THE EXPLORATION OF POTENTIAL SPINAL MANIPULATION

THE EXPLORATION OF POTENTIAL SPINAL

MANIPULATION EFFECTS

Brogan Williams

College of Functional Movement Clinicians,

Auckland, NZ

ABSTRACT

Objective: The goal of this narrative review was to

describe research regarding the potential mechanisms

behind spinal manipulation.

Methods: The search was conducted through Google

Scholar, PubMed, ResearchGate, and the standard

Google search engine. The inclusion criteria had

no limit regarding the date or type of research.

Keywords used to direct the search were: Spinal

Manipulation; Chiropractic adjustment; High Velocity,

Low Amplitude; Thrust; Manipulation; Manual Therapy;

Lumbar Adjustment; Low Back Adjustment; Lumbar

Manipulation; Low Back Manipulation; Thoracic

Adjustment; Thoracic Manipulation; Cervical

Adjustment; Cervical Manipulation.

Results: 164 papers were used in this review. These

include experimental evidence case studies, case

series, randomized control trials, research reviews,

research articles, population studies, cohort studies,

case-control studies, as well as medical textbooks.

The underlying mechanism of HVLA thrust, or spinal

manipulation (SM) has been highly examined for many

years and was further explored in this review. Various

theories have been established throughout the

literature covering both physiological and neurological

mechanisms, such as the local physiological and

biochemical changes that occur to the synovial joint

structures and surrounding soft tissue- altering synovial

uid viscosity, increasing blood ow, altering tissue

pliability and modulating pain perception via gate theory

and/or descending inhibition. Neurological effects have

also been highlighted regarding the impact of spinal

manipulation on the brain via changes to afferent/

efferent impulses, potentially altering the state of our

immune system, brain neuroplasticity, proprioception,

cortical drive and function of the prefrontal cortex.

Conclusion: This review provides a framework for a

better understanding of the potential mechanisms

involved in spinal manipulation. (J Contemporary Chiropr

2024;7:32-50)

Key Indexing Terms: Chiropractic; Osteopathy; Spinal

Manipulation; Cavitation

INTRODUCTION

The objective of this study is to contribute to the

body of evidence related to spinal manipulation (SM).

The amount of research behind spinal manipulation

is growing; however, little attention has been paid to

the possible impact SM may have. The purpose of this

paper is to not only describe the effects of SM and the

possible mechanisms responsible but also to encourage

clinicians to use the modality in practice.

What is spinal manipulation?

Spinal Manipulation (SM) (also known as an adjustment)

is a high-velocity, low-amplitude (HVLA) thrust directed

at spinal segments and/or joints in the human body. (1)

SM distinguishes itself from other manual techniques

by the speed by which the thrust is delivered and the

audible cavitation that can often be heard as the uid

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7

within the synovial membrane is redistributed. (2,3)

This occurs as the joint is swiftly being taken beyond its

active range of motion and into the paraphysiological

space, and involves the spontaneous redistribution

of pressure, creation of gas and absorption in an

enclosed uid-lled system, consistent with a

process called tribonucleation. (2-4). The underlining

mechanism of HVLA thrust, or spinal manipulation (SM)

has been speculative for decades. Some of the more

common theories focus on the local physiological and

biochemical changes that occur to the synovial joint

structures and the surrounding soft tissue – altering

synovial uid viscosity, increasing blood ow, altering

tissue pliability and modulating pain perception via gate

theory and/or descending inhibition. (5- 9) Others focus

more on the possible neurological impact SM could

have on the body, such as how the changes to afferent

and efferent impulses to and from the brain could be

impacting our immune system, brain neuroplasticity,

proprioception, cortical drive and prefrontal cortex

functions. (10- 15) Although the techniques are similar

(chiropractic adjustments, spinal manipulation and

HVLA), the purpose for using this technique varies

from health profession to health profession, with the

objective behind the technique being the dening factor;

however, it is mostly associated with chiropractors and

osteopaths, many of whom exclusively use the HVLA

technique.

DISCUSSION

Methods

The goal of this narrative review was to nd and

appraise a multitude of relevant research and studies

regarding the possible mechanisms behind chiropractic

adjustments and/or spinal manipulation (SM). The

reported effects of SM in the literature are quite

extensive and require an in-depth review to fully cover

the breadth of currently available research. The search

was conducted primarily through Google Scholar,

PubMed, ResearchGate and the standard Google search

engine. Keywords used to direct the search were:

Spinal Manipulation; Chiropractic adjustment; High

Velocity, Low Amplitude; Thrust; Manipulation; Manual

Therapy; Osteopathic treatment; Lumbar Adjustment;

Low; Back Adjustment; Lumbar Manipulation; Low

Back Manipulation; Thoracic Adjustment; Thoracic

Manipulation; Cervical Adjustment; Cervical

Manipulation.

Results

164 resources were located and used in this review,

this includes experimental evidence case studies, case

series, randomised control trials, research reviews,

research articles, population studies, cohort studies,

case-control studies, and medical textbooks.

Neuroplasticity

Neuroplasticity is the brain’s ability to change, rewire,

reorganise and alter neural connections due to external

and environmental information – sometimes in the form

of new information, sensory stimulation and/or various

types of perceived damage. (16) When our body goes

through a series of negative adaptive changes, it is

called maladaptation or maladaptive changes (17), and

this happens frequently. One example is pain. The site

of pain isn’t necessarily the cause of it, the severity of

pain isn’t always equal to the degree of tissue damage,

and the feeling of pain isn’t always due to the ring of

nociceptive neurons. (18) Rather, tissue damage and the

ring of nociceptors is only 1 part of the process, and in

totality, pain is extremely complicated and modulated

by the brain; this impacts how our brain perceives the

world, the environment and the information that is

available around us. (19) In fact, the literature shows that

chronic pain (greater than 3 months) has this effect on

the brain, a maladaptation. (20) Studies show structural

and functional changes to the brain when chronic pain

is present. This includes synapse plasticity, glial cell

changes, spinal cord adaptations, and alterations to grey

matter volume, among others. (21) Ultimately, chronic

pain serves as an example of maladaptive plastic

changes to the brain, and how the brain can create faulty

inner maps, changing the brain itself. (10) This research

leads us away from the traditional structural pathology

models of understanding pain and directs us toward a

more neuroplasticity model, one that acknowledges not

only all the many variables involved in and around pain

but also how it can compromise one’s neurophysiology

and possibly alter one’s awareness and adaptability.

(10,13-15)

Changes occur all the time on the spectrum between

positive and negative adaptation between the brain and

body, and these changes again are not only driven by

physical, pathological or biological factors, but a range

of things that can include emotions, thoughts, various

types of mental and/or physical trauma and many

different types of daily life stressors such as sleep, diet,

exercise, work and even social interactions. (22,23) By

the time any real symptoms begin to appear, it is likely

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7

some amount of maladaptation has been occurring,

the patient simply unaware of it. By understanding the

sheer complexity of pain, we can gather a greater overall

understanding of how injuries really occur and how they

work. For example, following low back injuries there

can be an array of neurological negative changes, all of

which modulated through the amygdala, hypothalamus,

hippocampus and prefrontal cortex (PFC), and NOT only

through nociception alone. (24-27).This supports the

narrative that communication between the brain and the

body is not only important but vital to an accurate inner

map or brain schema. (10)

Beyond the acute period of low back pain, there can

be multiple physical changes to the tissues, such as

muscle brosis, fatty inltration, twitch ber changes,

muscle atrophy, hypomobility and even degeneration at

the joints (28); and although this is important and can

cause long-term dysfunction, we also see neurological

motor decits, such as cerebrocortical activity, postural

motor changes, altered motor control of the spine and

trunk muscles, delayed reex responses, reduced feed-

forward activation and changes in proprioception. (29-

34) There is a growing body of research showing that

chiropractic adjustments and/or spinal manipulation

have an impact on central processing. (35) Studies show

that post-manipulation there is an improvement in

cortical drive, mental rotation, multimodal integration,

cerebellum modulation and joint position sense; as

well as changes to sensory motor integration, altered

H-reex/V-waves and cerebellum communication. (13-

39)

This suggests that spinal manipulation improving

spinal function has an impact on neuroplasticity and

a neurological modulation effect on how the body

interprets information and the brain’s awareness and

ability to perceive the world around it – such as visual

and sound information, body position awareness,

objects in space and mental rotation. (40) More research

and quality literature are still needed as this is not yet a

full picture; however, it is a peek into how powerful and

benecial spinal manipulation could be. (10)

Prefrontal Cortex

We are only now beginning to realise how much of an

impact “stress” can truly have on the body and mind.

Adverse childhood experiences (ACE) studies show

a strong, graded relationship between exposure to

household dysfunction and abuse (stress) during

childhood and increased health risks for many causes

of death in adults, including various mental disorders,

such as depression, bipolar, anxiety disorders and

suicide. (41) In fact, further ACE studies showed children

who experienced ACE had a higher risk of chronic pain

later in life. (42) One study showed that as the ACE score

increased so did the prevalence of chronic headaches,

showing a frightening relationship between early life

stressors and chronic pain/mental health. (43) The

more we learn about stress, the more we begin to

understand the profound physiological, emotional and

mental effects the stress neuromatrix can have on our

bodies, our quality and quantity of sleep, the pain we

feel, inammation and our overall well-being. (44) These

stressors can impact how our brain perceives pain

and information; ultimately causing a stress induced

maladaptive neuroplasticity in the brain. (10)

The prefrontal cortex (PFC) is like the administrator

of the brain. Often associated with performing our

executive higher functions, the PFC orchestrates our

actions, thoughts, moods and emotions; it even plays

a role in processing pain. (45) It is the region of higher

intelligence as a species, helping us differentiate

between right and wrong, resolving internal conicts,

problem-solving and the suppression of unwanted

emotional urges regulating our personality. (46) Among

many other things, the PFC has many connections with

multiple areas of the brain, allowing the processing

of multimodal sensory inputs which helps modulate

our various behaviors. (47) Recent studies have shown

that the stress neuromatrix has a rather signicant

impact on the prefrontal cortex (PFC) by shutting down

PFC regulation during major stress. (27) Furthermore,

research shows that a decrease in grey matter in the

medial PFC has been seen in people with chronic pain.

(48)

This opens the door to a greater understanding of how

stress truly impacts the body and mind. It becomes

a vicious cycle of stress, pain, maladaptive changes,

PFC inhibition, physical and psychological issues.

(24) A 2016 study showed that spinal manipulation

affects sensorimotor integration in the prefrontal

cortex. (40) Furthermore, a 2007 study showed cervical

manipulation alters cortical somatosensory processing

and a 2010 study showed that spinal manipulation

(SM) may also alter the cortical integration of dual

somatosensory input, theorizing to one of the possible

mechanisms responsible for the reduction in pain an

improvement in functional ability following SM. (15,49)

More research is needed to strengthen these ndings

and provide more details around this association;

however, this is an interesting concept suggesting the

extent of neurological response from SM.

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7

Proprioception

The functional spinal unit is heavily dense with various

sensory receptors since the deep paraspinal muscles

play a crucial role in proprioceptive signalling, providing

a "neural image" of our spine and the movement within,

around or involved with it. A lack of incoming afferent

information can inhibit the brain from reacting in

real time, causing altered efferent output/abnormal

proprioception and other dysfunction. (50)

There is some research to support this notion, showing

an increase in proprioception post spinal manipulation

through a mechanism called sensorimotor integration,

which is the ability to incorporate sensory inputs that

provide information about one's body and the external

environment to inform and shape motor output. (13-14)

For example, one study showed a signicant increase in

ankle dorsiexion range of motion and proprioception in

subjects with chronic recurrent ankle sprains following

chiropractic adjustments/spinal manipulation. (51)

Another, by Haavik and Murphy, showed an increase

in elbow joint position sense and proprioception

following cervical chiropractic adjustments/spinal

manipulation, and a randomized controlled trial (RCT) in

2016 showed an improvement in sensorimotor, multi-

sensory integration, ankle joint sense, stepping reaction

times and proprioception awareness in a group of 60

participants following chiropractic care. (6,13)

Feed-Forward Activation

One key area of interest is the positive impact

chiropractic adjustments have on feed forward

activation (FFA). Feed forward activation times have

been hypothesized to be a common prerequisite for

avoiding injury. (52) Studies show that prior to limb

movement, various "core" muscles/supportive and

postural trunk muscles contract rst to stabilize and

protect the structural systems involved, which are often

the lumbar spine, connective tissues and joints. (53)

This is also supported by McGill’s “proximal stiffness”

theory, which he has tested over the course of his 30-

year career and had great success with helping clients

all around the world abolish their low back pain. (54,55)

Further research also demonstrates that athletes with

LBP have a signicant decrease in measured FFA, which

includes reduced muscle activation, less co-contraction

patterns and decreased abdominal endurance. (56) In

recent years, it has become somewhat controversial

whether "corrective exercises" can improve FFA

(57), or produce not much of an effect at all, with

research displaying both outcomes. However, 1 RCT

demonstrated a signicant amount of improvement

(38.4%) in FFA times following a sacroiliac joint

manipulation. (58)

Strength, MVC and Muscle Activation

An increase in “strength” is usually the last thing people

associate with spinal manipulation, but there have been

studies documenting this. Strength can be dened in

a number of ways, but in this situation we are seeing

a short-term increase post spinal manipulation that

indicates a clear increase to what was tested prior. One

method of testing is by measuring the participant’s

maximal voluntary contraction (MVC) pre-and post SM,

often on a movement such as plantar exion and/or

elbow exion, while some studies have tested muscles

like the anterior tibilalis and the abductor pollicus

brevis. (59) Regardless, the point is to monitor a muscle’s

force output and the electrical potentials generated

by the muscle cells, to give an indication of both

strength output and muscle activation or muscle bre

recruitment. (5) A helpful way to measure the amount of

change that is occurring post SM is to measure H-reex

and V-waves also, H-reex being associated with

increased resistance to muscular fatigue and V-waves

being associated with an increase in neural drive to

the muscle cells, as it reects the magnitude of motor

output from the descending pathways. (60,61)

In 2018, a randomised controlled study of 11 athletes

showed an increase in V-wave and MVC aka strength and

corticospinal excitability following a single session of

chiropractic care. (5) Moreover, a 1996 study showed that

30 college students displayed an increase in quadriceps

femoris muscle strength following a manipulation to

the L3/4 motion segment. The authors concluded an

overall statistically signicant increase in strength

was observed. (62) Additionally, a recent randomized

controlled crossover study showed a substantial

increase of plantar exor muscle strength in chronic

stroke patients following a single session of chiropractic

care and an older 1999 study showed a decrease in

muscle inhibition and an increase in knee extensor ROM

and muscle activation in patients with anterior knee

pain following a sacroiliac joint chiropractic adjustment.

(36,63)

Finally, a study from 2002 consisting of 16 patients with

chronic neck pain, reduced cervical ROM and bicep/arm

muscle inhibition demonstrated an increase in ROM,

decrease in pain, decrease in muscle inhibition and an

increase in elbow exion strength following a cervical

spine manipulation/adjustment. (64) Although this may

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7

seem signicant, it is a very interesting glimpse into the

neurology of an adjustment, it does however suggest

a need for studies that gather long-term data and not

only short-term changes. More conclusive studies are

needed for a strong conclusion; however, it is exciting

to see the possible benets of SM explored, especially

when it comes to strength, even if it is short term only.

Pain

Pain is complicated and a signicant issue in today’s

society. For example, lower back pain (LBP) specically

is a major issue for our health system, leading people

(who are in pain) to consider drugs such as non-steroidal

anti-inammatory drugs (NSAIDs), opioids and muscle

relaxants. (65) In fact, 1 in 4 people are reported to have

experienced LBP within the last 3 months (66), and 75-

85% of the USA population have experienced it within

their lifetime. (67) It doesn't stop there, because reports

show that up to 94% of elite athletes experience LBP too

(68), which makes sense as roughly 5-10% of all injuries

in athletes are lower-back related (69).

There is high-quality research demonstrating the

effectiveness and ecacy of chiropractic and spinal

manipulation for pain. The Manga Report presented

an overwhelming body of evidence concluding that

chiropractic care is both more cost-effective than

traditional medical management and more effective

at treating LBP than alternative treatments. (70)

Furthermore, a 2006 retrospective case study found

chiropractic adjustments may be suitable and effective

at decreasing lower back pain for pregnant women.

(71) Additionally, Descarreaux et al found that long-

term maintenance chiropractic care (adjustments and

spinal manipulation) was effective at decreasing even

chronic pain. What's more, another paper showed

spinal manipulation to be effective at treating chronic

tension-like headaches; demonstrating better long-

term therapeutic benets than amitriptyline. (72,73)

Likewise, a 1999 randomized control study consisting

of 77 patients demonstrated spinal manipulation to be

more effective at decreasing pain than acupuncture

and NSAIDs (74), and a 2001 systematic review of 9 trials

and over 600 patients suggessted cervical manipulation

was effective at treating chronic headaches, even

better than massage and some medication. (75) Finally,

a 2010 study shows manual therapy (manipulation and

mobilisation) to have better pain outcomes than certain

specic exercise interventions alone (76), and a 2012

meta-analysis demonstrates that spinal manipulation

increases a patient's pain threshold, helping them better

regulate pain. (9)

Descending inhibition

Descending inhibition is widely understood as a pain

modulation effect that occurs when a stimulus received

by the body elicits descending projections from the

brain down to the spinal cord, providing a reduction in

the pain that is perceived by the patient. (77) Although

not fully understood, there are many theories about the

exact mechanism that causes these analgesic effects

following spinal manipulation, although it is widely

theorized that it is a neurophysiological modulation

effect of some kind caused by descending inhibition. (8)

This mechanism is not exclusive to spinal manipulation,

but likely any sensory input that is competing (so to

speak) with the noxious or painful input signals, almost

like a gate (more on that later). Regardless of the exact

mechanism of how this is occurring, as discussed above

there is a fair amount of research and literature showing

the effects adjustments or spinal manipulation can have

on pain and the perception of incoming pain signals.

(9,70-74) This seems to be a well-known fact, with $8.1

billion annually being spent on manual therapies alone in

the US. (78)

The descending inhibitory modulation circuits include

various neurotransmitters, most notably oxytocin,

serotonin, vasopressin, adenosine, endocannabinoids

and endogenous opioids (EO). It is also relevant to

note that the analgesic response from human touch

is mediated by EO. (79- 83) These neurotransmitters

have been found to interact with the periaqueductal

grey (PAG) of the midbrain and rostral ventromedial

medulla (RVM) in a way that modulates the pain circuits

and output of the brain. (8) The PAG was identied in

the 1960s for its noticeable descending projections into

the RVM and dorsal horn of the spinal cord and for its

ability to mediate pain and opioid-based analgesia. It is

now widely accepted that the PAG-RVM-SC pathway is

one of the essential neurological circuitry for opioid-

based pain modulation or anti-nociception. (77) Animal

studies found that neurons were inhibited by “noxious”

stimuli and the term “DNIC'' was created (diffuse noxious

inhibitory control). (84) This term later became referred

to as CPM (conditioned pain modulation). Human

research and studies have since shown clear local

and segmental hypoalgesic effects following spinal

manipulation with the understanding that the HVLA

thrust does have a profound inuence on the descending

inhibitory pain mechanism. (85,86).

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7

Gate Theory

Within the central pain modulatory system (CPM) (as

discussed above), is another well-known mechanism

that attempts to explain how pain could be modulated

through non-noxious input stimuli, the gate control

theory. (87) This theory of pain perception states that

non-noxious input can suppress pain by modulating the

output through inhibiting the nociceptors at the dorsal

root that inform the brain. (88,89) Like a gate, when the

system is triggered by touch or a spinal manipulation,

that pathway is open, closing the pathway that was

facilitating pain. The non-threatening input stimulates

the low-threshold A beta-bers that inhibit the incoming

pain signals from the A-delta and C afferent bers.

(88) Our A-beta bers within our spinal nerves carry

information like touch from the brain to body, and the

body to brain – these bers are myelinated, larger and

faster than the A-delta and C bres, which are smaller

and have a slower speed conduction rate. (90)

Psychosocial Factors

The inuence of non-physiological factors playing a

role in pain modulation is a concept we cannot overlook.

A patient’s condence in the practitioner or doctor

providing the treatment may have an impact on clinical

outcomes. The power imbalance between the patient

and the doctor sometimes evokes an expectation

that the intervention is going to work. What’s more,

patients can be inuenced by social cues, positive

reinforcement, the environment and even the clinician’s

personality. These factors can sometimes have a

placebo effect on the patient. (91). Although the exact

mechanism of how this is happening is still unknown,

one’s expectations can in fact inuence his or her’s

chemistry and physiology, resulting in the patient

experiencing similar effects to the “sham” treatment

they were told they were having. For example, one study

showed that following the administration of a placebo

that was communicated to the patients as a stimulant,

the patients experienced a spike in blood pressure,

heart rate and reaction speed. However, when the same

placebo pill was given, but told to be a sleeping pill, the

patient experienced the opposite effects. (92)

A 2013 study consisting of 146 patients ranging between

35-65 years of age who were experiencing either

knee osteoarthritis or a meniscus tear found that an

arthroscopic partial meniscectomy was no better than

a sham surgical procedure. Now, of course, there are

likely multiple factors contributing to this result but it

questions what other variables played a role and had

an impact on these patient outcomes. (93) A recent

study in the United States which examined the placebo

effect over 23 years through 84 trials found it becoming

increasingly stronger. It may be that the placebo effect

is becoming stronger due to the increase of direct-to-

consumer drug advertising in America – which alters the

expectation from the public that the drug “must work”

as they are targeted to believe that via the advertising.

(94) Furthermore, a 2007 study found that placebo

interventions can improve physical disease processes

of peripheral organs more easily and effectively than

biochemical processes. (95)

Range of Motion

In addition to the pain research, adjustments and spinal

manipulation have been shown to also facilitate better

movement by improving ROM. Range of motion is crucial

for the health and function of all joints, especially

throughout the spine; it also has a profound impact

on rehabilitation post injury, as restoring passive and

active ROM becomes paramount when progressing an

injury back to full health and function. The mechanisms

responsible for the ROM increase are still largely

unknown; however, many believe it is caused by the

various neurophysiological changes that occur during

spinal manipulation. For example, taking the joint

beyond its paraphysiological space can cause changes

to the surrounding soft tissue structures (96), remodel

the state and viscosity of the facet joint’s synovial uid

(97), briey alter the spinal joints mechanics (98), and

elicit physiological changes modulated through the

nervous system, like muscle tonicity, pain modulation,

sensory changes and improved feedback abilities.

(87,99-101)

When we look at the literature, there are numerous

high quality studies showing the positive impact spinal

manipulation has on ROM. In fact, in a 2008 randomized

controlled study 17 young athletes demonstrated an

increase in hip extension ROM following sacroiliac

(SI) joint manipulation. (102) Furthermore, a 2006

study showed a greater increase in ROM and decrease

in pain following chiropractic manual therapy and

heat treatment opposed to heat treatment alone. (7)

Additionally,further studies have shown an increase in

knee ROM, an increase in cervical (neck) ROM and an

increase in ankle dorsiexion. (51,63,64,103)

Adverse Events

A chiropractic adjustment or spinal manipulation is a

specic high-velocity, low-amplitude thrust, a type

of manual therapy that has been implemented by

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7

chiropractors and other health professions for over

100 years, with research showing that it’s an effective

method and treatment for chronic pain (104,105)

increasing ROM (98), improving healing outcomes (106)

and increasing proprioception awareness. (40)

Is it safe? There have been some literature reviews

and case reports that suggest an association between

cervical artery dissections and cervical manipulations

or adjustments. (107) It’s also important to note that

these studies failed to prove any actual causation

between cervical adjustments and stroke. Furthermore,

a study in 2008 concluded the correlation is likely

caused by patients seeking chiropractic care while

already experiencing the symptoms of a stroke, such as

headaches, migraines or neck pain; all symptoms that

chiropractors are see frequently. (108)

A 2002 study showed that a single high-velocity, low-

amplitude thrust only represents 1/9th of the strain it

would take to reach mechanical failure of a vertebral

artery. (109) Furthermore, a population, case-control,

case-crossover study looked at a population of 100

million and concluded there to be no evidence of ANY

excess risk of vertebral artery dissection or stroke

associated with chiropractic care compared to primary

care. (108) The key takeaway here is the importance of a

thorough history and quality, detailed spinal examination

prior to any treatment; to screen for patients who may

be experiencing the early stages of a stroke.

Other Mechanisms of Action

Spinal manipulation is mostly known or associated

with a cavitation, which is not only often believed to be

the technical inclusion criteria for a successful thrust

but also most of the time strangely satisfying for the

patient. As many people likely already now, the noise is

not the bones cracking or any other extreme process

for that matter, but gas in the synovial uid quickly

redistributing within the joint and causing a reduction

in pressure and a popping sound. (100) In order for a

synovial joint to reach this stage, it requires a high-

velocity thrust taking the joint into its paraphysiological

barrier. (96)

There are various ideas and theories out there around

how and why spinal manipulation has such a profound

effect. However, the mechanical mechanism of action is

often explained through key theories that have emerged

most commonly in the research and literature.

1. The release of spinal segments that have

become restricted or have undergone various

displacements. (98,103,110,111)

2. The physiological emancipation of trapped

synovial folds or intraarticular meniscoids

(96,100,112,113)

3. The restoration of movement and function

disrupting periarticular restrictions and

adhesions (1,102,110,114)

4. The stimulation of mechanoreceptors causing a

relaxation effect to tight or hypertonic muscles

via the “reex” theory. (99,100,115,116)

Among these four theories, a recent critical review

deemed only one of them (trapped synovial folds

or intra-articular meniscoids) is likely viable as a

reasonable and plausible explanation for the mechanism

responsible for the clinical outcomes we see with spinal

manipulation. (96) However, there is also evidence

to suggest that the gapping of the facet joints, or

separation of the zygapophyseal joints during the

cavitation process, is associated with other various

physiological outcomes, in which the cavitation is

necessary for them to occur. (117,118).

Additionally, another well-known theory within

chiropractic is the dentate-ligament-mediated cord

distortion theory. Although little has been published on

this theory, many chiropractors use it to support the

upper cervical technique (euphemistically called the

Hole-in-one technique (HIO)) which was made famous by

B.J Palmer in the 1920s/30s. (119) John Grostic was the

chief proponent of this theory. He claimed the thickness

of the dentate ligament in the cervical region could

cause compression and cord tension throughout the

entire spine and become irritated upon cervical exion.

(120,121) Many chiropractors found that adjusting the

cervical spine exclusively provided results throughout

the entire spine and body and could affect conditions

such as back or hip pain. (122).

Grostic believed that dysfunction at the dentate

ligament was what was causing interference to the

spinal cord and thus the nervous system (traditional

chiropractic subluxation theory). He narrowed it down

to two key mechanisms; 1) Mechanical irritation to the

dentate ligament, and 2) Ischemia or lack of blood ow

due to traction of the dentate ligament. Interestingly

enough, Jarzem et al set out to nd whether this was

even plausible; and concluded, using animal models,

that spinal mechanical traction does cause a reduction

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7

in blood ow and an interruption to somatosensory

action potentials. (123) Since the Grostic theory was

published in 1988, a thick segment of connective tissue

has been identied decades later directly between the

rectus capitis posterior minor muscle, the dura and

the posterior atlanto-occipital membrane. This bridge

of connective tissue is thought to stabilize the upper

cervical region and prevent brainstem compression

during cervical movement; however, it has also been

associated with causing cervico-genic headaches.

(124,125)

What’s more, many hypothesized that if Grostic’s theory

was correct, then restoring alignment in the cervical

spine should elicit a reduction in blood pressure, as

one of the two mechanisms of the dentate theory is

blood ow stasis. In 2007, Bakris et al. performed a

double blind, placebo-controlled study that concluded

that a National Upper Cervical chiropractic procedure

(adjustment) of the atlas lowered systolic and diastolic

blood pressure. (126) The autonomic system may be

involved in mediating the effects of spinal manipulation,

from changes in thermography, HRV, pupillary reex to

potential blood pressure changes. (12,128-130) However,

in this specic case, further research several years later

found no signicant change in systolic and diastolic

blood pressure compared to the sham procedure. (127)

Muscle Activity

Changes in muscle activity and tonicity is nothing new

for manual practitioners when dealing with sore spots,

aches and pains! However, does it have any real clinician

relevance and can we use it as an objective measure

on whether a treatment was successful? Dening the

“tonus” of a muscle can be dicult – as to the patient

it may feel “tight”, hard or maybe stuck; and to the

clinician it may feel hypertonic, hot and maybe a little

tougher or harder – but what does this really mean?

Beyond the traditional inammatory signs that may alter

how the muscle is presenting; such as heat, redness,

loss of function, edema and pain, a tight muscle could

really include some or none of these accompanying

factors. Muscle stiffness, so to speak, could be

caused by many things, such as muscle damage post

workout, electrolyte imbalances, mineral deciencies,

neuromuscular changes and sometimes serious

underlying myopathies or disease. (131-133). Whether you

call it a muscle spasm, a knot, or a tight muscle, more

may be happening than one thinks. Muscles adapt and

change based on the forces that are applied onto them,

or the bones or structures to which they are attached.

Sometimes postural alterations, actual physical

imbalances or simply just working out too hard can

cause those muscles to tighten or lengthen. (134)

One theory that explains this model well is the upper-

and-lower cross syndrome. Although this theory

is outdated and many now believe it is a gross over

simplication for a more complicated system, I will

use it as a means to further explore this topic. Keep in

mind, this is still taught largely in physiotherapy and

chiropractic institutions around the world. Moving on,

upper cross syndrome is a musculoskeletal diagnosis

that is largely involved with posture and prolonged

static positions. The upper cross refers to the pectoralis

muscles, deep cervical exors, levator scapula,

trapezius and serratus anterior, which form a cross

spanning across the upper body. (135-137) Poor posture

(among other things) causes a forward head carriage

and rolled forward internally rotated shoulders, resulting

in tight pectoralis muscles, tight upper trapezii, weak

or tense (lengthened) deep neck exors, levator scapula

and lower trapezii or serratus anterior, and accompanied

by pain. (138) The posture or lack of movement for

various reasons cause this tension, tightness and pain

through the musculoskeletal system, and this happens

throughout the whole body.

The Pain-Spasm-Pain Cycle

Another common theory is “the pain-spasm-pain cycle,”

which describes muscular hypertonicity as a response

to pain, leading to the muscle spasm causing nerve

compression, tissue dysfunction or ischemic pain. (101).

One of the leading theories why spinal manipulation

interacts with muscle hyperactivity is via muscular

reexogenic responses, since spinal manipulation may

disrupt the pain-spasm cycle by evoking the appropriate

muscular reex pathway and reducing muscle activity.

(4) There are studies showing a link between thermal

asymmetries and increased paraspinal muscle activity

in patients who are experiencing back pain, showing

that the link is evident between pain and muscle

hypertonicity. (139,140) What’s more, we have studies

showing an alteration to those thermal asymmetries

and muscle activation following spinal manipulation.

However, some studies conclude SM increases muscle

activation, and some say it decreases. (129,141).

However, although this may be confusing, we have

already discussed the importance of strength, muscle

activity and how SM can improve muscle strength. It

thus makes sense that contextually the body responds

using the force from the SM in the most advantageous

way possible. (5,62,114)

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7

Segmental Facilitation (Motor Neurons)

In addition to the above theories, Korr’s theory of

segmental facilitation must be considered. (142) The

theory states that segments of the spine that constantly

are barraged with stimulus become facilitated and

over-sensitive, leading to an ongoing central excitatory

state. (143) Furthermore, Denslow et al demonstrated

back in 1947 that areas of the spinal cord associated

with somatic dysfunction also had an increase in hyper-

responsiveness and seemed to remain in a state of

maintained facilitation. (144) Korr believed that these

sites of somatic dysfunction mirrored sites of pain,

and these areas over time allowed the build-up of

gamma-motor neurons due to the increased trac

of stimuli through that specic spinal segment level.

The increase in gamma neuron activity caused muscle

hypertonicity by facilitating the excitement of alpha

neurons and participated in the pain-spasm-pain cycle.

(101) Ultimately Korr’s answer to this painful problem

was manipulation, theorizing that the bombardment of

neurological afferent input from spinal manipulation

caused a distracting and calming effect on the gamma

neurons. (142) Gamma motor neurons are low motor

neurons (LMNs) that contribute to muscle contraction;

however, they play an important role in modulating

tension in muscle spindles that interact with alpha

motor neurons, allowing them to re and perform full

muscle contraction. Alpha motor neurons primarily work

to generate force via innervating extrafusal muscle

bers, while gamma motor neurons alter muscle spindle

sensitivity by innervating intrafusal muscle bers. (145)

Autonomic Changes

The autonomic system is responsible for regulating

involuntary body functions such as blood ow, heart

rate, digestion and breathing while controlling blood

vessels, organs and glands. Dysautonomia is often

dened as a disorder of the autonomic nervous

system that causes disturbances to these autonomic

functions, ultimately resulting in poor health outcomes.

The autonomic system is also responsible for the

sympathetic and parasympathetic divisions, which

regulate ght and ight (sympathetic) and rest and

digest (parasympathetic) systems. The body requires

balance in order to function optimally; however, these

systems that were designed to help humans survive

thousands of years ago can become overly active and

stimulated, often leaning towards the sympathetic

range, leaving people in a constant state of ght or

ight, providing an environment conducive to autonomic

dysfunction. (146)

Healthcare professionals do have the ability to

measure how the autonomic system is functioning via

the variability of the space in between heart beats;

a higher heart rate variability (HRV) is better, as low

variability between heart beats indicates a system that

is not adapting eciently to the stresses being placed

upon it. In fact, a 1994 study showed that monitoring a

patient’s HRV was an accurate way of measuring cardiac

autonomic tone. (147) Furthermore, a study from 2016

concluded measuring HRV as an accurate operator

fatigue analysis system reducing the risks that occur as

a consequence of a fatigued operator. (148)

Furthermore, certain healthcare providers such as

chiropractors claim they can test the sympathetic and

parasympathetic systems via paraspinal thermography,

which through infrared technology detects the varying

degrees of temperatures across the surface of the skin.

A 2011 study showed excellent intra-examiner and inter-

examiner reproducibility of paraspinal thermography

when using a commercially available unit and a 2007

study showed an excellent reliability of data by three

different methods of computer-aided thermal pattern

analysis. (149,150). The idea is, a healthy system will

adapt in symmetrical temperature alterations through

the process of vasoconstriction/vasodilation. This is

regulated via sympathetic pre-ganglionic signals that

are part of the body's autonomic thermoregulation

system. (151) A 2-part study from 1988 consisting of 144

patients demonstrated a strong link between those

with low back pain/sciatica and thermal asymmetries,

indicating temperature asymmetry may be an effective

tool in evaluating patients with such conditions. (140)

There is some evidence showing spinal manipulation

and chiropractic care can impact both HRV and

spinal thermography. One study showed noticeable

thermography changes to the L5 region following a

lumbar L5 adjustment while a second, retrospective

case series, showed a signicant improvement of HRV

in patients receiving continuous chiropractic care.

(129,130). Additionally, a 2009 randomized control trial

consisting of 51 participants showed an increase in

HRV and parasympathetic activity following a lumbar

chiropractic adjustment. (12) Additionally, there has

been research showing changes to both blood pressure

and the pupillary reex following spinal manipulation,

indicating ANS involvement. (130,152) It is also widely

accepted that there are considerable interactions

between the autonomic nervous system and how we

perceive pain, indicating that there may be some level of

involvement happening regarding the modulation of pain

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7

following SM which is being regulated through the

ANS. (153)

Sympathetic Nervous System and the Hypothalamic-

Pituitary-Adrenal Axis

Stress has a very large impact on the human body, so

it is not surprising the complicated systems that have

been developed throughout evolution to help the human

species manage and coordinate the body’s response to

stress. The hypothalamus is widely known for its ability

to coordinate incoming stress. The hypothalamic-

pituitary-adrenal axis (HPA axis) is a complex

neuroendocrine pathway consisting of various negative

feedback loops that operate to manage the body’s

homeostasis. (154) When the body is subjected to stress,

in whatever way that may present, the sympathetic

nervous system (SNS) mediates an initial response as

a mechanism of protection; the release of epinephrine

and norepinephrine will prepare you to ght or ight,

raising your heart rate and perspiration. (155)

Additionally, the HPA axis is also engaged which starts

by the hypothalamus responding to the elevated

hormones and change in physiology and secreting

corticotropin-releasing hormone or CRH into the

bloodstream. CRH causes the pituitary gland to release

adrenocorticotropic hormone or ACTH and this hormone

is what acts on the adrenal glands causing the secretion

of glucocorticoids like cortisol. (156)

Cortisol is intriguing, because cortisol pretty much

enhances anything in your body that is likely to be

useful during a highly stressful time and inhibits

anything that is not useful- like pain; furthermore,

cortisol is known to be a potent anti-inammatory

and a hormone that helps modulates inammation.

(157) A 2019 randomised controlled study consisting of

100 healthy participants concluded that cortisol does

in fact affect pain sensitivity and a 2015 longitudinal

cohort study concluded that a hyporesponsive HPA

axis and low cortisol response to stress was associated

with musculoskeletal pain in young adults. (158,159) It

is important to note that when stress is consistently

prolonged and tempers into the chronic state, this

HPA axis can turn from a healthy adaptation to a

maladaptation causing both pain and inammation

dysfunctions. This ties into what was discussed earlier

in this review when it touched on maladaptive neural

changes and neuroplasticity.

It is also important to mention that the SNS is also

associated with pain modulation. Schlereth and Birklein

state that the activation of the SNS in healthy subjects

CONCLUSION

The underlying mechanism of HVLA thrust, or spinal

manipulation (SM) has been highly speculated for

decades, and was further explored in this review.

usually supresses pain and nociceptive transmission

by descending inhibition. (160) The release of EOs,

endorphins, serotonin, noradrenaline and GABA during

an acute, fast stressful experience is extremely

important, as these chemical mediators work to

inhibit the action potentials causing pain resulting in

descending pain inhibition and a reduction in pain. (161)

The effects induced by spinal manipulation on the

nervous system, immune system, HPA axis and

endocrine systems have been investigated for years

with many contrasting and conicting results; however,

it is clear something is happening and we may not

fully understand it all yet. (162) For example, a 2017

study showed an observed change in HPA activity via

salivary cortisol following SM. (163) Additionally, many

have explored this as a viable and plausible mechanism

underlying the clinical success we see with SM. (4)

There is even evidence showing that SM is effective at

reducing temporal summation, which is the increased

build-up of pain due to multiple repetitive nociceptive

stimuli. (164) Moving forward we need more high-quality

clinical trials looking at how SM exactly impacts the SNS,

HPA axis and the neuro-endocrine systems.

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7

Spinal Manipulation Effects (review summary)

Various theories have been established throughout the

literature covering both physiological and neurological

mechanisms, such as the local physiological and

biochemical changes that occur to the synovial joint

structures and surrounding soft tissue – altering

synovial uid viscosity, increasing blood ow, altering

tissue pliability and modulating pain perception via

gate theory and/or descending inhibition. Neurological

effects have also been highlighted regarding the

impact of spinal manipulation on the brain via changes

to afferent/efferent impulses; potentially altering the

state of our immune system, brain neuroplasticity,

proprioception, cortical drive and function of the

prefrontal cortex. This review provides a framework

for a better understanding and deeper comprehension

of the potential mechanisms involved in spinal

manipulation. This study is not only for the researcher,

but also for the clinician, doctor, physical therapist, and

other professionals who treat patients on a daily basis.

In order to give the best evidence-based treatment

possible, I hope that this review will offer high-quality,

consolidated, palatable information that will help to

clarify and equip the appropriate individuals to further

expand their practice in line with the research.

REFERENCES:

1. LaPelusa A, Bordoni B. High velocity low amplitude

manipulation techniques [Internet]. PubMed.

Treasure Island (FL): StatPearls Publishing; 2022.

Available from: https://www.ncbi.nlm.nih.gov/

books/NBK574527/

2. Kawchuk GN, Fryer J, Jaremko JL, Zeng H, Rowe

L, Thompson R. Real-time visualization of joint

cavitation. PLoS One 2015;15:e0119470

3. Ikels KG. Production of gas bubbles in fluids by

tribonucleation. J Appl Physiol 1970;28:524-527

4. Gyer G, Michael J, Inklebarger J, Tedla JS. Spinal

manipulation therapy: Is it all about the brain? A

current review of the neurophysiological effects

of manipulation. J Integr Med 2019;17:328-337

5. Christiansen TL, Niazi IK, Holt K, et al. The effects

of a single session of spinal manipulation on

strength and cortical drive in athletes. Eur J Appl

Physiol 2018;118:737-749.

6. Holt KR, Haavik H, Lee ACL, Murphy B, Elley CR.

Effectiveness of chiropractic care to improve

sensorimotor function associated with falls risk

in older people: A randomized controlled trial. J

Manipulative Physiol Ther 2016;39:267-278.

7. Beyerman KL, Palmerino MB, Zohn LE, Kane GM,

Foster KA. Efficacy of treating low back pain

and dysfunction secondary to osteoarthritis:

chiropractic care compared with moist heat alone.

Manipulative Physiol Ther 2006;29:107-114.

8. Vigotsky AD, Bruhns RP. The role of descending

modulation in manual therapy and its analgesic

implications: a narrative review. Pain Res Treat

2015;15:1-11.

9. Coronado RA, Gay CW, Bialosky JE, Carnaby GD,

Bishop MD, George SZ. Changes in pain sensitivity

following spinal manipulation: a systematic review

and meta-analysis. J Electromyogr Kinesiol

2012;22:752-767

10. Haavik H. The reality check. Auckland: Haavik

Chiropractic; 2014

11. Dafny N. Anatomy of the Spinal Cord (Section 2,

Chapter 3) Neuroscience online: an electronic

textbook for the neurosciences. Tmc.edu.

2019. Available from: https://nba.uth.tmc.edu/

neuroscience/m/s2/chapter03.html

12. Roy RA, Boucher JP, Comtois AS. Heart rate

variability modulation after manipulation in pain-

free patients vs patients in pain. J Manipulative

Physiol Ther 2009;32:277-286

13. Haavik H, Murphy B. Subclinical neck pain and

the effects of cervical manipulation on elbow

joint position sense. J Manipulative Physiol Ther

2011;34:88-97

14. Haavik H, Murphy B. The role of spinal manipulation

in addressing disordered sensorimotor integration

and altered motor control. J Electromyogr Kinesiol

2012;22:768-776

15. Haavik-Taylor H, Murphy B. Cervical spine

manipulation alters sensorimotor integration:

A somatosensory evoked potential study. Clin

Neurophysiol 2007;118:391-402

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7

16. Rugnetta M. Neuroplasticity: different types,

facts, & research. In: Encyclopædia Britannica

[Internet]. 2018. Available from: https://www.

britannica.com/science/neuroplasticity

17. Definition of Maladaptation [Internet]. www.

merriam-webster.com. Available from: https://

www.merriam-webster.com/dictionary/

maladaptation

18. Vachon-Presseau E, Centeno MV, Ren W, et al. The

emotional brain as a predictor and amplifier of

chronic pain. J Dental Res 2016;95:605-612

19. Doidge N. The brain that changes itself : stories

of personal triumph from the frontiers of brain

science. New York: Penguin Books; 2014

20. Weiss T. Plasticity and cortical reorganization

associated with

pain. Z Psychol. 2016;224:71-9

21. Kuner R, Flor H. Structural plasticity and

reorganisation in chronic pain. Nat Rev Neurosci

2016;18:20-30

22. Heffner KL, France CR, Trost Z, Mei Ng H, Pigeon

WR. Chronic low back pain, sleep disturbance, and

interleukin-6. Clin J Pain 201;27:35-41

23. Cheatle MD, Foster S, Pinkett A, Lesneski M, Qu

D, Dhingra L. Assessing and managing sleep

disturbance in patients with chronic pain.

Anesthesiol Clin 2016;34:379-393

24. Arco AD, Mora F. Neurotransmitters and prefrontal

cortex–limbic system interactions: implications

for plasticity and psychiatric disorders. J Neural

Transm 2009;116:941-952

25. Amat J, Baratta MV, Paul E, Bland ST, Watkins LR,

Maier SF. Medial prefrontal cortex determines

how stressor controllability affects behavior and

dorsal raphe nucleus. Nat Neurosci 2005;8:365-

371

26. Van Der Kolk B. The body keeps the score: Brain,

mind, and body in the healing of trauma. New York:

Penguin Books; 2015

27. Arnsten AFT. Stress signalling pathways that

impair prefrontal cortex structure and function.

Nat Rev Neurosci 2009;10:410-422.

28. Hodges PW, Danneels L. Changes in structure

and function of the back muscles in low back

pain: different time points, observations,

and mechanisms. J Orthop Sports Phys Ther

2019;49:464-476

29. Jacobs JV, Henry SM, Nagle KJ. Low back

pain associates with altered activity of the

cerebral cortex prior to arm movements that

require postural adjustment. Clin Neurophysiol

2010;121:431-440.

30. Kiers H, van Dieën JH, Brumagne S, Vanhees L.

Postural sway and integration of proprioceptive

signals in subjects with LBP. Hum Mov Sci

2015;39:109-120

31. Benoist M. Reviewer’s comments concerning

“Altered breathing patterns during lumbopelvic

motor control tests in chronic low back pain: a

case-control study”. Europ Spine J 2009;18:1074-

1075

32. Cholewicki J, Silfies SP, Shah RA, et al. Delayed

trunk muscle reflex responses increase the risk of

low back injuries. Spine. 2005;30:2614-2620

33. Vasseljen O, Unsgaard-Tøndel M, Westad C, Mork

PJ. Effect of core stability exercises on feed-

forward activation of deep abdominal muscles in

chronic low back pain. Spine 2012;37:1101-1108

34. Georgy EE. Lumbar repositioning accuracy as a

measure of proprioception in patients with back

dysfunction and healthy controls. Asian Spine J

2011;5:201-207

35. Navid MS, Lelic D, Niazi IK et al. The effects of

chiropractic spinal manipulation on central

processing of tonic pain - a pilot study

using standardized low-resolution brain

electromagnetic tomography (sLORETA). Sci Rep

2019;9

36. Holt K, Niazi IK, Nedergaard RW, Duehr J, Amjad I,

Shafique M, et al. The effects of a single session

of chiropractic care on strength, cortical drive,

and spinal excitability in stroke patients. Sci Rep

2019;9

37. Haavik H, Niazi IK, Holt K, Murphy B. Effects of 12

weeks of chiropractic care on central integration

of dual somatosensory input in chronic pain

patients: a preliminary study. J Manipulative

Physiol Ther. 2017;40(3):127–138.

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7

38. Niazi IK, Türker KS, Flavel S, Kinget M, Duehr

J, Haavik H. Changes in H-reflex and V-waves

following spinal manipulation. Exp Brain Res

2015;233:1165-1173

39. Kelly DD, Murphy BA, Backhouse DP. Use of

a mental rotation reaction-time paradigm

to measure the effects of upper cervical

adjustments on cortical processing: A pilot study.

J Manipulative Physiol Ther 2000;23:246-251

40. Lelic D, Niazi IK, Holt K et al. Manipulation of

dysfunctional spinal joints affects sensorimotor

integration in the prefrontal cortex: a brain source

localization study. Neural Plast 2016;2016:1-9

41. Felitti VJ, Anda RF, Nordenberg D et al.

Relationship of childhood abuse and household

dysfunction to many of the leading causes of death

in adults: the adverse childhood experiences (ACE)

Study. Am J Prev Med 2019;56:774-786

42. Sachs-Ericsson NJ, Sheffler JL, Stanley IH, Piazza

JR, Preacher KJ. When emotional pain becomes

physical: adverse childhood experiences, pain,

and the role of mood and anxiety disorders. J Clin

Psychol 2017;73:1403-1428.

43. Anda R, Tietjen G, Schulman E, Felitti V, Croft

J. Adverse childhood experiences and frequent

headaches in adults. Headache 2010;50:1473-1481

44. Dusang K. How stress can affect your sleep

[Internet]. Baylor College of Medicine. 2019.

Available from: https://www.bcm.edu/news/how-

stress-can-affect-your-sleep

45. Lorenz J, Minoshima S, Casey KL. Keeping pain

out of mind: the role of the dorsolateral prefrontal

cortex in pain modulation. Brain 2003];126:1079-91

46. Science of Psychotherapy. Prefrontal cortex |

the science of psychotherapy. The Science of

Psychotherapy. 2017. Available from: https://www.

thescienceofpsychotherapy.com/prefrontal-

cortex/

47. Tomasello F, Angileri FF, Conti A. Book Review:

Youmans and Winn neurological surgery, 7th

edition, 4-volume set. Neuro 2017;82:247-248

48. Kang D, McAuley JH, Kassem MS, Gatt JM, Gustin

SM. What does the grey matter decrease in the

medial prefrontal cortex reflect in people with

chronic pain? Euro J Pain 2018;23:203-219

49. Taylor HH, Murphy B. Altered central integration

of dual somatosensory input after cervical

spine manipulation. J Manipulative Physiol Ther

2010;33:178-188

50. Meier ML, Vrana A, Schweinhardt P. Low back

pain: the potential contribution of supraspinal

motor control and proprioception. Neuroscientist

2018;25:583-596

51. Köhne E, Jones A, Korporaal C, Price JL,

Brantingham JW, Globe G. A prospective, single-

blinded, randomized, controlled clinical trial of

the effects of manipulation on proprioception

and ankle dorsiflexion in chronic recurrent

ankle sprain [Internet]. ResearchGate. 2007.

Available from: https://www.researchgate.net/

publication/285776350_A_prospective_single-

blinded_randomized_controlled_clinical_trial_of_

the_effects_of_manipulation_on_proprioception_

and_ankle_dorsiflexion_in_chronic_recurrent_

ankle_sprain

52. Silfies SP, Mehta R, Smith SS, Karduna AR.

Differences in feedforward trunk muscle activity

in subgroups of patients with mechanical low back

pain. Arch Phys Med Rehab 2009;90:1159-1169

53. Gibson J, McCarron T. Feedforward muscle

activity: an investigation into the onset and

activity of Internal oblique during two functional

reaching tasks. J Bodyw Mov Ther 2004;8:104-113

54. Lee B, McGill S. The effect of core training on

distal limb performance during ballistic strike

manoeuvres. J Sports Sci 2016;35:1768-1780

55. McGill S. Low Back Disorders. Champaign,

IL;Windsor, Ont.:Human Kinetics;2002

56. Correia JP, Oliveira R, Vaz JR, Silva L, Pezarat-

Correia P. Trunk muscle activation, fatigue and

low back pain in tennis players. J Sci Med Sport

2016;19:311-216

57. Tsao H, Hodges PW. Immediate changes in

feedforward postural adjustments following

voluntary motor training. Exp Brain Res

2007;181:537-546

58. Marshall P, Murphy B. The effect of sacroiliac joint

manipulation on feed-forward activation times of

the deep abdominal musculature. J Manipulative

Physiol Ther 2006;29:196-202

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7

59. Haavik H, Niazi I, Jochumsen M, Sherwin D, Flavel

S, Türker K. Impact of spinal manipulation on

cortical drive to upper and lower limb muscles.

Brain Sci 2016;7:2

60. Aagaard P, Simonsen EB, Andersen JL,

Magnusson P, Dyhre-Poulsen P. Neural adaptation

to resistance training: changes in evoked

V-wave and H-reflex responses. J App Physiol

2002;92:2309-2318

61. Ekblom MMN. Improvements in dynamic plantar

flexor strength after resistance training are

associated with increased voluntary activation

and V-to-M ratio. J App Physiol 2010;109:19-26

62. Pollard H, Ward G. Strength change of quadriceps

femoris following a single manipulation of the

L3/4 vertebral motion segment: A preliminary

investigation. J Neuromusculoskeletal Syst

1996;4:137-144

63. Suter E, McMorland G, Herzog W, Bray R. Decrease

in quadriceps inhibition after sacroiliac joint

manipulation in patients with anterior knee pain. J

Manipulative Physiol Ther. 1999;22:149-153

64. Suter E, McMorland G. Decrease in elbow flexor

inhibition after cervical spine manipulation in

patients with chronic neck pain. Clin Biomech

2002;17:541-544

65. Institute for Quality and Efficiency in Health Care

(IQWiG). Low back pain: What role does medication

play in the treatment of non-specific back pain?

[Internet]. Nih.gov. Institute for Quality and

Efficiency in Health Care (IQWiG); 2019. Available

from: https://www.ncbi.nlm.nih.gov/books/

NBK284957/

66. Deyo RA, Mirza SK, Martin BI. Back pain prevalence

and visit rates. Spine 2006;31:2724-2727

67. Hoiriis KT, Pfleger B, McDuffie FC, Cotsonis G,

Elsangak O, Hinson R, et al. A Randomized clinical

trial comparing chiropractic adjustments to

muscle relaxants for subacute low back pain. J

Manipulative Physiol Ther 2004;27:388-398

68. Trompeter K, Fett D, Brüggemann G, Platen

P. Prevalence of back pain in elite athletes

. www.germanjournalsportsmedicine.

com. 2018. Available from: https://www.

germanjournalsportsmedicine.com/archive/

archive-2018/issue-7-8/prevalence-of-back-pain-

in-elite-athletes/

69. University of Maryland Medical Center. Low back

pain in athletes. Umms.org. 2019 [cited 2019 Sep

30]. Available from: https://www.umms.org/

ummc/health-services/orthopedics/services/

spine/patient-guides/low-back-pain-athletes

70. Manga P, Angus DE, Swan WR. Effective

management of low back pain: it’s time to

accept the evidence. J Canadian Chiropr Assoc

1993;37:221-229

71. Lisa A. Chiropractic spinal manipulation for low

back pain of pregnancy: a retrospective case

series. J Midwifery Womens Health 2006;51:e7-10

72. Descarreaux M, Blouin JS, Drolet M, Papadimitriou

S, Teasdale N. Efficacy of preventive spinal

manipulation for chronic low-back pain and related

disabilities: a preliminary study. J Manipulative

Physiol Ther 2004;27:509-514

73. Boline PD, Kassak K, Bronfort G, Nelson C,

Anderson AV. Spinal manipulation vs. amitriptyline

for the treatment of chronic tension-type

headaches: a randomized clinical trial. J

Manipulative Physiol Ther 1995;18:148-154

74. Giles L, Muller R. Chronic spinal pain syndromes:

A clinical pilot trial comparing acupuncture,

a nonsteroidal anti-inflammatory drug, and

spinal manipulation. J Manipulative Physiol Ther

1999;22:376-381

75. Bronfort G, Assendelft WJJ, Evans R, Haas

M, Bouter L. Efficacy of spinal manipulation

for chronic headache: A systematic review. J

Manipulative Physiol Ther. 2001;24:457-66.

76. Miller J, Gross A, D’Sylva J, Burnie SJ, Goldsmith

CH, Graham N, et al. Manual therapy and exercise

for neck pain: A systematic review. Man Ther

2010;15:334-354

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7

77. Loyd DR, Murphy AZ. The role of the

periaqueductal gray in the modulation of pain

in males and females: are the anatomy and

physiology really that different? Neural Plast

2009;1:12

78. Nahin RL, Barnes PM, Stussman BJ, Bloom B.

Costs of complementary and alternative medicine

(cam) and frequency of visits to cam practitioners:

United States, 2007. Natl Health Stat Report

2009;18:1-14

79. Fields HL, Heinricher MM, Mason P.

Neurotransmitters in nociceptive modulatory

circuits. Ann Rev Neurosci 1991;14:219-245

80. Lundeberg T, Uvnäs-Moberg K, Ågren G, Bruzelius

G. Anti-nociceptive effects of oxytocin in rats and

mice. Neurosci Lett 1994;170:153-157

81. Ossipov MH, Dussor GO, Porreca F. Central

modulation of pain. J Clin Invest 2010;120:3779-

3787

82. Adams ML, Brase DA, Welch SP, Dewey WL. The

role of endogenous peptides in the action of opioid

analgesics. Ann Emerg Med.1986;15:1030-1035

83. Little JW, Ford A, Symons-Liguori AM et al.

Endogenous adenosine A3 receptor activation

selectively alleviates persistent pain states. Brain

2015;138:28-35

84. Le Bars D, Dickenson AH, Besson J. Diffuse

noxious inhibitory controls (DNIC). II. Lack of

effect on non-convergent neurones, supraspinal

involvement and theoretical implications. Pain

1979;6:305-327

85. Alonso-Perez JL, Lopez-Lopez A, La Touche

R, Lerma-Lara S, Suarez E, Rojas J, et al.

Hypoalgesic effects of three different manual

therapy techniques on cervical spine and

psychological interaction: A randomized clinical

trial. J Bodyw Mov Ther 2017;21(4):798-803

86. 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. J Back and Musculoskelet Rehabil

2014;27:377-382

87. Melzack R, Wall PD. Pain mechanisms. Science

1965;150:971-978

88. Mendell LM. Constructing and deconstructing the

gate theory of pain. Pain 2014;155:210-216

89. Narale K. Gate control theory of pain. https://

www.physio-pedia.com. Physiopedia; 2022 [cited

2023 Dec 9]. Available from: https://www.physio-

pedia.com/index.php?title=Gate_Control_Theory_

of_Pain&oldid=303475.

90. Yam M, Loh Y, Tan C, Khadijah Adam S, Abdul Manan

N, Basir R. General pathways of pain sensation

and the major neurotransmitters involved in pain

regulation. Int J Mol Sci 2018;19:2164

91. Harvard Health Publishing. The power of the

placebo effect. Harvard Health. 2021. Available

from: https://www.health.harvard.edu/mental-

health/the-power-of-the-placebo-effect

92. Saling J. What Is the Placebo Effect? WebMD.

2022. Available from: https://www.webmd.com/

pain-management/what-is-the-placebo-effect

93. Sihvonen R, Paavola M, Malmivaara A et al.

Arthroscopic partial meniscectomy versus sham

surgery for a degenerative meniscal tear. N Engl J

Med 2013;369:2515-2524

94. Tuttle AH, Tohyama S, Ramsay T et al. Increasing

placebo responses over time in U.S. clinical trials

of neuropathic pain. Pain 2015;156:2616-2626

95. Meissner K, Distel H, Mitzdorf U. Evidence for

placebo effects on physical but not on biochemical

outcome parameters: a review of clinical trials.

BMC Med 2007;5:3

96. Evans DW. Mechanisms and effects of spinal

high-velocity, low-amplitude thrust manipulation:

Previous theories. J Manipulative Physiol Ther

2002;25:251-262

97. Tamer TM. Hyaluronan and synovial joint: function,

distribution and healing. Interdiscip Toxicol

2013;6:111-125.

98. Millan M, Leboeuf-Yde C, Budgell B, Descarreaux

M, Amorim MA. The effect of spinal manipulative

therapy on spinal range of motion: a systematic

literature review. Chiropr Man Ther 2012;20:1

99. Potter L, McCarthy C, Oldham J. Physiological

effects of spinal manipulation: a review of

proposed theories. Phys Ther Rev 2005;10:163-170

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7

100. Evans DW, Breen AC. A biomechanical model for

mechanically efficient cavitation production

during spinal manipulation: prethrust position

and the neutral zone. J Manipulative Physiol Ther

2006;29:72-82

101. Roland MO. A critical review of the evidence for

a pain-spasm-pain cycle in spinal disorders. Clin

Biomech 1986;1:102-109

102. Sandell J, Palmgren PJ, Björndahl L. Effect of

chiropractic treatment on hip extension ability

and running velocity among young male running

athletes. J Chiropr Med 2008;7:39-47

103. Whittingham W, Nilsson N. Active range of motion

in the cervical spine increases after spinal

manipulation (toggle recoil). J Manipulative Physiol

Ther 2001;24:552-555

104. Cassidy JD, Lopes AA, Yong-Hing K. The

immediate effect of manipulation versus

mobilization on pain and range of motion in the

cervical spine: a randomized controlled trial. J

Manipulative Physiol Ther 1992;15:570-575

105. Haneline MT, Cooperstein R. Chiropractic care

for patients with acute neck pain: results of a

pragmatic practice-based feasibility study. J

Chiropr Med 2009;8:143-155

106. Salehi A, Hashemi N, Imanieh MH, Saber M.

Chiropractic: is it efficient in treatment of

diseases? review of systematic reviews. Int J

Community Based Nurs Midwifery 2015;3:244-254

107. Turner RC, Lucke-Wold BP, Boo S, Rosen CL,

Sedney CL. The potential dangers of neck

manipulation & risk for dissection and devastating

stroke: an illustrative case & review of the

literature. Biomed Res Rev 2018;2

108. Cassidy JD, Boyle E, Côté P et al. Risk of

vertebrobasilar stroke and chiropractic care. Eur

Spine J 2008;17:176-183

109. Symons BP, Leonard T, Herzog W. Internal forces

sustained by the vertebral artery during spinal

manipulative therapy. J Manipulative Physiol Ther

2002;25:504-510

110. Williams B. The clinical and subjective outcomes

associated with spinal manipulation: A case study.

J Med Res Innov 2022;6:19-21

111. Williiams B, Redmon S. The effects of extremity

manipulation on plantar fascia pain: a case report.

J Contemp Chiropr 2023;6:88-91

112. Duquette S. The use of spinal manipulation to treat

an acute on field athletic injury: a case report. J

Can Chiropr Assoc 2016;60

113. Cramer GD, Ross K, Pocius J et al. Evaluating the

relationship among cavitation, zygapophyseal joint

gapping, and spinal manipulation: an exploratory

case series. J Manipulative Physiol Ther 2011;34:2-

114. Williams B, Louis M, Gyer G. A research survey

on performance enhancement through spinal

manipulation in a strength athlete population - a

pilot study. J Contemp Chiropr 2023;6:185-190

115. Physiopedia contributor. Spinal manipulation.

Physiopedia. 2023 [cited 2023 Dec 9]. Available

from: https://www.physio-pedia.com/Spinal_

Manipulation#:~:text=Spinal%20manipulation%20

has%20been%20thought

116. Shambaugh P. Changes in electrical activity in

muscles resulting from chiropractic adjustment:

a pilot study. J Manipulative Physiol Ther

1987;10:300-304

117. Brennan PC, Kokjohn K, Kaltinger CJ et al.

Enhanced phagocytic cell respiratory burst

induced by spinal manipulation: potential role

of substance P. J Manipulative Physiol Ther

1991;14:399-408

118. Brennan PC, Triano JJ, McGregor M, Kokjohn K,

Hondras MA, Brennan DC. Enhanced neutrophil

respiratory burst as a biological marker for

manipulation forces: duration of the effect and

association with substance P and tumor necrosis

factor. J Manipulative Physiol Ther 1992;15:83-89

119. Nash J, Johnson CD, Green BN. Hole in one: a

history of its founding. Chiropr Hist 1996;16:76-80

120. Grostic J. Dentate ligament-cord distortion

hypothesis. Chiropractic Res J 1988;1:47-55

121. Senzon SA. The chiropractic vertebral subluxation

part 9: complexes, models, and consensus from

1979 to 1995. J Chiropr Humanit 2018;25:130-145

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7

122. Eriksen K, Rochester RP, Hurwitz EL. Symptomatic

reactions, clinical outcomes and patient

satisfaction associated with upper cervical

chiropractic care: A prospective, multicenter,

cohort study. BMC Musculoskel Disord 2011;12

123. Jarzem PF, Quance DR, Doyle DJ, Begin LR,

Kostuik JP. Spinal cord tissue pressure during

spinal cord distraction in dogs. Spine 1992;17:227-

234

124. Nash L, Nicholson H, Lee ASJ, Johnson GM, Zhang

M. Configuration of the connective tissue in the

posterior atlanto-occipital interspace: a sheet

plastination and confocal microscopy study. Spine

2005;30:1359-1366

125. Alix ME, Bates DK. A proposed etiology of

cervicogenic headache: The neurophysiologic

basis and anatomic relationship between the

dura mater and the rectus posterior capitis minor

muscle. J Manipulative Physiol Ther 1999;22:534-

539

126. Bakris G, Dickholtz M, Meyer PM, Kravitz G, Avery

E, Miller M, et al. Atlas vertebra realignment

and achievement of arterial pressure goal in

hypertensive patients: a pilot study. J Hum

Hypertens 2007;21:347-352

127. Goertz CM, Salsbury SA, Vining RD, Long CR,

Pohlman KA, Weeks WB, et al. Effect of spinal

manipulation of upper cervical vertebrae on blood

pressure: results of a pilot sham-controlled trial. J

Manipulative Physiol Ther 2016;39:369-380

128. Haas A, Russell D. Sustained improvement of heart

rate variability in patients undergoing a program

of chiropractic care: a retrospective case series.

Chiropr J Aus. 2017;45:338-358

129. Roy RA, Boucher JP, Comtois AS. Paraspinal

cutaneous temperature modification after spinal

manipulation at l5. J Manipulative Physiol Ther

2010;33:308-314

130. Win NN, Jorgensen AMS, Chen YS, Haneline

MT. Effects of upper and lower cervical spinal

manipulative therapy on blood pressure and heart

rate variability in volunteers and patients with

neck pain: a randomized controlled, cross-over,

preliminary study. J Chiropr Med 2015;14:1-9

131. Lau WY, Kato H, Nosaka K. Water intake after

dehydration makes muscles more susceptible to

cramp but electrolytes reverse that effect. BMJ

Open Sport Exerc Med 2019;5:e000478

132. Peake JM, Neubauer O, Della Gatta PA, Nosaka K.

Muscle damage and inflammation during recovery

from exercise. J Appl Physiol 2017;122:559-570

133. Stiff-Person Syndrome Information Page. National

Institute of Neurological Disorders and Stroke.

www.ninds.nih.gov. 2023. Available from: https://

www.ninds.nih.gov/Disorders/All-Disorders/Stiff-

Person-Syndrome-Information-Page

134. Brautigam V. Why do muscles tighten up?. www.

acefitness.org. 2011 [cited 2022 Jun 11]. Available

from: https://www.acefitness.org/resources/

everyone/blog/1478/why-do-muscles-tighten-up/

135. Bayattork M, Seidi F, Minoonejad H, Andersen LL,

Page P. The effectiveness of a comprehensive

corrective exercises program and subsequent

detraining on alignment, muscle activation,

and movement pattern in men with upper

crossed syndrome: protocol for a parallel-group

randomized controlled trial. Trials 2020;21:255

136. Izraelski J. Assessment and treatment of muscle

imbalance: the Janda approach. J Canadian

Chiropr Assoc 2012;56:158

137. Janda V. On the concept of postural muscles and

posture in man. Aust J Physiother 1983;29:83-84

138. Mujawar J, Sagar J. Prevalence of upper cross

syndrome in laundry workers. Indian J Occup

Environ Med 2019;23:54

139. Lewis S, Holmes P, Woby S, Hindle J, Fowler N.

The relationships between measures of stature

recovery, muscle activity and psychological

factors in patients with chronic low back pain. Man

Ther 2012;17:27-33

140. Uematsu S, Jankel WR, Edwin DH et al.

Quantification of thermal asymmetry: part 2:

application in low-back pain and sciatica. J

Neuro1988;69:556-561

141. Ferreira ML, Ferreira PH, Hodges PW. Changes

in postural activity of the trunk muscles

following spinal manipulative therapy. Man Ther

2007;12:240-248

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7

142. Korr IM. Somatic dysfunction, osteopathic

manipulative treatment, and the nervous system:

A few facts, some theories, many questions. J Am

Osteopath Assoc1986;86:97-102

143. Kring. Segmental facilitation facilitated

segment. 2009 [cited 2022 Jun 19]. Available

from: https://aaompt.org/aaompt_data/

documents/2009sessions/richard.pdf

144. Denslow JS, Korr IM, Krems AD. Quantitative

studies of chronic facilitation in human

motoneuron pools. Am J Physiol 1947;150:229-238

145. Friese A, Kaltschmidt JA, Ladle DR, Sigrist

M, Jessell TM, Arber S. Gamma and alpha

motor neurons distinguished by expression of

transcription factor Err3. Proc Natl Acad Sci

2009;106:13588-13593

146. Waxenbaum JA, Varacallo M, Reddy V. Anatomy,

autonomic nervous system. Nih.gov. Stat Pearls

Publishing; 2019. Available from: https://www.

ncbi.nlm.nih.gov/books/NBK539845/

147. Stein PK, Bosner MS, Kleiger RE, Conger BM. Heart

rate variability: A measure of cardiac autonomic

tone. Am Heart J 1994;127:1376-1381

148. Hilal AL. HRV-based operator fatigue analysis

and classification using wearable sensors. IEEE

Conference Publication. ieeexplore.ieee.org.

2006 [cited 2023 Dec 10]. Available from: https://

ieeexplore.ieee.org/document/7473750

149. Hart J, Omolo B, Boone WR, Brown C, Ashton A.

Reliability of three methods of computer-aided

thermal pattern analysis. J Canadian Chiropr

Assoc 2007;51:175-185.

150. McCoy M, Campbell I, Stone P, Fedorchuk C,

Wijayawardana S, Easley K. Intra-examiner and

inter-examiner reproducibility of paraspinal

thermography. andreu a, editor. PLoS ONE

2011;6:e16535

151. McCorry LK. Physiology of the autonomic nervous

system. Am J Pharm Educ 2007;71:78

152. Sillevis R, Cleland J, Hellman M, Beekhuizen K.

Immediate effects of a thoracic spine thrust

manipulation on the autonomic nervous system: a

randomized clinical trial. J Man Manipulative Ther

2010;18:181-190

153. Benarroch EE. Pain-autonomic interactions.

Neurol Sci 2006;27:S130-3

154. Sheng JA, Bales NJ, Myers SA, Bautista AI,

Roueinfar M, Hale TM, et al. the hypothalamic-

pituitary-adrenal axis: development,

programming actions of hormones, and maternal-

fetal interactions. Front Behav Neurosci

2021;14:601939.

155. Dunlavey CJ. Introduction to the hypothalamic-

pituitary-adrenal axis: healthy and dysregulated

stress responses, developmental stress and

neurodegeneration. J Undergrad Neurosci Educ

2018;16:R59-60

156. Chrousos GP. Stress and disorders of the stress

system. Nat Rev Endocrinol 2009;5:374-381.

157. Hannibal KE, Bishop MD. Chronic stress, cortisol

dysfunction, and pain: a psychoneuroendocrine

rationale for stress management in pain

rehabilitation. Phys Ther 2014;94:1816-1825

158. Benson S, Siebert C, Koenen LR et al. Cortisol

affects pain sensitivity and pain-related emotional

learning in experimental visceral but not somatic

pain. Pain 2019;160:1719-1728

159. Paananen M, O’Sullivan P, Straker L et al. A low

cortisol response to stress is associated with

musculoskeletal pain combined with increased

pain sensitivity in young adults: a longitudinal

cohort study. Arthritis Res Ther 2015;17:355

160. Schlereth T, Birklein F. The sympathetic nervous

system and pain. Neuromol Med 2008;10:141-7

161. Swift A. Understanding the effect of pain and

how the human body responds. Nursing Times

2018. Available from: https://www.nursingtimes.

net/clinical-archive/pain-management/

understanding-the-effect-of-pain-and-how-the-

human-body-responds-26-02-2018/

162. Colombi A, Testa M. The effects induced by

spinal manipulative therapy on the immune and

endocrine systems. Med 2019;55

163. Sampath KK, Botnmark E, Mani R et al.

Neuroendocrine response following a thoracic

spinal manipulation in healthy men. J Orthop

Sports Phys Ther 2017;47:617-27

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7

164. Bishop MD, Beneciuk JM, George SZ. Immediate

reduction in temporal sensory summation after

thoracic spinal manipulation. Spine J 2011;11:440-

446

Spinal Manipulation Mechanisms

Williams

J Contemp Chiropr 2024, Volume 7