If you trained more than a decade or two ago, there’s a good chance you were taught that pain works like a fire alarm: damage a tissue, a signal travels up to the brain, and the brain reads out a pain level roughly proportional to the harm done. It’s a tidy model. It’s also, we now know, badly incomplete, and understanding why matters for how you explain pain to clients, how you set expectations, and how you talk about what your hands are actually doing.
This article walks through the big shifts in pain science over the last 20 years, points you to the research behind them, and explains why staying curious about ongoing trials, not just settled findings, is part of practising well.
From “damage in, pain out” to a much messier picture
The old model has a name: the specificity model, built on a simple, direct wiring diagram between injury and brain. It was already being challenged in the 1960s by Ronald Melzack and Patrick Wall’s gate control theory, which proposed that signals from the body are modulated, turned up or down, before they ever reach conscious awareness. But it’s really in the last two decades that this idea has been tested, refined, and turned into something clinically usable.
The current dominant framework is the biopsychosocial model: pain is understood as an output shaped by biological factors (tissue state, inflammation, and genetics), psychological factors (mood, beliefs, past experience, and expectation), and social factors (work, relationships, culture, and access to support), all interacting rather than sitting in separate boxes. A 2007 landmark review in *Psychological Bulletin* helped cement this as the field’s dominant explanatory framework, (https://pubmed.ncbi.nlm.nih.gov/17592957/), and subsequent research has kept building the evidence base, including a 2023 review tracing how the model has evolved in physiotherapy practice (https://www.tandfonline.com/doi/full/10.1080/10833196.2023.2177792) and a major 2021 *Lancet* series on the burden and best practice around chronic pain (https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)00393-7/abstract).
What this means practically: a client’s pain intensity is a real, valid experience, but it is not a straightforward measure of tissue damage. Someone can have significant pain with a scan that looks unremarkable, and someone else can have a striking scan finding with barely any pain at all. That mismatch used to confuse clinicians. Now it’s expected.
The brain can turn its own volume up: central sensitisation
Perhaps the single biggest development for hands-on therapists to understand is central sensitisation, a well-documented process in which the nervous system becomes more responsive over time, amplifying pain signals even after the original tissue problem has settled. It’s part of why some pain persists long after healing should have finished, and why light touch or gentle movement can sometimes provoke pain that seems out of proportion to the stimulus.
A detailed 2021 review in Lancet Rheumatology lays out the mechanisms and clinical implications of central sensitisation (https://pubmed.ncbi.nlm.nih.gov/38279393/), and the concept now sits inside a broader classification introduced by the International Association for the Study of Pain (IASP): nociplastic pain, a third pain category alongside the familiar nociceptive (tissue-based) and neuropathic (nerve-damage-based) types. The IASP’s own explainer on the nociplastic pain concept (https://www.iasp-pain.org/publications/pain-research-forum/papers-of-the-week/paper/the-concept-of-nociplastic-pain-where-to-from-here/) is worth bookmarking, and conditions like fibromyalgia and some forms of chronic low back pain and widespread pain are increasingly understood through this lens.
This isn’t just theory. Brain-imaging research funded by the NIH found that people with chronic back pain of unclear origin could learn, through a structured psychological approach, to reduce the pain-related activity in their own brains, with 66% pain-free or nearly pain-free (https://www.nih.gov/news-events/nih-research-matters/retraining-brain-treat-chronic-pain) after a month of treatment, an effect that largely held a year later. That’s a striking result, and it’s exactly the kind of finding that reshapes how clinicians talk to clients about pain in the brain without it sounding dismissive.
Pain itself got redefined
In 2020, the IASP did something that doesn’t happen often: it rewrote the official definition of pain for the first time since 1979. The revised definition (https://pmc.ncbi.nlm.nih.gov/articles/PMC8975204/) describes pain as an unpleasant sensory and emotional experience associated with, or resembling, actual or potential tissue damage, and drops the old requirement that pain be verbally described. Two changes matter here for you: pain no longer has to be tied to demonstrable tissue damage to be legitimate, and people who can’t verbally report pain (infants, and some patients with dementia or severe illness) are properly included. It’s a small wording change with a large practical effect on how seriously unexplained pain is taken in clinic.
What this means for your hands-on work
For a long time, manual therapies were explained mechanically: releasing adhesions, realigning joints, breaking down scar tissue. Current research paints a more nuanced picture. A recent clinical review makes the case that manual therapy works primarily through neurophysiological, not purely biomechanical, mechanisms; mechanical input to the tissues triggers a cascade of nervous system, hormonal, and psychological responses, rather than physically repositioning structures. Reviews summarised in resources like Physiopedia’s overview of central sensitisation (https://www.physio-pedia.com/Central_Sensitisation) describe how manual therapy can activate the body’s own descending pain-inhibiting pathways for a period after treatment.
This connects to a second thread of research: the role of context and the therapeutic relationship itself. Harvard Medical School’s Program in Placebo Studies, led by Ted Kaptchuk, has spent two decades demonstrating that the ritual, attention, and expectation built into a treatment session are not fake effects to be embarrassed about, they’re measurable, real contributors to outcomes. His 2008 paper on reconceptualising the placebo effect as contextual healing (https://journals.sagepub.com/doi/10.1258/jrsm.2008.070466) and a 2018 piece in The BMJ on open-label placebo (https://pmc.ncbi.nlm.nih.gov/articles/PMC6889847) (where patients knowingly take a placebo and still improve) are genuinely worth reading. A review specifically on placebo mechanisms in manual therapy (https://pmc.ncbi.nlm.nih.gov/articles/PMC3172952/) argues that practitioners should think of context and relationship as an active ingredient of treatment, not a nuisance variable to control away.
For acupuncture specifically, mechanistic research has moved well beyond “does it work?” into “how?.” The IASP’s own fact sheet on acupuncture for pain relief (https://www.iasp-pain.org/resources/fact-sheets/acupuncture-for-pain-relief/) summarises evidence for local effects (adenosine release at the needling site), spinal inhibitory circuits, descending pain-modulation pathways, and endogenous opioid release. Neuroimaging studies have gone further still, showing that acupuncture measurably changes activity in brain networks (https://www.frontiersin.org/journals/neurology/articles/10.3389/fneur.2026.1809628/full) involved in pain processing. Evidence Based Acupuncture’s summary of pain research (http://www.evidencebasedacupuncture.org/present-research/pain/) is a useful, regularly updated overview if you want to go deeper, and a good example of the kind of independent, trial-referenced source we’re pointing you towards throughout this piece.
The guidance caught up: NICE’s 2021 rethink
UK practice changed formally in April 2021, when NICE published guideline NG193 on chronic primary pain (https://www.nice.org.uk/guidance/ng193). It’s a genuinely significant document for complementary therapists because it moved away from many standard pharmacological approaches and towards the kind of care many of you already provide.
The headline recommendations for chronic primary pain (pain lasting more than three months with no clear underlying condition) are:
– A supervised group exercise programme
– Psychological therapy, either ACT or CBT
– A single course of acupuncture or dry needling, delivered by an appropriately trained healthcare professional in a community setting, within certain cost and delivery conditions
By contrast, NICE recommends against commonly reached-for options like paracetamol, NSAIDs, opioids, and several electrotherapy modalities for chronic primary pain, citing insufficient evidence of benefit relative to harm. The full NICE recommendations page (https://www.nice.org.uk/guidance/ng193/chapter/recommendations) and the committee’s reasoning behind the acupuncture recommendation (https://www.nice.org.uk/guidance/ng193/chapter/Rationale-and-impact) are both worth reading directly.
Landmark studies worth knowing by name
A handful of trials and papers come up again and again in this field. Knowing them by name helps you follow the conversation and speak confidently with GPs and other healthcare professionals:
– Raja et al., 2020: the IASP’s revised definition of pain, published in “Pain”(https://pmc.ncbi.nlm.nih.gov/articles/PMC8975204/)
– Nijs et al., 2021: the mechanisms of central sensitisation, in “Lancet Rheumatology” (https://pubmed.ncbi.nlm.nih.gov/38279393/)
– Ashar et al., 2021: pain reprocessing therapy and brain imaging in chronic back pain, “JAMA Psychiatry”, covered by NIH (https://www.nih.gov/news-events/nih-research-matters/retraining-brain-treat-chronic-pain)
– Kaptchuk and Miller, 2018: open-label placebo, in The BMJ (https://pmc.ncbi.nlm.nih.gov/articles/PMC6889847)
– NICE NG193, 2021: chronic primary pain guideline (https://www.nice.org.uk/guidance/ng193), thought to be the single most relevant UK policy document for your practice
Why the trials still running matter just as much
It’s tempting to treat the evidence as a finished product, a settled list of what works. It isn’t, and that’s a good thing. A few reasons ongoing and future trials deserve your attention, not just completed ones:
Trial registries protect you from being misled. Studies have found that unregistered or poorly registered trials are more prone to outcome switching and spin, reporting the results that turned out favourable rather than the ones the researchers originally set out to measure. A detailed analysis of acupuncture trial registration (https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0223305) found spin present in a meaningful proportion of published trials with non-significant results. Following registries like ClinicalTrials.gov or the ISRCTN registry lets you see what a trial promised to measure before you read what it claims to have found.
Mechanistic questions are still open. We understand a lot more about how acupuncture, manual therapy, and exercise reduce pain than we did 20 years ago, but questions about optimal dosing, which patients respond best, and how long effects last are still being actively researched, including newer neuroimaging and meta-analytic work such as this 2025 systematic review of acupuncture’s brain mechanisms in low back pain (https://pmc.ncbi.nlm.nih.gov/articles/PMC12575243/).
Guidance will keep shifting as evidence accumulates. NICE guidelines are periodically reviewed and updated, and NG193 itself explicitly flagged areas needing more research, including the long-term durability of acupuncture’s effects and the case for repeat courses. What’s recommended today reflects the evidence available at the time of writing, so staying aware of new trial results, rather than assuming the guidance is frozen, is part of practising to current standards.
Bringing it into the treatment room
None of this science is only for journal reading, it changes what you say to clients:
– Explain pain without minimising it. “Your pain is real, and your nervous system may have become more sensitive over time” lands very differently, and more accurately, than “there’s nothing structurally wrong.”
– Don’t apologise for the relationship itself. The quality of attention, explanation, and trust you offer is a legitimate, evidence-supported part of why manual therapies help, not a soft add-on to the “real” treatment.
– Set expectations honestly. Where evidence (like NICE’s acupuncture recommendation) is strong short-term but less certain long-term, say so. Clients trust practitioners more, not less, when the limits of the evidence are acknowledged.
– Keep one eye on new research. You don’t need to read every trial, but following a source like Evidence Based Acupuncture (http://www.evidencebasedacupuncture.org/present-research/pain/) or the NICE guidance pages for updates keeps your explanations current.
Where this leaves you
Pain science hasn’t stood still, and neither has the case for the kind of hands-on, relationship-centred care many complementary therapists already provide. The shift from “pain equals damage” to a fuller biopsychosocial, nervous-system-aware picture doesn’t undercut your work. If anything, it gives you a much better vocabulary for explaining what you’re doing and why it helps. Keep the client in front of you as the priority, keep an eye on what NICE and the wider research community publish next, and you’ll be practising in step with where the evidence genuinely stands.
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FAQs
Q: What is central sensitisation, and why does it matter for pain?
A: Central sensitisation is a well-documented process in which the nervous system becomes more responsive over time, amplifying pain signals even after an original injury has healed. It helps explain why some pain persists or feels disproportionate to any visible tissue damage, and it’s a key reason pain science moved away from treating pain as a direct readout of tissue harm.
Q: Did the official definition of pain actually change?
A: Yes. In 2020, the International Association for the Study of Pain (IASP) revised its definition of pain for the first time since 1979. The update describes pain as an unpleasant sensory and emotional experience associated with, or resembling, actual or potential tissue damage, meaning pain no longer needs demonstrable tissue damage, or even a verbal description, to be considered valid.
Q: What does NICE currently recommend for chronic primary pain in the UK?
A: NICE guideline NG193 (2021) recommends supervised group exercise, psychological therapies (ACT or CBT), and a single course of acupuncture or dry needling delivered by an appropriately trained professional, while advising against several common medications for chronic primary pain due to insufficient evidence of benefit.
Q: Does this mean manual therapy and acupuncture only work through placebo effects?
A: No. Research shows manual therapies and acupuncture produce measurable neurophysiological effects, including activation of the body’s own pain-inhibiting pathways and changes in brain activity. Separately, research also shows that context, expectation, and the therapeutic relationship are real, active contributors to outcomes, not evidence that a treatment “doesn’t work”.
Q: Why should practitioners pay attention to ongoing clinical trials, not just published results?
A: Because trial registries help guard against selective or misleading reporting of results, because mechanistic questions (like dosing and durability of effects) are still being actively studied, and because clinical guidance is periodically updated as new evidence emerges, treating the current evidence base as permanently fixed, risks falling behind best practice.
Author – Michelle Bebbington – Course Coordinator and Assessor
References
NIH, PubMed, and PMC
– Raja SN, et al. (2020). The revised International Association for the Study of Pain definition of pain. https://pmc.ncbi.nlm.nih.gov/articles/PMC8975204/
– Nijs J, et al. (2021). Central sensitisation in chronic pain conditions: latest discoveries and their potential for precision medicine. *Lancet Rheumatology*. https://pubmed.ncbi.nlm.nih.gov/38279393/
– NIH Research Matters (2021). Retraining the brain to treat chronic pain. https://www.nih.gov/news-events/nih-research-matters/retraining-brain-treat-chronic-pain
– Kaptchuk TJ, Miller FG (2018). Open label placebo: can honestly prescribed placebos evoke meaningful therapeutic benefits? *The BMJ*, via PMC. https://pmc.ncbi.nlm.nih.gov/articles/PMC6889847
– Bialosky JE, et al. Placebo response to manual therapy: something out of nothing? https://pmc.ncbi.nlm.nih.gov/articles/PMC3172952/
– Analysis of acupuncture trial registration and reporting bias. https://journals.plos.org/plosone/article?id=10.1371%2Fjournal.pone.0223305
– Neuroimaging evidence for central mechanisms of acupuncture in non-specific low back pain (2025 systematic review). https://pmc.ncbi.nlm.nih.gov/articles/PMC12575243/
NICE
– NICE Guideline NG193: Chronic pain (primary and secondary) in over 16s. https://www.nice.org.uk/guidance/ng193
– NG193 Recommendations. https://www.nice.org.uk/guidance/ng193/chapter/recommendations
– NG193 Rationale and impact (acupuncture). https://www.nice.org.uk/guidance/ng193/chapter/Rationale-and-impact
BMJ
– Kaptchuk TJ, Miller FG (2018). Open-label placebo: can honestly prescribed placebos evoke meaningful therapeutic benefits? *BMJ* 2018;363:k3889.
Harvard Medical School
– Program in Placebo Studies, Harvard Medical School and Beth Israel Deaconess Medical Center: research on contextual healing and open-label placebo. https://journals.sagepub.com/doi/10.1258/jrsm.2008.070466
– Harvard Health Publishing. Stopping pain before it turns chronic. https://www.health.harvard.edu/pain/stopping-pain-before-it-turns-chronic
International Association for the Study of Pain (IASP)
– Acupuncture for Pain Relief (fact sheet). https://www.iasp-pain.org/resources/fact-sheets/acupuncture-for-pain-relief/
– The concept of nociplastic pain: where to from here? https://www.iasp-pain.org/publications/pain-research-forum/papers-of-the-week/paper/the-concept-of-nociplastic-pain-where-to-from-here/
Evidence Based Acupuncture
– Acupuncture for Pain: An Evidence-Based Review. http://www.evidencebasedacupuncture.org/present-research/pain/
NHS
– NHS: 10 ways to ease pain. https://www.nhs.uk/live-well/pain/10-ways-to-ease-pain/
Other peer-reviewed sources
– The biopsychosocial approach to chronic pain: scientific advances and future directions. *Psychological Bulletin*, 2007. https://pubmed.ncbi.nlm.nih.gov/17592957/
– The biopsychosocial model of pain in physiotherapy: past, present, and future (2023 review). https://www.tandfonline.com/doi/full/10.1080/10833196.2023.2177792
– Chronic pain: an update on burden, best practices, and new advances. *The Lancet*, 2021. https://www.thelancet.com/journals/lancet/article/PIIS0140-6736(21)00393-7/abstract
– Physiopedia: Central Sensitisation (overview and clinical summary). https://www.physio-pedia.com/Central_Sensitisation