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Introduction Passive heat treatment has been suggested to improve glycemic control in individuals with type 2 diabetes mellitus (T2DM). Previous studies have focused predominantly on hot water immersion and traditional sauna bathing, as opposed to the more novel method of infrared-based sauna bathing. Here, the impact of a single infrared sauna session on post-prandial glycemic control was assessed in older individuals with T2DM. Methods In this randomized controlled crossover trial, 12 participants with T2DM (male/female: 10/2, age: 69±7 y, BMI: 27.5±2.9 kg/m2) rested in an infrared sauna twice: once in a heated (60°C) and once in a thermoneutral (21°C) condition for 40 min, immediately followed by a 2-h oral glucose tolerance test (OGTT). Venous blood samples were obtained to assess plasma glucose and insulin concentrations and to determine the whole-body composite insulin sensitivity index. Results Body core and leg skin temperature were higher following the heated condition compared to the thermoneutral condition (38.0±0.3 vs. 36.6±0.2°C and 39.4±0.8 vs. 31.3±0.8°C, respectively; P<0.001 for both). The incremental area under the curve (iAUC) of plasma glucose concentrations during the OGTT was higher after the heated condition compared to the thermoneutral condition (17.7±3.1 vs. 14.8±2.8 mmol/L/120 min; P<0.001). No differences were observed in plasma insulin concentrations (heated: 380±194 vs. thermoneutral: 376±210 pmol/L/120 min; P=0.93) or whole-body composite insulin sensitivity indexes (4.5±2.8 vs. 4.5±2.1; P=0.67). Conclusions A single infrared sauna session does not improve postprandial blood glucose handling in individuals with T2DM. Future studies should assess the effect of more prolonged application of infrared sauna bathing on daily glycemic control. [ABSTRACT FROM AUTHOR]

Combat sports athletes often undergo rapid body mass loss (BML), which presents health risks. Hydration testing has been proposed as a possible solution to reduce or eliminate rapid BML. However, combat sports athletes may exhibit distinct physiological characteristics due to repeated exposure to BML. Thus, traditional and emerging hydration biomarkers should be investigated to determine their potential suitability for field use in this cohort. This study examined whether BML can explain changes in serum and urine osmolality (SosmΔ, UosmΔ), tear osmolarity (TosmΔ), hematocrit (HctΔ), and urine‐specific gravity (USGΔ) after mild–moderate passive dehydration. Biomarker reliability was also assessed across two trials. Fifteen male and female combat sports athletes (age: 26.3 ± 5.3 years, body mass: 67.7 ± 9.9 kg) underwent a sauna protocol twice (5–28 days apart) aiming for 4% BML. The average BML in Trials 1 and 2 was 3.0 ± 0.7%. Regression analysis revealed that BML explained HctΔ (R2 = 0.22, p = 0.009) but not SosmΔ (R2 = 0.11, p = 0.079) or other biomarkers. Intraclass correlation coefficients (ICCs) were significant for all biomarkers except TosmΔ (ICC = 0.06, p = 0.37) and post‐Tosm (ICC = 0.04, p = 0.42); post‐Hct performed best (ICC = 0.82, p < 0.001). Contingency tables with post‐Sosm (295 mOsm/kg) and post‐USG (1.020) cutoffs revealed an 80% true negative rate (TNR) and a 62% true positive rate (TPR). Increasing the Sosm cutoff to 301 mOsm/kg decreased the TNR to 52% but increased the TPR to 83%. Although blood parameters were most sensitive to BML, they could only explain 11%–22% of biomarker variation. The typical USG cutoff misclassified 42% of athletes postdehydration, and reliability was generally poor‐moderate. Alternative strategies should be pursued to manage rapid BML in combat sports. [ABSTRACT FROM AUTHOR]

Air-source heat pumps (ASHPs), as an active device, are widely used in building heating and cooling processes. However, in severe cold regions, they face reduced heating efficiency and frosting problems in winter. This paper proposes a new heating solution by coupling an ASHP with passive heating systems. It combines an ASHP with passive sunrooms and heat storage systems for heating. Through software simulations and mathematical modeling, the new scheme is compared and analyzed against traditional ASHP solutions to explore the performance of this scheme in rural houses in severe cold regions of China during winter. According to simulation and calculation analysis, on the coldest day of winter, the coupling scheme can provide approximately 99.41 kWh of heat to the indoors, which exceeds the 86.67 kWh required to maintain an indoor temperature of 20 °C. The system's power consumption is 36.96 kWh, which is 66.88% lower than that of traditional heat pump heating. The study shows that the coupling system of an ASHP and passive heating has a good heating effect in severe cold regions. For the situation of insufficient solar energy at night, the design of phase-change materials and heat storage media can meet heating needs throughout the day. [ABSTRACT FROM AUTHOR]

Pre-exercise passive heating attenuates muscle damage caused by eccentric exercise in rats where the induction of heat shock proteins (HSPs) confers a myoprotective effect. We investigated whether pre-exercise hot water immersion (HWI) confers similar benefits in humans. Eleven recreational male athletes were immersed in 41°C water up to 60 min or until rectal temperatures reached 39.5°C. After a 6 h rest, the participants performed an eccentric downhill run for 1 h at −4% gradient to induce muscle damage. An endurance capacity test at 75% VO2max was conducted 18 h later. The control trial was similar except that participants were immersed at 34°C. Blood samples were collected to assess HSPs levels, creatine kinase, and lactate dehydrogenase activities. Plasma eHSP70 was higher post-immersion in HWI trials (1.3 ± 0.4 vs 1.1 ± 0.4; p = 0.005). Plasma eHSP27 was higher before (p = 0.049) and after (p = 0.015) endurance test in HWI. Leukocytic p-HSP27 was increased 18 h after HWI (0.97 ± 0.14 vs 0.67 ± 0.11; p = 0.04). Creatine kinase and lactate dehydrogenase activities were increased by 3-fold and 1.5-fold, respectively, after endurance test in HWI but did not differ across trials (p > 0.05). Mean heart rates were higher during eccentric run and endurance test in HWI as compared to control (p < 0.05). Endurance capacity was similar between trials (57.3 ± 11.5 min vs 55.0 ± 13.5 min; p = 0.564). Pre-exercise heating increased the expression of plasma eHSPs and leukocytic p-HSP27 but did not reduce muscle damage nor enhance endurance capacity. [ABSTRACT FROM AUTHOR]

Purpose: Soccer substitutes are exposed to periods of limited activity before entering match-play, likely negating benefits of active warm-ups. This study aimed to determine the effects of using a passive heat intervention following a pre-match, and half-time warm-up, on muscle and core temperature in soccer players during ambient (18 °C) and cold (2 °C) conditions. Methods: On four occasions, 8 male players, completed a pre-match warm-up, followed by 45 min of rest. Following this, participants completed a half-time re-warm-up followed by an additional 45 min of rest, simulating a full match for an unplaying substitute. During periods of rest, participants wore either standardised tracksuit bottoms (CON), or heated trousers (HEAT), over typical soccer attire. Results: Vastus lateralis temperature declined less in HEAT compared to CON following the 1st half in 2 °C (Δ − 4.39 ± 0.81 vs. − 6.21 ± 1.32 °C, P = 0.002) and 18 °C (Δ − 2.48 ± 0.71 vs. − 3.54 ± 0.88 °C, P = 0.003). These findings were also observed in the 2nd half for the 2 °C (Δ − 4.36 ± 1.03 vs. − 6.26 ± 1.04 °C, P = 0.002) and 18 °C (Δ − 2.85 ± 0.57 vs. − 4.06 ± 1 °C, P = 0.018) conditions. In addition, core temperature declined less in HEAT compared to CON following the 1st (Δ − 0.41 ± 0.25 vs. − 0.84 ± 0.41 °C, P = 0.037) and 2nd (Δ − 0.25 ± 0.33 vs. − 0.64 ± 0.34 °C, P = 0.028) halves of passive rest in 2 °C, with no differences in the 18 °C condition. Perceptual data confirmed that participants were more comfortable in HEAT vs. CON in 2 °C (P < 0.01). Conclusions: Following active warm-ups, heated trousers attenuate the decline in muscle temperature in ambient and cold environments. [ABSTRACT FROM AUTHOR]

This study aims to evaluate the energy-saving potential of passive solar heating systems in diverse global climates and introduce a new indicator, the passive solar heating indicator (PSHI), to enhance the efficiency of building designs. By collecting climate data from 600 cities worldwide through a simulation model, the present study employs polynomial regression to analyze the impact of outdoor temperature and solar radiation intensity on building energy savings. It also uses K-means cluster analysis to scientifically categorize cities based on their energy-saving potential. The findings underscore the benefits of both direct and indirect solar heating strategies in different climates. Significantly, the PSHI shows superior predictive accuracy and applicability over traditional indices, such as the irradiation temperature difference ratio (ITR) and the irradiation degree hour ratio (C-IDHR), especially when outdoor temperatures are close to indoor design temperatures. Moreover, the application of a cluster analysis provides hierarchical guidance on passive heating designs globally, paving the way for more accurate and customized energy-efficient building strategies. [ABSTRACT FROM AUTHOR]

Objective: We examined sex‐specific microvascular reactivity and hemodynamic responses under conditions of augmented resting blood flow induced by passive heating compared to normal blood flow. Methods: Thirty‐eight adults (19 females) completed a vascular occlusion test (VOT) on two occasions preceded by rest with or without passive heating in a randomized, counterbalanced order. Skeletal muscle tissue oxygenation (StO2, %) was assessed with near‐infrared spectroscopy (NIRS), and the rate of desaturation and resaturation as well as maximal StO2 (StO2max) and prolonged hypersaturation (area under the curve, StO2AUC) were quantified. Before the VOT, brachial artery blood flow (BABF), vascular conductance, and relative BABF (BABF normalized to forearm lean mass) were determined. Sex × condition ANOVAs were used. A p‐value ≤.05 was considered statistically significant. Results: Twenty minutes of heating increased BABF compared to the control (102.9 ± 28.3 vs. 36.0 ± 20.9 mL min−1; p <.01). Males demonstrated greater BABF than females (91.9 ± 34.0 vs. 47.0 ± 19.1 mL min−1; p <.01). There was no sex difference in normalized BABF. There were no significant interactions for NIRS‐VOT outcomes, but heat did increase the rate of desaturation (−0.140 ± 0.02 vs. −0.119 ± 0.03% s−1; p <.01), whereas regardless of condition, males exhibited greater rates of resaturation and StO2max than females. Conclusions: These results suggest that blood flow is not the primary factor causing sex differences in NIRS‐VOT outcomes. [ABSTRACT FROM AUTHOR]

The world is experiencing increased frequency, duration, and severity of life-threatening heat extremes. Most hospitalizations and excess deaths during extreme heat events are associated with preexisting diseases in older adults. As climate change persists, the global population ages and the number of individuals with chronic diseases expands, more people are at risk of adverse health outcomes during extreme heat events. Therefore, proactive preventive measures are urgently needed to mitigate heat-related health risks within these populations. In this context, passive heat therapy (e.g., hot baths, saunas, and water-perfused suits) emerges as a promising countermeasure to improve physiological resilience to a warming planet. Passive heating improves cardiovascular function and overall health in older adults and individuals living with chronic diseases, offering the prospect of reducing cardiovascular strain during hotter days. Moreover, some studies suggest that passive heat therapy can be an effective strategy for heat acclimation (i.e., improved thermoregulation). This review describes the existing literature on the effects of passive heat therapy on cardiovascular and thermoregulatory responses in individuals with higher heat-related health risks and explores the use of passive heating as a strategy for heat acclimation to mitigate health risks during extreme heat events. NEW & NOTEWORTHY: Passive heat therapy improves cardiovascular function and health in middle-aged and older adults living with or without chronic diseases. In addition, preliminary studies indicate that passive heat interventions can induce heat acclimation, improving thermoregulatory responses. Thus, passive heat therapy could serve as a preventive measure for people at risk of adverse health outcomes during extreme heat events, improving resilience to ongoing climate change. [ABSTRACT FROM AUTHOR]

Exercise and passive heating induce some similar vascular hemodynamic, circulating blood marker, and perceptual responses. However, it remains unknown whether post exercise hot water immersion can synergise exercise derived responses and if they differ from hot water immersion alone. This study investigated the acute responses to post moderate‐intensity exercise hot water immersion (EX+HWI) when compared to exercise (EX+REST) and hot water immersion (HWI+HWI) alone. Sixteen physically inactive middle‐aged adults (nine males and seven females) completed a randomized cross‐over counterbalanced design. Each condition consisted of two 30‐min bouts separated by 10 min of rest. Cycling was set at a power output equivalent to 50% V̇o2 peak. Water temperature was controlled at 40°C up to the mid sternum with arms not submerged. Venous blood samples and artery ultrasound scans were assessed at 0 (baseline), 30 (immediately post stressor one), 70 (immediately post stressor two), and 100 min (recovery). Additional physiological and perceptual measures were assessed at 10‐min intervals. Brachial and superficial femoral artery shear rates were higher after EX+HWI and HWI+HWI when compared with EX+REST (p < 0.001). Plasma nitrite was higher immediately following EX+HWI and HWI+HWI than EX+REST (p < 0.01). Serum interleukin‐6 was higher immediately after EX+HWI compared to EX+REST (p = 0.046). Serum cortisol was lower at 30 min in the HWI+HWI condition in contrast to EX+REST (p = 0.026). EX+HWI and HWI+HWI were more enjoyable than EX+REST (p < 0.05). Irrespective of whether hot water immersion proceeded exercise or heating, hot water immersion enhanced vascular and blood marker responses, while also being more enjoyable than exercise alone. [ABSTRACT FROM AUTHOR]

Whether glucose concentration increases during heat exposure because of reduced peripheral tissue uptake or enhanced appearance is currently unknown. This study aimed to report glucose concentrations in both capillary and venous blood in response to a glucose challenge during passive heating (PH) to assess whether heat exposure affects glucose uptake in healthy males. Twelve healthy male participants completed two experimental sessions, where they were asked to undertake an oral glucose tolerance test (OGTT) whilst immersed in thermoneutral (CON, 35.9 (0.6) °C) and hot water (HWI, 40.3 (0.5) °C) for 120 min. Venous and capillary blood [glucose], rectal temperature, and heart rate were recorded. [Glucose] area under the curve for HWI venous (907 (104) AU) differed from CON venous (719 (88) AU, all P < 0.001). No other differences were noted (P > 0.05). Compared with CON, HWI resulted in greater rectal temperature (37.1 (0.3) °C versus 38.6 (0.4) °C, respectively) and heart rate (69 (12) bpm versus 108 (11) bpm, respectively) on cessation (P < 0.001). An OGTT results in similar capillary [glucose] during hot and thermoneutral water immersion, whereas venous [glucose] was greater during HWI when compared with CON. This indicates that peripheral tissue glucose uptake is acutely reduced in response to HWI. Abbreviations: AUC: Area under the curve; CON: Thermoneutral immersion trial; HWI: Hot water immersion trial; OGTT: Oral glucose tolerance test; PH: Passive heating; $${\bar T_{{\rm{msk}}}}$$ T ˉ m s k : Mean skin temperature; Trec: Rectal temperature [ABSTRACT FROM AUTHOR]

Purpose: Rowers can be in marshaling areas for up to 20 to 25 min before the start of a race, which likely negates any benefits of an active warm-up, especially in cold environments. It is unknown if using a heated jacket following a standardized rowing warm-up can improve 2000-m rowing performance. Methods: On 2 separate occasions, 10 trained male rowers completed a standardized rowing warm-up, followed by 25 min of passive rest before a 2000-m rowing time trial on a rowing ergometer. Throughout the passive rest, the participants wore either a standardized tracksuit top (CON) or an externally heated jacket (HEAT). The trials, presented in a randomized crossover fashion, were performed in a controlled environment (temperature 8°C, humidity 50%). Rowing time-trial performance, core body temperature, and mean skin temperature, along with perceptual variables, were measured. Results: During the 25-min period, core body temperature increased in HEAT and decreased in CON (Δ0.54°C [0.74°C] vs −0.93°C [1.14°C]; P =.02). Additionally, mean skin temperature (30.22°C [1.03°C] vs 28.86°C [1.07°C]) was higher in HEAT versus CON (P <.01). In line with the physiological data, the perceptual data confirmed that participants were more comfortable in HEAT versus CON, and subsequently, rowing performance was improved in HEAT compared with CON (433.1 [12.7] s vs 437.9 [14.4] s, P <.01). Conclusion: The data demonstrate that an upper-body external heating garment worn following a warm-up can improve rowing performance in a cool environment. [ABSTRACT FROM AUTHOR]

Purpose: Examine the effects of 42°C hot‐water immersion on muscle contraction function and motor unit discharge rates. Voluntary and evoked contraction assessments were examined first with a concomitant increase in the core and muscle temperature, and thereafter with increased muscle temperature but cooled core temperature. Methods: Fifteen participants (24.9 ± 5.6 years) performed neuromuscular assessments before, after, and ~15‐min after either 90‐min of 42°C (hot) or 36°C (control) water immersion. Maximal voluntary contraction (MVC) assessment of knee extension was performed along with surface electromyography (sEMG) (vastus lateralis and medialis [VL, VM]) and voluntary activation level (VAL). Resting evoked twitch was elicited for peak torque and time to peak torque analysis. In addition, the VL and VM motor unit discharge rates (MUDR) were measured. Results: After hot‐water immersion (core temperature ↑1°C; muscle temperature ↑2.4°C), MVC torque and VAL decreased (p < 0.05). The sEMG (VL and VM) and peak twitch torque did not change (p > 0.05), while time to peak torque decreased (p = 0.007). The VL and VM MUDR decreased, showing a time effect, after both water immersion conditions (36 and 42°C) (p > 0.001). Fifteen minutes after the hot‐water immersion (core temperature at baseline; muscle temperature ↑1.4°C), MVC torque returned to baseline, but VAL remained lower. The sEMG (VL and VM) remained unchanged. Peak twitch torque increased (p < 0.002) and time to peak torque remained lower (p = 0.028). The MUDR remained lower after both water immersion conditions (p < 0.05). Conclusion: Increased core temperature evoked by 42°C hot‐water immersion decreases MVC torque and VAL. However, a passive increase in muscle temperature improved evoked muscle contractile function (i.e., time to peak torque [after] and peak twitch torque [~15 min after]). Moreover, a passive increase in muscle temperature reduced the required MUDR to attain the same torque. [ABSTRACT FROM AUTHOR]

The current global energy challenges require strategies to increase energy-independence across regions and individual countries in order to facilitate and foster the utilization of passive energy sources. As such, solar energy utilization for covering and offsetting building heating loads is a sustainable way to reduce energy consumption (electricity, gas etc.) for space heating. Trombe wall technology is a passive building solar heating system that can be modified and applied to mild and cold regions. This work presents a review of Trombe wall system's feasibility and applications across different climatic regions. Trombe wall systems are applicable as a secondary space heating source in mid-sunshine and cold regions. However, a number of design and structural aspects must be thoroughly considered, including the incorporation of PCMs, and the integration of PV/BIPV elements and other performance-improving aspects to enhance the system's thermal performance and output. The findings of this work can be used in potential future assessments of the Trombe wall system's technology in different climatic regions. [ABSTRACT FROM AUTHOR]

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Passive hyperthermia induces a range of physiological responses including augmenting skeletal muscle mRNA expression. This experiment aimed to examine gene and protein responses to prolonged passive leg hyperthermia. Seven young participants underwent 3 h of resting unilateral leg heating (HEAT) followed by a further 3 h of rest, with the contralateral leg serving as an unheated control (CONT). Muscle biopsies were taken at baseline (0 h), and at 1.5, 3, 4, and 6 h in HEAT and 0 and 6 h in CONT to assess changes in selected mRNA expression via qRT-PCR, and HSP72 and VEGFα concentration via ELISA. Muscle temperature (Tm) increased in HEAT plateauing from 1.5 to 3 h (+ 3.5±1.5°C from 34.2±1.2°C baseline value; P < 0.001), returning to baseline at 6 h. No change occurred in CONT. Endothelial nitric oxide synthase (eNOS), Forkhead box O1 (FOXO-1), Hsp72, and VEGFα mRNA increased in HEAT (P < 0.05); however, post hoc analysis identified that only Hsp72 mRNA statistically increased (at 4 h vs. baseline). When peak change during HEAT was calculated angiopoietin 2 (ANGPT-2) decreased (-0.4 ± 0.2-fold), and C-C motif chemokine ligand 2 (CCL2) (+ 2.9±1.6-fold), FOXO-1 (+ 6.2±4.4-fold), Hsp27 (+ 2.9 ± 1.7-fold), Hsp72 (+ 8.5±3.5-fold), Hsp90a (+ 4.6±3.7-fold), and VEGFα (+ 5.9 ±3.1-fold) increased from baseline (all P < 0.05). At 6 h Tm were not different between limbs (P = 0.582; CONT = 32.5±1.6°C, HEAT = 34.3±1.2°C), and only ANGPT-2 (P = 0.031; -1.3±1.4-fold) and VEGFα (P = 0.030; 1.1 ±1.2-fold) differed between HEAT and CONT. No change in VEGFα or HSP72 protein concentration were observed over time; however, peak change in VEGFα did increase (P < 0.05) in HEAT (+140±184 pg·mL-1) versus CONT (+ 7±86 pg·mL-1). Passive hyperthermia transiently augmented ANGPT-2, CCL2, eNOS, FOXO-1, Hsp27, Hsp72, Hsp90a and VEGFα mRNA, and VEGFα protein. [ABSTRACT FROM AUTHOR]

Declines in muscle force, power, and contractile function can be observed in older adults, clinical populations, inactive individuals, and injured athletes. Passive heating exposure (e.g., hot baths, sauna, or heated garments) has been used for health purposes, including skeletal muscle treatment. An acute increase in muscle temperature by passive heating can increase the voluntary rate of force development and electrically evoked contraction properties (i.e., time to peak twitch torque, half-relation time, and electromechanical delay). The improvements in the rate of force development and evoked contraction assessments with increased muscle temperature after passive heating reveal peripheral mechanisms' potential role in enhancing muscle contraction. This review aimed to summarise, discuss, and highlight the potential role of an acute passive heating stimulus on skeletal muscle cells to improve contractile function. These mechanisms include increased calcium kinetics (release/reuptake), calcium sensitivity, and increased intramuscular fluid. [ABSTRACT FROM AUTHOR]

Trombe walls provide a passive source of heating and ventilation for buildings. However, Trombe walls can also cause overheating during hot and sunny weather conditions. In this work, we investigate the potential of a multifunctional Trombe wall design, comprising a tinted acrylic sheet submerged in a water wall that functions as a thermal storage medium. The tinted acrylic sheet absorbs incident light, which is then converted to heat and absorbed by the water. The proposed Trombe wall can function as a tinted semi-transparent window to add aesthetic value. Furthermore, heated water rises to the top of the Trombe wall where it can be removed, which provides the dual benefit of preventing overheating and providing a source of preheated water for applications within the building. Experimental results performed on a laboratory-scale Trombe wall prototype showed that the percentage of solar-simulated light energy incident onto the Trombe wall prototype, over a period of five hours, that was stored as thermal energy in the water increased from 60.3% to 83.2% when tinted glass was inserted in the water storage wall. Furthermore, the temperature of the water at the top of the Trombe wall reached ~56 °C, which is suitable to be used as pre-heated water in building applications. [ABSTRACT FROM AUTHOR]

This investigation assessed the psycho-physiological and performance effects of hot water immersion (HWI) implemented either before or after a repeated-sprint training in hypoxia (RSH) session conducted in the heat. Ten participants completed three RSH trials (3 × 10 × 5-s sprints), conducted at 40°C and simulated altitude of 3000 m. A 30-min monitoring period preceded and followed all exercise sessions. In PRE, the pre-exercise period was HWI, and the post-exercise period was seated rest in temperate conditions. This combination was reversed in POST. In CON, participants were seated in temperate conditions for both periods. Compared to CON, PRE elicited a reduction in power output during each repeated-sprint set (14.8–16.2%, all p < 0.001), and a significantly higher core temperature (Tc) during the pre-exercise period and throughout the exercise session (p < 0.001 and p = 0.025, respectively). In POST, power output and Tc until the end of exercise were similar to CON, with Tc higher at the conclusion of the post-exercise period (p < 0.001). Time across the entire protocol spent ≥38.5°C Tc was significantly longer in PRE (48.1 ± 22.5 min) than POST (31.0 ± 11.3 min, p = 0.05) and CON (15.8 ± 16.3 min, p < 0.001). Employing HWI following RSH conducted in the heat provides effective outcomes regarding physiological strain and cycling performance when compared to pre-exercise or no HWI. [ABSTRACT FROM AUTHOR]

Background: Prior to exercise, a warm-up routine has been suggested to be an imperative factor in task readiness with the anticipation that it will enhance performance. One of the key benefits of a warm-up is the increase in muscle and core temperature, which can be achieved in a variety of ways. An effective way to achieve improvements in core and muscle temperature is by performing an active warm-up. However, lengthy transition periods between an active warm-up and exercise performance are known to cause a decline in core and muscle temperature, thereby reducing performance capability. As such, methods are needed to assist athletes during transition periods, to maintain the benefits of a warm-up with the aim of optimising performance. Accordingly, the purpose of this review is to systematically analyse the evidence base that has investigated the use of passive heating to aide sporting performance when a transition period is experienced. Methods: A systematic review and meta-analysis were undertaken following relevant studies being identified using PubMed, Web of Science, and EBSCO. Studies investigating the effects of passive heating strategies during the transition period between an active warm-up and exercise performance were included. The quality of the included studies were assessed by two independent reviewers using a modified version of the Physiotherapy Evidence Database scale. Results: Seven studies, all high quality (mean = 7.6), reported sufficient data (quality score > 5) on the effects of passive heating strategies on exercise performance, these studies consisted of 85 well-trained athletes (78 male and 7 female). Passive heating strategies used between an active warm-up and exercise, significantly increased peak power output in all studies (ES = 0.54 [95% CI 0.17 to 0.91]). However, only a favourable trend was evident for exercise performance (ES = 1.07 [95% CI − 0.64 to 0.09]). Conclusions: Based upon a limited number of well-conducted, randomised, controlled trials, it appears that passive heating strategies used between an active warm-up and exercise have a positive impact on peak power output. Although, additional research is necessary to determine the optimum procedure for passive warm-up strategies. [ABSTRACT FROM AUTHOR]

Trombe walls figure among many passive devices used in the Mediterranean climate to minimize heating demands in residential buildings. The thickness of this massive wall is a critical parameter that influences the effectiveness of the system. Insufficient wall thickness conducts to an important interior temperature fluctuation, and huge wall thickness will increase costs and thermal resistance. In this paper, the optimum thickness of four different construction materials (concrete, stone, adobe, and brick), which can be used in the Trombe wall, was determined using an energetic and economic analysis. The energetic results with TRNSYS software show that the best materials, which can contribute to a reduction by 50% in heating loads of a single room, are stone and concrete. For the economic analysis, the life cycle cost and the payback period were calculated for each construction material. The results show that the optimum thickness for stone and concrete are, respectively, 34 and 32 cm with a payback period of 2.85 and 2.65 years. [ABSTRACT FROM AUTHOR]

Passive hot water immersion (PHWI) provides a peripheral vasculature shear stimulus comparable to low-intensity exercise within the active skeletal muscle, whereas moderate- and high-intensity exercise elicit substantially greater shear rates in the peripheral vasculature, likely conferring greater vascular benefits. Notably, few studies have compared postintervention shear rates in the peripheral and cerebral vasculature after high-intensity exercise and PHWI, especially considering that the postintervention recovery period represents a key window in which adaptation occurs. Therefore, we aimed to compare shear rates in the internal carotid artery (ICA), vertebral artery (VA), and common femoral artery (CFA) between high-intensity exercise and whole body PHWI for up to 80 min after intervention. Fifteen healthy (27 ± 4 yr), moderately trained individuals underwent three time-matched interventions in a randomized order that included 30 min of whole body immersion in a 42°C hot bath, 30 min of treadmill running and 5 × 4-min high-intensity intervals (HIIE). There were no differences in ICA (P = 0.4643) and VA (P = 0.1940) shear rates between PHWI and exercise (both continuous and HIIE) after intervention. All three interventions elicited comparable increases in CFA shear rate after intervention (P = 0.0671); however, CFA shear rate was slightly higher 40 min after threshold running (P = 0.0464) and slightly higher, although not statistically, for HIIE (P = 0.0565) compared with PHWI. Our results suggest that timeand core temperature-matched high-intensity exercise and PHWI elicit limited changes in cerebral shear and comparable increases in peripheral vasculature shear rates when measured for up to 80 min after intervention. [ABSTRACT FROM AUTHOR]

Impaired endothelial insulin signaling and consequent blunting of insulin-induced vasodilation is a feature of type 2 diabetes (T2D) that contributes to vascular disease and glycemic dysregulation. However, the molecular mechanisms underlying endothelial insulin resistance remain poorly known. Herein, we tested the hypothesis that endothelial insulin resistance in T2D is attributed to reduced expression of heat shock protein 72 (HSP72). HSP72 is a cytoprotective chaperone protein that can be upregulated with heating and is reported to promote insulin sensitivity in metabolically active tissues, in part via inhibition of JNK activity. Accordingly, we further hypothesized that, in individuals with T2D, 7 days of passive heat treatment via hot water immersion to waist level would improve leg blood flow responses to an oral glucose load (i.e., endogenous insulin stimulation) via induction of endothelial HSP72. In contrast, we found that: 1) endothelial insulin resistance in T2D mice and humans was not associated with reduced HSP72 in aortas and venous endothelial cells, respectively; 2) after passive heat treatment, improved leg blood flow responses to an oral glucose load did not parallel with increased endothelial HSP72; and 3) downregulation of HSP72 (via small-interfering RNA) or upregulation of HSP72 (via heating) in cultured endothelial cells did not impair or enhance insulin signaling, respectively, nor was JNK activity altered. Collectively, these findings do not support the hypothesis that reduced HSP72 is a key driver of endothelial insulin resistance in T2D but provide novel evidence that lower-body heating may be an effective strategy for improving leg blood flow responses to glucose ingestion-induced hyperinsulinemia. [ABSTRACT FROM AUTHOR]

Background: Many significant ecosystems, including important non-forest woody ecosystems such as the Cerrado (Brazilian savannah), are under threat from climate change, yet our understanding of how increasing temperatures will impact native vegetation remains limited. Temperature manipulation experiments are important tools for investigating such impacts, but are often constrained by access to power supply and limited to low-stature species, juvenile individuals, or heating of target organs, perhaps not fully revealing how entire or mature individuals and ecosystems will react to higher temperatures. Results: We present a novel, modified open top chamber design for in situ passive heating of whole individuals up to 2.5 m tall (but easily expandable) in remote field environments with strong solar irradiance. We built multiple whole-tree heating structures (WTHSs) in an area of Cerrado around native woody species Davilla elliptica and Erythroxylum suberosum to test the design and its effects on air temperature and humidity, while also studying the physiological responses of E. suberosum to short-term heating. The WTHSs raised internal air temperature by approximately 2.5 °C above ambient during the daytime. This increased to 3.4 °C between 09:00 and 17:00 local time when thermal impact was greatest, and during which time mean internal temperatures corresponded closely with maximum ambient temperatures. Heating was consistent over time and across WTHSs of variable size and shape, and they had minimal effect on humidity. E. suberosum showed no detectable response of photosynthesis or respiration to short-term experimental heating, but some indication of acclimation to natural temperature changes. Conclusions: Our WTHSs produced a consistent and reproducible level of daytime heating in line with mid-range climate predictions for the Cerrado biome by the end of the century. The whole-tree in situ passive heating design is flexible, low-cost, simple to build using commonly available materials, and minimises negative impacts associated with passive chambers. It could be employed to investigate the high temperature responses of many understudied species in a range of complex non-forest environments with sufficient solar irradiance, providing new and important insights into the possible impacts of our changing climate. [ABSTRACT FROM AUTHOR]

In this study, a passive solar house prototype was built using Trombe wall and was tested in the semi-arid region of Batna, in eastern Algeria. Traditional local materials (stone and adobe) were used for the construction of the thermal storage wall. A new local bio-based material made from date palm trunks was used for the insulation of the passive house prototype. For a better understanding of passive house heating and for a comparative study, a numerical simulation, using Fluent, was carried out. The aim of this study was to supply recommendations for improving the passive systems and to participate to the energy consumption control in the building sector. The results show that the experimental and numerical simulation results are in good agreement. The optimal orientation of the solar passive house has been determined, which is at 160° southeast. The use of local and bio-based materials has proven its effectiveness in the construction of the passive house. The thermal behavior of date palm wood has been found to be close to those of insulation materials commonly used in buildings. That means it has the same thermal insulation ability (thermal conductivity). On the other hand, the results show that the thermal efficiency of the passive solar heating system, with an adobe wall is significantly higher (50%) than that with a stone wall (30.7%). [ABSTRACT FROM AUTHOR]

Aerobic exercise induces mast cell degranulation and increases histamine formation by histidine decarboxylase, resulting in an ~150% increase in intramuscular histamine. The purpose of this study was to determine if the increase in skeletal muscle temperature associated with exercise is sufficient to explain this histamine response. Specifically, we hypothesized that local passive heating that mimics the magnitude and time course of changes in skeletal muscle temperature observed during exercise would result in increased intramuscular histamine concentrations comparable to exercising values. Seven subjects participated in the main study in which pulsed short-wave diathermy was used to passively raise the temperature of the vastus lateralis over 60 min. Heating increased intramuscular temperature from 32.6°C [95% confidence interval (CI) 32.0°C to 33.2°C] to 38.9°C (38.7°C to 39.2°C) (P < 0.05) and increased intramuscular histamine concentration from 2.14 ng/mL (1.92 to 2.36 ng/mL) to 2.97 ng/mL (2.57 to 3.36 ng/mL) (P < 0.05), an increase of 41%. In a follow-up in vitro experiment using human-derived cultured mast cells, heating to comparable temperatures did not activate mast cell degranulation. Therefore, it appears that exercise-associated changes in skeletal muscle temperature are sufficient to generate elevations in intramuscular histamine concentration. However, this thermal effect is most likely due to changes in de novo histamine formation via histidine decarboxylase and not due to degranulation of mast cells. In conclusion, physiologically relevant increases in skeletal muscle temperature explain part, but not all, of the histamine response to aerobic exercise. This thermal effect may be important in generating positive adaptations to exercise training. [ABSTRACT FROM AUTHOR]

A dual-channel solar thermal storage wall system with eutectic phase change material is studied. The full-day cooling load in summer and heating load in winter can be both decreased by this novel system. To investigate the airflow in the dual channel, mixed area assumptions based on the experimental results are summarized. Dynamic mathematical models of the system under four work modes are established and verified by the experimental results. The average RMSD (root mean square deviation) value is 0.35% in summer and 0.95% in winter. By analyzing the heat flux, the combination of dual channel and PCM is proven to decrease and delay cooling load both in the daytime and nighttime of summer. In winter's daytime, the thermal efficiency is promoted by the dual channel. And in winter's nighttime, the system is able to heat the room constantly by the PCM boards. Based on parameter researches, the optimum phase change temperature range and the optimum thickness of the PCM are 26–30 °C, 1.5 cm in summer and 16–22 °C, 0.6 cm in winter respectively. To reach the optimum annual thermal performance, the coverage area is 2 m2 for this system. [ABSTRACT FROM AUTHOR]

Purpose: We examined whether eccrine sweat glands ion reabsorption rate declined with age in 35 adults aged 50–84 years. Aerobic fitness (VO2max) and salivary aldosterone were measured to see if they modulated ion reabsorption rates. Methods: During a passive heating protocol (lower leg 42 °C water submersion) the maximum ion reabsorption rates from the chest, forearm and thigh were measured, alongside other thermophysiological responses. The maximum ion reabsorption rate was defined as the inflection point in the slope of the relation between galvanic skin conductance and sweat rate. Results: The maximum ion reabsorption rate at the forearm, chest and thigh (0.29 ± 0.16, 0.33 ± 0.15, 0.18 ± 0.16 mg/cm2/min, respectively) were weakly correlated with age (r ≤ − 0.232, P ≥ 0.05) and salivary aldosterone concentrations (r ≤ − 0.180, P ≥ 0.179). A moderate positive correlation was observed between maximum ion reabsorption rate at the thigh and VO2max (r = 0.384, P = 0.015). Salivary aldosterone concentration moderately declined with age (r = − 0.342, P = 0.021). Whole body sweat rate and pilocarpine-induced sudomotor responses to iontophoresis increased with VO2max (r ≥ 0.323, P ≤ 0.027) but only moderate (r = − 0.326, P = 0.032) or no relations (r ≤ − 0.113, P ≥ 0.256) were observed with age. Conclusion: The eccrine sweat glands' maximum ion reabsorption rate is not affected by age, spanning 50–84 years. Aldosterone concentration in an aged cohort does not appear to modulate the ion reabsorption rate. We provide further support for maintaining cardiorespiratory fitness to attenuate any decline in sudomotor function. [ABSTRACT FROM AUTHOR]

The thermoneutral zone (TNZ) defines the range of ambient temperatures at which resting metabolic rate (MR) is at a minimum. While the TNZ lower limit has been characterized, it is still unclear whether there is an upper limit, that is, beyond which MR during rest increases, and if so, what physiological upregulations explain this. We take the first step to fill this knowledge gap by measuring MR and multiple physiological variables in participants exposed to ambient heat stress while resting. Thirteen participants were exposed for an hour to 28℃‐50% relative humidity (RH) air, and both 40 and 50℃ each in 25% RH and humid (50% RH) conditions. Core and skin temperatures, blood pressure, sweat‐, heart‐, and breathing‐rate, minute ventilation, and movement levels were recorded throughout each condition. MR increased 35% (p =.015) during exposure to 40℃‐25% RH compared to baseline and a further 13% (p =.000) at in 50℃‐50%RH. This was not explained by increased fidgeting (p =.26), suggesting physiological upregulation. However, while greater heat stress invoked increases in heart rate (64%, p =.000), minute ventilation (78%, p =.000), and sweat rate (74%. p =.000) when comparing 50℃‐50% RH with baseline, the exact size of their relative energy cost is unclear and, therefore, so is their contribution to this increase in MR. Our study shows clear evidence that resting MR increases in humans at high temperature—there is a metabolic upper critical temperature, at least as low as 40℃. Further studies should pinpoint this value and fully explain this increased MR. [ABSTRACT FROM AUTHOR]

China's rural houses are mostly courtyard-style independent houses. Such houses have certain characteristics, e.g., small mutual influences between houses, strong transformation flexibility, and an easier approach to using the natural environment to develop passive energy-saving characteristics. Therefore, rural houses have large energy-saving potential. In this study, for the first time, the cold alleys between buildings were used as an energy source for passive cooling and ventilation. Traditional houses in Shuhe, China, were used as a case study. The cold alleys in the settlements were used to compensate for the natural conditions in summer, and the cold air in the cold alley was introduced into each room using hot-press ventilation and by employing an accumulation effect from a corresponding patio. The room was ventilated and cooled, and air ducts were used to connect the rooms on both sides of the patio to improve the cooling efficiency. The research variables included the existence or non-existence of wall heat radiation (WHR), and the importance and influence of the WHR on the indoor conditions were verified. The cold air trapped in the new system formed an air partition wall, effectively blocking the direct influence of solar radiation on the room, reducing the heat transfer rate of the residential wall, and consuming part of the heat. In winter, based on using air ducts as supporting members, a glass roof was added to the patio, which improved the heat storage capacity of the patio and turned it into a constant-temperature heater for heating the building interior. Based on calculations, in the new system without WHR, the annual cooling load reduction was 55,417.33 kWh. With WHR, the annual cooling load reduction was 28,537.57 kWh. The annual cooling load of the air insulation wall of the new system was reduced to 1133.7 kWh. In winter, using the glass roof to increase the heat storage capacity of the patio reduced the heating load to 54,537.78 kWh. [ABSTRACT FROM AUTHOR]

New Findings: What is the topic of this review?We have conducted a systematic review and meta‐analysis on the current evidence for the effect of heat therapy on blood pressure and vascular function.What advances does it highlight?We found that heat therapy reduced mean arterial, systolic and diastolic blood pressure. We also observed that heat therapy improved vascular function, as assessed via brachial artery flow‐mediated dilatation. Our results suggest that heat therapy is a promising therapeutic tool that should be optimized further, via mode and dose, for the prevention and treatment of cardiovascular disease risk factors. Lifelong sauna exposure is associated with reduced cardiovascular disease risk. Recent studies have investigated the effect of heat therapy on markers of cardiovascular health. We aimed to conduct a systematic review with meta‐analysis to determine the effects of heat therapy on blood pressure and indices of vascular function in healthy and clinical populations. Four databases were searched up to September 2020 for studies investigating heat therapy on outcomes including blood pressure and vascular function. Grading of Recommendations, Assessment, Development and Evaluations (GRADE) was used to assess the certainty of evidence. A total of 4522 titles were screened, and 15 studies were included. Healthy and clinical populations were included. Heat exposure was for 30–90 min, over 10–36 sessions. Compared with control conditions, heat therapy reduced mean arterial pressure [n = 4 studies; mean difference (MD): −5.86 mmHg, 95% confidence interval (CI): −8.63, −3.10; P < 0.0001], systolic blood pressure (n = 10; MD: −3.94 mmHg, 95% CI: −7.22, −0.67; P = 0.02) and diastolic blood pressure (n = 9; MD: −3.88 mmHg, 95% CI: −6.13, −1.63; P = 0.0007) and improved flow‐mediated dilatation (n = 5; MD: 1.95%, 95% CI: 0.14, 3.76; P = 0.03). Resting heart rate was unchanged (n = 10; MD: −1.25 beats/min; 95% CI: −3.20, 0.70; P = 0.21). Early evidence also suggests benefits for arterial stiffness and cutaneous microvascular function. The certainty of evidence was moderate for the effect of heat therapy on systolic and diastolic blood pressure and heart rate and low for the effect of heat therapy on mean arterial pressure and flow‐mediated dilatation. Heat therapy is an effective therapeutic tool to reduce blood pressure and improve macrovascular function. Future research should aim to optimize heat therapy, including the mode and dose, for the prevention and management of cardiovascular disease. [ABSTRACT FROM AUTHOR]

New Findings: What is the central question to this study?Do the sweat glands' maximum ion reabsorption rates increase following heat acclimation in healthy older individuals and is this associated with elevated aldosterone concentrations?What is the main finding and its importance?Sweat gland maximum ion reabsorption rates improved heterogeneously across body sites, which occurred without any changes in aldosterone concentration following a controlled hyperthermic heat acclimation protocol in healthy older individuals. We examined whether the eccrine sweat glands' ion reabsorption rates improved following heat acclimation (HA) in older individuals. Ten healthy older adults (>65 years) completed a controlled hyperthermic (+0.9°C rectal temperature, Tre) HA protocol for nine non‐consecutive days. Participants completed a passive heat stress test (lower leg 42°C water submersion) pre‐HA and post‐HA to assess physiological regulation of sweat gland ion reabsorption at the chest, forearm and thigh. The maximum ion reabsorption rate was defined as the inflection point in the slope of the relation between galvanic skin conductance and sweat rate (SR). We explored the responses again after a 7‐day decay. During passive heating, the Tb thresholds for sweat onset on the chest and forearm were lowered after HA (P < 0.05). However, sweat sensitivity (i.e. the slope), the SR at a given Tre and gross sweat loss did not improve after HA (P > 0.05). Any changes observed were lost during the decay. Pilocarpine‐induced sudomotor responses to iontophoresis did not change after HA (P ≥ 0.801). Maximum ion reabsorption rate was only enhanced at the chest (P = 0.001) despite unaltered aldosterone concentration after HA. The data suggest that this adaptation is lost after 7 days' decay. The HA protocol employed in the present study induced partial adaptive sudomotor responses. Eccrine sweat gland ion reabsorption rates improved heterogeneously across the skin sites. It is likely that aldosterone secretion did not alter the chest sweat ion reabsorption rates observed in the older adults. [ABSTRACT FROM AUTHOR]

Passive heating has emerged as a therapeutic intervention for the treatment and prevention of cardiovascular disease. Like exercise, heating increases peripheral artery blood flow and shear rate, which is thought to be a primary mechanism underpinning endothelium-mediated vascular adaptation. However, few studies have compared the increase in arterial blood flow and shear rate between dynamic exercise and passive heating. In a fixed crossover design study, 15 moderately trained healthy participants (25.6 ± 3.4 yr) (5 female) underwent 30min of whole body passive heating (42°C bath), followed on a separate day by 30min of semi-recumbent stepping exercise performed at two workloads corresponding to the increase in cardiac output (Qc) (Δ3.72 L·min-1) and heart rate (HR) (Δ40 beats/min) recorded at the end of passive heating. At the same Qc (Δ3.72 L·min-1 vs. 3.78 L·min-1), femoral artery blood flow (1,599 mL/min vs. 1,947 mL/min) (P = 0.596) and shear rate (162 s-1 vs. 192 s-1 )(P = 0.471) measured by ultrasonography were similar between passive heating and stepping exercise. However, for the same HRMATCHED intensity, femoral blood flow (1,599 mL·min-1 vs. 2,588 mL·min-1) and shear rate (161 s-1 vs. 271 s-1) were significantly greater during exercise, compared with heating (both P = <0.001). The results indicate that, for moderately trained individuals, passive heating increases common femoral artery blood flow and shear rate similar to low-intensity continuous dynamic exercise (29% VO2max); however, exercise performed at a higher intensity (53% VO2max) results in significantly larger shear rates toward the active skeletal muscle. [ABSTRACT FROM AUTHOR]

Purpose: To determine the vastus lateralis muscle temperature kinetics during and after passive heating, to exam the effect of sex on thermoregulatory responses, and the thermal safety and tolerance of the 42 °C hot-water immersion protocol. Methods: Thirty participants (15 males, 15 females) underwent a 2 h 42 ºC hot-water immersion to the waist level. Vastus lateralis, rectal and skin temperature, thermal sensation, heart rate and blood pressure (BP) were measured during the passive heating and recovery period. Participant recovery was monitored until muscle temperature returned to baseline. Results: Vastus lateralis temperature increased to a maximal value of 39.0 ± 0.11 °C (P < 0.001), reaching a plateau after ~ 83.5 min of hot-water immersion and returning to baseline after ~ 115.8 min of recovery. Despite the anthropometric differences between males and females (e.g., height, body mass, body fat %, and fat thickness; P < 0.05), thermoregulatory responses showed no differences between sexes (P > 0.05). No change was found in systolic BP (~ 117 mmHg; P = 0.061). Peak rectal temperature (38.8 ± 0.14 °C; P < 0.001), heart rate (~ 100 bpm; P < 0.001), and diastolic BP (↓ ~ 13 mmHg; P < 0.001) during the hot-water immersion indicated the safety of the protocol. While skin temperature (~ 35.4 °C; P < 0.001) and thermal sensation (~ 5.95 AU; P < 0.001) confirmed protocol tolerance. Conclusion: These data demonstrate lower-body 42 °C hot-water immersion to increase vastus lateralis temperature and plateau ~ 2.8 °C above baseline. This amplitude of muscle temperature change aligns with reported cellular adaptation and muscle growth. Thermal strain incurred from this protocol appears safe and tolerable, positioning it well for health-related prescription. [ABSTRACT FROM AUTHOR]

Purpose: Aging is associated with progressive loss of active muscle mass and consequent decreases in resting metabolic rate and body temperature, and slowing of nerve conduction velocities and muscle contractility. These effectors compromise the ability of the elderly to maintain an upright posture during sudden balance perturbation, increase the risk of falls, and lead to self-imposed reduction in physical activity. Short-term superficial acute heating can modulate the neural drive transmission to exercising muscles without any marked change in deep-muscle temperature. Methods: To determine whether the short-term (5 min) application of local passive knee-surface heating (next-to-skin temperature, ~ 44 °C) in healthy older subjects of both sexes (64–74 years; eight men/eight women) enhances reflex excitability, we compared the voluntarily and electrically induced ankle muscle torque production and contractile properties with those of healthy younger subjects of both sexes (21–35 years, 10 men/10 women). Results: The application of local heating (vs. control) increased the maximal Hoffman reflex (Hmax), the maximal volitional wave (Vsup) amplitude, and the Hmax/Mmax amplitude ratio, and decreased Vsup latency only in older adults. In the older adults (vs. younger adults), the application of local heating (vs. control trial) was accompanied by a significant increase in maximal voluntary peak torque, rate of torque development, and isokinetic peak torque of plantar flexion/dorsiflexion muscle contraction. Conclusion: The spinal and supraspinal reflex excitability of older adults increased during local knee-heating application. The improved motor drive transmission observed in older adults was accompanied by increased voluntarily induced torque production of the ankle muscles during isometric/isokinetic contractions. [ABSTRACT FROM AUTHOR]

Athletes use cold water immersion, cryotherapy chambers, or icing in the belief that these strategies improve postexercise recovery and promote greater adaptations to training. A number of studies have systematically investigated how regular cold water immersion influences long-term performance and muscle adaptations. The effects of regular cold water immersion after endurance or high-intensity interval training on aerobic capacity, lactate threshold, power output, and time trial performance are equivocal. Evidence for changes in angiogenesis and mitochondrial biogenesis in muscle in response to regular cold water immersion is also mixed. More consistent evidence is available that regular cold water immersion after strength training attenuates gains in muscle mass and strength. These effects are attributable to reduced activation of satellite cells, ribosomal biogenesis, anabolic signaling, and muscle protein synthesis. Athletes use passive heating to warm up before competition or improve postexercise recovery. Emerging evidence indicates that regular exposure to ambient heat, wearing garments perfused with hot water, or microwave diathermy can mimic the effects of endurance training by stimulating angiogenesis and mitochondrial biogenesis in muscle. Some passive heating applications may also mitigate muscle atrophy through their effects on mitochondrial biogenesis and muscle fiber hypertrophy. More research is needed to consolidate these findings, however. Future research in this field should focus on 1) the optimal modality, temperature, duration, and frequency of cooling and heating to enhance long-term performance and muscle adaptations and 2) whether molecular and morphological changes in muscle in response to cooling and heating applications translate to improvements in exercise performance. [ABSTRACT FROM AUTHOR]

Neurodegenerative diseases involve the progressive deterioration of structures within the central nervous system responsible for motor control, cognition, and autonomic function. Alzheimer's disease and Parkinson's disease are among the most common neurodegenerative disease and have an increasing prevalence over the age of 50. Central in the pathophysiology of these neurodegenerative diseases is the loss of protein homeostasis, resulting in misfolding and aggregation of damaged proteins. An element of the protein homeostasis network that prevents the dysregulation associated with neurodegeneration is the role of molecular chaperones. Heat shock proteins (HSPs) are chaperones that regulate the aggregation and disaggregation of proteins in intracellular and extracellular spaces, and evidence supports their protective effect against protein aggregation common to neurodegenerative diseases. Consequently, upregulation of HSPs, such as HSP70, may be a target for therapeutic intervention for protection against neurodegeneration. A novel therapeutic intervention to increase the expression of HSP may be found in heat therapy and/or heat acclimation. In healthy populations, these interventions have been shown to increase HSP expression. Elevated HSP may have central therapeutic effects, preventing or reducing the toxicity of protein aggregation, and/or peripherally by enhancing neuromuscular function. Broader physiological responses to heat therapy have also been identified and include improvements in muscle function, cerebral blood flow, and markers of metabolic health. These outcomes may also have a significant benefit for people with neurodegenerative disease. While there is limited research into body warming in patient populations, regular passive heating (sauna bathing) has been associated with a reduced risk of developing neurodegenerative disease. Therefore, the emerging evidence is compelling and warrants further investigation of the potential benefits of heat acclimation and passive heat therapy for sufferers of neurodegenerative diseases. [ABSTRACT FROM AUTHOR]

Hot-water immersion following exercise in a temperate environment can elicit heat acclimation in endurance-trained individuals. However, a delay between exercise cessation and immersion is likely a common occurrence in practice. Precisely how such a delay potentially alters hot-water immersion mediated acute physiological responses (e.g., total heat-load) remains unexplored. Such data would aid in optimizing prescription of post-exercise hot-water immersion in cool environments, relative to heat acclimation goals. Twelve male recreational runners (mean ± SD; age: 38 ± 13 years, height: 180 ± 7 cm, body mass: 81 ± 13.7 kg, body fat: 13.9 ± 3.5%) completed three separate 40-min treadmill runs (18°C), followed by either a 10 min (10M), 1 h (1H), or 8 h (8H) delay, prior to a 30-min hot-water immersion (39°C), with a randomized crossover design. Core and skin temperatures, heart rate, sweat, and perceptual responses were measured across the trials. Mean core temperature during immersion was significantly lower in 1H (37.39 ± 0.30°C) compared to 10M (37.83 ± 0.24°C; p = 0.0032) and 8H (37.74 ± 0.19°C; p = 0.0140). Mean skin temperature was significantly higher in 8H (32.70 ± 0.41°C) compared to 10M (31.93 ± 0.60°C; p = 0.0042) at the end of the hot-water immersion. Mean and maximal heart rates were also higher during immersion in 10M compared to 1H and 8H (p < 0.05), despite no significant differences in the sweat or perceptual responses. The shortest delay between exercise and immersion (10M) provoked the greatest heat-load during immersion. However, performing the hot-water immersion in the afternoon (8H), which coincided with peak circadian body temperature, provided a larger heat-load stimulus than the 1 h delay (1H). [ABSTRACT FROM AUTHOR]

Purpose: This study examined the effects of combined cooling and lower body heat maintenance during half-time on second-half intermittent sprint performances.Methods: In a repeated measures design, nine males completed four intermittent cycling trials (32.1 ± 0.3 °C and 55.3 ± 3.7% relative humidity), with either one of the following half-time recovery interventions; mixed-method cooling (ice vest, ice slushy and hand cooling; COOL), lower body passive heating (HEAT), combined HEAT and COOL (COMB) and control (CON). Peak and mean power output (PPO and MPO), rectal (Tre), estimated muscle (Tes-Mus) and skin (TSK) temperatures were monitored throughout exercise.Results: During half-time, the decrease in Tre was substantially greater in COOL and COMB compared with CON and HEAT, whereas declines in Tes-Mus within HEAT and COMB were substantially attenuated compared with CON and COOL. The decrease in TSK was most pronounced in COOL compared with CON, HEAT and COMB. During second-half, COMB and HEAT resulted in a larger decrease in PPO and MPO during the initial stages of the second-half when compared to CON. In addition, COOL resulted in an attenuated decrease in PPO and MPO compared to COMB in the latter stages of second-half.Conclusion: The maintenance of Tes-Mus following half-time was detrimental to prolonged intermittent sprint performance in the heat, even when used together with cooling. [ABSTRACT FROM AUTHOR]

Polycystic ovary syndrome (PCOS) is associated with high rates of obesity and metabolic dysfunction. Repeated passive heat exposure (termed heat therapy) is a novel lifestyle intervention for improving health in obese women with PCOS. The purpose of this study was to examine changes in metabolic function in obese women with PCOS following heat therapy. Eighteen age- and BMI-matched obese women with PCOS (age: 27 ± 1 yr, BMI: 41.3 ± 1.1 kg/m−2) were assigned to heat therapy (HT) or time control (CON). HT participants underwent 30 one-hour hot tub sessions over 8–10 wk, while CON participants completed all testing but did not undergo heat therapy. Before (Pre), at the mid-point (Mid), and following (Post) 8–10 wk of heat therapy, metabolic health was assessed using a 2-h oral glucose tolerance test, a subcutaneous abdominal fat biopsy (Pre-Post only), and other blood markers relating to metabolic function. HT participants exhibited improved fasting glucose (Pre: 105 ± 3, Post: 89 ± 5mg/dl; P = 0.001), glucose area under the curve (AUC) (Pre: 18,698 ± 1,045, Post: 16,987 ± 1,017 mg·dl−1·min−1; P = 0.028) and insulin AUC (Pre: 126,924 ± 11,730, Post: 91,233 ± 14,429 IU l−1·min−1; P = 0.012). Adipocyte insulin signaling (p-AKT at Ser-473 with 1.2 nM insulin) increased in HT (Pre: 0.29 ± 0.14, Post: 0.93 ± 0.29 AU; P = 0.021). Additionally, serum testosterone declined in HT participants (Pre: 51 ± 7, Post: 34 ± 4 ng/dl; P = 0.033). No parameters changed over time in CON, and no change in BMI was observed in either group. HT substantially improved metabolic risk profile in obese women with PCOS. HT also reduced androgen excess and may improve PCOS symptomology. [ABSTRACT FROM AUTHOR]

Passive heat therapy (PHT) has been proposed as an alternative intervention to moderate-intensity continuous training (MICT) in individuals who are unable or unwilling to exercise. This study aimed to make the first comparison of the effect of PHT and MICT on 1) skeletal muscle capillarization and endothelial-specific endothelial nitric oxide synthase (eNOS) content and 2) mitochondrial density, glucose transporter 4 (GLUT4), and intramuscular triglyceride (IMTG) content. Twenty young sedentary males (21 ± 1 yr, body mass index 25 ± 1 kg/m2) were allocated to either 6 wk of PHT (n = 10; 40-50 min at 40°C in a heat chamber, 3×/wk) or MICT (n = 10; time-matched cycling at ~65% V̇o2peak). Muscle biopsies were taken from the vastus lateralis muscle before and after training. Immunofluorescence microscopy was used to assess changes in skeletal muscle mitochondrial density (mitochondrial marker cytochrome c oxidase subunit 4), GLUT4, and IMTG content, capillarization, and endothelial-specific eNOS content. V̇o2peak and whole body insulin sensitivity were also assessed. PHT and MICT both increased capillary density (PHT 21%; MICT 12%), capillary-fiber perimeter exchange index (PHT 15%; MICT 12%) (P < 0.05), and endothelial-specific eNOS content (PHT 8%; MICT 12%) (P < 0.05). However, unlike MICT (mitochondrial density 40%; GLUT4 14%; IMTG content 70%) (P < 0.05), PHT did not increase mitochondrial density (11%, P = 0.443), GLUT4 (7%, P = 0.217), or IMTG content (1%, P = 0.957). Both interventions improved aerobic capacity (PHT 5%; MICT 7%) and whole body insulin sensitivity (PHT 15%; MICT 36%) (P < 0.05). Six-week PHT in young sedentary males increases skeletal muscle capillarization and eNOS content to a similar extent as MICT; however, unlike MICT, PHT does not affect skeletal muscle mitochondrial density, GLUT4, or IMTG content. [ABSTRACT FROM AUTHOR]

Background: Although acute thermal stress appears to be one of the most effective stressors that increase the intra- and extracellular concentrations of heat shock protein 72 (Hsp72), 17b-estradiol has been shown to inhibit heat-induced Hsp72 expression. Materials and Methods: To determine whether severe whole-body hyperthermia (increase in rectal temperature up to 39.5 °C) induced by lower-body heating is a sufficient stimulus to modulate hormonal (17b-estradiol, progesterone, prolactin, epinephrine, and norepinephrine) and extracellular Hsp72 responses, we investigated young adult women (21 ± 1 yr). Results and Conclusions: In the present study, we show that a severe whole-body hyperthermia (increase in rectal temperature of approximately 2.6 °C and heart rate of approximately 80 bpm from baseline) was sufficient to increase 17b-estradiol, progesterone, and prolactin and catecholamine norepinephrine concentration. Moreover, we show that the concentration of extracellular Hsp72 and catecholamine epinephrine were not affected by severe whole-body hyperthermia in young adult women. From the functional point of view, expression of ovarian hormones induced by passive heat stress may have therapeutic potential for young adult women in, for example, estrogen treatment and overall women's health. [ABSTRACT FROM AUTHOR]

Heat acclimation protocols—both active and passive—have been employed by athletes in an effort to attenuate the detrimental effects of heat stress on physical capacities and sports performance. Active strategies have been extensively reviewed, but have various practical and economic limitations. The purpose of this review was therefore to provide an overview of the passive strategies that have received less attention, yet may be more practical or economically viable; recommendations for athletes are also provided. With a systematic search of the relevant databases ending in June 2018, 16 articles on passive heat acclimation that met the inclusion criteria were included in the review. The review highlighted that passive heat acclimation strategies can successfully induce heat adaptations, evident by reports of improved exercise performance, thermoregulatory, cardiovascular, and perceptual responses accompanying such interventions. Based on the review it is apparent that the use of sauna, hot-water immersion and environmental chambers may be used to provide heat stress under passive conditions, for the purpose of acclimation. To maximize the thermoregulatory-adaptive responses, exercise bouts should be employed prior to passive heat stress, rather than passive heating alone, with a minimal delay between exercise and the application of heat stress. Heating bouts should have a minimum duration of 30 min per session and be employed on consecutive days, when possible, with a minimum of 6–7 exposures to induce adaptation. This review identified that information regarding the magnitude of performance changes that can occur, as well as the perceptual responses to passive heating protocols is limited. Future research should investigate the use of passive heat exposures before and/or after repeated heat training sessions, to assess if a further boost to heat adaptation can be achieved with this strategy. [ABSTRACT FROM AUTHOR]

Regular exercise-induced acute inflammatory responses are suggested to improve the inflammatory profile and insulin sensitivity. As body temperature elevations partly mediate this response, passive heating might be a viable tool to improve the inflammatory profile. This study investigated the acute and chronic effects of hot water immersion on inflammatory and metabolic markers. Ten sedentary, overweight men [body mass index (BMI): 31.0 ± 4.2 kg/m2, mean ± SD] were immersed in water set at 39°C for 1 h (HWI) or rested for 1 h at ambient temperature (AMB). Venous blood was obtained before the session, immediately postsession, and 2 h postsession for assessment of monocyte intracellular heat shock protein-72 (iHsp72) and plasma concentrations of extracellular Hsp72 (eHsp72), interleukin-6 (IL-6), fasting glucose, insulin, and nitrite. Thereafter, participants underwent a 2-wk intervention period, consisting of 10 hot water immersion sessions (INT). Eight BMI-matched participants (BMI: 30.0 ± 2.5 kg/m2) were included as control (CON). Plasma IL-6 and nitrite concentrations were higher immediately following HWI compared with AMB (IL-6 P < 0.001, HWI: 1.37 ± 0.94 to 2.51 ± 1.49 pg/ml; nitrite P = 0.04, HWI: 271 ± 52 to 391 ± 72 nM), whereas iHsp72 expression was unchanged (P = 0.57). In contrast to resting iHsp72 expression (P = 0.59), fasting glucose (P = 0.04; INT: 4.44 ± 0.93 to 3.98 ± 0.98 mmol/l), insulin (P = 0.04; INT: 68.1 ± 44.6 to 55.0 ± 29.9 pmol/l), and eHsp72 (P = 0.03; INT: 17 ± 41% reduction) concentrations were lowered after INT compared with CON. HWI induced an acute inflammatory response and increased nitric oxide bioavailability. The reductions in fasting glucose and insulin concentrations following the chronic intervention suggest that hot water immersion may serve as a tool to improve glucose metabolism. NEW & NOTEWORTHY A single hot water immersion (HWI) session induces an acute increase in plasma interleukin-6 and nitrite concentrations but does not acutely elevate heat shock protein-72 expression in monocytes [intracellular Hsp72 (iHsp72)]. A chronic HWI intervention reduces fasting glucose and insulin concentrations in the absence of changes in resting iHsp72. Therefore, HWI shows potential as a strategy to combat chronic low-grade inflammation and improve glucose metabolism in individuals without the physical capacity to do so using exercise. [ABSTRACT FROM AUTHOR]

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Summary: Consensus guidelines have attempted to standardize the measurement and interpretation of pulse wave velocity (PWV); however, guidelines have not addressed whether hydration status affects PWV. Moreover, multiple studies have utilized heat stress to reduce arterial stiffness which may lead to dehydration. This study utilized two experiments to investigate the effects of dehydration on PWV at rest and during passive heat stress. In experiment 1, subjects (n = 19) completed two trials, one in which they arrived euhydrated and one dehydrated (1·2[1·0]% body mass loss). In experiment 2, subjects (n = 11) began two trials euhydrated and in one trial did not receive water during heat stress, thus becoming dehydrated (1·6[0·6]% body mass loss); the other trial subjects remained euhydrated. Using Doppler ultrasound, carotid‐to‐femoral (central) and carotid‐to‐radial (peripheral) PWVs were measured. PWV was obtained at a normothermic baseline, and at a 0·5°C and 1°C elevation in rectal temperature (via passive heating). In experiment 1, baseline central PWV was significantly higher when euhydrated compared to dehydrated (628[95] versus 572[91] cm s−1, respectively; P<0·05), but peripheral PWV was unaffected (861[117] versus 825[149] cm s−1; P>0·05). However, starting euhydrated and becoming dehydrated during heating in experiment 2 did not affect PWV measures (P>0·05), and independent of hydration status peripheral PWV was reduced when rectal temperature was elevated 0·5°C (−74[45] cm s−1; P<0·05) and 1·0°C (−70[48] cm s−1; P<0·05). Overall, these data suggest that hydration status affects measurements of central PWV in normothermic, resting conditions. Therefore, future guidelines should suggest that investigators ensure adequate hydration status prior to measures of PWV. [ABSTRACT FROM AUTHOR]

Intense, large muscle mass exercise increases circulating microvesicles, but our understanding of microvesicle dynamics and mechanisms inducing their release remains limited. However, increased vascular shear stress is generally thought to be involved. Here, we manipulated exercise-independent and exercise-dependent shear stress using systemic heat stress with localized single-leg cooling (low shear) followed by single-leg knee extensor exercise with the cooled or heated leg (Study 1, n = 8) and whole-body passive heat stress followed by cycling (Study 2, n = 8). We quantified femoral artery shear rates (SRs) and arterial and venous platelet microvesicles (PMV-CD41+) and endothelial microvesicles (EMV-CD62E+). In Study 1, mild passive heat stress while one leg remained cooled did not affect [microvesicle] (P ≥ 0.05). Singleleg knee extensor exercise increased active leg SRs by ~12-fold and increased arterial and venous [PMVs] by two- to threefold, even in the nonexercising contralateral leg (P < 0.05). In Study 2, moderate whole-body passive heat stress increased arterial [PMV] compared with baseline (mean±SE, from 19.9±1.5 to 35.5±5.4 PMV.μL-1.103, P < 0.05), and cycling with heat stress increased [PMV] further in the venous circulation (from 27.5±2.2 at baseline to 57.5±7.2 PMV.lL -1.103 during cycling with heat stress, P < 0.05), with a tendency for increased appearance of PMV across exercising limbs. Taken together, these findings demonstrate that whole-body heat stress may increase arterial [PMV], and intense exercise engaging either large or small muscle mass promote PMV formation locally and systemically, with no influence upon [EMV]. Local shear stress, however, does not appear to be the major stimulus modulating PMV formation in healthy humans. [ABSTRACT FROM AUTHOR]

Purpose: Prior evidence indicates that acute heat stress and aerobic exercise independently reduce arterial stiffness. The combined effects of exercise and heat stress on PWV are unknown. The purpose of this study was to determine the effects of heat stress with passive heating and exercise in the heat on arterial stiffness.Methods: Nine participants (n = 3 females, 47 ± 11 years old; 24.1 ± 2.8 kg/m2) completed four trials. In a control trial, participants rested supine (CON). In a passive heating trial (PH), participants were heated with a water-perfusion suit. In two other trials, participants cycled at ~50% of [Formula: see text] in a hot (~40 °C; HC trial) or cool (~15 °C; CC trial) environment. Arterial stiffness, measured by PWV, was obtained at baseline and after each intervention (immediately, 15, 30, 45, and 60 min post). Central PWV (C PWV) was assessed between the carotid/femoral artery sites. Upper and lower peripheral PWV was assessed using the radial/carotid (U PWV) and dorsalis pedis/femoral (L PWV) artery sites. The mean body temperature (T B) was calculated from the skin and rectal temperatures.Results: No significant changes in T B were observed during the CON and CC trials. As expected, the PH and HC trials elevated T B 2.69 ± 0.23 °C and 1.67 ± 0.27 °C, respectively (p < 0.01). PWV did not change in CON, CC, or HC (p > 0.05). However, in the PH trial, U PWV was reduced immediately (-107 ± 81 cm/s) and 15 min (-93 ± 82 cm/s) post-heating (p < 0.05).Conclusions: Heat stress via exercise in the heat does not acutely change arterial stiffness. However, passive heating reduces U PWV, indicating that heat stress has an independent effect on PWV. [ABSTRACT FROM AUTHOR]

Increasing physical activity remains the most widely publicized way of improving health and wellbeing. However, in populations that benefit most from exercise (EX), adherence is often poor and alternatives to EX are important to bring about health improvements. Recent work suggests a role for passive heating (PH) and heat shock proteins (HSP) in improving cardio-metabolic health. The aim of this study was to investigate the expression of HSP70 and interleukin-6 in response to either EX or PH and the subsequent effect on glucose control. Fourteen males volunteered and were categorized lean (BMI 23.5 ± 2.2 kg·m−2) or overweight (29.2 ± 2.7 kg·m−2) and completed 60 minutes of either moderate cycling at a fixed rate of metabolic heat production (EX) or warm water immersion in 40°C water (PH). Extracellular HSP70 increased from baseline in both conditions with no differences between PH (0.98 ± 1.1 ng·mL−1) or EX (0.84 ± 1.0 ng·mL−1, p = 0.814). IL-6 increased following both conditions with a two-fold increase after PH and four-fold after EX. Energy expenditure increased by 61.0 ± 14.4 kcal·h−1 (79%) after PH. Peak glucose concentration after a meal immediately following PH was reduced when compared with EX (6.3 ± 1.4 mmol·L−1 versus 6.8 ± 1.2 mmol·L−1; p < 0.05). There was no difference in 24-hour glucose area under the curve (AUC) between conditions. These data indicate the potential for thermal therapy as an alternative treatment and management strategy for those at risk of developing metabolic disease where adherence, or ability to EX, may be compromised. [ABSTRACT FROM AUTHOR]