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

The multifaceted benefits of passive heat therapies for extending the healthspan: A comprehensive review with a focus on Finnish sauna

Passive heat therapy is characterized by exposure to a high environmental temperature for a brief period. There are several types of passive heat therapy which include hot tubs, Waon therapy, hydrotherapy, sanarium, steam baths, infrared saunas and Finnish saunas. The most commonly used and widely studied till date are the Finnish saunas, which are characterized by high temperatures (ranging from 80-100°C) and dry air with relative humidity varying from 10-20%. The goal of this review is to provide a summary of the current evidence on the impact of passive heat therapies particularly Finnish saunas on various health outcomes, while acknowledging the potential of these therapies to contribute to the extension of healthspan, based on their demonstrated health benefits and disease prevention capabilities. The Finnish saunas have the most consistent and robust evidence regarding health benefits and they have been shown to decrease the risk of health outcomes such as hypertension, cardiovascular disease, thromboembolism, dementia, and respiratory conditions; may improve the severity of musculoskeletal disorders, COVID-19, headache and flu, while also improving mental well-being, sleep, and longevity. Finnish saunas may also augment the beneficial effects of other protective lifestyle factors such as physical activity. The beneficial effects of passive heat therapies may be linked to their anti-inflammatory, cytoprotective and anti-oxidant properties and synergistic effects on neuroendocrine, circulatory, cardiovascular and immune function. Passive heat therapies, notably Finnish saunas, are emerging as potentially powerful and holistic strategies to promoting health and extending the healthspan in all populations.

The influence of extreme thermal stress on the physiological and psychological characteristics of young women who sporadically use the sauna: practical implications for the safe use of the sauna

Background

Many individuals who use the sauna at a temperature of 120°C of higher are not aware of the negative consequences of extreme thermal stress. Despite extensive research into sauna use, the impact of extreme thermal stress on the physiological and psychological characteristics of sauna users have not been examined to date.

Aim

The aim was to determine the effect of 20 min sauna sessions with a temperature of 80°C and 120°C on the physiological and psychological characteristics of women who sporadically visit the sauna.

Methods

The study was conducted on 22 full-time female university students. Physical activity (PA) levels were evaluated with the Polish short version of the International Physical Activity Questionnaire (IPAQ). Anthropometric characteristics were measured before the first sauna session by the InBody270 body composition analyzer. Physiological parameters, including heart, energy expenditure, physical effort, and blood pressure (systolic blood pressure - SBP, and diastolic blood pressure - DBP), were assessed indirectly using Polar V800 heart rate monitors and the Omron M6 Comfort blood pressure monitor. The participants' wellbeing was assessed with the Profile of Mood States (POMS) questionnaire. The presence of significant correlations between heat exhaustion and heat stress variables and syncope during the second sauna session was examined with the use of classification and regression trees (CRT) and the cross-validation technique.

Results

Twenty-minute sauna sessions with a temperature of 80°C and 120°C induced a significant (p < 0.001) decrease in the values of SBP (excluding the temperature of 120°C), DBP, and body mass, as well as a significant increase in HR and forehead temperature. Exposure to a temperature of 80°C led to a significant (p < 0.001) increase in vigor with a simultaneous decrease in tension, depression, anger, fatigue, and confusion. In turn, sauna bathing at a temperature of 120°C had an opposite effect on the above mood parameters. Vomiting and confusion were the main predictors of syncope that occurred in some of the surveyed women.

Conclusion

Excessive air temperature can induce symptoms characteristic of heat exhaustion and heat stress nausea, heavy sweating, fast weak or strong HR, high body temperature, and confusion. Therefore, sauna bathing at a temperature of 80°C can be recommended to women who sporadically use the sauna, whereas exposure to a temperature of 120°C is not advised in this group of sauna users. The present findings provide highly valuable inputs for managing wellness and SPA centers.

Judo specific fitness test performance variation from morning to evening: specific warm-ups impacts performance and its diurnal amplitude in female judokas

BACKGROUND

A number of specific tests are used to standardize competition performance. Specific Judo fitness test (SJFT) can be applied by considering the start of the competition qualifiers in the morning and the continuation of the final competitions in the evening. The improvement of test performances can be achieved with warm-up for elevating heart rate (HR) and muscle temperature such as raise, activate, mobilise, potentiate (RAMP) protocols.

PURPOSE

The aim of this study is to evaluate the effects of different warm-up protocols on SJFT at different times of the day in female judokas.

METHODS

Ten volunteer women participated in this study, who regularly participated in judo training for more than 5 years and actively competed in international competitions. Judokas completed SJFT, either after no warm-up, or RAMP protocols like specific warm-up (SWU), and dynamic warm-up for two times a day in the morning: 09:00-10:00 and in the evening: 16:00-17:00, with at least 2 days between test sessions. The following variables were recorded: throws performed during series A, B, and C; the total number of throws; HR immediately and 1 min after the test, and test index after different warm-ups.

RESULTS

When analyzed evening compared to the morning without discriminating three warm-up protocols, evening results statistically significant number of total throws performed during series A, B, and C, the total number of throws; HR immediately and 1 min after the test, and test index than morning results (p < 0.01). Moreover, RAMP protocols interaction with time have demonstrated an impact on SJFT for index [F₍₂₎ = 4.15, p = 0.024, η_p²: 0.19] and changes after 1 min HR [F_(1.370)= 7.16, p = 0.008, η_p²: 0.29]. HR after 1 min and test index results were statistically significant in favor of SWU (p < 0.05).

CONCLUSIONS

In conclusion, SJFT performance showed diurnal variation and judo performances of the judokas can be affected more positively in the evening hours especially after RAMP protocols.

The Prevalence of Use of Various Post-Exercise Recovery Methods after Training among Elite Endurance Athletes

There is now compelling evidence of the effectiveness of a range of post-exercise recovery techniques, including extended nights of sleep, cold water immersion, massage, and compression garments. Currently, limited information is available on post-exercise recovery methods used by elite endurance athletes. Therefore, this study investigated the actual methods of recovery used in this group of athletes. Google Forms were used to collect information on the recovery methods used by elite endurance track and field athletes (n = 153, 61.4% men, 38.6% women; average age: 22.7 ± 4.6 years). The most used methods of recovery were sauna bathing (96.7%), massage (86.9%), daytime nap (81.0%), and long night sleep (at least 9h) (61.4%). Recovery methods with proven effectiveness such as cold water immersion and compression garments were rarely used (15.0% and 7.8%, respectively). Overall, recovery methods were used more often when the tiers of the track and field athletes were higher. Massage and sauna bathing were the most used methods of post-exercise recovery among Russian endurance track and field athletes. In most cases, they were used in conjunction with short daytime nap and long night sleep. Higher tier athletes were more likely to use sauna bathing, massage, long night sleep, and daytime nap but not cold water immersion and compression garments as recovery methods; however, all these methods except for cold water immersion were widely used among elite-tier athletes.

The Effects of Repeated Thermal Stress on the Physiological Parameters of Young Physically Active Men Who Regularly Use the Sauna: A Multifactorial Assessment

The aim of this study was to determine the effects of thermal stress (TS) on changes in blood biochemical parameters and fluid electrolyte levels in young adult men with moderate and high levels of physical activity. Thirty men (22.67 ± 2.02 years) were exposed to four 12-min sauna sessions (temperature: 90–91 °C; relative humidity: 14–16%) with four 6-min cool-down breaks. The evaluated variables were anthropometric, physiological, and hematological characteristics. The mean values of HR_avg (102.5 bpm) were within the easy effort range, whereas HR_peak (143.3 bpm) values were within the very difficult effort range. A significant increase was noted in pO2 (p < 0.001), total cholesterol (p < 0.008), HDL (p < 0.006) and LDL cholesterol (p < 0.007). Significant decreases were observed in the SBP (by 9.7 mmHg), DBP (by 6.9 mmHg) (p < 0.001), pH (p < 0.001), aHCO₃- (p < 0.005), sHCO3- (p < 0.003), BE (ecf) (p < 0.022), BE (B), ctCO₂ (for both p < 0.005), glucose (p < 0.001), and LA (p < 0.036). High 72-min TS did not induce significant changes in the physiological parameters of young and physically active men who regularly use the sauna, excluding significant loss of body mass. We can assume that relatively long sauna sessions do not disturb homeostasis and are safe for the health of properly prepared males.

Autonomic Nervous System Response to Far-Infrared Sauna Exposure in Firefighters

OBJECTIVES

Fire departments have employed far-infrared sauna (FIRS) use as part of post-fire call protocols to address concerns related to carcinogens. The inability of the autonomic nervous system (ANS) to fully recover following an emergency call, as demonstrated by heightened sympathetic nervous system activity and delayed parasympathetic nervous system reactivation, has been implicated as a potential factor related to sudden cardiac death. The use of a sauna post-fire call, which has been demonstrated to elevate body temperature, may interfere with the ability of the ANS to fully recover. The purpose of this study was to examine ANS responses to FIRS exposure in firefighters (FFs) with (EX) and without (NONEX) prior maximal exercise.

METHODS

Sixteen career FFs participated in this study. Body temperature (TEMP), heart rate (HR), heart rate variability (HRV), blood pressure (BP), and blood lactate (La─) were measured at the start of each testing session, following a maximal exercise test (EX only), and immediately after a 15-min FIRS exposure for NONEX and EX.

RESULTS

In NONEX, TEMP increased (P < 0.001); however, there was no change in HR, HRV, BP, or La─. In EX, BP remained unchanged while TEMP, HR, and La─ were significantly (P < 0.001) greater than baseline following FIRS exposure and HRV was significantly (P = 0.018) lower than baseline.

CONCLUSIONS

These findings indicate that FIRS following maximal exercise did support some ANS recovery, but may interfere with restoration of body temperature and parasympathetic nervous system reactivation, potentially influencing post-call cardiovascular risk in FFs.

Rate of Force Development as an Indicator of Neuromuscular Fatigue: A Scoping Review

Because rate of force development (RFD) is an emerging outcome measure for the assessment of neuromuscular function in unfatigued conditions, and it represents a valid alternative/complement to the classical evaluation of pure maximal strength, this scoping review aimed to map the available evidence regarding RFD as an indicator of neuromuscular fatigue. Thus, following a general overview of the main studies published on this topic, we arbitrarily compared the amount of neuromuscular fatigue between the "gold standard" measure (maximal voluntary force, MVF) and peak, early (≤100 ms) and late (>100 ms) RFD. Seventy full-text articles were included in the review. The most-common fatiguing exercises were resistance exercises (37% of the studies), endurance exercises/locomotor activities (23%), isokinetic contractions (17%), and simulated/real sport situations (13%). The most widely tested tasks were knee extension (60%) and plantar flexion (10%). The reason (i.e., rationale) for evaluating RFD was lacking in 36% of the studies. On average, the amount of fatigue for MVF (-19%) was comparable to late RFD (-19%) but lower compared to both peak RFD (-25%) and early RFD (-23%). Even if the rationale for evaluating RFD in the fatigued state was often lacking and the specificity between test task and fatiguing exercise characteristics was not always respected in the included studies, RFD seems to be a valid indicator of neuromuscular fatigue. Based on our arbitrary analyses, peak RFD and early phase RFD appear even to be more sensitive to quantify neuromuscular fatigue than MVF and late phase RFD.

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.

Sauna bathing frequency in Finland and the impact of COVID-19

OBJECTIVES

Recent research has revealed multiple potential health benefits of frequent sauna bathing. Finland is a country with extraordinary sauna culture and bathing opportunities. However, coronavirus disease 2019 (COVID-19) pandemic introduced regulations and unprecedented closures to shared sauna facilities. In this study we aimed to examine the previously unknown baseline bathing frequency and its possible change during the epidemic.

DESIGN

We investigated several aspects of sauna bathing with self-reports: the frequency, its possible changes, reasons for change, and beliefs about its health effects among a representative sample of thousand Finns aged 18-75 years. This online survey was administered in May 2020.

RESULTS

Before the pandemic, 59 % of our respondents had enjoyed sauna at least once a week. Since the pandemic began, up to 23 % had reduced or stopped their bathing. This was often due to restricted sauna access. However, 11 % of respondents bathed more frequently and attributed this change to seeking relaxation and passing time. These findings demonstrate a surprising flexibility in this health-promoting national pastime. Men were more active bathers than women overall and women under 35 enjoy sauna more seldom than older women. Only 7.9 % of all respondents bathed at least four times a week, exceeding a suggested threshold for maximum health benefits.

CONCLUSIONS

Finnish people are active sauna bathers. The COVID-19 pandemic demonstrated that the frequency of bathing is dependent on good access to sauna facilities. This flexibility and wide access could be exploited to improve public health in the long term if more frequent bathing became a standard.

Does sauna bathing protect against dementia?

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Frequent sauna bathing predicted decreased risk of dementia in a cohort from Finland.

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Result was independent of several dementia risk factors, and was not modified by sex.

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Findings support suggested benefits of sauna and passive body heating in the brain.

Repeated heat exposure like sauna bathing is suggested to beneficially affect against dementia development. The epidemiological evidence is, however, scarce. Therefore, we studied the association between heat exposure during sauna bathing (i.e., the frequency of sauna bathing, frequency of heat sessions, length of stay in heat, sauna temperature) and the subsequent risk of dementia. A prospective cohort study was conducted based on 13,994 men and women aged 30–69 and free from dementia diagnosis from the Finnish Mobile Clinic Follow-up Survey. During a follow-up of 39 years, a total of 1805 dementia patients were diagnosed. The sauna bathing data was gathered from a questionnaire. Analyses based on the Cox model included the sauna bathing variables and the potential confounding factors. Sauna bathing frequency was related to a reduced risk of dementia after adjustment for the potential sociodemographic, lifestyle, and metabolic risk factors of dementia considered. The hazard ratio of dementia between individuals sauna bathing 9–12 times per month in comparison with those not sauna bathing or sauna bathing less than four times per month was 0.47 (95% CI = 0.25–0.88) during the first 20 years of follow-up and 0.81 (95% CI = 0.69–0.97) during the whole follow-up. The results are in line with the hypothesis that sauna bathing provides protection against dementia. Further studies are required to verify the suggested benefits of sauna bathing.

Acute Hemodynamic Responses to Combined Exercise and Sauna

This study investigated acute hemodynamic, plasma volume and immunological responses to four loading protocols: sauna only, and sauna after endurance, strength or combined endurance and strength exercise. Twenty-seven healthy, slightly prehypertensive men (age 32.7±6.9 years) were measured at PRE, MID (after exercise), POST, POST30min and POST24h. The measurements consisted systolic and diastolic blood pressure, heart rate, body temperature and concentrations of high-sensitive C-reactive protein, white blood cells and plasma volume measurements. Endurance+sauna showed significant decreases in systolic blood pressure at POST (–8.9 mmHg), POST30min (–11.0 mmHg) and POST24h (–4.6 mmHg). At POST30min, significant decreases were also observed in sauna (–4.3 mmHg) and combined+sauna (–7.5 mmHg). Diastolic blood pressure decreased significantly from -5.4 to –3.9 mmHg at POST in all loadings. Plasma volume decreased significantly at MID in all exercise loadings and at POST in endurance+sauna and strength+sauna. Plasma volume increased significantly (p < 0.01) in endurance+sauna and combined+sauna at POST24h. White blood cells increased following all exercise+sauna loadings at MID, POST and POST30min, whereas high sensitive C-reactive protein showed no changes at any measurement point. The combination of endurance exercise and sauna showed the greatest positive effects on blood pressure. Both loadings including endurance exercise increased plasma volume on the next day.