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The Heartwood Review / About / Methodology

Methodology

How studies reach The Heartwood Review, how each entry is written and checked, and what the Review will not do. Published so that a reader can judge the process, not just the result.

Edited by Gregg H. Grossman. Published by Teak & Marble Atelier, Ltd., which sells sauna, cold-plunge and red-light equipment (why we say so). The Heartwood Review is not itself a peer-reviewed publication. Nothing here is medical advice or a claim about any TMA product.

Scope

Human research on cold-water immersion, contrast therapy, traditional and infrared sauna bathing, and photobiomodulation (red and near-infrared light), published in peer-reviewed journals indexed in PubMed or Europe PMC. Animal and cell studies, conference abstracts, preprints, trade publications and manufacturer white papers are outside scope.

Where studies come from

A daily search runs the queries below against PubMed, and a monthly sweep looks back for anything the daily search missed. Every match becomes a candidate; nothing is added by hand from a reading list, a press release or a request. The queries are published here verbatim so that the selection can be checked.

Cold plunge
("cold water immersion"[ti] OR "cold-water immersion"[ti] OR "cold plunge"[ti] OR "ice bath"[ti] OR "winter swimming"[ti] OR "whole-body cryotherapy"[ti] OR "whole body cryotherapy"[ti] OR "cold exposure"[ti]) AND humans[mh] AND english[la] NOT (mice[ti] OR rats[ti] OR murine[ti] OR rodent*[ti] OR fish[ti] OR storage[ti] OR "shelf life"[ti] OR heatstroke[ti] OR "heat stroke"[ti] OR drowning[ti] OR cadaver*[ti])
Contrast therapy
("contrast water therapy"[ti] OR "contrast water immersion"[ti] OR "contrast bath"[ti] OR "contrast baths"[ti] OR "contrast bathing"[ti] OR "contrast therapy"[ti] OR "contrast immersion"[ti] OR "hot-cold immersion"[ti] OR "hot and cold water immersion"[ti] OR "alternating hot and cold"[ti] OR (sauna[ti] AND ("cold water"[ti] OR "cold-water"[ti] OR "cold plunge"[ti] OR "cold exposure"[ti]))) AND humans[mh] AND english[la] NOT (mice[ti] OR rats[ti] OR murine[ti] OR "contrast-enhanced"[ti] OR "contrast agent"[ti] OR "contrast media"[ti])
Traditional sauna
(sauna[ti] OR "sauna bathing"[ti] OR "Finnish sauna"[ti] OR "passive heat therapy"[ti]) AND humans[mh] AND english[la] NOT (infrared[ti] OR mice[ti] OR rats[ti] OR murine[ti] OR occupational[ti])
Infrared sauna not yet listed
("infrared sauna"[ti] OR "far-infrared sauna"[ti] OR "far infrared sauna"[ti] OR "Waon therapy"[ti] OR Waon[ti] OR "infrared heat"[ti] OR "far-infrared therapy"[ti] OR "far infrared therapy"[ti] OR (infrared[ti] AND (sauna[tiab] OR "heat therapy"[tiab] OR "thermal therapy"[tiab] OR hyperthermia[tiab]))) AND humans[mh] AND english[la] NOT (mice[ti] OR rats[ti] OR murine[ti] OR spectroscop*[ti] OR thermograph*[ti] OR imaging[ti] OR textile*[ti] OR fabric*[ti] OR garment*[ti] OR "near-infrared"[ti] OR "near infrared"[ti] OR photothermal[ti] OR nano*[ti] OR tumor*[ti] OR tumour*[ti] OR cancer*[ti] OR thermometr*[ti] OR tympanic[ti] OR ear[ti])
Red light therapy
(photobiomodulation[ti] OR "red light therapy"[ti] OR "red-light therapy"[ti] OR "low-level laser therapy"[ti] OR "low level laser therapy"[ti] OR "near-infrared light"[ti] OR "LED photobiomodulation"[ti]) AND (skin[tiab] OR wrinkle*[tiab] OR collagen[tiab] OR rejuvenation[tiab] OR muscle[tiab] OR "muscle recovery"[tiab] OR exercise[tiab] OR performance[tiab] OR "wound healing"[tiab] OR hair[tiab] OR sleep[tiab]) AND humans[mh] AND english[la] NOT (animals[mh] NOT humans[mh]) NOT (oral[ti] OR mucositis[ti] OR dental[ti] OR dentin[ti] OR pulpitis[ti] OR endodontic*[ti] OR periodont*[ti] OR implant*[ti] OR cancer[ti] OR oncolog*[ti] OR chemotherap*[ti] OR radiotherap*[ti] OR transcranial[ti] OR stroke[ti] OR mice[ti] OR rats[ti] OR murine[ti] OR "in vitro"[ti] OR orthodont*[ti] OR tooth[ti] OR teeth[ti] OR molar*[ti] OR gingiv*[ti] OR bruxism[ti] OR temporomandibular[ti] OR palat*[ti] OR maxillofacial[ti] OR dentistry[ti] OR animal*[ti] OR preclinical[ti] OR "in vivo"[ti] OR canine[ti] OR equine[ti] OR dogs[ti] OR horses[ti] OR rabbit*[ti] OR porcine[ti] OR swine[ti] OR veterinar*[ti] OR zebrafish[ti])

What qualifies

A candidate is considered when it is a study in humans, published in an indexed journal, available in English, and reports an outcome a reader could care about: a physiological measure, a symptom, a performance or recovery measure, or an adverse event. Systematic reviews and meta-analyses are included and labelled as such. The Review does not select for direction of effect: a well-conducted null result is as eligible as a positive one, and reviews that find marketing claims outrunning the evidence are published alongside the rest.

What receives extra scrutiny

A candidate is flagged for additional editorial attention, and more often declined, when any of the following applies: the study concerns treating, curing or preventing a named disease; it involves a vulnerable population (children, pregnancy, frail elderly people, psychiatric patients); it reports adverse events or raises safety concerns; the sample is very small (fewer than fifteen participants); industry funding is disclosed; the abstract is ambiguous; or the finding could be misread as a claim about consumer equipment.

How an entry is written and checked

A first draft of each summary is produced by software from the published article: the question the study asked, the design, the sample and duration, what it found, its limits, and a plain-language note on what the finding does and does not mean. The draft is written in the Review's own words and reproduces no abstract text. Gregg H. Grossman, the editor, then reads the draft against the source, corrects or rejects anything the source does not support, checks that the design, sample and limits are stated accurately and prominently, and approves or declines the entry. Nothing is published without that step, and no entry is published automatically. Each entry records the date it was last reviewed.

What every entry shows

The journal, year and citation; the study design and the design line (for example, “randomized crossover, 20 adults, four weeks”); a link to the original article by DOI and PubMed identifier; what the study found; the limits worth knowing; and a short note on what the finding means for a reader. Entries do not give protocols, temperatures, durations or dosages as recommendations, and do not give medical advice.

What the Review will not do

The Review never names, describes or links to any product sold by its publisher, never ties a finding to any equipment, and never links to the publisher's store. An automated check refuses any entry whose text mentions the publisher or its products, and the same check runs on the weekly email before it is sent; the editor's review is the second check. The Review carries no advertising, sponsorship, affiliate links or paid placement, and does not take suggestions from manufacturers, including its publisher's own product team. People who call or write to the publisher about its products are given a link to the Review, not a summary of a study.

Independence and funding

The Heartwood Review is published by Teak & Marble Atelier, Ltd., which sells sauna, cold-plunge and red-light equipment. Its editor selects and approves studies without regard to whether the findings favor those products. The Review is funded entirely by the publisher and has no other source of revenue or support. The editor is also the publisher's founder; that conflict is disclosed on every page rather than managed by pretending it does not exist, and the rules above are the safeguard.

The numbers

As of 24 October 2026: 45 studies published, 181 declined by the editor, 128 awaiting review. Declined studies are not shown; the count is published so that the proportion is on the record.

Corrections

Write to concierge@teakandmarbleatelier.com with the subject line “Heartwood Review correction”, citing the entry and the source. See the corrections policy.