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What the Latest Research Says About Heat and Future Possibilities

Brooke Thomson

Nov 4, 2021

For centuries different types of heat therapy have been used in different cultures. Hot tubs, hot baths, steam rooms, and heat packs are all aligned with the same stress and muscle easing therapy. Which leads us to answering the timeless question, “When do you apply heat and when do you apply ice?" This article focuses on the why and how heat therapy is utilized (and from why and how we can deduce when), and for "Fire and Ice" this article pairs with this one.

Does a hot bath reduce stress? Does a sauna after a work-out evade muscle soreness? Does a paraffin wax bath work for arthritis?

Heat Therapy and Muscle Pain: Sore Muscles, Cramps, Spasms

  • As A Painkiller: Heat acts as an analgesic to the nervous system. What this means is that will reduce the sensation of pain the same way ibuprofen or Tylenol will. Some studies show that a group who received heat instead of Tylenol for muscular pain (without specific injury) reported less pain and had improved flexibility and strength after heat.

  • For Cramps: For cramps and spams relieving pain sometimes means breaking a pain response cycle. So subduing pain will additionally signal to the muscle to stop cramping in response to the pain (3)

  • After Workout: This overview that examined the work of many studies found that applying heat does delay muscle soreness more than ice or painkillers and significantly improves mobility.

  • Fascia: Heat reduces stiffness in connective tissues aka fascia (by raising the tissue metabolism) coupled with a neurological response. A tissue temperature increase of 1 degree Celsius led to an increase of 10-15% in tissue metabolism (increasing elasticity). Even if heat only penetrates surface-level fascia, it can be speculated that surface level tension relief neurologically transmits deeper tissue levels to release as well.

  • Muscle Repair: Increased circulation due to heat will bring more oxygen, nutrients, collagen, and fluidity to the area. If a tissue metabolism has decreased, this will assist in repair and regeneration. If there is dead tissue, circulation and lymphatic fluids will clear the debris.

  • Circulation: In addition to opening blood vessels for increased circulation, some studies support repeated heat over time may encourage the blood vessels to generate offshoot branches. This is especially interesting for heart health and athletic performance

Joint Pain: Wear-and-Tear and Osteo-Arthritis

  • Heat will increase circulation and possibly increase collagen in joints that diminishes with age

  • Increased circulation will bring elasticity and fluidity to muscles and tendons surrounding a stiff or achy joint, meaning better ease of movement and less pain

  • Heat’s role acting as an analgesic will also bring physical pain relief for joint pain

  • Heat will bring more circulation and fluidity to the joint. Often hands and feet (with lots of joints) are the first areas with arthritis and as extremities the easiest part of the body to heat/cool. Cold hands with arthritis can be alleviated with heat increasing circulation to the joints.

  • Surface level heat may not be able to reach connective tissue in bigger joints like shoulders and hips. This is why a physical therapist may use an ultrasound to heat inside a joint instead of on the joint surface.

  • Considering all, it’s been well established that heat or a wax paraffin treatment will alleviate arthritis, but there’s not much to show that it will actively heal or mitigate joint pain over time. So it's a short term fix.

Auto-Immune Disorders: Rheumatoid Arthritis, Fibromyalgia, MS

  • Heat can help relieve autoimmune pain with no very little downturn or risk, and there’s a chance it caimprove symptoms. Many online sources for these conditions suggest using heat therapy in addition to many other remedies and medical treatment

  • Heat therapy might improve functionality of progressed fibromyalgia patients. This study conducted with 104 patients showed improved functionality for people who received repeated heat therapy (through light) compared to people who did not use heat therapy

  • There is some continuing but promising research on full body heat therapy like saunas for long term increase in lymphatic system circulation and increased immunology. (5)

  • Heat should not be used on joints that that have recently been inflamed, triggered, or in the middle of a “flare up”.

  • Conditions like Fibromyalgia and MS symptoms can be very sensitively triggered by temperature sooo… doctor recommendation first.

Future of Heat Therapy: Cardiovascular Health & Weight Loss

  • Recently there has been positive outcomes in studies using heat for cardiovascular health and even

diabetes. This is built on a history of research that shows heat promotes circulation, expansion of blood vessels and possibly the generation of new blood vessels through the body.

  • Heat therapy has been shown to increase elasticity of aortic walls, lower blood pressure, and ease the sympathetic nervous system. Studies conducted with diabetic patients and women with PCOs have had promising results that heat may have a positive influence in treatment. Research on the role that heat could play is ongoing.

What Can A Hot Bath Do?

For ages a spa, hot bath, hot springs, or sauna has been used as a straightforward relaxation ritual in many cultures. As clinical anxiety, depression, and other mental health issues appear to be on the rise, so does the constant marketing promotion of self-care products. Can simply taking a hot bath or a spa day assist in mental health?

Given the physiological effects of heat therapy, it’s not surprising that a hot bath can help alleviate muscle tension and take the edge off of a long day. However, there’s a lot more research conducted on how a cold plunge or cold shower will have a clinical difference in serotonin and mood affecting hormones than a sauna or bath.

As put forward by Dr. Edward Shorter in Psychology Today, “Is Heat an Antidepressent?” clinical psychology may be resistant to include ancient practices or a spa day as “real psychology” even though it’s been used to alleviate mental stress way before Freud was born.

Following the practices of spas and hot springs over centuries, we often find both hot and cold plunges together – creating “contrast therapy”. For more information on contrast therapy, reference here.

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Online Reads:

Freiwald J, Magni A, Fanlo-Mazas P, et al. A Role for Superficial Heat Therapy in the Management of Non-Specific, Mild-to-Moderate Low Back Pain in Current Clinical Practice: A Narrative Review. Life (Basel). 2021;11(8):780. Published 2021 Aug 2. doi:10.3390/life11080780

Sverre Grimnes, Ørjan G Martinsen, Chapter 4 - Passive Tissue Electrical Properties, Editor(s): Sverre Grimnes, Ørjan G Martinsen, Bioimpedance and Bioelectricity Basics (Third Edition), Academic Press, 2015, Pages 77-118, ISBN 9780124114708

Whitney Lowe, Leon Chaitow, Chapter 3 - Thermal modalities as treatment aids, Editor(s): Whitney Lowe, Leon Chaitow, Orthopedic Massage (Second Edition), Mosby, 2009, Pages 27-42, ISBN 9780443068126,

Romeyke T, Scheuer H, Stummer H. Fibromyalgia with severe forms of progression in a multidisciplinary therapy setting with emphasis on hyperthermia therapy – a prospective controlled study. Clin Interv Aging. 2015;10:69-79

Jeziorski K. Hyperthermia in rheumatic diseases. A promising approach? Reumatologia. 2018;56(5):316-320. doi: 10.5114/reum.2018.79503. Epub 2018 Oct 31. PMID: 30505014; PMCID: PMC6263304.

Dorothea Zauner, Franz Quehenberger, Josef Hermann, Christian Dejaco, Martin H. Stradner, Tatjana Stojakovic, Hannes Angerer, Beate Rinner & Winfried B. Graninger (2014) Whole body hyperthermia treatment increases interleukin 10 and toll-like receptor 4 expression in patients with ankylosing spondylitis: A pilot study, International Journal of Hyperthermia, 30:6, 393-401, DOI: 10.3109/02656736.2014.956810

Ely BR, Clayton ZS, McCurdy CE, et al. Heat therapy improves glucose tolerance and adipose tissue insulin signaling in polycystic ovary syndrome. Am J Physiol Endocrinol Metab. 2019;317(1):E172-E182. doi:10.1152/ajpendo.00549.2018

Ely BR, Francisco MA, Halliwill JR, et al. Heat therapy reduces sympathetic activity and improves cardiovascular risk profile in women who are obese with polycystic ovary syndrome. Am J Physiol Regul Integr Comp Physiol. 2019;317(5):R630-R640. doi:10.1152/ajpregu.00078.2019

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