How Chiropractic Adjustments Work

What is a chiropractic adjustment?

A chiropractic adjustment — more precisely, a spinal manipulative therapy (SMT) or high-velocity, low-amplitude (HVLA) thrust — is a controlled manual technique applied to a specific spinal or extremity joint. The practitioner positions the joint at or near the end of its available range, then applies a precise, brief force through a specific vector.

The total duration of the thrust is typically measured in milliseconds — far too fast to be a stretch, and too brief for the surrounding muscles to generate a significant protective response. The technique requires a precise contact point, a specific patient position, a particular direction of force, and controlled depth. These variables are not interchangeable — they are what makes a skilled adjustment different from a generic mobilisation.

The goal is to restore normal joint motion at a segment that has become restricted — and, through the neurological effects of the technique, to reduce the aberrant sensory input from that joint that is influencing muscle tone and pain sensitivity in the surrounding region.

Adjustments are applied to the spinal joints (cervical, thoracic, and lumbar) and to peripheral joints including the hip, shoulder, elbow, wrist, ankle, and foot — depending on what the assessment reveals.

What is the sound?

The audible pop or crack that sometimes accompanies a chiropractic adjustment is one of the most commonly misunderstood aspects of the technique. It is not bones rubbing together, not the spine cracking, and not an indication that anything has been broken or damaged.

The sound is a cavitation event within the synovial fluid of the joint. Synovial joints contain a small amount of synovial fluid, which in turn contains dissolved gases — primarily carbon dioxide and nitrogen. When the joint surfaces are rapidly distracted by the thrust, the pressure within the joint cavity drops momentarily. This causes dissolved gas to come out of solution rapidly, forming a gas bubble. The audible pop is the sound of that bubble forming — not bursting.

Following cavitation, there is a brief refractory period during which the same joint cannot be made to cavitate again. The gas gradually re-dissolves into the synovial fluid over the following several minutes.

Importantly, the therapeutic effect of an adjustment does not depend on whether cavitation occurs. A technique that achieves the same joint positioning and neurological response without an audible pop is equally valid clinically. The sound is a physical byproduct of the technique — not its mechanism of action.

The proposed mechanisms

Research into why spinal manipulation produces its clinical effects has identified several plausible neurophysiological mechanisms. These are not mutually exclusive — they likely operate simultaneously and to varying degrees depending on the clinical presentation and the technique applied.

• 1
  Joint mechanoreceptor activation The joint capsule and surrounding tissues contain a dense network of mechanoreceptors — sensory receptors that respond to mechanical deformation, pressure, and movement. The brief, high-velocity thrust of an adjustment activates muscle spindle afferents (Group I and II), Golgi tendon organ afferents, and smaller-diameter Group III/IV fibres in a way that normal voluntary movement cannot replicate. This barrage of proprioceptive input reaches the spinal cord and brain within milliseconds, where it modulates pain signals and alters muscle tone across the surrounding region. [7, 8]
• 2
  Reflex inhibition of muscle guarding When a joint is restricted or painful, the surrounding muscles commonly enter a state of heightened tone — a protective reflex that itself perpetuates restriction and discomfort. The mechanoreceptor barrage generated by a spinal adjustment can inhibit this guarding response through spinal cord processing, producing a reduction in local muscle hypertonicity that often outlasts the technique. Animal studies demonstrate that spinal manipulation produces both excitatory and inhibitory paraspinal EMG responses — and that in symptomatic patients, the inhibitory response tends to predominate. [8]
• 3
  Descending pain modulation Spinal manipulation activates descending pain inhibitory pathways — the brain's own system for reducing pain signal intensity. This is mediated through supraspinal structures including the periaqueductal grey (PAG), the rostral ventromedial medulla (RVM), and the anterior cingulate cortex, with downstream release of endogenous opioids and serotonin. The clinical consequence is a measurable reduction in both local and regional pain sensitivity following manipulation — a hypoalgesic effect documented in systematic reviews of experimental pain studies. [7, 9]
• 4
  Restoration of segmental proprioception Joints restricted in their normal range of movement produce altered sensory input to the central nervous system — information that influences motor control, muscle coordination, and load distribution at adjacent levels. Restoring normal segmental mobility normalises this sensory stream. Research using transcranial magnetic stimulation (TMS) to measure motor cortex excitability has shown that spinal manipulation can alter corticospinal drive — with manipulation producing a 20% reduction in stretch reflex amplitude in patients who experienced joint cavitation, suggesting a resetting of hyperactive spinal reflex pathways. [10]
• 5
  Reversal of arthrogenic muscle inhibition When a joint is injured, inflamed, or mechanically restricted, aberrant afferent input from that joint actively inhibits the surrounding musculature — a phenomenon known as arthrogenic muscle inhibition (AMI). This is not the same as disuse atrophy. AMI is a neural inhibition of voluntary muscle activation driven by nociceptive and mechanoreceptive signals from the joint itself. It has been documented in the knee, hip, shoulder, and ankle, and explains why muscles that appear intact on imaging can feel weak and unresponsive following joint dysfunction. Restoring normal joint motion — by removing the source of aberrant afferent input — is one mechanism by which manipulation can reduce AMI and restore normal muscle activation patterns. Randomised controlled trial evidence shows that conservative spinal manipulation reduces knee-extensor inhibition in patients with low back and sacroiliac dysfunction. [11, 12]

The relative contribution of each mechanism varies by presentation, technique, and the individual patient's neurological state. Current research supports the view that the effects of spinal manipulation are primarily neurophysiological rather than purely mechanical — the benefit is not simply about moving a bone "back into place." A 2025 overview of 136 studies on the neuromuscular response to high-velocity, low-amplitude manipulation concluded that evidence for EMG, reflex, and proprioceptive changes is growing, though effect sizes and response patterns differ by spinal region and patient population. [13]

What the research says

Spinal manipulation has one of the better evidence bases among manual therapy techniques, particularly for specific presentations. The evidence is strongest for neck pain, cervicogenic headache, and low back pain — and for the use of manipulation within a multimodal approach rather than as a standalone intervention.

A 2012 systematic review of manual therapies for cervicogenic headache assessed eight RCTs and found that spinal manipulation and mobilisation produced significant reductions in headache frequency, intensity, and associated disability — with effect sizes comparable to those seen with prophylactic medication. Multimodal approaches combining joint and soft tissue therapy produced superior outcomes to unimodal treatment. [1]

For cervical radiculopathy — arm pain arising from nerve root irritation in the neck — a well-designed RCT found that a combination of manual therapy (including cervical and thoracic manipulation), supervised exercise, and cervical traction produced significantly greater improvements in pain, disability, and patient-perceived recovery at six months compared to home exercise alone: 62% success in the manual therapy group versus 32% in the exercise-only group. [3]

A Harvard-led systematic review and meta-analysis of six RCTs (pooled n=677) found that spinal manipulation produced a statistically significant reduction in migraine days compared to control conditions — a finding that holds even accounting for the methodological limitations across the included trials. [4]

The 2017 JOSPT Neck Pain Clinical Practice Guidelines recommend thoracic manipulation combined with cervical range-of-motion exercise for patients with neck pain and mobility deficits, and conditionally recommend cervical manipulation within a multimodal approach — reflecting the evidence base for manipulation as one component of a broader programme rather than a primary standalone intervention. [2]

When we use adjustments — and when we don't

At Elevate Health Care, spinal and joint adjustment is applied when the clinical assessment identifies a specific joint restriction that is contributing to the mechanical picture — and when the technique is appropriate for that patient's presentation, history, and tissue state.

It is not applied as a routine intervention to every patient or on every visit. The decision is based on what the movement analysis and palpatory assessment reveal — and, in this clinic, frequently follows fascial treatment rather than preceding it. Addressing fascial densification first often changes what the joint assessment reveals and can reduce the need for or degree of adjustment required.

If you have questions about whether adjustment is likely to be part of your management, this is something Steve will discuss with you at your initial assessment — before any technique is applied.

What to expect

• Before
  Assessment always comes first No adjustment is applied at the first visit without a thorough movement and palpatory assessment. This determines whether adjustment is appropriate, at which level, in which direction, and how much force is indicated. You will be asked about your history, any relevant imaging, and any contraindications before any technique is used.
• During
  A brief, controlled technique The adjustment itself lasts a fraction of a second. You may or may not hear a sound — both are normal. Most people describe the sensation as a pressure followed by immediate release. It should not produce sharp pain. If a particular position or technique is uncomfortable, tell Steve — there is almost always an alternative approach to the same joint.
• After
  Mild local soreness is common and normal Some local muscle soreness in the 24–48 hours following an adjustment is common, particularly if the surrounding musculature was in a state of heightened tone. This is a normal response and generally settles quickly. Significant worsening of symptoms beyond this window, or new neurological symptoms, should be reported promptly.
• Response
  Individual responses vary Some people notice an immediate change in mobility or pain following adjustment. Others notice a gradual change over the following 24–48 hours as the neurophysiological effects settle. The response depends on the presentation, how long it has been present, and what else is contributing to the mechanical picture. Steve will discuss realistic expectations with you at your initial assessment.