Proprioception, the Pain Gate,
and Chiropractic Care

Mark Sontag, MD, graduated from McGaw Medical Center of Northwestern University (Evanston, Illinois), in 1983. His practice specialty is physiatry (physical medicine and rehabilitation). He practices in San Mateo, CA. In 2000, the San Francisco Chronicle newspaper profiled Dr. Sontag, as follows (1):

Sharks’ Team Doctor Calls the Shots
Menlo Park Physician Aims for Zero Pain

Friends of Dr. Mark Sontag of Portola Valley, CA, like to joke that he’s “a man for all seasons.”

A specialist in sports medicine and rehabilitation, Sontag is a team doctor for the San Francisco Giants, the San Jose Sharks, and the San Jose SaberCats, as well as a consulting spinal physician for the Oakland Raiders and Menlo Colleges athletic programs. He has also treated players for the San Francisco 49ers.

In July 2000, Dr. Sontag and colleagues opened the Sports, Pain, and Rehabilitative Care Center in Menlo Park for the treatment of chronic and acute pain sufferers. Their patients are not elite athletes, but people with chronic pain syndrome who have undergone previous medical or surgical treatment with little or no relief.

Sontag has developed a theory about the levels of pain tolerance among athletes that now forms this center’s treatment model.

Sontag, a certified physiatrist, said “neurological studies show that motion tends to block pain impulses to the brain.” In the case of some athletes, this enables them to perform at almost superhuman levels.

Sontag has established a pecking order of pain tolerance that puts hockey players at the highest pain threshold and baseball players at the lowest, with football players somewhere in the middle.

Eventually, he came to believe that there was a correlation between pain thresholds and how much continuous movement a particular sport demands of an injured athlete. “The more action, the less pain is likely to be felt, and I’ve observed that this applies not only to athletes but for others too.”

As examples, football has a relatively brief burst of action wrapped around lengthy strolls back to the huddle, timeouts, and other and scheduled delays.

By comparison, hockey matches are 60 minutes of almost continuous action, while in baseball, players may not do much for several innings at a time.

The key concept from Dr. Sontag is:

“neurological studies show that motion
tends to block pain impulses to the brain.”

This review centers around this concept of motion blocking pain.

•••••

In 1962, Ronald Melzack (d. 2019, age 90 years) and Patrick Wall (d. 2001, age 75 years), forever changed our understanding of pain and pain management when they published a study in the journal Brain, titled (2):

On the Nature of Cutaneous Sensory Mechanisms

Three years later, Melzack and Wall updated their pain theory and published their findings in the journal Science in an article titled (3):

Pain Mechanisms
A New Theory

Ronald Melzack, PhD, was a Canadian psychologist working at McGill University. Patrick Wall, MD, was a British neuroscientist and pain expert; he was also the first editor of the journal Pain. Their pain theory is today known as the “Gate Control Theory of Pain.”

A very simplified explanation of their Gate Control Theory of Pain is that the pain electrical signal to the cortical brain (small diameter afferents) can be inhibited by non-painful electrical signals arising from other sensory afferents (large diameter afferents). Representative reference book comments include:

The perception of pain is dependent upon the balance of activity in large (mechanoreceptor) and small (nociceptive) afferents. (4)

If large myelinated fibers (mechanoreceptors) were selectively stimulated, then normal “balance” of activity between large (mechanoreceptor) and small (nociceptive) fibers would be restored and the pain would be relieved. (4)

“Pain is not simply a direct product of the activity of nociceptive afferent fibers but is regulated by activity in other myelinated afferents that are not directly concerned with the transmission of nociceptive information.” (5)

“The idea that pain results from the balance of activity in nociceptive and non-nociceptive afferents was formulated in the 1960s and was called the gate control theory.” (5)

“Simply put, non-nociceptive afferents ‘close’ and nociceptive afferents ‘open’ a gate to the central transmission of noxious input.” (5)

“The balance of activity in small- and large-diameter fibers is important in pain transmission…” (5)

Melzack and Wall’s Gate Control Theory of Pain was reviewed and confirmed in 2002 in the British Journal of Anaesthesia in an article titled (6):

Gate Control Theory of Pain Stands the Test of Time

This article restates that the electrical transmission and perception of pain is subject to modulation by non-nociceptive neurological electrical signals. These non-nociceptive neurological electrical signals emanate from large diameter nerve fibers, such as mechanoreceptors.

The author notes that pain can be modulated (reduced) by the firing of

large diameter mechanoreceptors causing pain inhibition.

•••••

In 1973, Candace Pert was a 26-year old graduate student working at Johns Hopkins University School of Medicine, when she discovered the existence of opioid receptors, the cellular binding site for endorphins and pain control, in the brainstem. Theoretically, activating these receptors could suppress pain by activating the descending pain inhibiting system. This would explain the pain suppression benefits of pain opiate drugs like morphine. Her study was published in the journal Science, titled (7):

Opiate Receptor: Demonstration in Nervous Tissue

Pert’s work was further detailed in 1974 in an article published in the Annals of Internal Medicine, titled (8):

The Opiate Receptor

Behind-the-scenes details of this exciting discovery are detailed in Pert’s 1997 book, titled Molecules of Emotion: The Science Behind Mind-Body Medicine (9).

The location for these opioid receptors is in the top of the brainstem, about where the brainstem attaches to the brain. This location is called the midbrain (mesencephalon). The exact location in the midbrain for these receptors is called the periaqueductal gray matter (PAG).

As noted above, stimulation of the periaqueductal gray matter for pain control initiates what is known as activating the descending pain inhibitory control system. Explanations included that stimulation of the periaqueductal gray matter (PAG) would close the Pain Gate.

Although pharmaceutical companies were undoubtedly excited about the greater understanding of the periaqueductal gray matter and its opioid receptors, they did not initially appreciate the problems with opioid drugs as related to tolerance, dependence, addiction, and death. Nor were they interested in the physiological studies showing that one could activate the periaqueductal gray matter for important pain suppression using non-pharmacological methods. These non-pharmacological methods could be done with few or no undesirable side effects. Examples include:

• In 1977, the journal Science published a study titled (10):

Pain Relief by Electrical Stimulation of the Central Gray Matter
in Humans and its Reversal by Naloxone

The authors of this study showed relief of intractable pain was produced in six human patients by stimulation of electrodes implanted in the periaqueductal gray matter. The authors suggested that satisfactory alleviation of persistent pain in humans may be obtained by electronic stimulation of “periaqueductal gray pain.”

• In his 1979 book, The Brain, The Last Frontier, Richard Restak, MD, reviews this research, stating (11):

“Within the periaqueductal gray, a deep-seated brainstem area lying along the floor of the third ventricle, neurosurgeons at the University of California in San Francisco placed indwelling stimulating electrodes for pain relief in six patients afflicted with chronic, unremitting pain. Whenever the patients began to experience pain, they were able to shut it off via the activation of a battery-operated stimulator about the size of a pack of cigarettes. After activating the stimulator, all six patients—in accordance with earlier findings in other pain patients—experienced dramatic, long-lasting, and repeatable pain relief.”

“In order to test the hypothesis that pain relief was genuine and not just an example of a ‘placebo response,’ one patient was outfitted with a stimulator containing a ‘dead’ battery. The patient, a fifty-one-year-old woman with severe back and leg pain caused by cancer of the colon, anxiously reported that her pain had returned and the stimulator ‘wasn’t working.’ Replacement of a new battery led to immediate pain relief.”

The application of chiropractic spinal adjusting for pain control using

Melzack and Wall’s Gate Control Theory of Pain was first done by Canadian orthopedic surgeon WH Kirkaldy-Willis in 1985 (12). In his 1985 publication, Dr. Kirkaldy-Willis notes:

“Spinal manipulation is essentially an assisted passive motion applied to the spinal apophyseal and sacroiliac joints.”

Melzack and Wall proposed the Gate Theory of Pain in 1965, and this theory has “withstood rigorous scientific scrutiny.”

“The central transmission of pain can be blocked by increased proprioceptive input.” Pain is facilitated by “lack of proprioceptive input.” This is why it is important for “early mobilization to control pain after musculoskeletal injury.”

The facet capsules are densely populated with mechanoreceptors. “Increased proprioceptive input in the form of spinal mobility tends to decrease the central transmission of pain from adjacent spinal structures by closing the gate. Any therapy which induces motion into articular structures will help inhibit pain transmission by this means.”

Stretching of facet joint capsules will fire capsular mechanoreceptors which will reflexively “inhibit facilitated motoneuron pools” which are responsible for the muscle spasms that commonly accompany low back pain.

In chronic cases, there is a shortening of periarticular connective tissues and intra-articular adhesions may form; manipulations (adjustments) can stretch or break these adhesions.

“In most cases of chronic low back pain, there is an initial increase in symptoms after the first few manipulations [probably as a result of breaking adhesions]. In almost all cases, however, this increase in pain is temporary and can be easily controlled by local application of ice.”

“However, the gain in mobility must be maintained during this period to prevent further adhesion formation.”

In this publication, Dr. Kirkaldy-Willis also presents the results of spinal manipulation in 283 patients with low back pain. In many ways, these patients were the worst of the worst. All of them suffered from chronic low back pain, all were disabled, and all had failed to improve subsequent to multiple treatment approaches.

The authors considered a good result from manipulation to be:

• “Symptom-free with no restrictions for work or other activities.”
• “Mild intermittent pain with no restrictions for work or other activities.”

The authors show that specific chiropractic adjustments could essentially “fix” 81% of referred joint dysfunction and 48% of nerve compressive back pain syndromes in these patients that were completely disabled and who have failed all prior treatment (including surgery), when they are appropriately adjusted daily for a period of at least 2–3 weeks. The authors note:

These patients were given a “two or three week regimen of daily spinal manipulations by an experienced chiropractor.”

“No patients were made worse by the manipulation, yet many experienced an increase in pain during the first week of treatment. Patients undergoing manipulative treatment must therefore be reassured that the initial discomfort is only temporary.”

“In our experience, anything less than two weeks of daily manipulation is inadequate for chronic low back pain patients.”

“The physician who makes use of this [manipulation] resource will provide relief for many back pain patients.”

In 1996, a study was published in the journal Pain, titled (13):

The Initial Effects of a Cervical Spine Manipulative Physiotherapy Treatment
on the Pain and Dysfunction of Lateral Epicondylalgia

The authors treated elbow pain in patients who were not suffering from radiculopathy or referred pain by only manipulating the dysfunctional joints of the patient’s cervical spine. The most commonly found biomechanical dysfunction was hypomobility of the joints of the lower cervical spine. The authors note:

“This study has demonstrated a clear hypoalgesic effect of a manipulative therapy technique [applied to the cervical spine] in the period immediately following its application in a group of patients with lateral epicondylalgia.”

The authors’ theoretical model to explain their results involved manipulative therapy activation of the hypoalgesic effects of the endogenous supraspinal pain inhibitory systems.

“The [manipulative] treatment technique used in this study provided a non-noxious sensory input at the cervical spine which resulted in a reduction of elbow pain that outlasted the duration of its application.” “This is thought to activate the descending pain inhibitory system as a major component of their pain-relieving effects.”

The descending pain inhibitory system is activated by stimulation of the periaqueductal gray (PAG).

“These findings indicate that manipulative therapy may constitute an adequate physical stimulus for activating descending pain inhibitory system.”

A common finding in other studies “was the predominance of hypomobility at the lower cervical motion segments.” It is feasible that part or all of the impairments in this study were “projected from the hypomobile cervical spine motion segment(s), and that the improvements gained following application of the [manipulative] technique resulted from treating the source of the pain.”

“Manipulative therapy [may] recruit the descending pain inhibitory system, through which it exerts a portion or all of its pain-relieving effects. That is, manipulative therapy applied to the cervical spine produces a sensory input which could be sufficient to activate the descending pain inhibitory system.”

In 2014, a study was published in the Journal of Back Musculoskeletal Rehabilitation, titled (14):

The role of the Descending Inhibitory Pain Mechanism
in Musculoskeletal Pain Following
High-velocity, Low Amplitude Thrust Manipulation:
A Review of the Literature

The objective of this review was to investigate the role of the descending inhibitory pain mechanism in musculoskeletal pain following high-velocity, low amplitude thrust manipulation. The authors state:

“Although the antinociceptive effect of high-velocity, low amplitude thrust manipulation has been recognized by numerous systematic reviews, the underlying mechanism for manipulation-related pain relief remains poorly understood. An increasing number of studies have explored its analgesic mechanism suggesting that the excitation of the descending inhibitory pain mechanism might play the most important role for musculoskeletal pain relief.”

“Findings from current literature support that high-velocity, low amplitude thrust manipulation has a profound influence on nociceptive stimulus via the possible activation of the descending inhibitory pain mechanism. It seems that the application of this technique activates the periaqueductal gray region area of the midbrain, stimulates the noradrenergic descending system and at the level of the spinal cord, the nociceptive afferent barrage is reduced and mechanical hypoalgesia is induced.”

In 2025, an article was published in the journal Scientific Reports titled (15):

The Impact of Spinal Manipulation on Lumbar Proprioception
and its Link to Pain Relief: A Randomized Controlled Trial

The authors, from the University of Zurich, Switzerland, investigated the effect of a single spinal manipulation intervention on lumbar proprioceptive function and its potential relationship with pain relief (analgesic) in patients with chronic low back pain (CLBP). This study was a single-blind randomized controlled trial of lumbar spinal manipulation (LMANIP) vs. lumbar spinal mobilization (LMOB) vs. no intervention (NI).

Participants were randomly assigned to one of the interventions:

• Lumbar spinal manipulation (LMANIP). LMANIP involved high-velocity low-amplitude (HVLA) spinal manipulation applied bilaterally in side-posture with a hypothenar contact over the region of the L5 vertebra. The clinical intent was to target the L4/L5 motion segment and gap the ipsilateral facet joint. The thrust was in a posterior-to-anterior direction, aligned with the facet joint plane.
• Lumbar spinal mobilization (LMOB). Instead of an HVLA thrust, a Grade III mobilization was performed up to the limit of the range of motion and held for a duration of 30 seconds.
• No intervention (NI). These subjects rested in a side-lying position for 30 seconds on each side, with no manual contact.

All study subjects were assessed using proprioceptive weighting. Proprioceptive weighting is the central nervous system’s process of assigning importance to sensory signals from muscles and joints and not from visual and/or vestibular inputs:

“Proprioceptive weighting (PW) is a crucial function of the human proprioceptive system, which is the capability of the central nervous system to selectively prioritize the most reliable proprioceptive inputs from key body stabilizers, such as the ankle and lumbar muscles, which are essential for maintaining posture and effective motor control.”

Proprioceptive weighting was assessed immediately before and after intervention by analyzing postural sway changes in the sagittal plane. The study used 90 healthy participants and 52 patients with non-specific CLBP.

The authors also explored whether improved proprioception following spinal manipulation was associated with the analgesic response.

The authors note:

“Low back pain (LBP) is one of the most prevalent health conditions, affecting approximately 80% of individuals at some point in their lives, and is a leading global health issue in terms of years lived with disability.”

“In the majority of LBP cases, there is no pathoanatomical cause identifiable, leading to a diagnosis of ‘non-specific LBP.’”

“Manual therapy, such as spinal manipulation (SM), is commonly used to treat non-specific chronic low back pain (CLBP).”

“Spinal manipulation (SM) therapy is a frequently used and guideline-recommended non-pharmacological intervention for both acute and chronic LBP.”

“It has been hypothesized that the mechanical forces applied during spinal manipulation (SM) influence proprioceptive function, which is often impaired in patients with CLBP.”

“SM can relieve pain and improve function.”

This study showed that a single session of spinal manipulation elicits an immediate (enhancing) effect on lumbar proprioceptive function. The authors proposed that the most likely mechanism for the pain control following spinal manipulation was the proprioceptive activation of the descending pain inhibition circuits. The authors state:

“The current results provide solid evidence that lumbar spinal manipulation has a notable impact on paraspinal proprioceptive mechanisms, potentially improving sensory integration in the lumbar spine, and enhancing balance and motor control.”

“Spinal manipulation to enhance proprioceptive input and translate more directly into pain relief.”

Conclusions

This study supports that spinal adjusting improves proprioception, and then suggests that improved proprioception suppressed pain, probably because of the activation of the descending pain inhibitory control system. This concept is consistent with Melzack’s and Walls’ Gate Theory of Pain, and this model is supported by the articles reviewed above.

Supporting these models, the February 2026 journal Scientific American published an article titled (16):

Heal Injuries Faster:
Toss Out the Old Advice that Rest is the Best Recovery Strategy

This article notes:

“In most cases, limiting motion does not promote healing. In fact, immobilization causes muscles to weaken and lose stability. An injured body part that is immobilized for too long is more likely to move from acute to chronic pain.”

“Instead of rest, ‘motion is the potion,’ and it is important to move far sooner than many imagine.”

“Injured tissue sends signals to the brain. Which is where we perceive pain.”

“There are also descending pain pathways from the brain back to the periphery of the body that inhibit and modulate the perception of pain.”

It is important to restate that motion activates the descending inhibition of pain circuits.

REFERENCES

1. Workman B; Sharks’ Team Doctor Calls the Shots; Menlo Park Physician Aims for Zero Pain; San Francisco Chronicle; October 6, 2000.
2. Melzack R, Wall PD; On the Nature of Cutaneous Sensory Mechanisms; Brain; June 1962; Vol. 85; pp. 331-356.
3. Melzack R, Wall PD; Pain Mechanisms: A New Theory; Science; November 19, 1965; Vol. 150; No. 3699; pp. 971-979.
4. Nolte J; The Human Brain; Mosby Year Book; 1993.
5. Kandel E, James Schwartz J, Jessell T; Principles of Neural Science; McGraw-Hill; 2000.
6. Dickenson AH; Gate Control Theory of Pain Stands the Test of Time; British Journal of Anaesthesia; June 2002; Vol. 88; No. 6; pp. 755-757.
7. Pert CB, Snyder SH; Opiate Receptor: Demonstration in Nervous Tissue; Science; March 9, 1973; Vol. 179; Article 4077; pp. 1011-1014.
8. Snyder SH, Pert CB, Pasternak GW; The Opiate Receptor; Annals of Internal Medicine; October 1974; Vol. 81; No. 4; pp. 534-540.
9. Pert C; Molecules of Emotion: The Science Behind Mind-Body Medicine; Simon & Schuster; 1997.
10. Hosobuchi Y, Adams JE, Linchitz R; Pain Relief by Electrical Stimulation of the Central Gray Matter in Humans and its Reversal by Naloxone; Science; July 8, 1977; Vol. 197(4299); pp. 183-186.
11. Restak R; The Brain, The Last Frontier; Warner Books; 1979; pp. 341-342.
12. Kirkaldy-Willis WH, Cassidy JD; Spinal Manipulation in the Treatment of Low back Pain; Canadian Family Physician; March 1985; Vol. 31; pp. 535-540.
13. Vicenzino B, Collins D, Wright A; The Initial Effects of a Cervical Spine Manipulative Physiotherapy Treatment on the Pain and Dysfunction of Lateral Epicondylalgia; Pain; November 1996; Vol. 68; No. 1; pp. 69-74.
14. Savva C, Giakas G, Efstathiou M; The role of the descending inhibitory pain mechanism in musculoskeletal pain following high-velocity, low amplitude thrust manipulation: A review of the literature; Journal of Back Musculoskeletal Rehabilitation; 2014; Vol. 27; No. 4; pp. 377-382.
15. Nyiro L, Dorig M, Meier ML and 6 more; The Impact of Spinal Manipulation on Lumbar Proprioception and its Link to Pain Relief: A Randomized Controlled Trial; Scientific Reports; November 26, 2025; Vol. 15; No. 1; Article 42136.
16. Denworth L; Heal Injuries Faster: Toss Out the Old Advice that Rest is the Best Recovery Strategy; Scientific American; February 2026; pp. 78 and 81.

“Authored by Dan Murphy, D.C. Published by ChiroTrust® – This publication is not meant to offer treatment advice or protocols. Cited material is not necessarily the opinion of the author or publisher.”