Heat increases blood flow causing muscles to relax, thus decreasing aches and soreness as connective tissues gain greater flexibility. It brings nutrient rich blood to surface areas.
Cold causes blood vessels to narrow which drives blood to the body’s core, thus nourishing and protecting the inner vital organs to ensure proper function while reducing the flow of blood to an injury. This reduces inflammation and inhibits pain. Pain reduction happens, in part, because the body’s pain receptors are particularly sensitive to changes in temperature so cooler temperatures slow the velocity of nerve transmission. The brain is momentarily distracted away from sending or receiving pain messages through the use of contrasting temperatures.
Hot/cold contrast results in alternating blood flow between internal organs and extremities which has been shown to reduce inflammation by improving circulation. The increase in blood flow may lead to oxygenation of blood which improves the healing process by causing hemoglobin (a protein in your blood involved in transporting oxygen) to get oxygen more efficiently into your tissues. It may also improve the transport of waste products and resolve edema. Stimulated blood flow even influences skin health by ensuring quick closure of pores and keeping the skin free of germs.
Cold plunging triggers the autonomic nervous system, which is a network of vessels and nerves split into two parts that control your response to stress. One part is the sympathetic nervous system which triggers your “fight or flight” response. The other part is the parasympathetic nervous system which helps to shut it down once the stress has passed. Upon entering the cold plunge tub, the initial shock of the cold water makes you take a sharp breath in and (probably) hold it. Your muscles will tense and your brain will try to convince you to get out of the tub. If you deliberately take a long slow exhale and relax, you will start to adjust to the cold. When this happens, the sympathetic nervous system slows down and the parasympathetic system takes over. It’s important to keep your breath steady when exposed to the cold water to keep the parasympathetic system working. By enduring this discomfort, you will begin to control your response to stress.
Contrast therapy acts as a pain reliever by numbing nerve endings. It works by exerting a physiological effect on the body’s pain gate mechanism. This temporarily alters the pain signals traveling to and from the brain, which can bring relief for chronic pain.
The cold water causes contraction of the lymphatic vessels, which then relax when in the heat. The expansion and contraction trigger lymphatic circulation allowing body waste to be eliminated and a “flushing” process to have a detoxifying effect on the body. Because the lymph system doesn’t have the same pumping action that the circulatory system does, this alternating between contraction and relaxation is effectively a “pump” to help move the lymph fluid efficiently throughout the body. When lymph gets stagnant, illness can occur, as well as increased inflammation from stagnant fluid. The pumping mechanism also helps boost the amount of nutrient-rich blood circulating around the body.
This same “pumping” action that happens from alternating between the hot and the cold can be seen in the muscles, where the hot to cold causes the muscles to pump similarly to how they do during light aerobic activity. This is especially beneficial for those who are injured or who are otherwise unable to engage in aerobic activity. Additionally, this “muscle pumping” helps to remove any metabolic waste products from the muscles and into the bloodstream for excretion.
Hippocrates believed that water therapy could alleviate fatigue, and doctors in the 18th century recommended cold baths to treat conditions like fever and rickets.
Boost Energy: “Plunging into cold water triggers the production of the neurotransmitter norepinephrine, a critical chemical in the body that helps regulate attention, focus, and energy. A daily cold plunge can help increase your levels of norepinephrine, thus simultaneously increasing your energy.” Dr. Rhonda Patrick https://www.athletespotential.com/uploads/2/4/7/3/24730224/cold-stress.pdf
Mood: “There is more and more evidence that a lack of norepinephrine can contribute to depression, meaning that a cold plunge might help to reduce depression and improve overall mood.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3131098/
Resilience: “A habit of cold plunging can do wonders for your mental and physical toughness.” https://thecoldplunge.com/blogs/blog/myth-busting-cold-plunge-whats-stopping-you
Physical Recovery: “Studies have shown a connection between cold plunging and blood vessel constriction, meaning that when we enter cold water our blood vessels will shrink, bringing our blood flow closer to the vital organs. After leaving the cold plunge tub, our blood vessels re-open which not only improves circulation but also helps to flush out parts of our immune system.” https://thecoldplunge.com/blogs/blog/what-are-the-benefits-of-cold-therapy
Discipline: “The key is sticking to a schedule. Once you have one habit built, the next one is that much easier.” https://thecoldplunge.com/blogs/blog/how-to-create-a-cold-plunge-routine
Circulatory Changes: “Studies show that cold water causes your heart rate to speed up, while hot water slows it down. Blood vessels open and close in a pulsing, pump-like motion.” https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4049052/
Reduces Fatigue: “A 2017 meta-analysis of the research found that contrasting hot and cold baths helped team sports players recover from fatigue 24-48 hours after the game.” https://pubmed.ncbi.nlm.nih.gov/27398915/
Removes Excess Lactic Acid: “…helping you recover from the soreness and fatigue of strenuous exercise.” https://pubmed.ncbi.nlm.nih.gov/17339133/ and https://pubmed.ncbi.nlm.nih.gov/17118706/
Thermic Stress: By using contrast therapy as your training, you can improve resilience and also cardiovascular health.
Immune System Booster: Our bodies have cold shock proteins (CSPs) and heat shock proteins (HSPs) that go dormant like your laptop when you put it into sleep mode if you never expose yourself to temperature extremes. Boot yourself back up with a quick sauna session, followed by a cold plunge or ice bath. A single Finnish sauna session has been shown to increase the number of white blood cells, which are responsible for taking out infections. Meanwhile, researchers in both Finland and Germany have demonstrated that regular sauna use reduces the incidence of both cold and flu by up to 30 percent.
Tame Anxiety and Depression & Improve Hormonal Balance: Cold water immersion at around 14 degrees Celsius has been shown to mimic or even exceed the positive effects of prescription SSRI drugs, improving feel-good hormone dopamine by 250 percent and norepinephrine by a whopping 530 percent.”
(https://www.xptlife.com/getting-to-the-heat-and-the-cold-of-the-matter-contrast-therapy-101-part-1): “Several studies found cold water immersion (CWI) significantly reduced the loss in maximal strength (Bailey, 2007; Leeder 2012; Pournot 2011), while dozens have overwhelmingly shown that a cold plunge reduces delayed onset muscle soreness (DOMS) that plagues so many athletes. On the flipside of the thermal therapy coin, the authors of one significant study discovered that a session in a sauna (heated to at least 212° F) can increase beta-endorphin, growth hormone, and testosterone concentrations while decreasing concentrations of the stress hormone cortisol.
Beyond the purely physical merits, combining heat and cold also offers us some psycho-emotional advantages as well. From a purely anecdotal standpoint, we can use these modalities to increase our resilience and develop mental strength. Former Navy SEAL and ultimate bad ass David Goggins often speaks about the need to “callous the mind,” so we can deal more resolutely with the hardships we create for ourselves in training and the unavoidable problems that crop up in everyday life. One way to achieve this is to expose ourselves to extreme conditions that force us way outside our comfort zone.
gethlth.com (https://gethlth.com/contrast-therapy/): “…there are many physiological changes that take place far beneath the skin that can improve your health. (1) Recent studies have shown that regular environmental stress (such as warm or cold temperatures) improves cardiovascular health (2), increases muscle blood flow (3), decreases risk of respiratory disease (4) and stroke (5), and even helps prevent Alzheimer’s disease and dementia. (6)Heat therapy, as seen in sauna, is also taking the stage for its value in challenging our endocrine system and improving insulin sensitivity (7), while cold therapy shares a similar spotlight for its activation of brown fat and improvements in adipose metabolism. (8) Contrast therapy, which is accomplished by alternating heat and cold (sauna, then cold plunge), has been effective in speeding up post-workout recovery (9), reducing inflammation (10), and improving sleep quality. (11)Most studies suggest that there is a dose-response relationship, meaning that the more frequently you participate in it, the greater the benefits. Most studies show that 4-7 times per week produces the most benefits. (12) Otherwise, listen to your body and ease your way into the more extreme temperatures.”
1. Heinonen I, Laukkanen JA. Effects of heat and cold on health, with special reference to Finnish sauna bathing. Am J Physiol Regul Integr Comp Physiol. 2018;314(5):R629-R638.
2. Kauppinen K. Sauna, shower, and ice water immersion. Physiological responses to brief exposures to heat, cool, and cold. Part II. Circulation. Arctic Med Res. 1989;48(2):64-74.
3. Kuhlenhoelter AM, Kim K, Neff D, et al. Heat therapy promotes the expression of angiogenic regulators in human skeletal muscle. Am J Physiol Regul Integr Comp Physiol. 2016;311(2):R377-391.
4. Kunutsor SK, Laukkanen T, Laukkanen JA. Sauna bathing reduces the risk of respiratory diseases: a long-term prospective cohort study. Eur J Epidemiol. 2017;32(12):1107-1111.
5. Kunutsor SK, Khan H, Zaccardi F, Laukkanen T, Willeit P, Laukkanen JA. Sauna bathing reduces the risk of stroke in Finnish men and women A prospective cohort study. Neurology. 2018;90(22):E1937-E1944.
6. Laukkanen T, Kunutsor S, Kauhanen J, Laukkanen JA. Sauna bathing is inversely associated with dementia and Alzheimer’s disease in middle-aged Finnish men. Age Ageing. 2017;46(2):245-249.
7. McCarty MF, Barroso-Aranda J, Contreras F. Regular thermal therapy may promote insulin sensitivity while boosting expression of endothelial nitric oxide synthase – Effects comparable to those of exercise training. Med Hypotheses. 2009;73(1):103-105.
8. van Marken Lichtenbelt WD, Vanhommerig JW, Smulders NM, et al. Cold-activated brown adipose tissue in healthy men. N Engl J Med. 2009;360(15):1500-1508.
9. Bieuzen F, Bleakley CM, Costello JT. Contrast water therapy and exercise induced muscle damage: a systematic review and meta-analysis. PLoS One. 2013;8(4):e62356.
10. Laukkanen JA, Laukkanen T. Sauna bathing and systemic inflammation. Eur J Epidemiol. 2018;33(3):351-353.
11. Hussain JN, Greaves RF, Cohen MM. A hot topic for health: Results of the Global Sauna Survey. Complementary Therapies in Medicine. 2019;44:223-234.
12. Laukkanen T, Khan H, Zaccardi F, Laukkanen JA. Association Between Sauna Bathing and Fatal Cardiovascular and All-Cause Mortality Events. Jama Intern Med. 2015;175(4):542-548.