Plasma ACTH, beta-endorphin, prolactin, growth hormone and luteinizing hormone levels after thermal stress, heat and cold

The hormesis principle of neuroplasticity and neuroprotection

Animals live in habitats fraught with a range of environmental challenges to their bodies and brains. Accordingly, cells and organ systems have evolved stress-responsive signaling pathways that enable them to not only withstand environmental challenges but also to prepare for future challenges and function more efficiently. These phylogenetically conserved processes are the foundation of the hormesis principle, in which single or repeated exposures to low levels of environmental challenges improve cellular and organismal fitness and raise the probability of survival. Hormetic principles have been most intensively studied in physical exercise but apply to numerous other challenges known to improve human health (e.g., intermittent fasting, cognitive stimulation, and dietary phytochemicals). Here we review the physiological mechanisms underlying hormesis-based neuroplasticity and neuroprotection. Approaching natural resilience from the lens of hormesis may reveal novel methods for optimizing brain function and lowering the burden of neurological disorders.

A study on neural changes induced by sauna bathing: Neural basis of the "totonou" state

Saunas are becoming increasingly popular worldwide, being an activity that promotes relaxation and health. Intense feelings of happiness have been reported shortly after enjoying a hot sauna and cold water, what is known in Japan as the "totonou" state. However, no research has investigated what occurs in the brain during the "totonou" state. In the present study, participants underwent a sauna phase, consisting of three sets of alternating hot sauna, cold water, and rest. We elucidated changes in brain activity and mood in the "totonou" state by measuring and comparing brain activity and emotional scales before and after the sauna phase and during the rest phase in each set. We found significant increases in theta and alpha power during rest and after the sauna phase compared to before the sauna phase. Moreover, in an auditory oddball task, the p300 amplitude decreased significantly and MMN amplitude increased significantly after the sauna phase. The increase in MMN indicates higher activation of the pre-attentional auditory process, leading to a decrease in attention-related brain activity P300. Hence, the brain reaches in a more efficient state. Further, the response time in behavioral tasks decreased significantly. In addition, the participants' subjective responses to the questionnaire showed significant changes in physical relaxation and other indicators after being in the sauna. Finally, we developed an artificial intelligence classifier, obtaining an average accuracy of brain state classification of 88.34%. The results have potential for future application.

3-Week passive acclimation to extreme environmental heat (100± 3 °C) in dry sauna increases physical and physiological performance among young semi-professional football players

This manuscript aims to evaluate the influence of a novel passive heat acclimation program among human participants in the physical performance, as well as in several physiological parameters. 36 male football players were acclimated using a dry sauna bath to extreme hot (100 ± 3 °C), performing a total of nine sauna sessions with a weekly frequency of three sessions. The players were randomly into the sauna group (SG; n = 18; age: 20.69 ± 2.09 years) and the control group (CG; n = 18; age: 20.23 ± 1.98 years). All participants performed maximal effort test until exhaustion as well as hamstring flexibility test before and after the acclimation program. Anthropometric, respiratory, circulatory, hematological and physiological variables were evaluated at the beginning and at the end of the survey. Statistical analysis consisted of a Mann-Whitney U test to determine differences between groups at the beginning and at the end of the survey and a Wilcoxon test for paired samples to compare the differences for each group separately. Additionally, size effects of the pre-post acclimation changes were calculated. After the acclimation program SG participants experienced a diminution in body weight (p < 0.01), body mass index (p < 0.01), body fat (p < 0.05) and fat percentage (p < 0.05) decreased. Hamstring flexibility (p < 0.05) and work capacity (p < 0.05) increased. External basal temperature decreased (p < 0.05) as well as post-exercise systolic and diastolic blood pressures (p < 0.05). Finally, maximal oxygen uptake (ml Kg^-1 min^-1) (p < 0.05), maximal minute ventilation (p < 0.05) and maximal breath frequency (p < 0.05) increased at the end of the intervention. There were no significant changes in the CG in any variable. Favorable adaptations have been observed in this survey, suggesting a beneficial effect of extreme heat acclimation on physical performance. Several of the observed responses seem interesting for sport performance and health promotion as well. However, this is a novel, extreme protocol which requires further research.

Sauna use as a lifestyle practice to extend healthspan

Sauna use, sometimes referred to as "sauna bathing," is characterized by short-term passive exposure to high temperatures, typically ranging from 45 °C to 100 °C (113 °F to 212 °F), depending on modality. This exposure elicits mild hyperthermia, inducing a thermoregulatory response involving neuroendocrine, cardiovascular, and cytoprotective mechanisms that work in a synergistic fashion in an attempt to maintain homeostasis. Repeated sauna use acclimates the body to heat and optimizes the body's response to future exposures, likely due to the biological phenomenon known as hormesis. In recent decades, sauna bathing has emerged as a probable means to extend healthspan, based on compelling data from observational, interventional, and mechanistic studies. Of particular interest are the findings from large, prospective, population-based cohort studies of health outcomes among sauna users that identified strong dose-dependent links between sauna use and reduced morbidity and mortality. This review presents an overview of sauna practices; elucidates the body's physiological response to heat stress and the molecular mechanisms that drive the response; enumerates the myriad health benefits associated with sauna use; and describes sauna use concerns.

Effect of Handgrip Training in Extreme Heat on the Development of Handgrip Maximal Isometric Strength among Young Males

The aim of this study was to evaluate the acute and adaptive effects of passive extreme heat (100 ± 3 °C) exposition in combination with a strength training protocol on maximal isometric handgrip strength. Fifty-four untrained male university students participated in this investigation. Twenty-nine formed the control group (NG) and 25 the heat-exposed group (HG). All the participants performed a 3-week isotonic handgrip strength training program twice a week with a training volume of 10 series of 10 repetitions with 45-s rest between series, per session. All the subjects only trained their right hand, leaving their left hand untrained. HG performed the same training protocol in hot (100 ± 3 °C) conditions in a dry sauna. Maximal isometric handgrip strength was evaluated each training day before and after the session. NG participants did not experience any modifications in either hand by the end of the study while HG increased maximal strength values in both hands (p < 0.05), decreased the difference between hands (p < 0.05), and recorded higher values than the controls in the trained (p < 0.05) and untrained (p < 0.01) hands after the intervention period. These changes were not accompanied by any modification in body composition in either group. The performance of a unilateral isotonic handgrip strength program in hot conditions during the three weeks induced an increase in maximal isometric handgrip strength in both hands without modifications to bodyweight or absolute body composition.

Endocrine Effects of Repeated Hot Thermal Stress and Cold Water Immersion in Young Adult Men

The aim of the study was to determine the effect of repeated hot thermal stress and cold water immersion on the endocrine system of young adult men with moderate and high levels of physical activity (PA). The research was conducted on 30 men aged 19–26 years (mean: 22.67 ± 2.02) who attended four sauna sessions of 12 min each (temperature: 90−91°C; relative humidity: 14–16 %). Each sauna session was followed by a 6-min cool-down break during which the participants were immersed in cold water (10−11°C) for 1 min. Testosterone (TES), cortisol (COR), dehydroepiandrosterone sulfate (DHEA-S), and prolactin (PRL) levels were measured before and after the sauna bath. The participants’ PA levels were evaluated using the International Physical Activity Questionnaire. Serum COR levels decreased significantly (p < .001) from 13.61 to 9.67 µg/ml during 72 min of sauna treatment. No significant changes (p >.05) were noted in the concentrations of the remaining hormones: TES increased from 4.04 to 4.24 ng/ml, DHEA-S decreased from 357.5 to 356.82 µg/ml, and PRL decreased from 14.50 to 13.71 ng/ml. After sauna, a greater decrease in COR concentrations was observed in males with higher baseline COR levels, whereas only a minor decrease was noted in participants with very low baseline COR values (r =−0.673, p <.001). Repeated use of Finnish sauna induces a significant decrease in COR concentrations, but does not cause significant changes in TES, DHEA-S, or PRL levels. Testosterone concentrations were higher in men characterized by higher levels of PA, both before and after the sauna bath.

Acute Neuromuscular and Hormonal Responses to Different Exercise Loadings Followed by a Sauna

Rissanen, JA, Häkkinen, A, Laukkanen, J, Kraemer, WJ, and Häkkinen, K. Acute neuromuscular and hormonal responses to different exercise loadings followed by a sauna. J Strength Cond Res 34(2): 313-322, 2020-The purpose of this study was to investigate acute responses of endurance (E + SA), strength (S + SA), and combined endurance and strength exercise (C + SA) followed by a traditional sauna bath (70° C, 18% relative humidity) on neuromuscular performance and serum hormone concentrations. Twenty-seven recreationally physically active men who were experienced with taking a sauna participated in the study. All the subjects performed a sauna bath only (SA) first as a control measurement followed by S + SA and E + SA (paired matched randomization) and C + SA. Subjects were measured PRE (before exercise), MID (immediately after exercise and before sauna), POST (after sauna), POST30min (30 minutes after sauna), and POST24h (24 hours after PRE). Maximal isometric leg press (ILPFmax) and bench press (IBPFmax) forces, maximal rate of force development (RFD) and countermovement vertical jump (CMVJ), serum testosterone (TES), cortisol (COR), and 22-kD growth hormone (GH22kD) concentrations were measured. All exercise loadings followed by a sauna decreased ILPFmax (-9 to -15%) and RFD (-20 to -26%) in POST. ILPFmax, RFD, and CMVJ remained at significantly (p ≤ 0.05) lowered levels after S + SA in POST24h. IBPFmax decreased in POST in S + SA and C + SA and remained lowered in POST24h. SA decreased ILPFmax and IBPFmax in POST and POST30min and remained lowered in ILPFmax (-4.1%) at POST24h. GH22kD, TES, and COR elevated significantly in all loadings measured in the afternoon in MID. SA only led to an elevation (15%) in TES in POST. The strength exercise followed by a sauna was the most fatiguing protocol for the neuromuscular performance. Traditional sauna bathing itself seems to be strenuous loading, and it may not be recommended 24 hours before the next training session. A sauna bath after the loadings did not further change the hormonal responses recorded after the exercise loadings.

Do people with anorexia nervosa use sauna baths? A reconsideration of heat-treatment in anorexia nervosa

The paper addresses the absence of reports about the sauna use among the weight loss strategies of patients with anorexia nervosa (AN). Because AN entails a relentless pursuit of thinness, it might be expected that these patients would frequently resort to saunas. The paper sustains that the absence of reports should not be taken to mean that sauna use is irrelevant to AN. Support for this possibility is founded in the apparent progress shown by AN patients whose treatment consisted of different strategies of heat supply, which included a protocol of sauna sessions. First recommended by W. Gull, heat-treatment may be relevant to hyperactivity, a significant clinical characteristic in AN. This treatment was developed as an extrapolation from animal research model, where a simple manipulation of ambient temperature (AT) was found to impede and reverse excessive running in food-restricted rats. Sauna use may have been unreported either because it impedes the development of the syndrome, or its benefits have been attributed to conventional treatments. The elucidation of sauna experience among AN patients may have potential implications for the role of heat in the treatment of AN.

Benefits and risks of sauna bathing

Although sauna bathing causes various acute, transient cardiovascular and hormonal changes, it is well tolerated by most healthy adults and children. Sauna bathing does not influence fertility and is safe during the uncomplicated pregnancies of healthy women. Some studies have suggested that long-term sauna bathing may help lower blood pressure in patients with hypertension and improve the left ventricular ejection fraction in patients with chronic congestive heart failure, but additional data are needed to confirm these findings. The transient improvements in pulmonary function that occur in the sauna may provide some relief to patients with asthma and chronic bronchitis. Sauna bathing may also alleviate pain and improve joint mobility in patients with rheumatic disease. Although sauna bathing does not cause drying of the skin-and may even benefit patients with psoriasis-sweating may increase itching in patients with atopic dermatitis. Contraindications to sauna bathing include unstable angina pectoris, recent myocardial infarction, and severe aortic stenosis. Sauna bathing is safe, however, for most people with coronary heart disease with stable angina pectoris or old myocardial infarction. Very few acute myocardial infarctions and sudden deaths occur in saunas, but alcohol consumption during sauna bathing increases the risk of hypotension, arrhythmia, and sudden death, and should be avoided.

Melatonin and the reduction or alleviation of stress

In a double blind and placebo controlled study designed to investigate the effect of melatonin administration at 13:00 hr on menstrual characteristics, prolactin, and premenstrual syndrome-like symptoms during simulated eastward travel, it was noted that melatonin reduces or alleviates the stress associated with the simulated travel. Bright lights were utilized to simulate eastward movement across six time zones. Melatonin (10 mg) was given to healthy females for 5 consecutive days during the late follicular and early luteal phases of the menstrual cycle. Hourly blood samples, used for analysis of melatonin and prolactin levels, were obtained for 24 hr before entering the dose administration phase of the study and again on the last dose day. Volunteers also completed a profile of moods state questionnaire upon waking on each of 8 days which overlapped the in-house dose administration days. The placebo group showed a prolactin peak at 13:00 hr (dose time) on the last dose day/blood draw, while the melatonin group showed a prolactin peak at 15:00 hr. The prolactin peak at 13:00 hr is likely the result of stress, since stress is known to elicit the release of prolactin. The peak at 15:00 hr in the melatonin group was likely elicited by the administration of melatonin. Stress reduction in the melatonin group was supported by results from the profile of moods state questionnaire. The melatonin group consistently demonstrated scores indicative of less stress.

The response on glucoregulatory hormones of in vivo whole body hyperthermia

This study was designed to examine the effects of in vivo hyperthermia on the circulating concentrations of a number of glucoregulatory hormones potentially involved in immunomodulation. Eight healthy male volunteers were immersed for 2 h in a hot water bath (water temperature 39.5 degrees C) (WI) during which period their rectal temperature rose to 39.5 degrees C. In a control study the subjects were immersed in thermoneutral water (water temperature 34.5 degrees C). Blood samples were collected before, at body temperature 38 degrees C (42.5 (30-52), median and range), minutes of hot WI, 39 degrees C (72.5 (58-97) minutes of hot WI), and 39.5 degrees C (at the end of 2 h of hot WI), as well as 1 and 2 h after cessation of 2 h of hot WI. In the control experiment blood samples were collected at identical time points. The growth hormone concentrations were elevated already at 38 degrees C to 24.2 (3.9-55.0) mU/l and peaked at 39 degrees C to 48.4 (20.8-81.5) mU/l compared to 0.3 (0.3-9.0) mU/l at baseline; at 39.5 degrees C the concentration declined to 31.6 (13.0-48.0) mU/l and further to 7.4 (0.8-17.3) mU/l 1 h after ending hot WI. The beta-endorphin levels were augmented at 39 degrees C and 39.5 degrees, to 8.0 (3.4-27.8) pmol/l and 8.1 (3.1-44.6) pmol/l, respectively, from 2.2 (0.7-5.6) pmol/l baseline. Glucagon levels raised from 23.0 (12.0-32.0) pmol/l to 32.0 (24.0-52.0) pmol/l at 39 degrees C, and to 38.5 (26.0-57.0) pmol/l at 39.0 degrees C. Insulin levels remained unchanged. Plasma glucose increased from 4.75 (4.2-7.6) mmol/l to 5.20 (4.6-5.6) mmol/l alone after 90 min of WI (temperature 39-39.5 degrees C). It is concluded that in vivo whole body WI hyperthermia increases the circulating levels of several essential glucoregulatory hormones.