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AQUATIC THERAPY ENCYCLOPEDIA™ · CONCEPT
Thermal effects of immersion (thermoneutral, warm and cold water)
Concept
Short entry
[Verified]
Full entry coming in 2027
Encyclopedia definition
Thermal effects of immersion: the effects of water temperature on an immersed person’s body temperature, heart rate, blood flow and comfort; because water stores and transfers heat so well, the body moves toward the temperature of the water rather than the reverse, which makes water temperature a working part of any aquatic treatment, from cold-water immersion below 15 °C to hot-spring baths near 40 °C.
Evidence label: [Verified] that the statements below match the cited reviews, trials and Evidence Library records, read on October 19, 2026.1–12 The advice on reporting temperature is this entry’s own recommendation [Proposed]. Numbers refer to the reference list below.
Credit and origin: Thermal effects are physics and physiology, not a technique with a founder. Water’s high capacity to store heat and its good heat transfer explain why an immersed body takes on the water’s temperature.1 [Verified]
Also called: Water temperature; thermoregulation in water; thermoneutral water or thermoneutral immersion1,2; warm-water immersion1; cold-water immersion (CWI) or cryotherapy3; cold water therapy4; contrast baths5
Scope note: this entry covers how water temperature affects the body and how temperatures are named. Mineral and hot-spring waters are covered under Balneotherapy. Fever, dehydration and heat strain in staff will have their own entries.
Usage note: “thermoneutral” is not one fixed number. A sports-recovery review groups 21–35 °C as thermoneutral, 20 °C or below as cold or cool, and 36 °C or above as warm;1 a Cochrane review defines cold-water immersion as below 15 °C;3 and 2025–2026 studies called water of 29.5 °C, 31–32 °C and 36 °C “thermoneutral.”6,7,8 Report the actual water and air temperatures rather than a label. [Proposed]
Cite this entry
How to cite
Salzman, A. (Ed.). (2026). Thermal effects of immersion (thermoneutral, warm and cold water). In Aquatic Therapy Encyclopedia™. ATU Educational Services, LLC; published by the Aquatic Therapy Foundation. https://aquatictherapyfoundation.org/encyclopedia/thermal-effects-of-immersion/
Permissions: You may quote and cite this entry with attribution. Reproducing or adapting full entries requires written permission from ATU Educational Services, LLC. Quoted material, trademarks and linked documents belong to their respective owners and are not covered by this permission.
Click a citation (or press and hold on a phone) to select it, then copy. Version 0.1 (beta): cite the version you used, because content may change. More details below.
Longer definition
- Why water temperature matters. Water has a high specific heat and transfers heat well. The human body stores less heat per kilogram than water (0.83 versus 1.00 kcal/kg·°C), so when a person is immersed it is the body that adjusts to the water temperature, not the water to the body.1 [Verified]
- What the body does. In head-out immersion, cooler water does not change cardiac output compared with thermoneutral water, but it changes heart rate and the share of blood flow going to muscle and fat; the lower muscle blood flow reduces maximal oxygen uptake.2 See Hydrostatic pressure and immersion physiology. [Verified]
- Temperatures in published studies. In the 2025–2026 Evidence Library, reported water temperatures run from 20 °C (cold-water cycling)9 to 40 °C (a hot-spring pool).10 Examples: 34–36 °C for older adults with knee osteoarthritis;11 a 30 °C training pool plus a 40 °C hot-spring pool for low back pain;10 and 36 °C for a child with severe motor impairment.8 About 45 of the 472 records give a temperature in °C or call the water thermoneutral.12 [Verified]
- Warm versus cold water training. In a 2026 randomized trial, 32 sedentary adults aged 60 to 75 with type 2 diabetes did water cycling three times a week for 12 weeks in warm (36 °C) or cold (20 °C) water. Both groups improved aerobic fitness, blood sugar control, blood fats and blood vessel function. Warm water gave extra gains in foot microvascular function, leg strength, trunk flexibility and oxidative stress, and cold water lowered blood pressure.9 [Verified]
- Cold-water immersion. A 2012 Cochrane review (water below 15 °C) of 17 small trials with 366 participants found some evidence that cold-water immersion after exercise reduces delayed-onset muscle soreness compared with rest; study quality was low, and most trials did not actively monitor harms.3 A 2025 review of cold water therapy for healthy aging found mostly small studies, with the best duration and temperature uncertain.4 [Verified]
- Contrast baths. A 2009 systematic review of 10 studies found that alternating hot and cold baths may increase blood flow near the skin and skin temperature, but the evidence on swelling was conflicting and no link to functional outcomes had been shown.5 [Verified]
- How to report it. Give the water temperature, the air temperature and the session length, as a 2026 hot-spring trial did (training pool 30 °C, hot-spring pool 40 °C, room 26–28 °C).10 [Verified] Labels such as “warm” or “thermoneutral” alone are not enough. [Proposed]
- Safety. This entry does not yet cover fever, dehydration or heat strain; see Thermoregulation, fever and dehydration in aquatic therapy (coming soon), Heat strain and dehydration in aquatic staff (coming soon) and Contraindications and precautions. [Proposed]
The evidence label after each statement shows how well it is sourced; it is not a grade of clinical effectiveness.
Search the Hot List™
The Evidence Library (our Hot List) is the searchable list of published studies and reviews on aquatic therapy.
The Hot List covers papers published from 2024 to 2026, so the Cochrane review and the older reviews are not in it. This search finds studies that report their water temperature; search “cold water” or “thermoneutral” for shorter lists.
Resource links
Professional and research pages. More links will be added as this entry is developed.
- Cold-water immersion for preventing and treating muscle soreness after exercise (Cochrane review, 2012)
- The properties of water and their applications for training (open-access review, 2014)
- A systematic review of the effectiveness of contrast baths (PubMed record, 2009)
References
Reference numbers match the evidence labels above.
1. Torres-Ronda L, del Alcázar XS. The properties of water and their applications for training. J Hum Kinet. 2014;44:237-248. doi:10.2478/hukin-2014-0129 PMID 25713684 (open access: PMC4327375)
2. Pendergast DR, Moon RE, Krasney JJ, Held HE, Zamparo P. Human physiology in an aquatic environment. Compr Physiol. 2015;5(4):1705-1750. doi:10.1002/cphy.c140018 PMID 26426465
3. Bleakley C, McDonough S, Gardner E, Baxter GD, Hopkins JT, Davison GW. Cold-water immersion (cryotherapy) for preventing and treating muscle soreness after exercise. Cochrane Database Syst Rev. 2012;2012(2):CD008262. doi:10.1002/14651858.CD008262.pub2 PMID 22336838. Free full text: PMC6492480
4. Kunutsor SK, Lehoczki A, Laukkanen JA. The untapped potential of cold water therapy as part of a lifestyle intervention for promoting healthy aging. Geroscience. 2025;47(1):387-407. doi:10.1007/s11357-024-01295-w PMID 39078461. Free full text: PMC11872954
5. Breger Stanton DE, Lazaro R, MacDermid JC. A systematic review of the effectiveness of contrast baths. J Hand Ther. 2009;22(1):57-69. doi:10.1016/j.jht.2008.08.001 PMID 18945584
6. Worley B, Thompson BJ, Carey J, Louder T. Acute effects of multi-joint eccentric exercise on lower-extremity muscle activation measured during land and water walking. Muscles. 2025;4(4):61. doi:10.3390/muscles4040061 PMID 41441448. Free full text: PMC12735957
7. Ivaniski-Mello A, Minetti AE, Martinez FG, Peyré-Tartaruga LA. An in-depth look at shallow-water walking: the mechanical determinants of the energy metabolic cost of shallow water walking in humans. Pflugers Arch. 2025;478(1):7. doi:10.1007/s00424-025-03130-3 PMID 41381885. Free full text: PMC12698785
8. Yabumoto T, Ajioka Y, Fujii H. Aquatic therapy for a 13-year-old with severe central hypotonia and motor impairment following post-transplant encephalopathy: a hypothesis-generating single-case study. Physiother Res Int. 2026;31(2):e70221. doi:10.1002/pri.70221 PMID 41999345
9. Suksom D, Suntraluck S, Panthong S, Tanaka H. Aquatic exercise training in warm versus cold water in elderly patients with type 2 diabetes. Med Sci Sports Exerc. 2026;58(4):726-732. doi:10.1249/MSS.0000000000003910 PMID 41347373
10. Qin L, Dong N, Zhao Y, et al. Study on the effect of aquatic exercise combined with hot spring bathing for patients with chronic low back pain: a randomized controlled trial. BMC Sports Sci Med Rehabil. 2026;18(1):218. doi:10.1186/s13102-026-01660-6 PMID 41857669. Free full text: PMC13123252
11. Kalkhoran ZB, Khanmohammadi R. The effects of aquatic therapy combined with transcranial direct current stimulation (tDCS) on proprioception and gait speed in older adults with knee osteoarthritis: an eight-week randomized sham-controlled trial. BMC Geriatr. 2025;25(1):676. doi:10.1186/s12877-025-06253-5 PMID 40898048. Free full text: PMC12403502
12. Aquatic Therapy Foundation. Evidence Library (Hot List): full dataset of 472 records (generated October 18, 2026), searched October 19, 2026. https://aquatictherapyfoundation.org/evidence-library/
About this entry
Competing interests: This entry was written by Aquatic Therapy University (ATU), a continuing-education provider owned by Andrea Salzman, MS, PT, who also serves as volunteer CEO of the Aquatic Therapy Foundation (ATF). ATU owns this content and licenses it to ATF for public education without charge. ATU teaches some of the methods described in the Encyclopedia. ATU teaching material is labeled [Expert opinion] unless it has been verified outside ATU, and it is not rated as evidence. Water temperature effects are physics and physiology, not a method developed by ATU.
How to cite this entry
Version 0.1 (beta) · Last updated October 19, 2026 · Permanent URL: https://aquatictherapyfoundation.org/encyclopedia/thermal-effects-of-immersion/
How to cite
Salzman, A. (Ed.). (2026). Thermal effects of immersion (thermoneutral, warm and cold water). In Aquatic Therapy Encyclopedia™. ATU Educational Services, LLC; published by the Aquatic Therapy Foundation. https://aquatictherapyfoundation.org/encyclopedia/thermal-effects-of-immersion/
Permissions: You may quote and cite this entry with attribution. Reproducing or adapting full entries requires written permission from ATU Educational Services, LLC. Quoted material, trademarks and linked documents belong to their respective owners and are not covered by this permission.
This is a beta entry. Cite the version you used, because content may change. Entries are drafted with AI assistance under the editorial direction of the Aquatic Therapy Foundation, checked against their cited sources, and corrected when errors are reported. Report errors to info@aquatictherapyfoundation.org.
Last updated October 19, 2026.
© 2026 ATU Educational Services, LLC. Licensed to the Aquatic Therapy Foundation, Inc. for public education. · Educational use only. This is not medical advice.