Trigger points are acidic and contain pain-causing metabolites
Sixteen pages on PainSci cite Shah 2008: 1. The Complete Guide to Trigger Points & Myofascial Pain 2. The Complete Guide to Low Back Pain 3. Complete Guide to Plantar Fasciitis 4. The Complete Guide to Chronic Tension Headaches 5. The Complete Guide to Neck Pain & Cricks 6. Basic Self-Massage Tips for Myofascial Trigger Points 7. Micro Muscles and the Dance of the Sarcomeres 8. Heat for Pain and Rehab 9. The Pressure Question in Massage Therapy 10. Why Drink Water After Massage? 11. Complete Guide to Frozen Shoulder 12. The Trigger Point Identity Crisis 13. Does Massage Increase Circulation? 14. Good quality summaries of most important scientific papers about trigger points
PainSci commentary on Shah 2008: ?This page is one of thousands in the PainScience.com bibliography. It is not a general article: it is focused on a single scientific paper, and it may provide only just enough context for the summary to make sense. Links to other papers and more general information are provided wherever possible.
This noteworthy study reported evidence from a novel microdialysis technique (in vivo tissue fluid sampling) that the biochemical milieu of trigger points may be extremely acidic — pH of 4.2! — and contain a lot of pain-causing metabolites.
Although "just one study" caution applies strongly, this is probably the best evidence to date supporting the integrated hypothesis of trigger point formation and/or perpetuation (Gerwin). It’s an improvement on an 2005 experiment (Shah). It is cogently summarized by Simons, and at length in my own article: Toxic Muscle Knots.
These findings have been questioned (in print) by Quintner et al in 2015, and (many years later still) by Moraska and Hickner in 2024. Their concerns are all reasonable, but they aren’t deal-breakers either — only replication can confirm or undermine the results. Until then, this data will remain just an intriguing clue.
Common issues and characteristics relevant to this paper: ?Scientific papers have many common characteristics, flaws, and limitations, and many of these are rarely or never acknowledged in the paper itself, or even by other reviewers. I have reviewed thousands of papers, and described many of these issues literally hundreds of times. Eventually I got sick of repeating myself, and so now I just refer to a list common characteristics, especially flaws. Not every single one of them applies perfectly to every paper, but if something is listed here, it is relevant in some way. Note that in the case of reviews, the issue may apply to the science being reviewed, and not the review itself.
- A high (and possibly unacknowledged) risk of bias and its consequences (p-hacking, etc).
- The research involves advanced/complicated methodology or statistics that may be prone to error/abuse.
original abstract †Abstracts here may not perfectly match originals, for a variety of technical and practical reasons. Some abstacts are truncated for my purposes here, if they are particularly long-winded and unhelpful. I occasionally add clarifying notes. And I make some minor corrections.
OBJECTIVES: To investigate the biochemical milieu of the upper trapezius muscle in subjects with active, latent, or absent myofascial trigger points (MTPs) and to contrast this with that of the noninvolved gastrocnemius muscle.
DESIGN: We used a microanalytic technique, including needle insertions at standardized locations in subjects identified as active (having neck pain and MTP), latent (no neck pain but with MTP), or normal (no neck pain, no MTP). We followed a predetermined sampling schedule; first in the trapezius muscle and then in normal gastrocnemius muscle, to measure pH, bradykinin, substance P, calcitonin gene-related peptide, tumor necrosis factor alpha, interleukin 1beta (IL-1beta), IL-6, IL-8, serotonin, and norepinephrine, using immunocapillary electrophoresis and capillary electrochromatography. Pressure algometry was obtained. We compared analyte concentrations among groups with 2-way repeated-measures analysis of variance.
SETTING: A biomedical research facility.
PARTICIPANTS: Nine healthy volunteer subjects.
INTERVENTIONS: Not applicable.
MAIN OUTCOME MEASURES: Preselected analyte concentrations.
RESULTS: Within the trapezius muscle, concentrations for all analytes were higher in active subjects than in latent or normal subjects (P<.002); pH was lower (P<.03). At needle insertion, analyte concentrations in the trapezius for the active group were always higher (pH not different) than concentrations in the gastrocnemius muscle. At all times within the gastrocnemius, the active group had higher concentrations of all analytes than did subjects in the latent and normal groups (P<.05); pH was lower (P<.01).
CONCLUSIONS: We have shown the feasibility of continuous, in vivo recovery of small molecules from soft tissue without harmful effects. Subjects with active MTPs in the trapezius muscle have a biochemical milieu of selected inflammatory mediators, neuropeptides, cytokines, and catecholamines different from subjects with latent or absent MTPs in their trapezius. These concentrations also differ quantitatively from a remote, uninvolved site in the gastrocnemius muscle. The milieu of the gastrocnemius in subjects with active MTPs in the trapezius differs from subjects without active MTPs.
related content
- “An in vivo microanalytical technique for measuring the local biochemical milieu of human skeletal muscle,” Shah et al, Journal of Applied Physiology, 2005.
Specifically regarding Shah 2008:
- “New Views of Myofascial Trigger Points: Etiology and Diagnosis,” Simons, Archives of Physical Medicine & Rehabilitation, 2008.
- Toxic Muscle Knots — Research suggests myofascial trigger points may be quagmires of irritating molecules
- “Letter to the Editor: Pumping the Brakes on the Biochemical Milieu of Myofascial Trigger Points,” Moraska et al, Archives of Physical Medicine & Rehabilitation, 2024.
- Trigger points debate greatly delayed (Member Post) —
This page is part of the PainScience BIBLIOGRAPHY, which contains plain language summaries of thousands of scientific papers & others sources. It’s like a highly specialized blog. A few highlights:
- Placebo analgesia in physical and psychological interventions: Systematic review and meta-analysis of three-armed trials. Hohenschurz-Schmidt 2024 Eur J Pain.
- Recovery trajectories in common musculoskeletal complaints by diagnosis contra prognostic phenotypes. Aasdahl 2021 BMC Musculoskelet Disord.
- Cannabidiol (CBD) products for pain: ineffective, expensive, and with potential harms. Moore 2023 J Pain.
- Moderators of the effect of therapeutic exercise for knee and hip osteoarthritis: a systematic review and individual participant data meta-analysis. Holden 2023 The Lancet Rheumatology.
- Inciting events associated with lumbar disc herniation. Suri 2010 Spine J.