Functional Responses of Chiropractic Adjustments

Christopher J. Colloca, D.C.

"The rational approach {in the treatment of chronic low back pain} should be based on at least three principles: 1) achievement of good function of all peripheral structures (skin, tissue, muscles, fascia, and joints); 2) development of reasonable good muscle balance; and 3) activation of the spino-cerebello-vestibular circuits on the sense of sensory motor stimulation, thus facilitating the most important afferent pathways and centers."

- Janda V. Treatment of chronic back pain. J Manual Medicine 1992; 6:166-8.

Our research, and that of others has clearly shown that chiropractic adjustments result in both biomechanical and physiological responses in the human body.

Significant neuromuscular reflex responses in the adjacent and sometimes distant spinal musculature have been recorded in numerous studies (Herzog et al., 1999;Symons et al., 2000;Colloca et al., 1999;Colloca and Keller, 2000).

It is thought that such reflexogenic stimulation is a plausible explanation of the mechanisms of spinal manipulation/chiropractic adjustment. Research has found that mechanical stimulation of mechanosensitive afferents have been found to inhibit nociception in interneuronal pools in the spinal cord and consequently inhibiting therefore pain perception (Gillette R.G., 1987;Gillette R.G., 1986;Gillette et al., 1998).

Inasmuch, beneficial effects of chiropractic adjustments are thought to be associated with mechanosensitive afferent stimulation and presynaptic inhibition of nociceptive afferent transmission in the modulation of pain (Wyke, 1980;Willis W. and Coggeshall R., 1991), inhibition of hypertonic muscles (Thabe, 1986;Herzog, 1996), and improved functional ability (Meade et al., 1995;Shekelle, 1994;Triano et al., 1995).

Studies have demonstrated the functional benefit of patients undergoing spinal manipulation in terms of outcome in acute, sub-acute, and chronic low back pain in randomized controlled clinical trials (Bigos et al., 1994;Shekelle et al., 1992;Koes et al., 1996;Skargren et al., 1998).

Chiropractic research, however, is considerably lacking experimental basic science experiments to understand the functional benefits of patients receiving chiropractic care.

Dr. Chris Colloca performing leg testing procedures during chiropractic adjusting assessment as Dr. Tony Keller collects sEMG data during the research protocol.
Since 1998, Dr. Tony Keller and I have collected data in my practice to investigate neuromuscular reflex responses of chiropractic adjustments.

As part of our research protocol, we measured isometric trunk extension efforts using surface electromyography (sEMG) in each patient and used this data as a baseline to compare neuromuscular reflex responses resulting from chiropractic thrusts.

With this protocol, we can normalize the data to each patient's own individual muscle function by taking an average of their 3 consecutive trunk extension tasks.

As a trunk extension efforts is performed, electrical activity of the paraspinal muscles can be ascertained using surface EMG.
However, since the isometric extension task is also a measure of the patient's spinal function, we have found that we can further assess pre-post extension efforts as a means of studying the effects of chiropractic on spinal function.

In 1998, we noticed an interesting trend of increased muscle output following adjustments delivered with an Activator Adjusting Instrument (AAI) and a stiffness assessment protocol.

It was evident that following our research protocol, upon post-testing trunk muscle activity was significantly increased.

While this was an interesting observation, it left us with more questions than answers.

Why did the patients have increased muscle output following our intervention? Was it a learned response - that patients are better at the task after having performed it the first time? Were they actually stronger after the research protocol? Was it the laying on of the hands that was responsible for the changes we saw? Were the results actually attributed to our intervention - the adjustment or stiffness protocol?

Force-time profiles of an Activator thrust at the maximum setting (SMT - Yellow) and zero setting (Sham-SMT - White).
With these questions unanswered, we recruited patients to participate in a controlled clinical trial.

We randomly assigned patients to a control group and a sham-adjustment group to compare to the active treatment group.

Patients in the sham-adjustment group received the same protocol as the active treatment group however, the AAI was placed in the zero-position.

In this position, the instrument produces a negligible force output as no excursion takes place from the instrument's stylus.

In the sham group, however, the patient still feels the instrument touching their spine and hears the same click that any other patient receiving an instrument adjustment hears.

The AAI has been shown to be effective as a sham intervention at this setting (Hawk et al., 1999). In the control group no intervention was given.

The patients simply rested in between trunk extension tasks for the same time period as the research protocol.

The three groups were then compared for any difference of pre-post muscle strength as assessed by electromyography.

We found that the active treatment group had a significant increase in muscle output following adjustments and the stiffness protocol, while no statistically significant pre-post change was observed in the sham or control groups.

We presented this research at the 2000 meeting of the International Society for the Study of the Lumbar Spine in Adelaide, Australia in May, 2000, and the manuscript appears in the December, 2000 issue of the Journal of Manipulative and Physiological Therapeutics.

Noteworthy, however, are some limitations to our study.

We cannot generalize that "adjustments" were responsible for the increase in muscle strength because the patients also received a stiffness assessment protocol consisting of 20 mechanical stimulations to the lumbar spine along selected spinous and transverse processes.

Secondly, we did not incorporate any trunk restrainment apparatuses or force measurement techniques, but rather collected the patients maximum isometric effort without restraint.

Recognizing these limitations, we have begun continuing projects to improve our protocol with our most recent research protocol in October, 2000.

We have collected data on another subgroup of patients who only received chiropractic adjustments according to strict technique protocol for further evaluation (as opposed to the addition of our stiffness assessment protocol).

We have recruited the assistance of an Arizona State University graduate student to assist in our research.

We are building us a trunk restrainment apparatus equipped with a force sensor for another data draw to begin in early 2001.

In addition, we have just equipped my office with state-of-the-art equipment to better functionally measure the outcomes of patients in clinical research.

This equipment includes various sensors such as computerized inclinometry, muscle strength, and algometry devices that we can incorporate using validated protocols.

We will continue this important work to better understand the effect of chiropractic care on the body, and we will continue to update you on our projects as they progress.


This work was supported, in part, through a grant from the National Institute of Chiropractic Research.


Bigos,S.J., Bowyer O., ,B.G., ,e.a., 1994. Acute Low Back Problems in Adults. Clinical Practice Guideline No. 14. AHCPR Publication No. 950642. Proceedings of Agency for Health Care Policy and Research, Public Health Service, U.S. Department of Health and Human Services.

Colloca,C.J. & Keller,T.S., 2000. Electromyographic reflex response to mechanical force, manually-assisted spinal manipulative therapy. Spine 2001, in press.

Colloca,C.J., Keller,T.S., Fuhr,A.W., 1999. Muscular and mechanical behavior of the lumbar spine in response to dynamic posteroanterior forces Proceedings of the 26th Annual Meeting of the International Society for the Study of the Lumbar Spine, Kona, Hawaii. Toronto: ISSLS: p.136A.

Gillette R.G., 1986. Potential antinocieptive effects of high level somatic stimulation - chiropractic manipulation therapy may coactivate both tonic and phasic analgesic systems. Some recent evidence. Trans Pac Consortium Res, 1, A4(1)-A4(9).

Gillette R.G., 1987. A speculative argument for the coactivation of diverse somatic receptor populations by forceful chiropractic adjustments. A review of the neurophysiologic literature. Manual Medicine, 3, 1-14.

Gillette,R.G., Kramis,R.C., Roberts,W.J., 1998. Suppression of activity in spinal nocireceptive 'low back' neurons by paravertebral somatic stimuli in the cat. Neurosci.Lett., 241,(1), 45-48.

Hawk,C., Azad,A., Phongphua,C., Long,C.R., 1999. Preliminary study of the effects of a placebo chiropractic treatment with sham adjustments. J.Manipulative Physiol Ther., 22,(7), 436-443.

Herzog,W., 1996. Mechanical, Physiologic, and Neuromuscular Considerations of Chiropractic Treatments. In: Lawrence,D.J., Cassidy,J.D., McGregor,M., Meeker,W.C., Vernon,H.T. (Eds.), Advances in Chiropractic, pp. 269-285. Mosby-Year Book, Inc., St. Louis.

Herzog,W., Scheele,D., Conway,P.J., 1999. Electromyographic responses of back and limb muscles associated with spinal manipulative therapy. Spine, 24(2), 146-152.

Koes,B.W., Assendelft,W.J., van der Heijden,G.J., Bouter,L.M., 1996. Spinal manipulation for low back pain. An updated systematic review of randomized clinical trials. Spine, 21(24), 2860-2871.

Meade,T.W., Dyer,S., Browne,W., Frank,A.O., 1995. Randomised comparison of chiropractic and hospital outpatient management for low back pain: results from extended follow up. BMJ, 311, 349-351.

Shekelle,P.G., 1994. Spinal manipulation. Spine, 19(7), 858-861.

Shekelle,P.G., Adams,A.H., Chassin,M.R., Hurwitz,E.L., Brook,R.H., 1992. Spinal manipulation for low-back pain. Ann Intern Med, 117(7), 590-598.

Skargren,E.I., Carlsson,P.G., Oberg,B.E., 1998. One-year follow-up comparison of the cost and effectiveness of chiropractic and physiotherapy as primary management for back pain. Subgroup analysis, recurrence, and additional health care utilization. Spine, 23(17), 1875-1883.

Symons,B.P., Herzog,W., Leonard,T., Nguyen,H., 2000. Reflex responses associated with activator treatment. J Manipulative Physiol Ther, 23(3), 155-159.

Thabe,H., 1986. Electromyography as a tool to document diagnostic findings and therapeutic results associated with somatic dysfunctions in the upper cervical spinal joints and sacroiliac joints. Manual Medicine, 2, 53-58.

Triano,J.J., McGregor,M., Hondras,M.A., Brennan,P.C., 1995. Manipulative therapy versus education programs in chronic low back pain. Spine, 20, 948-955.

Willis W. & Coggeshall R., 1991. Sensory mechanisms of the spinal cord. Plenum Press, New York.

Wyke,B., 1980. Articular Neurology and Manipulative Therapy. In: Idczak,R.M., Dewhurst,D., Glasgow,E.F., Tehan,P., Ward,A.R. (Eds.), Apects of Manipulative Therapy. Proceedings of a Multidisciplinary International Conference on Manipulative Therapy, Melbourne, August, 1979, pp. 67-72. Lincoln Institute of Health Sciences, Carlton, Victoria.

Related Research on Functional Responses of Chiropractic Adjustments

Cassidy,J.D., Lopes,A.A., Yong-Hing,K., 1992. The immediate effect of manipulation versus mobilization on pain and range of motion in the cervical spine: a randomized controlled trial [see comments]. J Manipulative.Physiol Ther., 15,(9), 570-575.

Cassidy,J.D., Quon,J.A., LaFrance,L.J., Yong-Hing,K., 1992. The effect of manipulation on pain and range of motion in the cervical spine: a pilot study [published erratum appears in J Manipulative Physiol Ther 1992 Nov-Dec;15(9):following table of contents] [see comments]. J Manipulative.Physiol Ther., 15,(8), 495-500.

Cassidy,J.D., Lopes,A.A., Yong-Hing,K., 1993. The immediate effect of manipulation vs. mobilization on pain and range of motion in the cervical spine: a randomized controlled trial [letter; comment]. J Manipulative.Physiol Ther., 16,(4), 279-280.

Floman,Y., Liram,N., Gilai,A.N., 1997. Spinal manipulation results in immediate H-reflex changes in patients with unilateral disc herniation. Eur.Spine J, 6,(6), 398-401.

Herzog,W., Nigg,B.M., Robinson,R.O., Read,L.J., 1987. Quantifying the effects of spinal manipulations on gait, using patients with low back pain: a pilot study. J.Manipulative.Physiol Ther., 10,(6), 295-299.

Herzog,W., Nigg,B.M., Read,L.J., 1988. Quantifying the effects of spinal manipulations on gait using patients with low back pain. J.Manipulative.Physiol Ther., 11,(3), 151-157.

Herzog,W., 1988. The relation between the resultant moments at a joint and the moments measured by an isokinetic dynamometer. J.Biomech., 21,(1), 5-12.

Johnson,H.H., 1993. The effect of manipulation on pain and range of motion in the cervical spine: a pilot study [letter; comment]. J Manipulative.Physiol Ther., 16,(3), 193.

Lehman,G.J. & McGill,S.M., 1999. The influence of a chiropractic manipulation on lumbar kinematics and electromyography during simple and complex tasks: a case study. J Manipulative Physiol Ther., 22,(9), 576-581.

McMorland,G. & Suter,E., 2000. Chiropractic management of mechanical neck and low-back pain: a retrospective, outcome-based analysis. J Manipulative Physiol Ther, 23,(5), 307-311.

Nall,S.K., 1982. The role of specific manipulation towards alleviating abnormalities in body mechanics and restoration of spinal motion. J Manipulative.Physiol Ther, 5,(1), 11-15.

Nilsson,N., Christensen,H.W., Hartvigsen,J., 1996. Lasting changes in passive range motion after spinal manipulation: a randomized, blind, controlled trial. J Manipulative.Physiol Ther., 19,(3), 165-168.

Osterbauer,P.J., De Boer,K.F., Widmaier,R., Petermann,E., Fuhr,A.W., 1993. Treatment and biomechanical assessment of patients with chronic sacroiliac joint syndrome. J.Manipulative.Physiol.Ther., 16,(2), 82-90.

Osterbauer,P.J., Derickson,K.L., Peles,J.D., Deboer,K.F., Fuhr,A.W., Winters,J.M., 1992. Three-dimensional head kinematics and clinical outcome of patients with neck injury treated with spinal manipulative therapy: a pilot study [published erratum appears in J Manipulative Physiol Ther 1992 Nov- Dec;15(9):following table of contents]. J.Manipulative.Physiol.Ther., 15,(8), 501-511.

Pollard,H. & Ward,G., 1998. The effect of upper cervical or sacroiliac manipulation on hip flexion range of motion. J Manipulative.Physiol Ther., 21,(9), 611-616.

Pope,M.H., Phillips,R.B., Haugh,L.D., Hsieh,C.Y., MacDonald,L., Haldeman,S., 1994. A prospective randomized three-week trial of spinal manipulation, transcutaneous muscle stimulation, massage and corset in the treatment of subacute low back pain. Spine, 19,(22), 2571-2577.

Suter,E., Herzog,W., Leonard,T.R., Nguyen,H., 1998. One-year changes in hind limb kinematics, ground reaction forces and knee stability in an experimental model of osteoarthritis. J.Biomech., 31,(6), 511-517.

Suter,E., McMorland,G., Herzog,W., Bray,R., 1999. Decrease in quadriceps inhibition after sacroiliac joint manipulation in patients with anterior knee pain. J Manipulative.Physiol Ther., 22,(3), 149-153.

Wood,T., Mathews,R., 1999. A clinical trial investigating the relative effect of an instrumental as opposed to a manual thrust manipulation in the treatment of cervical spine dysfunction-a pilot study. Proceedings of Foundation for Chiropractic Research and Education.

Wood,T.G., Colloca,C.J., Matthews,R., 2001. A pilot randomized clinical trial on the relative effect of instrumental (MFMA) versus manual (HVLA) manipulation in the treatment of cervical spine dysfunction. J Manipulative Physiol Ther, in press.

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