manipulative thrust is delivered in frequency ranges at or near the resonant frequency. In this regard, spinal manipulative therapy 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 for therapeutic outcome.

J Manipulative Physiol Ther. 2000 Oct;23(8):521-30. [PMID:11050608]

Author information: Keller TS, Colloca CJ, Fuhr AW. Department of Mechanical Engineering, University of Vermont, Burlington, VT 05405, USA.

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Muscular and Soft-Tissue Contributions of Dynamic Posteroanterior Spinal Stiffness

September 21, 2000 Activator I, Conference Presentation, Neurophysiological, Research,

Abstract

The stress-strain relationships of human spinal ligaments and  muscles indicate that the spinal musculature play a major role in spine  stability (1, 2). Low-loading rate, quasi-static assessments of  posteroanterior (PA) spinal stiffness have correlated increased PA spine  stiffness to voluntary contracture of the lumbar extensor muscles (3,  4), No study, however, has examined the contributions of lumbar extensor  muscle and high-loading rate dynamic PA spinal stiffness. The objective  of this study was to quantify PA dynamic spinal stiffness at rest and  during maximal voluntary contraction (MVC) efforts in patients with LBP.  Twenty-two consecutive patients with LBP underwent dynamic spinal  stiffness assessment in the prone resting position and during lumbar  extensor muscle MVC, A hand-held Activator Adjusting Instrument equipped  with an impedance head was used to deliver high-loading rate( < 0,1  msec) PA manipulative thrusts (450 N) to the L3 spinous process for  spinal stiffness assessment using a previously validated technique (5).  Surface, linear enveloped, electromyographic (sEMG) recordings were  obtained during the thrusts from electrodes (8 leads) located over the  L3 and L5 erector spinae and data was normalized to subject individual  MVC’s. The accelerance (peak acceleration/peak force, kg-1) or stiffness  index was calculated for each of the thrusts and compared for the  resting and active MVC trials using a 2-tailed, paired t-test. A  significantly increased spine stiffness index (8.36%) (P=0.012) was  found upon MVC trials compared to prone resting stiffness indices.  Lumbar spine extensor MVC contributes to increased PA lumbar spine  stiffness. These findings corroborate the findings of others and add  support to the significance of the trunk musculature in providing spinal  stability.

Reference: Christopher J. Colloca, D.C.1, Tony S. Keller, Ph.D. 2 Daryn E. Seltzer, D.C.3, Arlan w. Fuhr, D.C.1;  Muscular and Soft-Tissue Contributions of Dynamic Posteroanterior  Spinal Stiffness; Proceedings of the International Conference on Spinal Manipulation,  Bloomington, MN September 21-23,2000.

1 Postdoctoral & Related Professional Education  Department Faculty, Logan College of Chiropractic, St. Louis, MO, USA;  National Institute of Chiropractic Research, Phoenix, AZ, USA; Private  Practice of Chiropractic, Phoenix, AZ, USA. 2 Professor, Department of Mechanical Engineering  & Department of Orthopedics and Rehabilitation, The University of  Vermont, Burlington, VT, USA. 3 National Institute of Chiropractic Research, Phoenix, AZ, USA; Private Practice of Chiropractic, Phoenix, AZ, USA.

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Lumbar Erector Spinae Reflex Responses to Mechanical Force, Manually- Assisted Thoracolumbar and Sacroiliac Joint Manipulation in Patients with Low Back Pain

September 21, 2000 Activator I, Conference Presentation, Neurophysiological, Research, Sacroiliac Joint,

ABSTRACT

The purpose of this study was to determine the neuromuscular  reflex responses of the erector spinae musculature to spinal  manipulative thrusts (SMTs) in patients with LBP. 20 (10 male/10 female,  mean age = 43 yrs.) consecutive LBP patients received MFMA SMTs  delivered to the transverse and spinous processes of T8, T12, L2, L4,  L5, and the sacral base and PSIS by means of an Activator Adjusting  Instrument (AAI) equipped with an impedance head. Surface, linear  enveloped, electromyographic (sEMG) recordings were obtained from  electrodes located bilaterally over the L5 and L3 erector spinae muscles  during each of the thrusts. Repeated pre. post isometric extension  strength tests were performed to normalize reflex data. 1600 sEMG  recordings were analyzed from 20 SMT treatments and comparisons were  made between segmental level, segmental contact point (spinous vs.  tranverse processes), and magnitude of the sEMG reflex response. SEMG  threshold was further assessed for correlation of patient self. reported  pain and disability, Consistent, but relatively localized sEMG reflex  responses occurred in response to the MFMA SMTs. 95 % of patients showed  a positive sEMG response to MFMA SMT, Patients with frequent to  constant LBP symptoms tended to have a more marked sEMG response in  comparison to patients with occasional to intermittent LBP. This is the  first study demonstrating neuromuscular reflex responses associated with  MFMA SMT in patients with LBP.

Reference: Christopher J. Colloca, D.C.1, Tony S. Keller, Ph.D. 2, Daryn E. Seltzer, D.C.3, Arlan W. Fuhr, D.C.1;  Lumbar Erector Spinae Reflex Responses to Mechanical Force, Manually-  Assisted Thoracolumbar and Sacroiliac Joint Manipulation in Patients  with Low Back Pain; Proceedings of the 2000 International Conference on Spinal  Manipulation, Bloomington, MN September 21-23,2000.

1 Postdoctoral & Related Professional Education  Department Faculty, Logan College of Chiropractic, St, Louis, MO, USA;  National Institute of Chiropractic Research, Phoenix, AZ, USA; Private  Practice of Chiropractic, Phoenix, AZ, USA. 2 Professor, Department of Mechanical Engineering  & Department of Orthopedics and Rehabilitation, The University of  Vermont, Burlington, VT, USA. 3 National Institute of Chiropractic Research, Phoenix, AZ, USA; Private Practice of Chiropractic, Phoenix, AZ, USA.

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Validation of the Force and Frequency Characteristics of the Activator Adjusting Instrument: Effectiveness as a Mechanical Impedance Measurement Tool

February 1, 1999 Activator I, Biomechanical, Research,

Abstract

OBJECTIVE:

To determine the dynamic force-time and force-frequency characteristics of the Activator Adjusting Instrument and to validate its effectiveness as a mechanical impedance measurement device; in addition, to refine or optimize the force-frequency characteristics of the Activator Adjusting Instrument to provide enhanced dynamic structural measurement reliability and accuracy.

METHODS:

An idealized test structure consisting of a rectangular steel beam with a static stiffness similar to that of the human thoracolumbar spine was used for validation of a method to determine the dynamic mechanical response of the spine. The Activator Adjusting Instrument equipped with a load cell and accelerometer was used to measure forces and accelerations during mechanical excitation of the steel beam. Driving point and transfer mechanical impedance and resonant frequency of the beam were determined by use of a frequency spectrum analysis for different force settings, stylus masses, and stylus tips. Results were compared with beam theory and transfer impedance measurements obtained by use of a commercial electronic PCB impact hammer.

RESULTS:

The Activator Adjusting Instrument imparted a very complex dynamic impact comprising an initial high force (116 to 140 N), short duration pulse (<0.1 ms) followed by several lower force (30 to 100 N), longer duration impulses (1 to 5 ms). The force profile was highly reproducible in terms of the peak impulse forces delivered to the beam structure (<8% variance). Spectrum analysis of the Activator Adjusting Instrument impulse indicated that the Activator Adjusting Instrument has a variable force spectrum and delivers its peak energy at a frequency of 20 Hz. Added masses and different durometer stylus tips had very little influence on the Activator Adjusting Instrument force spectrum. The resonant frequency of the beam was accurately predicted by both the Activator Adjusting Instrument and electronic PCB impact hammer, but variations in the magnitude of the driving point impedance at the resonant frequency were high (67%) compared with the transfer impedance measurements obtained with the electronic PCB impact hammer, which had a more uniform force spectrum and was more repeatable (<10% variation). The addition of a preload-control frame to the Activator Adjusting Instrument improved the characteristics of the force frequency spectrum and repeatability of the driving point impedance measurements.

CONCLUSION:

These findings indicate that the Activator Adjusting Instrument combined with an integral load cell and accelerometer was able to obtain an accurate description of a steel beam with readily identifiable geometric and dynamic mechanical properties. These findings support the rationale for using the device to assess the dynamic mechanical behavior of the vertebral column. Such information would be useful for SMT and may ultimately be used to evaluate the [corrected] biomechanical effectiveness of various manipulative, surgical, and rehabilitative spinal procedures.

J Manipulative Physiol Ther. 1999 Feb;22(2):75-86. [PMID:10073622]

Author information: Keller TS, Colloca CJ, Fuhr AW. Department of Mechanical Engineering, University of Vermont, Burlington, USA.

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