Thermal stress modalities have been around for hundreds of years, from the ancient Roman baths to Finnish sauna houses. There is evidence to show that ancient cultures all around the world practiced some form of heat stress therapy. Recently, scientific evidence has suggested heat stress therapy can provide a variety of physiological benefits in a range of populations, including athletes, the elderly, and those at risk for cardiovascular disease and obesity.
Thermal stress therapy or heat stress therapy is a therapeutic method that utilizes heat or elevated temperature in a controlled environment to provoke physiological adaptations and health benefits. Different types of heat stress therapy include;
Dry Sauna: temperature controlled room that produces dry heat from pouring hot water on rocks over a fire or via electric heaters. The modality is intended to induce perspiration.
Steam Room: temperature controlled room that produces a wet heat with steam. The modality is intended to induce perspiration.
Infrared Sauna: temperature controlled room that produces heat via infrared lighting. This modality is designed to heat the body directly instead of increasing the temperature of the air within the sauna.
The majority of the evidence comes from studies that used data from dry sauna modalities. In my opinion, the type of heat stress modality is less relevant as they all induce perspiration and increase body temperature effectively enough to induce adaptations. Availability and affordability are more important factors when deciding which thermal stress modality is right for you.
Athletes who compete outdoors or in hot temperatures should recognize the importance of heat acclimation, especially those who train year round in colder climates but then compete in warmer climates. Physiological benefits of heat acclimation include a lower resting core temperature, greater plasma volume and an increased sweat rate. All of which would result in performance benefits as individuals would stay cooler longer and reduce body temperature more efficiently.
A biochemical marker for heat acclimation includes up-regulation of heat shock proteins (HSP). HSP’s provide a protective function to the body during times of stress, including decreased gastrointestinal permeability during exercise. In the average healthy adult, heat acclimation can be obtained by elevating core temperature by 1-2 degrees for a sustained 60-90 minutes over the span of 4-10 days.
Heat acclimation promotes an increase in plasma volume and blood flow to the heart which results in a lower heart rate and strain on the cardiovascular system during times of exercise stress. The relaxing effect of the sauna has also been shown to have a therapeutic effect of lowering blood pressure in patients with hypertension. Individuals with stable coronary heart disease are at very low risk during sauna therapy but are encouraged to consume adequate water intake and consult with their physician.
Human growth hormone (HGH) plays an important role in muscle protein synthesis, bone growth, blood glucose regulation and fat metabolism. Heat stress elicits a growth hormone release, which signals another hormone known as insulin like growth factor-1 (IGF-1) to increase muscle protein synthesis, this occur via the mTOR pathway. IGF-1 also inhibits a pathway known as FOXO, which results in less muscle protein degradation. A natural release of HGH occurs during sleep and post exercise, therefore the best time to use sauna therapy to induce or elevate HGH levels is after an exercise bout or in the morning in a fasted state.
Insulin resistance is a large issue for the obese population, one mechanism that causes insulin resistance includes a decrease in glucose uptake in skeletal muscle. Heat stress therapy increases activity of a glucose transporter known as GLUT4 whose primary function is to store carbohydrates in skeletal muscle, thus improving an individual’s ability to store carbohydrates and reducing blood sugar levels.
Thermal stress therapies that induce whole body hyperthermia result in a rapid response of anti-depressant symptoms in those who experience depression. Heat stress also increases BDNF expression, a brain derived neurotropic factor that increases neurogenesis (the growth of new brain cells) and prolongs the life of existing brain cells. Heat stress has also been found to induce a release of a peptide called dynorphin, which has opioid like effects on the body and is responsible for a dysphoria/high sensation post exercise or post sauna therapy.
Phytoestrogens are dietary estrogens found in food. Xenoestrogens are a hormone like substance that mimics estrogen in the body. Both of these bind to estrogen receptors to elicit an estrogen like hormonal response. Some studies have found that the act of perspiration is the most effective way to rid the body of these artificial estrogens and plant derived estrogens.
Studies on thermal therapy were conducted short term, long time exposure to heat stress can result in negative physiological effects. Including neuromuscular impairment, dehydration and endotoxemia; which is an in increase in gut permeability that results in food or bacteria entering the blood stream and causing an immune response. To avoid these risk factors do not eat a large meal prior to sauna use. Be sure to drink an adequate amount of water before, during and after sauna use. Single use plastics high in BPA should never be used during sauna therapy as BPA is a xenoestrogen. When exposed to heat or sunlight, BPA will leach into water and oils more effectively.
Commercial gym saunas have a safety mechanism to prevent the temperature from reaching dangerous levels. Be sure to read the safety instructions of your sauna unit. The units of water and salt consumed are based on my body weight and are not accurate for everyone.
The use of cold stress with a cold shower is not needed for heat acclimation however I include it to increase metabolism, improve immune response, and control inflammation. Most studies that used the dry sauna modality recommended a minimum of 20 minutes per session 4-7 days a week. For first time users, try to build up to 20 minutes at a time by starting with 5-10 minutes and slowly progressing until your body can handle a full session.
Dry saunas can be an effective method for inducing heat acclimation and provide a range of physiological benefits including;
If you’re willing to sit in a hot box with a bunch of other sweaty people for 20 minutes, you’ll notice some great changes to your body over time. But if you can’t take the heat, get out of the sauna.
David recently completed his internship at the Iron Performance Center. He is the owner of Powerhouse Hypertrophy; a specialized personal training company catered towards aesthetics and wellness. David specializes in natural bodybuilding, nutrition and all things aesthetic.
