ABSTRACT. The accumulated stresses of training and/or competition may temporarily cause impairments in physiological and/or muscular function leading to suboptimal performance. Recovery strategies during training/competition are therefore critical interventions to maximize athletic performance and/or training adaptations. The application of cryotherapy to previously exercised limbs has become a widely used recovery method in acute and chronic settings and is typically used in the immediate treatment and management of soft tissue injuries. Acute and repeated exposure to cryotherapy causes a range of physiological and psychological adjustments, including, vascular, metabolic and perceptual alterations that have important implications for exercise performance recovery and training adaptations. The proposed vascular benefits of acute cryotherapy exposure, which are often the most overt, are related to reductions in body/local temperatures, microvascular blood flow and oedema that may influence the inflammation response and/or performance recovery. Whilst initial studies have assessed the thermal and vascular responses to acute bouts of cryotherapy after exercise the specific effects of variations in the severity and duration of the cryotherapy bout as well as the effect on muscle blood flow are less clear. The aim of this talk is to critically examine the current state of knowledge pertaining to the vascular and thermoregulatory responses of cryotherapy for sport and exercise performance.

ABSTRACT. Progressive increases in training stimuli are critical to facilitate optimal beneficial physiological and performance adaptations. The accumulated stresses of training and/or competition may temporarily cause impairments in physiological and/or muscular function leading to suboptimal performance though, particularly if inadequate recovery periods are provided. A balance therefore exists between training/competition and recovery to maximize athletic performance. Recovery modalities are therefore commonplace in training regimens to abrogate training/competition-induced physiological and functional deficits and speed up the recovery process. Cryotherapy, applied using cold water immersion (CWI) or other methods such as whole-body cryotherapy (WBC), is a popular and widely used recovery method. CWI consists of immersing the limb(s) or body into water of a reduced temperature, typically 10-15ºC for 5-10 min. WBC involves the participant standing in a chamber that fills with a safe, but extremely cold gas, maintained at −110−190°C for 2-5 minutes. Although there is evidence for the use of cryotherapy in maintaining/preserving within and between day performance, findings are not always positive, however, which is likely a result of variations in the type of exercise model, the index of exercise performance, the ‘dose’ of cryotherapy, the level of athlete and the duration of recovery examined. The proposed mechanisms of the benefits of cryotherapy exposure are numerous and include, reductions in body/local temperatures, microvascular blood flow, oedema, exercise-induced muscle damage, cardiovascular strain, as well as alterations to the autonomic and central nervous systems and reducing perceived soreness. Further research is needed to elucidate the mechanisms by which cryotherapy enhances recovery to enable a more guided practice with regards to periodization of recovery alongside longer term goals for training-induced adaptations, especially due to cryotherapy-induced enhancements in muscle oxidative adaptations to endurance training but impaired hypertrophic/strength adaptations derived from resistance training. The aim of this lecture is to critically examine the efficacy of cryotherapy for sport and exercise performance.

ABSTRACT. Introduction: The use of whole-body cryotherapy (WBC) in medicine, health and sports domains is increasing. While different studies (Lombardi et al. 2017, Rose et al. 2017) are focussing on the physiological mechanisms and its efficacy, hardly any studies are looking into the used WBC protocol. It is unclear how different dosages of WBC affect the thermal state, which is surprising as this thermal state is regarded as the proxy for the resultant effects. This study aimed to assess the effects of different WBC dosages on the thermal state response. Methods:10 healthy volunteers, 4 female and 6 male (33±7,9 years, 172±9,0cm and 76,3±13,4kg) participated and were exposed to two different protocols; protocol A= 4 minutes at -90°C (30s pre-exposure to -60°C) and protocol B= 3 minutes at -125°C (30s pre-exposure to -90°C). The thermal state was monitored by measuring core- and skin temperature, thermal sensation and thermal comfort prior (15 minutes), during and after exposure (45 minutes). Results: Thermal state was reduced after both protocols. Protocol B resulted in a significantly (p<0.05) lower skin temperature, thermal sensation, and comfort compared to protocol A, while core temperature was not significantly affected. Big intra-individual differences in both protocols were identified. In 3 out of 10 participants the local shin temperature directly after exposure following protocol B was lower than 8°C, which is generally accepted as the critical barrier concerning shins problems. Conclusions: The thermal state response is significantly affected by a difference in WBC dosage. To provide effective as well as safe WBC exposures it is pivotal to acknowledge treatment temperature as the more critical factor. Customization of the WBC treatment protocols is warranted to prevent safety-related issues.

ABSTRACT. Historically cold application (cryotherapy) was used in the treatment of soft tissue injury, however more recently its popularity stems from an ability to reduce perceptions of delayed onset muscle soreness (DOMS) often associated with intense exercise, with the added potential to induce acute subsequent performance benefits (Leeder et al., 2012). Whilst the acute recovery period is vital for restoration of energy stores and recovery from exercise induced damage, it is also the window for mediating adaptation to the exercise stimulus via cell signalling and remodelling.

In recent years many labs have been able to show post-exercise cooling can enhance the gene expression of the so called “master regulator“ of mitochondrial biogenesis, PGC-1α, above the exercise response alone (Slivka et al., 2013; Ihsan et al., 2014; Joo et al., 2016; Allan et al., 2017). In doing so it could be suggested this might lead to enhanced endurance adaptations via improved mitochondrial biogenesis. Indeed, regular cooling following training sessions has been shown to enhance PGC-1α protein content (Ihsan et al., 2015), some markers of cellular stress response and signalling molecules related to mitochondria biogenesis (Aguiar et al., 2016).

However, research seems to show a paradoxical response between adaptation towards a more endurance or resistance phenotype. Acute post-exercise cold water immersion is suggested to dampen gene transcription associated with ribosome biogenesis (Figueiredo et al., 2016) whilst attenuating acute changes in satellite cell numbers and activity of kinases that regulate muscle hypertrophy (Roberts et al., 2015). Interestingly this is associated with further implications when post-exercise CWI is regularly used, such as dampened gains in muscle mass and strength following 12 weeks of strength training (Roberts et al., 2015).

Therefore, the aim of the presentation is to critically discuss the contrasting research and suggest correct application of these methods moving forwards.

ABSTRACT. The available literature details the physiological, perceptual, and performance effects of cryotherapy with some equivocal results. The use of a one-size-fits-all approach to post-exercise recovery, in addition to use of varying exercise modalities, populations and environmental conditions are likely to contribute to the contrasting reports of the efficacy of cold-water immersion and whole-body cryotherapy. Moreover, whilst there is limited consistency between studies when the effects of post exercise cryotherapy are viewed at the cohort level; where individual data are presented, even greater heterogeneity is evident. The aim of this presentation is to critically discuss these inconsistent results and attempt to establish if the basis for these findings is the inter-individual responses to cold exposure.

ABSTRACT. Introduction: For athletes, passive heating immediately following exercise offers a pragmatic alternative to active heat acclimation (Zurawlew et al., 2018). Post-exercise sauna bathing for ~3 weeks improves exercise performance in the heat (e.g. VO2max, total work in a time trial) although hallmark heat acclimation adaptations were not examined (Tyka et al., 2008). We hypothesised that post-exercise sauna bathing interspersed across 3 weeks of endurance training would induce hallmark heat acclimation adaptations (i.e., reduced rectal [Trec] and skin [Tsk] temperatures, heart rate [HR], and perceived exertion [RPE] and thermal tolerance) when exercising at a standardised workload.

Method: Seventeen trained middle-distance runners (11 female; age 20±2 years, BMI 21±1, VO2max 56.0±9.1 mlkgmin-1) performed a running heat tolerance test (30-minutes, 9 kph/2% gradient, 40°C/40%RH; RHTT) before (PRE) and after (POST) 3-weeks normal training (CON; n=6) or normal training with 30-minutes post-exercise sauna bathing (101-108°C) 3±1 times per week (SAUNA; n=11).

Results: SAUNA accumulated 10±1 post-exercise sauna sessions, totalling 290±48 minutes of exposure over 3 weeks. During RHTTpost, SAUNA exhibited reduced peak Trec (-0.3±0.3 °C; p<0.01), peak Tsk (-0.2±0.3 °C; p=0.01), peak HR (-11±11 bpm; p<0.01), peak RPE (12±2 vs 10±2; p=0.01), peak thermal sensation (10±1 [“Hot”] vs 9±1 [“Warm”]; p=0.02), and peak thermal comfort (5±2 [“Uncomfortable”] vs 4±2 [between “Slightly Uncomfortable” and “Uncomfortable”]; p=0.01). Total body sweat loss did not change (p=0.57). CON exhibited no changes in these physiological and psychophysical variables (all p>0.05), except for a reduced sweat loss (-0.2±0.2 kg; p=0.04).

Conclusions: These data support our hypothesis that 3 weeks post-exercise sauna bathing reduces cardiovascular strain, core and skin temperatures, and improves perceived tolerance during exercise heat stress. Therefore, post-exercise sauna bathing is an effective and pragmatic method of heat acclimation.

References Zurawlew et al., (2018). Front Physiol, 9, 1824. Tyka et al., (2008). Med Sport, 12(4), 150-154.

ABSTRACT. Glenda Anderson1, Samuel Chalmers1, Carolyn Broderick2,3, Ollie Jay1 1 The University of Sydney, Thermal Ergonomics Laboratory, Faculty of Health Sciences, Sydney, NSW, Australia 2 Tennis Australia, Melbourne, VIC, Australia 3 University of New South Wales, Faculty of Medicine, Sydney, NSW, Australia Introduction: Heat stress risk assessments for large participation elite sport events are often calculated using environmental parameters provided by independent local weather stations. However, the application of these values to actual on-site conditions is questionable. Method: Hourly air temperature (Tair), black globe temperature (Tglobe), relative humidity (RH) and wind speeds were measured with custom-made environmental measurement units (EMU) courtside at a stadium and outer tennis court throughout Australian Tennis Open in Melbourne, Australia (January 2019). Values for Tair, RH and wind speed were compared to those simultaneously issued by the nearest Australian Bureau of Meteorology (BOM) weather station (Melbourne Olympic Park). Results: Daily maximum values from BOM underestimated on-court Tair on all days for both stadium (-2.6˚C; 95%CI [-0.6 to -4.5˚C]) and outer (-2.2˚C; [-2.3 to -2.1˚C]) courts. Simultaneous RH values from BOM were subsequently overestimated for both stadium (+4.8%; [+3.1 to +11.9%]) and outer (+3.2%; [+1.6 to +4.8%]) courts, but absolute humidity values were similar. Wind speed values from BOM overestimated court-side values for the outer court (+2.6 m/s; [+1.9 to +3.0 m/s]), and stadium court (+2.2 m/s; [+1.7 to +2.7 m/s]). On the hottest tournament day, peak Tair values from BOM underestimated highest values measured on-site by 3.8˚C (outer court: 43.8˚C). While not reported by BOM, peak Tglobe on this day was 55.6ºC (stadium) and 54.7˚C (outer court). Conclusions: Environmental data issued by BOM underestimates Tair and overestimates RH and wind speeds for both stadium and outer courts. These data highlight the importance of monitoring courtside environment conditions for the accurate assessment of local thermal conditions that can be subsequently used for the optimal implementation of an extreme heat policy.

ABSTRACT. Introduction: When working in extreme heat, the Australian Army refer to work tables that assume body core temperatures will on average peak at 38.5°C at the end of work. We examined the sex-based differences in peak body core temperature following four work and recovery cycles in the heat.

Method: Fourteen males (M: 32 ± 8.21yr; 179.78 ± 4.82cm; 76.5 ± 6.4kg, 54.39 ± 8.68ml/kg/min) and thirteen females (F: 31.2 ± 7.25yr; 166 ± 6.73cm; 58.06 ± 6.09kg, 51.73 ± 7.18ml/kg/min) performed four successive bouts of treadmill walking in 32.5°C Wet Bulb Globe Temperature (WBGT) at a constant work rate, alternating between 35 minutes (~600W) and 55 minutes (~400W), each separated by 30-min seated rest at 28°C WBGT as per current work tables. Participants wore standardised military clothing including body armour and a helmet. Women were tested on days 5-8 of their menstrual cycle. Peak heart rate (HR), rectal (Tc) and 4-site mean skin temperature (Ts) were compared across exercise periods. Statistical analyses were conducted using repeated measures ANOVA.

Results: Peaks in Tc were significantly different between the exercise bouts (E1-4) (M: E1 38.20 ±0.31°C, E2 38.36 ±0.34°C, E3 38.49 ±0.42°C, E4 38.32 ±0.41°C / FE1 38.05 ±0.40°C, E2 38.09 ±0.37°C, E3 38.33 ±0.38°C, E4 38.15 ±0.35°C) (P=<0.001), but not between males and females (P=0.163). Five males and four females reached 38.5°C by the conclusion of the fourth work. There was no difference in peak HR (P=0.522) or peak Ts (P=0.336) between males or females, nor between exercise bouts (HR: P=0.194) (Ts: P=0.586).

Conclusions: Participants on average did not meet the assumed body core temperature of 38.5°C within four work and recovery cycles. These findings indicate the current work tables can apply to both males and females across four work bouts.

ABSTRACT. The effect of acute caffeine ingestion on thermoregulatory responses to exercise in the heat– a double-blind, placebo-controlled, randomised trial

Lindsey Hunt^a; Yorgi Mavros^a, Lily Hospers^a, and Ollie Jay^ab

^a University of Sydney, Sydney, Australia ^b Charles Perkins Centre, University of Sydney, Sydney, Australia

Introduction: In most thermoregulatory research, participants are asked to abstain from consuming caffeine, prior to participation, due to an assumed confounding effect on core temperature, skin blood flow and/or sweating responses. Yet, evidence supporting this notion appears inconclusive. Our aim was to assess the impact of acute caffeine ingestion on thermoregulatory responses to exercise in moderate heat.

Method: 14 moderately fit (VO2MAX: 42.3±10.1 ml·kg-1·min-1) individuals (9 men and 5 women) cycled at a fixed metabolic heat production of 7 W·kg-1 for 60 minutes on two separate occasions, 60 minutes after ingesting either a 5 mg·kg-1 caffeine (CAF) or a 5 mg·kg-1 maltodextrin placebo (PLA) pill, in a counter-balanced order. Environmental conditions of 30.6±0.9°C, 31±1% RH were chosen to ensure compensable heat stress conditions.

Results: The rise in Teso from baseline (ΔTeso) was greater in CAF 0.93±0.39°C relative to PLA 0.76±0.40°C (P<0.001). Cutaneous vascular conductance on the forearm was attenuated in CAF (39.1 ± 11.5 %CVCmax) versus PLA (49.9 ± 21.6 %CVCmax) (P=0.034), there were no differences observed on the upper back (P=0.55). No differences between conditions were observed for end-exercise whole body sweat loss (CAF:0.68±0.14 kg, PLA:0.65±0.14 kg; P=0.20), or local sweat rate on the forearm (CAF:0.89±0.28 mg·cm-2·min-1, PLA:0.78±0.27 mg·cm-2·min-1; P=0.19) and upper back (CAF:0.96±0.35 mg·cm-2·min-1, PLA 0.88±0.30 mg·cm-2·min-1; P=0.12). Rating of perceived exertion (P=0.80) and thermal comfort (P=0.76) were also similar between conditions.

Conclusions: CAF significantly attenuated skin blood flow on the forearm compared to PLA and led to a greater ΔTeso after 60 minutes of exercise in the moderate heat. These findings may support the current practice in which research participants abstain from all sources of caffeine prior to their participation in studies that involve thermoregulatory measures. Any potential interaction between caffeine-habituation state and an acute dose of caffeine on thermoregulatory responses, however, remains unclear and warrants further investigation.

ABSTRACT. Introduction: Maximal voluntary torque (MVT) is impaired when hyperthermic due to a reduction in the central nervous system’s capacity to voluntarily drive the available force capacity of muscle. Rate of torque development (RTD) is considered more functionally relevant than MVT in some situations and neural drive is a key determinant of RTD. Head and neck cooling can improve endurance performance when hyperthermic, but its effects on neural drive are unclear. The purpose of this study was to investigate head and neck cooling on thermal perception during whole-body hyperthermia on MVT, RTD, neural drive and the contractile properties of the muscle.

Method: 9 participants completed two trials in HOT conditions (50°C, 40% RH), involving light exercise before passive heating to a rectal temperature (Tre) of 39.5°C. During one trial, the head and neck was continuously cooled (HOTcool) using a towel soaked in ice water. At Tre=39.5°C neuromuscular measurements were completed to assess MVT, voluntary activation and EMG at MVT normalised to maximal M-wave. Voluntary RTD and normalised EMG were measured over 0-50, 0-100, 0-150 and 0-200 ms. Involuntary RTD at 0-50 ms was measured during evoked octets at 300 Hz. Thermoregulatory and perceptual variables were measured throughout.

Results: MVT and RTD, and their neuromuscular determinants were unaffected by cooling (P > 0.05). Neck (-20%) and head (-12%) temperature were lower in HOTcool, as were thermal sensation of the head (-36%) and body (-12%) and thermal comfort (body) (-23%). Time to target Tre was increased (71%) in HOTcool, and not all participants were able to reach 39.5°C. Tre (-0.3%) and skin temperature (-6%) were lower in HOTcool (P < 0.05), but heart rate was similar (P > 0.05).

Conclusions: Head and neck cooling did not affect MVT, RTD, or the neuromuscular determinants of these functional variables despite improving perceptions of thermal strain.

ABSTRACT. Exercise training sessions are included into heat-acclimation programmes to potentiate increases in core temperature. Consequently, a training effect may contribute to aerobic gains in individuals of a sub-elite fitness level after participating in such protocols. We investigated whether 10 moderate-intensity exercise sessions can independently enhance aerobic performance in both trained and untrained individuals. We recruited trained (57.9 ± 6.2 mL·kg-1·min-1, n=10) and untrained (41.7 ± 5.0 mL·kg-1·min-1, n=10) young males to exercise daily for 60min at 50% peak power output (Wpeak) for 10 days. Pre- and post-training, the participants were tested on a cycle ergometer in normoxic (23°C, 50% RH, 20.9% FiO2; NOR), hypoxic (23°C, 50% RH, 13.5% FiO2; HYP) and hot (35°C, 50% RH, 20.9% FiO2; HE) conditions in a randomized and counterbalanced order. The exercise tests consisted of two stages; a 30-min steady-state exercise followed by incremental exercise to exhaustion. The steady-state exercise was performed at 40% NOR Wpeak to evaluate thermoregulatory function and gross mechanical efficiency (GME). Following the training protocol, V̇O2max increased by 9.2 ± 8.5% (p = 0.024) and 10.2 ± 15.4% (p = 0.037) only in the untrained group in NOR and HE, respectively. Wpeak increases were largely correlated with baseline values in NOR (r = -0.58, p = 0.010) and HYP (r = -0.52, p = 0.018). GME improved only in HYP in the trained individuals while the anaerobic threshold remained unaffected. Peak sweat rate increased for both groups in HE whereas the forehead sweating response was activated at a lower rectal temperature post-training only in the trained group across environments. We demonstrate that a 10-day exercise training protocol might elicit a training effect in the untrained but not in the trained males. Accordingly, heat-acclimation protocol-associated performance benefits in the trained individuals are most likely not modulated by the exercise stimulus per se.

ABSTRACT. Introduction: Data about skin temperature (Tsk) has been found to be important, amongst others, for understanding thermoregulatory and cardiovascular responses, for the evaluation of thermal strain, for estimating mean body temperature or for understanding perceptual responses. As different types of contact sensors are used for the measurement of Tsk in scientific studies, knowledge about the inter-sensor agreement and reliability is needed for a better understanding and comparability between studies. The aim of this work was to assess the inter-sensor agreement and reliability among three types of contact Tsk during rest and physical activity.

Method: Three types of Tsk sensors (custom thermistor consisting of a glass-encapsulated NTC thermistor set inside a small volume of silicone elastomer encapsulant, Grant thermistors, and iButtons) were applied on fourteen adult males; each completed one experimental session (~24°C, ~46% relative humidity; RH) involving 40min baseline seated rest, 45min exercise (cycle ergometer) and 40min recovery rest. Tsk was measured at four body sites using each sensor type and weighted-mean Tsk was calculated. Finally, sensor data was corrected according to a conventional calibration procedure. Absolute mean difference (AMD) for Tsk from different sensors was compared at different time points.

Results: A good agreement between sensors was found during baseline rest and before sweating during exercise (AMD < 0.12°C). After onset of sweating during exercise through to 20min following exercise, the range for AMD increased to [0.17 0.31]°C and returned to [0.03 0.08]°C at the end of recovery rest.

Conclusions: The systematic inter-sensor differences and variation following the onset of sweating during exercise indicate the application of Tsk data during heat stress cannot be assumed as independent of the sensor-attachment system. In order to ensure comparability between sensor systems, new calibration procedures for a detailed characterization of the sensor-skin interaction (particularly for sweating conditions) have to be considered.

ABSTRACT. This talk will provide experimental data that confirms recent epidemiological findings that prior illness is a significant risk factor for heat stroke. The experimental data demonstrate that even in the absence of overt clinical symptoms of illness, mice with previous viral illness experienced more severe heat stroke compared to naïve animals that never experienced a prior illness. Importantly, heat stroke severity was increased despite no effect on the thermoregulatory response to heat exposure, but was related to dysfunction of inflammatory and coagulation pathways. Attendees will gain a better understanding of the impact of prior illness on heat stroke susceptibility and how physiological and immunological pathways can interact to mediate the systemic inflammatory response to these stressors.

ABSTRACT. Introduction: Heat stroke results in central nervous system dysfunction, organ failure, and death. While core body temperature over 40 °C has been used for diagnosis, no definitive test exists to measure severity or predict outcome. Heat stroke induces similar inflammatory responses to infection, and prior infection exacerbates pathology. Immune involvement in heat stroke pathology provides an opening for quantification of severity and prognostic timecourse. Method: Mice were implanted with radiotelemetry devices and injected with poly I:C, LPS, or saline. After 48 or 72 hours, mice were exposed to heat (T=39.5 °C) until reaching a maximum core body temperature Tc,max=42.4 °C. Radiotelemetry recording of Tc was performed until mice were sacrificed at one of three time points: Tc,max, 1 day, or 7 days. A complete blood count was performed, and concentrations of plasma coagulation factors and liver granzyme-B were assessed by ELISA. Partial least squares modeling identified a signature of blood factors correlating with heat stroke pathology as measured by Tc and granzyme-B concentration. Results: Complete blood count results predict circadian change in Tc, an indication of heat stroke severity, and separate subjects based on heat stroke timecourse. Heat stroke decimates immune cell populations, but levels return after removal from heat. Low platelet levels correlate with heat stroke severity, and their large size and broad size distribution indicate new, active platelets. This signature strengthens at later time points. Increased levels of soluble thrombomodulin and D-dimer indicate coagulopathy, with lower D-dimer levels in the most severe cases suggesting fibrinolytic resistance. Conclusions: Severe heat stroke cases present with high levels of factors indicating coagulopathy. Despite thrombocytopenia, platelets are large with a broad size distribution. Levels of clotting factors increase in more severe heat stroke, with potential fibrinolytic resistance in the most severe cases, resulting in elevated organ damage pathology.

ABSTRACT. Thermoregulatory responses can be compromised in severely burned individuals. Surgical treatment of deep burns involves the excision of damaged tissue (often inclusive of sweat glands) and the subsequent transplantation of grafts from non-injured donor sites onto wounded areas. Removal of skin grafts disrupts the innervation and structural integrity of sweat glands within a graft, culminating in a suppressed sweating response within grafted sites. The ensuing reduction in evaporative heat loss potential results in exacerbated elevations in core temperature during exercise-heat stress, the magnitude of which is strongly associated with the surface area of remaining non-grafted skin that can participate in evaporative heat dissipation. It follows that for burn survivors undertaking exercise training, competing in athletics, or performing work in occupational heat stress, combinations of physical activity and environmental heat will heighten the risk of heat-related illness/injury compared to non-injured individuals. This presentation will highlight recent research on the thermoregulatory consequences of burn injuries/skin grafting, with emphasis on: (i) modelling the thermoregulatory effects of burn injuries/skin grafting based on the interplay between various physiological and physical properties known to influence heat balance and heat illness risk; (ii) recent data from our laboratory examining the interactive effects of burn injuries and various biophysical factors; and (iii) potential strategies to minimize the risk of heat illness/injury among burn survivors exposure to heat stress. Attendees will gain a better understanding of the thermoregulatory impairments that accompany burn injuries, and the implications for heat illness/injury risk of such individuals in occupational settings.

ABSTRACT. Exertional heat illnesses represent a continuum of medical conditions with potentially severe consequences that can affect physically active individuals in both hot and cool environments. The severity of exertional heat illnesses can escalate from heat exhaustion, to heat injury, and on to heat stroke, which is characterized by high body temperatures (>40ºC), profound central nervous system dysfunction, organ and tissue damage, and can lead to death. However, when repeatedly exposed to conditions that are sufficiently stressful to elicit profuse sweating and elevate skin and core temperature (i.e. heat acclimation), adaptations develop that can that reduce the risk of exertional heat stroke. The adaptations include plasma volume expansion, better maintenance of fluid balance, enhanced sweating and cutaneous blood flow responses, as well as acquired thermal tolerance through the heat shock response. Notwithstanding these adaptations, exercise in certain contexts (e.g. environmental heat stress, competitive setting) may lead to, or increase the likelihood of experiencing exertional heat stroke. This is in response to exercise in the heat being associated with various internal (e.g. heat production, illness) and external (e.g. thermal environment) factors that may diminish the benefits conferred by heat acclimation. Contextualising heat acclimation as a protective mechanism and its efficacy as a strategy to protect against heat stroke during exercise therefore requires to be evaluated.

ABSTRACT. Introduction: The heat tolerance test (HTT) is designed as a surrogate clinical tool to examine the ability of soldiers/athletes who have been succumbed to exertional heat stroke (EHS) to return to duty/practice under conditions that might put them in risk to a recurrent episode. Over the years it has become clear that the test applies not only to those who have already been affected by EHS but also as a clinical diagnostic tool in preventing potential heat injuries. The following case reflects the validity of the test in in this regard. Methods: A 20 years old soldier, healthy except for Familial Mediterranean Fever and no history of any heat injury. He was referred for a HTT by the military base physician after casually mentioning that he did not sweat since childhood. On questioning he told of headaches and palpitations after short walks in the sun and of cooling himself frequently with tap water when trying to participate in popular sports activities. Results: The test lasted 40 min. and was stopped because the soldier felt exhausted. Rectal temperature had risen steeply; last measurements of rectal temperature and heart rate were: 38.5oC and 160 bpm, respectively with no tendency to plateau. The probability of heat tolerance (PHT) was lower than 0.5. Sweat rate was 75 g/hr. According to all parameters the soldier was diagnosed as heat intolerant. Conclusions: The HTT is a standardized test to evaluate the ability to sustain an exercise-heat stress with the ability to differentiate between heat tolerant and heat intolerant individuals. The test enabled to substantiate the diagnosis of hypohidrosis, reducing the risk of EHS. It follows that in any case of a thermoregulatory malfunction the HTT results may be used as a clinical indication in the prevention of potential heat stroke.

ABSTRACT. Introduction: The purpose of this work is to present the preliminary experimental re-sults and computational analysis of the newborn's brain cooling process. Hypothermal therapy is considered as an effective method of treatment hypoxic-ischemic encephalopathy. Although neonatologists agree that this should be standardized and improved, there is still a lot of opened questions. How long should therapy last? How to manage the rewarming process? Should the head be cooled selectively? Therefore, the interdisciplinary team was built to research the heat transfer and thermoregulation processes in the human body. Method: Heat flux delivered to the cooling medium as well as the intensity of external heat sources are being recorded on-line during the cooling process at University Clini-cal Hospital in Opole. The measurements and medical data from patients undergoing brain cooling therapy are analysed and utilized to formulate the boundary conditions of the heat transfer calculations. In the current stage of research, the simplified numer-ical model is being built by means of ANSYS Fluent code. It includes the water flowing inside the plastic pipes being in contact with the tissues: an outer skin, inner skin, fat, bone, and brain. The basic thermoregulation model of metabolic heat generation and blood perfusion were implemented. The preliminary model is aimed at verification of adopted assumptions and to test its sensitivity to the model input parameters. Results: Based on the sensitivity analysis, the blood temperature, contact resistance and conductivity of plastic pipes material were identified to have crucial input on sim-ulation results. Conclusions: Results show the importance of the accurate determination of indicated values to tune a complete numerical model of the heat transfer in the neonatal body during a selective brain cooling process.

ABSTRACT. Introduction: The current analysis of the Heat Tolerance Test (HTT), which allows the evaluation of the body's response to an exercise-heat stress is based on the dynamics of rectal temperature and heart rate. Sweat rate, which reflects the potential ability to dissipate heat and thus may serve as an adjuvant parameter to determine tolerance to heat has never been analyzed. The purpose of this study is to investigate the correlation between a subject's sweat rate and a diagnosis of heat intolerance. Method: Data related to male subjects who had suffered from heat stroke and participated in a HTT were analyzed retrospectively. This database consisted of the results of 378 HTTs from the Institute of Military Physiology, the Israel Defense Forces. Sweat rates were examined in correlation with a diagnosis of heat intolerance. Results: From the examined cohort 311 tests were considered as negative, reflecting a state of tolerance to heat (HT) and 67 were found to be positive, reflecting a state of heat intolerance (HI). The average sweat rate of the 378 HTTs was 781±240 g/hr (in the range of 200-1200 g/hr). When sub-divided into the HT and the HI groups, the average sweat rate in the HT group was significantly (p=0.05) higher than the HI group (792± 223 g/hr, and 730±291 g/hr, respectively). Conclusions: Subjects who failed the test and were defined as HI had a lower sweat rate than those with a normal physiological response. Furthermore, subjects with a sweat rate in the first quartile have a 2.2 times greater risk of being diagnosed as HI. Decreased sweat rates may be part of the pathophysiology leading to HI and consequently to higher risk of exertional heat stroke.

ABSTRACT. Introduction: Heat is a common stressor and drives many adaptations. Three practical modes of heating are exercise in hot conditions, spa bathing, and sauna. These may differentially affect vascular pressures, shear stress, neuroendocrine responses, and thermal distributions - but their relative effects appear unreported. We compared three common modes of heat stress for their thermal and cardiovascular impacts during heating and for up to 24 h afterward.

Method: Thirteen, healthy, active participants (5 women), completed four regimes of 5 daily 60-min exposures: Spa (40ºC); Sauna (55ºC, 55% rh); Exercise in humid heat (40ºC, 50% rh; ExHeat); and a Thermoneutral bath (36ºC; Control). Regimes were in randomised order, 6-wk apart. Differences (p<0.05) reported below are from Linear Mixed Models analyses performed in R, for acute data pooled across days within each mode.

Results: Heating: Sauna was poorly tolerated (42  10 min) despite lower peak rectal temperature than ExH (38.5 vs 38.9 ºC) and no additional hypotension. Thus, thermal impulse in Sauna was only 71% of that in Spa and ExH, despite higher sweat rates (~18%) and skin temperature (peak: 40.2ºC). Average heart rate during Spa didn’t exceed Control and was 23 bpm below Sauna, which was 37 bpm below ExH (145 bpm). Plasma volume rose ~7% during immersion, regardless of heating. Aldosterone concentration rose 1.4 and 0.6 fold in ExH and Sauna, while ANP responses were variable. Recovery (from first exposure only): ExH elicited the only clear postexercise hypotension (-8 mm Hg at 0.75 h) and rebound plasma volume expansion (+5.7% at 24 h). Arterial pressure was unchanged at 24 h, irrespective of prior heating mode.

Conclusions: Combined exercise and heat stress, and the augmented metabolic and cardiovascular strain not evident with passive heating, may be required to elicit short-term cardiovascular benefits in healthy adults.

ABSTRACT. INTRODUCTION

Age-adjusted heat-related mortality indicates elderly women are more susceptible to extreme heat compared to men. Changing female sex hormones (e.g. oestrogen and progesterone) are thought to influence cerebral blood flow (CBF), with possible implications for heat-related mortality. Therefore, the aim of this study is to perform a systematic review of the current literature on changing female sex hormones and CBF.

METHODS

Three databases (EMBASE, MEDLINE and Web of Science) were searched and identified texts were screened by two independent reviewers (RJD, BDS). Inclusion criteria were articles from the earliest available date to December 2018 on adult CBF and female sex hormones. Articles were excluded if both themes were not addressed, were animal studies or involved adolescents under 18 years. Middle cerebral artery velocity (MCAv) data from included texts were collated and changes between a ‘low hormone phase’ and ‘high hormone phase’ (e.g. Low: non-pregnant vs. High: 3rd trimester pregnancy) were calculated.

RESULTS

48 studies met inclusion criteria. 27 reported measures of CBF with MCAv the most frequent measure (n=14). Overall, MCAv was 3.7% greater in low hormone phases when compared to phases of elevated female sex hormones (68.6±11.0 vs. 66.1±12.9cm/s). Within life-stages, pregnancy (n=6) had the greatest decrease in MCAv from a low to high hormone phase (-9.5%; Low: 65.8±6.4 vs. High: 58.9±3.7 cm/s) and ovarian hyperstimulation (n=1) the greatest increase (6.2%; Low: 97±13 vs. High:103±14 cm/s). Changes in MCAv from low to high hormone levels across the menstrual cycle (n=3), with HRT use (n=2), and with menopause (n=2) were -0.5%, -2.3%, and -0.1%, respectively.

DISCUSSION

Lower levels of female sex hormones generally appear to cause an increase in CBF, with the exception of ovarian hyperstimulation. To fully elucidate how changing female sex hormones may influence heat-related mortality, other indices of cerebrovascular function (e.g. autoregulation) should be examined.

ABSTRACT. Introduction: Strenuous exercise-heat stress adversely distrupts GI barrier integrity and appears central in the development of exertional heat stroke (EHS). The development of assessment techniques to determine GI barrier integrity is consequently an important step in the prevention, diagnosis and treatment of EHS. This study investigated the reliability of the gold-standard dual-sugar absorption test (DSAT) in serum and several promising GI barrier integrity biomarkers in response to a military style exercise-heat stress intervention.

Method: Fourteen healthy males completed two separate exercise-heat stress interventions (EHSI). The EHSI consisted of two 40 minute-bouts of fixed-intensity (6 km.h-1 on 7% gradient) treadmill walking in the heat (35°C/25% relative humidity) interspersed by a 20-minute recovery period. Venous blood samples were collected pre, post and 1-hour post exercise. The DSAT was determined in serum at 90- and 150-minutes post sugar probe ingestion using high-performance liquid chromatography. Intestinal Fatty-Acid Binding Protein (I-FABP) and Lipopolysaccharide Binding Protein (LBP) were determined pre-to-post exercise by ELISA. A battery of reliability statistical tests (e.g. Pearson’s correlation (r), coefficient of variation (CV), limits of agreement (LoA)) were utilised to compare between-trial responses.

Results: Whole-body thermoregulatory (peak rectal temperature 38.63 ± 0.28 vs. 38.46 ± 0.37°C) and cardiovascular (peak heart rate 164 ± 13 vs. 161 ± 16 beats.min-1) responses were similar between trials. The DSAT offered acceptable reliability at both 1.5 (0.028 ± 0.012 vs. 0.025 ± 0.014; r= 0.90; CV= 11.5%; LoA= -0.003) and 2.5 hours (0.033 ± 0.015 vs. 0.034 ± 0.016; r= 0.94; CV= 12.2%; LoA= 0.001) following probe ingestion. I-FABP responses increased from pre-to-post EHSI’s (p = 0.85), though reliability was poor-to-moderate (Δ 769 ± 453 vs. 790 ± 377 pg.ml-1; r= 0.59; CV= 36.6%; LoA= -19 pg.ml-1).

Conclusions: GI barrier integrity was reduced following a moderate-intensity military EHSI. The DSAT offered acceptable levels of reliability, though I-FABP concentrations showed greater between-trial variation.

ABSTRACT. Introduction: Exercise has long been considered a cornerstone in the treatment regimen for patients with type 2 diabetes mellitus (T2D). However, T2D tends to place individuals at greater risk for heat-related illness during physical activity due to an impaired capacity to dissipate heat, which may be exacerbated by cardiovascular complications. This study aimed to detect potential differences in heart rate variability (HRV) in older middle-aged men with well-controlled T2D compared to age-matched controls during and following exercise under heat. Method: Twenty-four habitually active older middle-aged men with well-controlled (n=12, 59.1±6.0 years) and without T2D (n=12, 60.5±3.4 years) performed three successive 30-min bouts of semi-recumbent cycling at increasingly greater fixed rates of metabolic heat production, at exercise intensities of 150 (Low), 200 (Moderate) and 250 (Vigorous) W/m2 (equivalent to ~37, ~50, and ~62% of their pre-determined VO2peak) each separated by a 15-min recovery in a hot-dry environment (40˚C, ~20% relative humidity). Eleven HRV indices (e.g. low and high frequency power, Shannon Entropy, and others) characterizing common domains of variability and complexity of heart rate were computed and assessed at baseline resting, end of exercise and recovery. Results: During exercise a significant time*group interaction on low-frequency power was observed (p=0.05), as the T2D group demonstrated decreased levels through time. During recovery, significant group differences (i.e., main effects of group) were observed in Shannon Entropy (p=0.03), as the T2D group showed reduced levels at each successive recovery periods indicating decreased parasympathetic activity. Conclusions: We show habitually active older middle-aged men with well-controlled T2D had weaker cardiac autonomic control during exercise and recovery in the heat placing them at a greater risk for cardiovascular complications. This study supports the importance of developing effective strategies to safeguard the health and well-being of older middle-aged adults with T2D who are engaged in physical activity.

ABSTRACT. Lily Hospersa, Matthew Cramerc and Ollie Jaya,b

aThermal Ergonomics Laboratory, Faculty of Health Sciences, The University of Sydney, NSW, Australia bCharles Perkins Centre, The University of Sydney, Sydney, NSW, Australia cInstitute for Exercise and Environmental Medicine, Texas Health Presbyterian Hospital Dallas and University of Texas Southwestern Medical Center, Dallas, TX, USA

Introduction: One treatment for primary hyperhidrosis, excessive sweating of plantar, palmar and/or axillary surfaces, is an endoscopic thoracic sympathectomy (ETS), a surgical procedure in which sympathetic ganglia are cut or excised to disrupt the innervation of sweat glands, ultimately reducing the skin surface area capable of sweat secretion. The purpose of this case study was to characterise the thermoregulatory responses of a 37-year-old male following an ETS (T2-T4). Specifically, we assessed the impact of this reduced effective surface area on maximum skin wettedness (max) and evaluated whether disproportionately higher sweat rates are observed in areas that remain innervated.

Method: Thermoregulatory responses were separately measured during a 70-min steady-state compensable heat stress exercise bout in 35C/42% relative humidity (RH); and during a humidity ramp protocol at a fixed ambient temperature of 35C with increasing RH (23-64%). Thermoregulatory measures included rectal (Tre), oesophageal (Toes), and 8-site mean skin (Tsk) temperatures, heart rate (HR), local sweat rate (LSR), skin blood flow (SkBF) and sweat gland density. In addition, technical absorbents assessed regional sweat rates (RSR) during the steady-state bout.

Results: The reduction in innervated skin surface area resulted in a max of 0.64 that falls outside previously reported max range (95% CIs) of [0.66 to 0.78], [0.76 to 0.92] and [0.90 to 1.00] for untrained and unacclimated, trained and unacclimated, and trained and heat-acclimated individuals, respectively (Ravanelli et al., 2018). Evidence of disproportionately higher sweat rates in innervated areas was supported by higher normalised median RSR on the thigh (1.32 vs 1.09) and lower back (1.77 vs 1.29) compared to existing sweat mapping data (Smith & Havenith, 2011).

Conclusions: Despite evidence of a compensatory increase in sudomotor output in skin areas with intact sudomotor apparatus, a lower max following ETS persists, potentially reducing the upper environmental limits for safe exercise/work in the heat.

ABSTRACT. Introduction: Multiple sclerosis (MS) patients are characterized by thermoregulatory failure, known as Uthoff’s phenomenon. Precisely, 60-80% of the MS patients present adverse clinical symptoms when their body temperature is increased. Thus, the development of treatment strategies to overcome the thermoregulatory problem in these patients is crucial. Given that cooling has been proposed as an effective method, the aim of this study is to examine whether the application of head cooling therapy during an exercise training session is capable to prevent the core temperature increase and to improve the patient’s functional ability and quality of life. Method: 10 MS patients (aged 25-50 years) with Expanded Disability Status Scale between 2 to 6.5 have agreed to participate in this study. Each participant will complete two different experimental conditions separated by one week. The first will include an exercise training session involving head cooling and neck wraps while the second session will be performed without cooling. The exercise training session will consist of 40 min continuous cycling where the participants will perform an incremental submaximal exercise protocol beginning at 45 W, increasing 10 W every 10 min for a total of four stages on a semirecumbent cycle ergometer in a 20oC room. Before and after the completion of both conditions each participant will perform a variety of functional ability tests. The evaluation of the core temperature and the assessment of the patient’s quality of life will also be performed. Results: This is an on-going study and the results will be presented at the conference. However, at the literature there is only one study where body cooling was applied and observed improvements in the participants’ functional ability. Conclusions: Based on our pilot trial results head cooling will be proved to be an effective strategy that could help patients with MS to overcome the thermoregulatory problems during physical working.

ABSTRACT. Rationale: Athletes with a spinal cord injury (SCI) have impaired thermoregulation, therefore it is important to accurately assess their thermal status. Esophageal temperature (Tes) provides the best surrogate of circulating blood temperature, however is impractical outside a laboratory. In contrast, gastrointestinal temperature (Tgi) is regularly used in field settings, yet there is typically a temporal lag in Tgi for a given Tes. Differences between Tgi and Tes may also be impacted by impaired splanchnic blood flow secondary to SCI. This study compared Tgi and Tes during and post-exercise in the heat in athletes with different SCI levels. Methods: 8 tetraplegic (TP; C5-C8), 7 high paraplegic (HP; T1-T5), 8 low paraplegic (LP; T6-L1) and 8 able-bodied (AB) exercised for 3x10-min with 3-min breaks, then rested for 30-min in 35°C and 50% RH while Tgi and Tes were measured. Estimated means and 95% confidence intervals are reported for within-group comparisons. Results: Within each group, absolute Tgi and Tes changed similarly with time throughout the trial (TP: p=0.389, HP: p=0.532, LP: p=0.344, AB: p=0.085), with Tgi consistently greater than Tes (TP; p=0.012, HP; p<0.001, LP; p<0.001, AB; p<0.001). Changes from baseline revealed no interaction of time and site for HP or LP, however ΔTes was higher than ΔTgi for TP after 20 and 30-min of exercise (ΔTes: 1.86°C [1.70, 2.02], ΔTgi: 1.32°C [1.16, 1.47], p=0.001), and for AB after 10-min (ΔTes: 0.33°C [0.24, 0.42], ΔTgi: 0.10°C [0.00, 0.19], p=0.001). Furthermore mean ΔTes was greater than ΔTgi throughout the trial for TP (p<0.01). Conclusion: Mean Tgi was higher than Tes during 30-min of exercise and passive-recovery, irrespective of SCI. However, due to the responsiveness of the two sites, ΔTes was greater than ΔTgi during exercise in TP. Peak Tgi may occur later than Tes, particularly in TP. Monitoring SCI individuals post-exercise until a reduction in Tgi is observed is recommended.

ABSTRACT. Introduction: Heat Shock Protein 90 (HSP90) enhances nitric oxide (NO) bioavailability by stabilizing the NO synthase (NOS) enzyme. In young men we previously showed that HSP90 inhibition attenuated cutaneous vascular conductance (CVC) during exercise, but not during rest or post-exercise recovery in the heat; an effect that was NOS-dependent. However, it remains to be determined if similar effects occur in young women. Therefore, the purpose of this study was to evaluate the effects of HSP90 inhibition on CVC in young women during rest, exercise, and recovery in the heat and to determine if this effect was NOS-dependent. Method: In nine habitually active young women (23±3 years), CVC (assessed via laser Doppler flowmetry) was measured at four forearm skin sites receiving either: 1) lactated Ringer’s (Control), 2) 178 µM Geldanamycin (Gelda, HSP90 inhibitor), 3) 10 mM NG-nitro-L-arginine methyl ester (L-NAME, NOS inhibitor) or 4) combined 178 µM Gelda + 10 mM L-NAME (G+L), via intradermal microdialysis. A 5% DMSO solution was used to fully dissolve Gelda, and was added to all sites for consistency. Participants rested in the heat (35°C) for 70 min, followed by 50 min of moderate-intensity exercise (~55% VO2peak) and 30 min of recovery. All testing was performed during the early follicular phase of the menstrual cycle. Results: Inhibition of HSP90 attenuated CVC by ~10% between 30-50 min of exercise (all P<0.05), but not during rest or post-exercise recovery (all P>0.05). NOS inhibition attenuated CVC by ~20% during rest and ~37% throughout exercise and recovery (all P<0.05). However, combined HSP90 and NOS inhibition was not different from NOS inhibition alone (all P>0.05). Conclusions: Consistent with our previous findings in young men, HSP90 inhibition attenuated CVC during exercise in the heat in young women in a NOS-dependent manner. Funding: Natural Science and Engineering Research Council of Canada (G.P. Kenny).

ABSTRACT. Introduction: The majority of studies examining the mechanisms of cholinergic vasodilatation in the skin have been performed on the forearm. While regional variations in such responses exist across different body areas, the underlying mechanisms behind this effect remain poorly understood. Nitric oxide (NO) synthase (NOS) is a well-established mediator of cholinergic vasodilatation due its modulating effects on NO bioavailability. However, the relative contribution of this enzyme across different body regions has yet to be examined. Therefore, the purpose of this study was to evaluate the NOS contribution to cutaneous vasodilatation across different body regions during cholinergic stimulation. Method: In eleven young men (24±3 years) cutaneous vascular conductance (CVC, assessed via laser-Doppler flowmetry) was measured at six skin sites. On each of the Forearm, Chest and Back, two sites were continuously perfused with either 1) lactated Ringer’s (Control) or 2) 10 mM Nω-Nitro-L-arginine (L-NNA, non-selective NOS inhibitor) via intradermal microdialysis. All six sites were continuously co-infused with five incremental doses of the acetylcholine mimetic, methacholine (1, 10, 100, 1000, 2000 mM; 25 min each), followed by infusion of 50 mM sodium nitroprusside to achieve maximum cutaneous vasodilatation. Results: Forearm CVC was significantly attenuated by L-NNA from 1 to 100 mM methacholine (all P<0.05), which was associated with a 20% reduction overall. Back CVC was attenuated by L-NNA from 10 to 100 mM methacholine (both P<0.05), associated with an 11% reduction overall. Chest CVC, however, was not influenced by L-NNA at any methacholine dose (all P>0.05; 8% reduction overall). Conclusions: Our preliminary data indicate that regional variations exist in the NOS component of cholinergic vasodilatation. Further exploration of the mechanisms influencing regional variations in cutaneous vasodilatation may help identify optimal sites for representing whole-body responses under various experimental conditions. Funding: Natural Science and Engineering Research Council of Canada (G. P. Kenny).

ABSTRACT. Introduction: Increased heat stress due to global warming has resulted in frequent accidents related to heat stroke. East Asia has areas prone to high temperatures and high relative humidity (RH) during the summer season, which leads to increases in the incidence of heat stroke among outdoor workers. It is well known that nausea, vomiting, and vertigo are initial symptoms of heat stroke. Heat stroke may increase human errors such as slips, trips, and falls, as distinct from heat stress. This study aimed to investigate the impaired balancing ability due to physiological responses with the prolonged workload and hot exposure.

Method: Eight healthy men participated in this experiment for measuring physiological responses and deterioration of balancing ability in response to a 4-h workload and heat exposure (34℃, 50%RH). The experiment protocol consists of four sets of the test (45 min of low-speed treadmill exercise and 15 min of recovery). The participants performed this test from morning to afternoon with 1h of lunchtime. Heart rate and body temperature were recorded during the test. Functional reach, 2 steps test, timed up and go, and Y-balance test was measured for functional balance test. Also, body sway length and area were tested.

Results: This study indicates that impaired balancing ability was affected by prolonged workload and heat exposure. The body temperature and body weight loss measured during workload with heat exposure were significantly high. The balancing ability parameters such as functional reach, timed up and go, sway length, and sway area showed a similar tendency, however, there were no significant differences.

Conclusions: Accumulation of physiological fatigue from prolonged workload and heat exposure seems to contribute to the impaired balancing ability.

ABSTRACT. Introduction: A physiological strain index (PSI) based on the combination of core body temperature and heart rate has been applied to estimate heat strain (Moran et al. 1998). A non-invasive index using thermal perception (PeSI) has been proposed (Tikuisis et al. 2002). However, most heat strain indexes are designed for young adults during heavy exercise under hot and dry environments. However, in 2018, about 60% of heat-related deaths in Korea were found in 65 years old or older people while walking or working in agricultural fields. This study evaluated heat strain of elderly males during light activities in hot and humid environments and suggested a non-invasive heat strain index for elderly people during heat waves. Method: Ten older males (74.7±4.0 yr, 157.3±6.1 cm, 66.7±5.8 kg) and 11 young males (23.5±2.3 yr in age, 167.2±7.0 cm in height, 73.7±10.0 kg in body weight) participated in four experimental conditions: 60-min sitting and 60-min walking at an air temperature of 30oC with 70%RH (WBGT 27oC) and 35oC with 70%RH (WBGT 32oC). During all trials, rectal temperature (Tre), ear canal temperature (Tear), 11 skin temperatures (Tsk), energy expenditure, heart rate (HR), total sweat rate (TSR), blood pressure (BP), thermal sensation (TS) and thermal comfort (TC) were recorded. Results and conclusions: The results showed that the elderly’s maximum exposure time at an air temperature of 35oC (70%RH) at rest were 167 min (Tre 38.5oC) and 193 min (Tre 39.0oC) as an alarm and a danger criterion, respectively, while no criteria were suggested at 30oC (70%RH) at rest. While walking, PSI estimated older males’s heat strain at a lower level becasue of their diminished heart rate capability compared to young males. A heat strain index based on foot temperature, ear canal temperature and thermal comfort for older males while walking was developed and evaluated. (More detailes will be reported in the revised abstract)

ABSTRACT. Introduction: Occupational heat stress is detrimental for human performance leading to significant labour loss. However, the magnitude of this problem remains unclear even in industries such as agriculture which are depended on manual labour conducted outdoors. Therefore, the aim of our study was to quantify the magnitude of heat-induced labour loss and examine the thermophysiological responses of agriculture workers during different seasons. Methods: During the last three years, we evaluated >1000 work hours via time-motion analysis on a second-by-second basis collected from 165 workers (age: 41.9±13.0 years; BMI: 25.8±4.8 kg/m2) while performing different agriculture jobs. Physiological data (core temperature, skin temperature, and heart rate) were collected from 22 individuals. Environmental data were recorded throughout the work shift using a portable weather station. The study has received funding from the European Union's Horizon 2020 research and innovation programme under the Grant agreement no. 668786. Results: Very strong relationships were identified between thermophysiological responses (core temperature: r=0.96; skin temperature: r=0.99; heart rate: r=0.93), labor loss (r=0.94) and air temperature (all p<0.001). Precisely, labour loss escalates from 3.9%, during low occupational heat stress (11-18°C), to 14.2% during high occupational heat stress (27-34°C), increasing by 0.65% for every 1°C increase in workplace temperature (R2=0.87, p<0.001). On the other hand, we found a negative relationship between metabolic rate (r=-0.33) and air temperature (p<0.001). Conclusions: Occupational heat stress affects the human thermophysiological responses leading to impaired capacity to perform work.

ABSTRACT. Introduction: Humans have evolved several cellular stress-response pathways including autophagy and the heat shock response to ensure survival under changing environmental conditions. Autophagy is a cytoprotective mechanism that plays a major role in cellular homeostasis and stress resistance, while the heat shock response suppresses protein toxicity and aggregation under environmental stressors such as increased ambient temperature. Elderly individuals are at greater risk for heat-related illness, which may be associated with dysfunction in these two major stress response pathways. The purpose of this study was to examine autophagy and the heat shock response in young and elderly adults during a day-long exposure to extreme heat.

Method: Peripheral blood mononuclear cells (PBMCs) were harvested from five young (22±2 years; one woman) and six elderly participants (70±3 years; two women) at 4.5-h and 9-h of resting exposure to extreme heat conditions (40°C, 10% relative humidity). Genes associated with autophagy (MAP1LC3B and p62/SQSTM1) and the heat shock response (HSPA1A) were analyzed via qRT-PCR. All values are reported as fold change relative to their respective baseline measurement.

Results: After 4.5-h of heat exposure, MAP1LC3B, p62/SQSTM1, and HSPA1A gene expression increased in young (1.70±2.09, 1.19±0.90, and 1.60±1.77, respectively) and elderly adults (1.39±0.38, 1.35±0.58, and 1.50±0.28, respectively). However, at 9-h there was a further increase in expression of measured genes in the young (2.57±3.78, 2.27±3.02, and 2.88±4.29, respectively), but not in the elderly adults (1.41±1.53, 1.44±1.35, and 1.58±1.64, respectively), despite a larger increase in rectal temperature in the elderly adults (0.97 vs. 0.52°C).

Conclusions: These preliminary findings indicate that older individuals experience blunting in both the autophagy and heat shock response pathways during a day-long extreme heat exposure, which may contribute to greater rates of heat-related illness in this population during extreme heat events.

ABSTRACT. BACKGROUND: Self-paced physical work in the heat is largely characterised by a stable working heart rate, integrating the stress of the physical work and the climate. At present, major public health agencies (WHO, CDC, NHS) advise against forced convection (e.g., electric fans) at air temperatures above 35°C, however without empirical basis. In this study, we provide the empirical evidence to evaluate these advisories by comprehensively re-examining the critical environmental limits for benefits of fans to physical work capacity (PWC) above the advised 35°C.

METHOD: A heterogeneous sample of 14 young adult males (8 semi-nude, 6 wearing protective coveralls) performed 242 experimental trials consisting of 1-hour treadmill walking at a fixed heart rate of 130 b·min-1. After a reference trial without heat stress (15°C, 50% rh), remaining trials were conducted across a wide range of air temperatures (35 to 50°C) and humidity (20 to 80% rh, 1.1 to 5.9 kPa water vapour pressure), each with and without wind at 4.0 m·s-1.

RESULTS: The effect of wind was dependent upon air temperature, humidity and protective clothing insulation. In minimal clothing, wind was beneficial up to 45°C, but only above 2.0 and below 4.7 kPa vapour pressure. For coveralls, wind was beneficial up to 40°C, above 2.0 and below 3.5 kPa. Fans typically impaired PWC beyond these critical environmental limits.

CONCLUSIONS: Contrary to current advice, fans can increase PWC at air temperatures above 35°C, allowing more work to be performed for the same cardiovascular strain. However, new guidelines for their safe use must incorporate air temperature, relative humidity, and whether protective clothing is required. In hot dry environments, exogenous skin wetting may be a safe addition or alternative to electric fan use.

ACKNOWLEDGEMENTS: Funding was provided by ‘Heat-Shield’, European Union's Horizon 2020 research and innovation programme under the Grant agreement no. 668786.

ABSTRACT. In this study, the human physiological response and rapid-reaction ability was investigated after the core temperature maintained during 38~38.5 °C for 20 min. It was found that the mean skin temperature increased from 32 ±0.5 °C to 37 ±0.5°C within 20 min and maintained until the end of the test. No statistic significant different was detected between the results of the visual retention and choice reaction time tests.

ABSTRACT. Introduction: Transient receptor potential vanilloid 4 (TRPV4) channels play an important role in the activity of sensory receptors including osmo-, mechano-, and thermo-receptors, and others. While these channels exist on vascular endothelial cells and eccrine sweat gland secretory cells in human skin, it remains unclear if they are functionally involved in the activation of cutaneous vasodilatation and sweating during a passive heat stress. Method: Twelve young adults (6 men, 6 women) were exposed to a moderate heat stress induced by increasing esophageal temperature of ~1.0ºC above resting levels using water-perfusion suits. Prior to and during heating, cutaneous vascular conductance and sweat rate were simultaneously measured at four intradermal microdialysis sites on the dorsal forearm continuously perfused with either 1) lactated Ringer (Control), 2) 5 % dimethyl sulfoxide (organic solvent) only, or one of the two following TRPV4 channel antagonists dissolved in 5 % dimethyl sulfoxide solution: 3) 200 µM HC 067047, or 4) 125 µM GSK 2193874. Following whole-body heating, 100 µM GSK1016790A, a TRPV4 channel agonist, was administered to the Control and both TRPV4 channel antagonist treated skin sites. Results: The administration of a TRPV4 channel antagonists did not modulate cutaneous vascular conductance and sweat rate during resting under a non-heat stress condition (pre-heating period). Similarly, no effect of the TRPV4 channel blockade was measured during whole-body heating. Furthermore, the administration of 5 % dimethyl sulfoxide alone had no effect throughout. Administration of TRPV4 channel agonist did not affect sweat rate, but it increased cutaneous vascular conductance at the Control site. This elevation in cutaneous vascular conductance was partly attenuated by both TRPV4 channel antagonists. Conclusions: We show that TRPV4 channels do not contribute to the heat loss responses of cutaneous vasodilatation and sweating during a whole-body moderate passive heat stress in young adults.

ABSTRACT. Introduction: Sweating efficiency (Eeff) is the fraction of secreted sweat that evaporates from the skin, and has been traditionally estimated using an oil-pan method. Our study explored the notion of estimating Eeff during exercise using a heat balance method.

Method: Nine participants walked on a treadmill for 75 minutes (5 km/h with a 2% (low heat production (Hprod); n=6) or 6% (high Hprod; n=3) gradient) in: 1) a high efficiency (34.0±0.1°C, 24.9±0.8% RH, 2.0 m/s air velocity), and 2) a low efficiency (34.7±0.5°C, 60.3±1.9% RH, no wind) trial. Both trials were conducted twice to assess repeatability. Hprod and body temperatures were measured continuously, and nude mass assessed after 0, 45 and 75 minutes. After 45-min (steady-state), we assumed Hprod, corrected for dry and respiratory heat loss, was equal to evaporative heat loss (Eloss). Body mass loss (45-75-min), corrected for respiratory and metabolic mass losses, was used to estimate evaporative potential (Epot). The percentage of Eloss relative to Epot equalled Eeff.

Results: With low Hprod, Eloss was 335±44 and 344±42 W in the high and low efficiency trials, respectively, whereas Epot was 375±65 and 388±81 W. With high Hprod, Eloss was 416±16 and 452±29 W in the high and low efficiency trials, respectively, whereas Epot was 499±24 and 695±102 W. Estimated Eeff values were 90±7% and 88±11% in the high and low efficiency trials with a low Hprod, but 84±6% and 58±13% in the high and low efficiency trials with a higher Hprod. Repeatability of the Eeff, measured as coefficient of variation, was 12.4%.

Conclusions: Differences in Eeff were detectable in the high Hprod condition, but not in the low Hprod condition. Accurate measurements of weight loss, Hprod, body temperatures and ambient conditions are essential, and present significant challenges to making this method viable. Work on refining this method is ongoing.

ABSTRACT. Introduction: Ballistic protection is critical to safeguarding against physical injuries on the battlefield. However, it also restricts the avenues for body heat exchange between the skin and environment. This study aimed to assess the effect of ballistic protection coverage on ensemble heat exchange properties and to estimate thermal strain. Method: Total thermal insulation (It), evaporative resistance (Ret), and Evaporative potential (im/clo) were measured on a heated sweating manikin according to ASTM standards (F1291-16, and 2370-16). Three clothing ensembles were evaluated. A combat uniform of long sleeve shirt and trousers, socks and boots (CON), to which a protective ballistic vest was added (BPC). The third ensemble included a combat uniform with additional extremity protection on the collar, shoulders and upper arm, waist, and abdominal flap, and a helmet (BPC-E). The Heat Strain Decision Aid predicted deep body temperature elevation during light (225 W), moderate (400 W), and heavy (654 W) work in 35 °C air temperature and 40% relative humidity (33 °C Wet-Bulb Globe Temperature). Results: BPC-E imposed greater restrictions to heat exchange (It 1.53 clo, Ret 0.038 kPa∙m2/W, im/clo 0.24) compared to the BPC (It 1.37 clo, Ret 0.033 kPa∙m2/W, im/clo 0.29) and CON (It 1.37 clo, Ret 0.031 kPa∙m2/W, im/clo 0.30) ensembles. For light, moderate, and heavy work, time to a deep body temperature elevation of 38.5 °C was 88, 54 and 32 min for BPC-E, 113, 59 and 35 min for BPC, and 122, 66 and 40 min for CON. Overall, work times were reduced ~20-30% for the BPC-E compared to CON, and 10-20% compared to BPC. Conclusions: Ballistic protection coverage around the upper body restricts heat exchange and elevates thermal strain. Risk management strategies, such as reduced exposure times, will be required in hot training environments where additional ballistic protection is worn.

ABSTRACT. Introduction: Cycling time trials are characterised by riders adopting aerodynamic positions to minimise drag. Adopting these aerodynamic positions may have an effect on heat strain, due to modifications in muscle recruitment, metabolic heat production (Hprod) and heat loss due to airflow changes. The aim of this study was to determine whether cycling in an aerodynamic position impacts upon Hprod. It was hypothesised that a change in hip angle would result in alterations to Hprod. Methods: Eleven trained male cyclists (Height 1.9±0.1 m; age 33±9 yrs; 〖V ̇O〗_(2 max) 57.5±7.6 mL.kg.min-1) visited the laboratory on five occasions to complete a graded exercise test. Hip angle was set at 12˚, 16˚, 20˚, 24˚ and the rider’s self-selected position. Blood lactate (Bla) and gastrointestinal temperature (Tgi) were recorded throughout, with metabolic rate (M) and Hprod calculated via indirect calorimetry. For each condition, power output, M and Hprod corresponding to a Bla value of 4 mmol.L-1 were determined. Results: Neither Tgi (P=0.096), nor power output (P=0.222) were different at 4 mmol.L-1 between hip angles. An effect of condition was evident for M and Hprod (both P<0.05). M was higher in control (1222±167 W) vs 12˚ (1150±166 W; P<0.05), and in 24˚ (1264±212 W) vs 12˚ (P<0.05). Consequently, Hprod was higher in 24˚ (983±168 W) compared to 12˚ (880 ± 125), with a positive relationship between hip angle and Hprod (R2=0.414, P<0.05). The ∆ power output at 4mmol.L-1 compared to control reduced as hip angle increased (R2=0.844, P<0.01). Conclusions: These data show that Hprod is sensitive to changes in hip angle, possibly due to an increase in muscle recruitment and consequently metabolic rate. Based on Tgi data, there may be increased heat loss associated with greater hip angle, which is likely due to increased airflow over the body. This requires further clarification.

ABSTRACT. Introduction: Progressive sweat-induced fluid loss without fluid replacement during prolonged exercise-heat stress (≥60 min) compromises cardiovascular and thermoregulatory function, although its effects on cardiac autonomic activity remain unclear. We examined heart rate variability (HRV), as a surrogate of cardiac autonomic activity, during prolonged exercise in the heat with and without fluid replacement. Methods: Ten young and healthy men performed 90-min of semi-recumbent cycling in dry-heat (40 °C; 20% relative humidity) at a fixed rate of metabolic heat production (600 W; ~46% V̇O2peak) without fluid replacement (No-FR; ~3.4% reduction in body mass). On a separate day, participants completed the same protocol with fluid replacement (FR) to offset sweat losses as determined in No-FR. Esophageal temperature and electrocardiogram were recorded throughout, with temperature and HRV averaged over the final 10-min of each 30-min interval during exercise. Results: Esophageal temperature and heart rate was elevated in No-FR compared to FR (all P ≤ 0.02). Compared to baseline (No-FR, -1.32 [0.22]; FR, -1.37 [0.23]), cardiac vagal index (CVI = log10[16 x SD1 x SD2]) was attenuated during exercise, with the magnitude of this reduction being greater in No-FR (90-min, -3.27 [0.20]) relative to FR (90-min, -2.84 [0.45]; all P < 0.05). Likewise, lnRMSSD was attenuated throughout exercise in both conditions (all P < 0.01), with a greater reduction in No-FR (all P ≤ 0.043). Finally, sample entropy was reduced at 90-min relative to baseline in both No-FR and FR (both P < 0.01), but was lower throughout exercise during the former (all P ≤ 0.03). Conclusions: Prolonged exercise in the heat was associated with reduced activity of HRV indices reflecting vagal tone, indicative of increased cardiac autonomic stress. Those alterations were blunted, however, when fluid was provided to offset progressive sweat losses, highlighting the importance of fluid maintenance during exercise in the heat.

ABSTRACT. Introduction: Public health guidelines on how to ensure babies’ thermal proception are available (e.g. dressing with 1 extra layer of clothing than the adult); yet little is known on the strategies that parents adopt to ensure their babies’ thermal protection when these are carried in a sling (i.e. babywearing). The aim of this study was to survey parents’ practices during babywearing with regards to baby dressing and thermal monitoring in the heat and cold.

Method: Participants undertook an anonymous online questionnaire aimed at establishing a) demographics; b) knowledge of guidelines for babies’ safety (e.g. thermal protection and sleeping position); c) babywearing practices in the heat and cold (e.g. number of clothing layers placed on babies); d) thermal monitoring (e.g. parts of the babies’ body used to determine their thermal state); e) subjective thermal responses (e.g. babies’ body parts that become hotter during babywearing).

Results: 317 responders (98% females) completed the questionnaire. Most participants carried their baby outdoor (66%), more than once a week (67%), and between 30 min and 1 h (53%). Only 33% of participants were aware of guidelines on baby dressing, whereas 97% of responders had knowledge of safe sleeping guidelines. Most participants reported to dress babies in 1 layer less than if using a pram during both warm (52%) and cold (52%) days. They also reported they would touch their babies’ skin to determine their temperature (90%), and that during both warm (87%) and cold days (95%), their babies’ trunk becomes the warmest regions.

Conclusions: We show that knowledge of public health guidelines for babies’ thermal protection during babywearing is comparatively low that of safe sleeping. Yet, we observed clear practices amongst parents for both baby dressing and thermal monitoring that consider the thermal impact of babywearing in both warm and cold ambient.

ABSTRACT. The physiological heat strain index (PSI) was developed to assess individuals’ heat strain within various settings, yet evidence supporting its use to accurately identify individuals at potential risk is limited. The aim of this study was to assess whether PSI can identify individuals at risk of heat induced fatigue (HIF). Fifteen females (24.2 ± 5.7 years; 1.69 ± 0.09 m²) and 21 males (26.9 ± 4.7 years; 1.95 ± 0.13 m²) completed nine trials, each consisting of two 40-60 mins of treadmill walking separated by ~20-mins rest, wearing permeable or impermeable clothing, either in 25 °C, 50% relative humidity (rh), 35 °C, 35% rh , or 40 °C, 25% rh, with or without solar radiation (~530 W m⁻²). Heart rate (HR), skin temperature (Tsk), rectal temperature (Tre), temperature sensation (TS) and thermal comfort (TC) were measured throughout. PSI was calculated using the equation by Moran (1998) with inital Tre and HR set at 37.0 °C and 70 bpm. End of trial PSI, HR, Tre, Tsk, rate of change (ROC) in Tsk and Tre and TS and TC were compared between the trials completed (C, 117 trials) and those terminated prematurley (HIF, 35 trials) using independent t-tests. End PSI did not significantly differ between HIF (6.98 ± 1.67) and C (6.71 ± 1.56). However, there was a significant difference between HIF and C in Tre-Tsk (0.9 ± 0.86 °C vs 1.29 ± 0.86 °C, respectively, P = 0.009) and in TS (18.03 ± 2.22 vs 15.70 ± 4.33, respectively, P = 0.008). In HIF, 42.24% of the cases had a PSI > 7.5 (considered ‘at risk’ from HIF). These results suggest PSI alone does not distinguish between individuals at risk of HIF, however, using additional measures of Tsk and TS may provide a better prediction of heat tolerance.

ABSTRACT. Introduction: This study aimed at evaluating the visibility of new and damaged firefighter protective clothing (FPC) by smoke and light intensity conditions.

Method: Eight male firefighters sat at a distance of 12 m from a FPC wearer and evaluated the visibility of FPC within the range of 0% (not visible) to 100% (very visible). Main experiments consisted of eight conditions: 2 smoke (smoke, no-smoke) × 2 light intensity (day, night) × 2 FPC conditions (new, flame-damaged). Additional experiments using light emitting diode (LED) bands and flashlights were performed in order to find auxiliary ways of improving the FPC visibility.

Results: Under the day condition, the visibility scores of new and damaged FPC were 2.1 ± 0.7% and 1.8 ± 0.7%, respectively, under the smoke condition, while the visibility scores were 100.0 ± 0.0% and 66.3 ± 6.3% under the no-smoke condition. There were significant differences in the visibility scores between smoke and no-smoke conditions (P <0.001), and between new and damaged FPC under the no-smoke condition (P <0.05). Under the night condition, the visibility scores were all 0% under the smoke condition, while the visibility scores were 10.1 ± 2.1% (new) and 5.4 ± 1.2% (damaged), under the no-smoke condition. Meanwhile, these visibility scores under the night-no smoke condition were improved up to 47.8% (new) and 45.3% (damaged) with the LED bands, and 45.0% (new) and 35.6% (damaged) with flashlights.

Conclusions: The visibility of FPC was degraded due to smoke obscuration and flame damage. This degradation was especially serious under the night-smoke condition, but it was confirmed to be able to improve when using LED bands and flashlights. Further studies in different smoke concentration levels and colours, and with various brightness, locations, sizes, and flashing patterns of different auxiliary tools are required for field application.

ABSTRACT. Introduction: Industrial sugarcane workers perform difficult, strenuous work under hot environmental conditions. It is possible that clothing and protective gear further exacerbates worker’s heat exposure as clothing has a strong thermal impact on humans. The aim of this study was to evaluate i) the thermal performance of clothing and protective gear used in sugarcane harvesting and chemical spraying tasks, and ii) workers’ predicted heat strain (PHS). Method: The thermal manikin Tore at Lund University was used to test the clothing insulation and the evaporative resistance of sugarcane harvester (SC) and chemical sprayer (CP) clothing sets. Tested clothing ensembles were acquired from Ingenio San Antonio, the largest sugar mill in Nicaragua, and are currently worn by field workers. Sugarcane field weather data, estimated activity levels and clothing parameters were entered into the PHS model (http://www.eat.lth.se/fileadmin/eat/Termisk_miljoe/PHS/PHS.html). Exposure characteristics were calculated hour by hour for temperature (ta=18.6-36.4 °C, tg=20.5-52.1 °C) and activity combinations. The curves of exposure limit were prepared based on core temperature and water loss. Results: Parameters for both clothing sets were all within the limits of PHS requirements (Icl,SC=0.107 m2K/W, Icl,CP=0.177 m2K/W; Recl,SC=13.2 m2Pa/W, Recl,CP=74 m2Pa/W). Heat exposure in chemical protective clothing was strongly limited by increasing core temperature, while cane cutters’ core temperature raised above 38 °C only at air temperatures above 34 °C, and for them dehydration was a stronger limitation: core temperature rise may trigger rest breaks, and during breaks people drink. Alternatively, dehydration is harder to notice subconsciously. Conclusions: Insulation and evaporative resistance values (total, regional and local) of typical clothes used in sugarcane fields are available. Although, accuracy of PHS method can be questioned, these data provide estimations of exposure time, rest break frequency and recommendations for regular water intake. Thus, enabling 1) evaluation of work situation and 2) better organisation of work schedule.

ABSTRACT. Introduction: Hot water immersion (HWI) therapy confers chronic health benefits, including reductions in fasting blood glucose concentration. The mechanisms behind this are unclear, and glucose metabolism directly following an acute HWI session is poorly explored. Therefore, the aim of this study was to investigate glycaemic control directly following HWI. Method: Ten participants (age: 25±6 years, body mass: 84±14 kg, height 1.85±0.09 m) were immersed in water to the neck (60 min at 39°C, HWI) or sat at room temperature (CON). One hour following this intervention, they performed a two-hour oral glucose tolerance test (OGTT), with blood collected before and after HWI/CON and during the OGTT. Plasma protein concentrations were quantified using enzyme-linked immunosorbent assays, and incremental areas under the curve (iAUC) determined for glucose and insulin. Results: Glucose iAUC during the OGTT was greater in HWI (HWI 233±88, CON 156±79 mmol·L-1·2h, P=0.02) whilst insulin iAUC was similar between conditions (HWI 4309±3660, CON 3893±3031 mU·L-1·2h, P=0.32). Body temperature increased to 38.6±0.2°C during HWI; during the OGTT body temperature did not differ between conditions (HWI 37.0±0.2, CON 36.9±0.4°C, P=0.34). Directly following HWI, plasma adrenaline and growth hormone concentrations increased 2.7 and 10.7-fold, respectively (P<0.001). No differences between conditions were found for the plasma concentrations of the gut hormones glucagon like protein-1, peptide YY, or acylated ghrelin (P>0.11) during the OGTT. Conclusions: HWI increased postprandial glucose concentration to an OGTT, despite no difference in body temperature or insulin during the OGTT between conditions. This change in glycaemic control might be explained by the residual effect of the HWI-induced stress hormones, which may act on hepatic glucose output or intestinal glucose uptake. Gut hormone kinetics during the OGTT were unaffected by HWI, therefore unlikely to explain the difference in the observed glucose response between conditions.

ABSTRACT. Introduction: Exercise performance can be compromised in hot and humid environments. The effects on cognitive performance are less well-known but thermal strain may impair complex cognitive function. Localised head cooling can alleviate thermal strain and improve exercise performance but data regarding the effectiveness of such cooling on cognitive performance is equivocal. Methods: Participants (n=10) completed two 165 min American Football simulations in the heat (36 °C and 50% RH). Each protocol had four quarters (Q1 – Q4) and consisted of sprints and plyometric push-ups separated by representative breaks. Participants wore full American football uniforms throughout. During one session (COOL), participants removed the helmet and donned a cooling hood during breaks longer than two minutes; the cooling hood covered the cheeks, forehead, head, and neck. Thermoregulatory and perceptual variables were measured throughout. Executive function and visuospatial learning were assessed using Spatial Working Memory (SWM) and Paired Association Learning (PAL) tests conducted before, midway (“half time” (HT)), and after exercise (FT). Cognitive performance data were analysed as changes from baseline due to intra-trial variability at this time-point. Results: Participants had lower head skin temperatures during all three testing windows and lower core and skin temperatures during the post-exercise testing window in COOL. Participants felt cooler and more comfortable when wearing the cooling hood. More correct choices were made at the 1st attempt in COOL at HT and FT whereas fewer were made without cooling. In the same test (PAL), fewer incorrect choices were made in COOL at HT and FT but more were made in CON at FT. Fewer strategic errors were made without cooling at HT and with cooling at FT compared to baseline. Conclusion: Wearing a cooling hood reduced the physiological and perceptual thermoregulatory strain and improved visuospatial learning and aspects of executive function compared to CON.

ABSTRACT. Introduction: Firefighting is physiologically a very demanding occupation. The combined effects of a hot working environment, protective clothing and heavy physical tasks may lead to cardiovascular and thermoregulatory strain. The aim of this study was to develop a smart technology-based assessment system to identify firefighter’s heat strain and to prevent heat-related illness. Method: Firstly, interviews of requirements were performed in five rescue departments. Secondly, human measurements were performed in laboratory conditions and at the Emergency Service College during their training program. Movesense sensor (Suunto, Finland) was used to measure individual heart rate, activity and temperature. Data transfer and route methods were developed for the sensor. Core temperature (Tc), skin temperatures (Ts) and heart rate (HR) were measured. Subjects’ physical characteristics and HRmax were measured or previously measured VO2max was used. In addition, thermal insulation and water vapour resistance of the firefighter clothing were measured. Results: In the interviews several topics were raised eg., location of the partner, ambient temperature, volume of the compressed air, heat and physical strain. Assessment of heat strain was chosen for this study because of its importance of their health and well-being. Simplified version (HTM_D) of the VTT Human Thermal Model (HTM) was developed. Parameters for the HTM_D were HR, Ts and thermal insulation of the clothing. Measured and calculated (by the model) Tc differed by 0.2 °C. HR and calculated Tc were then used to estimate the physiological strain index (PSI) according to Moran et al. (1993). Conclusions: HTM_D can be used to assess PSI of a firefighter in real time. HTM_D together with smart Movesense technology is a useful tool for fire officers to monitor firefighters’ health and safety during their demanding tasks. Saved database can be used to explore individual cumulative exposures to heat strain.

This study was partly supported by Business Finland

ABSTRACT. Introduction: The Colorado trail race (CTR) is an extreme endurance mountain bike (MTB) race requiring participants to complete 500-miles (800km) of racing between Denver and Durango in the Rocky Mountains. The race is unsupported and includes 70,000 feet (21,336m) of cumulative ascent with a peak altitude of 13,200 ft (4,023m) at which there is acute mountain sickness risk. Here we describe a case-study of an entrant to the 2018 CTR. Method: Participant characteristics were: 47-year-old male, height 1.73m, 61kg, BMI, 20.3kg.m2. The participant completed incremental lactate threshold (LT) tests to establish training intensities and training progression; final LT was used to estimate the decrement to sustainable power output at altitude; he also completed dietary and hydration assessment. At baseline and during the CTR the participant reported sleep quality and mood disturbances (10-point Likert scale), rating of perceived exertion (RPE) and recorded race pace and elevation using GPS. He supplemented with iron to facilitate haematological acclimatisation. Results: The participant’s LT at sea-level was 225 to 250 Watts (W) with a peak power output of 356W. We extrapolated a range of possible decrements to PPO at 4000m (4.5, 6.3 and 7.5%) in line with published literature potentially reducing PPO to 250, 225 and 225W; assuming no acclimatisation. We suggested that he should “sleep low, ride high” to maximise resting race recovery. He finished 6th overall in 5 days 6 hours, averaging 4.1mph with 2.5 hours of sleep per night. He reported depression (5) and anxiety (9) peaks (day 4), fatigue (10) and RPE peaks (20) on day 5 and that heat load and dehydration were significant problems. Conclusions: The CTR is a significant endurance challenge that takes place in a high-altitude, hot environment with limited access to support provisions. Completion of the CTR results in profound cumulative fatigue and mood disturbance.

ABSTRACT. Introduction: Current three layered firefighter protective clothing (FPC) can prevent 2nd degree burns from several seconds of heat and flame exposure at 84 kW•m-2. However, structural fires, due to their various building materials, occasionally reach over 84 kW•m-2. Lately, it is developing an FPC capable of withstanding exposure to higher heat, such as 125 kW•m-2, while maintaining comfort has been an issue. This study evaluated the protective and comfort functions of a newly-developed FPC with layered Nomex honeycomb fabric. Method: We developed a new FPC using Nomex honeycomb fabric (as the middle layer of the FPC (HPC)) and examined its flame protection using a flame manikin and its heat-resistance using a thermal manikin. A maximum oxygen consumption test (VO2max) was carried out with firefighters. Through a simulated firefighting task protocol with firefighters, performance and mobility were evaluated. All the tests and trials were compared to the current FPC. Results: The estimated surface area for a 2nd degree burn was lower for HPC than for the current FPC. HPC had 0.21 higher clo than the current FPC. VO2max was reduced to 14% (current FPC) and 12% (HPC) compared with wearing light sports wear, but no significant difference in VO2max between the current FPC and HPC was found. Completion time to accomplish the simulated firefighters’ task was 14 min (FPC) and 13 min (HPC). There were not a remarkable differences between FPC and HPC in thermal sensation, thermal comfort, and sweat sensation. Conclusions: These results indicate that the newly developed Nomex honeycomb FPC can 1) minimize skin burns when facing sudden high risk situations, and 2) not impair firefighters’ maximal performance or subjective perceptions when compared to the current FPC.

ABSTRACT. Introduction: The benefits of ice and caffeine individually on performance is well established. However, to date little is known on the combination and application to repeated sprint performance in the heat.

Method: Twelve male team-sport athletes (age 29 ± 6 y, mass 82.0 ± 6.3 kg, height 180.4 ± 6.5cm) completed eight randomly assigned trials, ingesting either water (w) at 25°C or ice slurry (i) at -1°C as follows; placebo (PLAw and PLAi), caffeine (5 mg·kg-1; CAFw, CAFi), carbohydrate (6%, 0.41g·kg-1 CHOw, CHOi), caffeine and carbohydrate (5 mg·kg-1 and 6%, 0.41g·kg-1 ; C+Cw, C+Ci) 40 min prior to completing 18 × 4-s maximal sprints in the heat (37.0 ± 1.1°C, RH 38.0 ± 1.9%). Rate of perceived exertion (RPE), thermal sensation and thermal comfort were sought 30 sec prior to start of each sprint.

Results: There was a significant reduction in rectal temperature (Tre) in ice slurry compared with corresponding water trials (Delta values of Tre between 1.3-1.6°C ; PLAw p=0.002, CAFw p=0.007, CHOw p=0.001, C+Cw p=0.008). CAFi had the highest mean power of 1008 ± 235W, yet whilst not significantly different to any other condition CAFi did show a meaningful difference (>36W) between PLAi (962 ± 202W) and CHOi (957 ± 210W). CAFw also produced high power outputs (mean 999 ± 197W) compared with the ice conditions (PLAi 962±202W, p=0.04, 95%CI 1.7,91.0 and CHOi 957±210W, p=0.04, 95%CI 3.5,127.9). Although importantly, CAFw showed greater decrement in performance than CAFi.

Conclusions: In hot conditions the ingestion of caffeinated beverage (CAFw) or caffeinated ice slurry (CAFi) consumed 40 min pre-exercise produced higher mean power repeated sprint outputs than non-caffeinated alternatives. These findings would be of benefit within intermittent team sports where repeated high power efforts are required but should be applied conservatively to minimise the negative decrement effects, and reduced early performance associated with ice slurry ingestion.

ABSTRACT. Introduction: Industrial workers are at risk from heat illness whenever they work for a prolonged time in hot and humid conditions. In 2018, ~1100 cases of heat injury are reported in Japan, despite a continuing focus on prevention. Wearable technology is now being adopted, but a system that accurately measures core temperature using wearable devices has yet to be reported. We propose a new model based on a dual-heat-flux method that predicts core temperature using data from patch-type sensors on the chest. Method: We performed experiments that compared our predicted temperatures (Tpre, revised dual-heat-flux method) with actual temperatures, both esophageal (Teso) and rectal (Trec), during exercise in hot conditions. Fifteen males and six females walked for 60 min at 4-5 km/h (at 35°C, 50% RH) while wearing standard work uniform. Seven male subjects among them participated in another trial with protective clothing. Results: In the work uniform, Teso, Trec, and Tpre increased from 37.1 ± 0.2°C, 37.0 ± 0.2°C, and 37.1 ± 0.3°C to 37.9 ± 0.1°C, 37.9 ± 0.1°C, and 37.9 ± 0.1°C (mean ± SD), respectively, during exercise. The difference between Tpre and Teso was 0.01 ± 0.18°C and that between Tpre and Trec was 0.26 ± 0.26°C, using data sampled at 5-minute intervals during exercise. In the protective clothing, Teso, Trec, and Tpre increased to 38.2 ± 0.2°C, 37.9 ± 0.3°C, and 38.0 ± 0.2°C after exercise. In this case, the difference between Tpre and Teso was –0.20 ± 0.23°C and that between Tpre and Trec was 0.30 ± 0.31°C. Conclusions: Error ranges for our model are similar to those in previous studies involving noninvasive core temperature measurements. Although our system uses simple wearable devices, influencing factors such as body size and composition, intense and upper-body exercise, and environmental temperature should be investigated in future work.

ABSTRACT. Introduction: Recent human studies have reported modulated profile of brachial artery shear stress (BA-SS) during lower limb exercise, which may be a key factor contributing to endothelial adaptations of the inactive upper limbs. During exercise, the BA primarily supplies the skin BF (SBF) to the glabrous (G; palm) and non-glabrous (NG; dorsal and forearm) regions; however, it remains unclear which between these is most responsible for upstream BA-SS profile. Therefore, the purpose of this study was to elucidate the effects of G and/or NG cutaneous vascular conductance (CVC), which were modulated by warming or cooling stimulation, on BA-shear rate (SR: an estimate of SS) during cycling exercise. Methods: Seven healthy young subjects performed 60-min cycling exercise, which corresponded to a heart rate of approximately 120 bpm. Between 20 and 50 min of the exercise, the NG+G or G skin regions of the right arm were warmed to 43°C or cooled to 15°C using a water bath. Each subject underwent four trials in a random order. Throughout the protocol, the diameter and blood velocity of the BA were simultaneously recorded using Doppler ultrasonography to calculate antegrade, retrograde and mean SRs. SBFs in the forearm (f) and palm (p) were also measured to calculate the CVC (SBF divided by mean arterial blood pressure). Results: At 20 min of the exercise, f-CVC and mean BA-SR significantly increased compared with resting baseline values in all trials. Subsequently, during NG+G warming stimulation, dramatic increases in f-CVC and concomitant BA-SR (primarily characterized by increased antegrade SR and decreased retrograde SR) were observed. By contrast, when the skin regions either G or NG+G were cooled, both CVCs and mean BA-SR were slightly but significantly decreased. Conclusions: NG CVC response possibly plays a major role in the modulation of BA-SS profile during lower limb exercise. [JSPS-KAKENHI (#17K01616 to YF)]

ABSTRACT. Introduction: There is a plethora of research available that describes the well-established muscle atrophy that occurs as a result of inactivity. However, the literature describes the expected average outcome and does little to discern the individual responses. As a result, we retrospectively analysed data collected from 3 separate bed rest studies to analyse individual variation.

Method:

The data used for the present analysis was collected from three bedrest projects: PlanHab (14 males; 21 days; Normoxic bedrest, Hypoxic bedrest ~4,000m, Hypoxic ambulation, ~4,000m), LunHab (16 males; 10 days; Normoxic bedrest, Hypoxic bedrest ~4,000m, Hypoxic ambulation, ~4,000m), and FemHab (15 females; 10 days; Normoxic bedrest, Hypoxic bedrest ~4,000m, Hypoxic ambulation, ~4,000m)

Participants took part in one or more of the interventions (normoxic bedrest, hypoxic bedrest and hypoxic ambulation) in a randomised cross over design. Muscle strength, mass and cross-sectional area (CSA) of the upper and lower leg were measured prior to and following each intervention using a dynamometer, dual-energy X-ray absorptiometry and peripheral quantitative computed tomography, respectively. All data was pooled to view “Global effect”.

Results: Global muscle strength, mass and CSA all reduced following the 3 interventions. Specifically, dorsiflexion and plantar flexion decreased by 6.7 ± 12.5 % and 2.8 ± 20.4 % respectively. Knee extension and flexion decreased by 5.0 ± 12.2 % and 5.0 ± 15.5 % respectively. Upper and lower leg Mass (-3.7 ± 4.4 % and -4.8 ± 5.1 %, respectively) and CSA (-4.4 ± 2.7 % and -7.8 ± 2.8 %, respectively) decreased.

Conclusions: Bed rest induced muscle atrophy is evident particularly in the lower leg concomitant with the largest individual variation present in the measured parameters.

Acknowledgements: This work is supported by the European Space Agency (ESA contract no. 4000124642/18/NL/PG/gm).

ABSTRACT. Rationale: In the previous study (Kakitsuba and Chen, UTCI2019), it was demonstrated that the subjects voted “warm” in the morning at 70% Rh and 80% Rh but “slightly warm” in the evening although mean sin temperature (Tsk) increased with time when seven male and seven female subjects were exposed to 60%, 70% and 80 % Rh at air temperature (Ta) of 28 oC from 9:00 to 18:30. In the present study, considering that diurnal change in physiological and psychological responses may be related to change in cutaneous warm and cold sensation thresholds, diurnal change in these thresholds was studied. Methods: Five male and five female young Japanese subjects were exposed to 60%, 70% and 80 % Rh at 28 oC from 9:00 to 18:30. Cutaneous warm and cold sensation thresholds at three sites were measured using 1-cm2 and 2-cm2 probes. Skin temperatures at four sites and tympanic temperature (Tty) were continuously monitored at 2-min intervals throughout the experimental period. In addition, thermal sensation and comfort votes were recorded. Results: The results showed that thermal sensation changed from “slightly warm” at morning to “neutral” at evening in all Rh conditions for the male subjects but such change was observed only at 80% Rh for the female subjects. The Tty and Tsk increased from morning to afternoon regardless of Rh and sex as observed in the previous study. The cutaneous threshold zone measured with 1-cm2 changed with time for the male subjects and that measured with 2-cm2 changed with time for the female subjects as observed by Kakitsuba and Mekjavic (Int. Physiol. J., 2018). Decrease in the cutaneous threshold zone from morning to afternoon was then confirmed at 70% and 80%. Conclusion: Thus, it can be suggested that diurnal change in psychological and physiological responses while Ta and Rh were maintained consistently during day time may be related to diurnal change in cutaneous sensation threshold zone.

ABSTRACT. Introduction: To achieve high sweating efficiency (SE) during prolonged exercise in humid heat is of critically important to attenuate thermoregulatory strain and thereby protecting the human body from over-heating. From the previous studies, SE was evaluated with a minimum air flow velocity (~0.3 m.s-1) in a hot environment at rest and during exercise. It has been assumed that SE is improved by increasing air flow velocity. Therefore, we examined the effect of air flow velocity on SE during prolonged exercise in hot-humid environment. Method: Twelve healthy males (Age: 23 ± 3 yr ; Height: 172.7 ± 6.9 cm ; Weight: 64.5 ± 7.3 kg ; % Body fat: 13.5 ± 3.2 ; BSA: 1.8 ± 0.1 m2 ; VO2max: 44.4 ± 7.8 mL.kg-1.min-1) performed a fixed-intensity cycling exercise (40% of their VO2max) for 60 min in 32 °C and 75 % RH environment with a low airflow of 0.20 ± 0.04 m.s-1 at the first 40 minutes and changing the frontal air flow of 1.12 ± 0.22 m.s-1 in the last 20 minutes by an electric fan. Total (TSR) and ineffective sweat rate (ISR) were measured continuously by two different weight scales throughout the exercise. Effective sweat rate (ESR) and SE were derived from sweat drippage and body mass changes from the weight scales. Results: Fan usage enhanced both ESR and SE whilst ISR was lower with fan (4.2 ± 0.6 vs 5.4 ± 0.9 g.m-2.min-1, P < 0.01: 63.4 ± 21.4 vs 80.4 ± 12.1 %, P < 0.01: 3.2 ± 2.3 vs 1.5 ± 1.1 g.m-2.min-1, P < 0.01). However, TSR remained similar before and after fan usage (7.4 ± 2.6 vs 6.9 ± 1.8 g.m-2.min-1, P = 0.16). Conclusions: We concluded that changing air flow velocity enhanced both ESR and SE during exercise in hot humid environment.

ABSTRACT. Introduction: The purpose of this study is to determine the time course of changes in sweat rate and sweat content during 10 consecutive days of heat acclimation (HA) and 5 consecutive days of re-acclimation (RA) after a 28 day decay period. Method: Eight participants (6 males, 2 females) completed 10 days of heat acclimation, including cycling for 60 minutes above 38.5 °C rectal temperature (controlled hyperthermia) in 33 °C and 65% relative humidity. Four of them (4 males) completed the 5 days of re-acclimation by controlled hyperthermia. Upper arm and back sweat was collected 3 times each day during heat exposure. Sweat rate, sweat [Na+], [Cl-], [K+] and [lactate] were determined. Results: Values are expressed as a percentage of heat acclimation day 1. Average sweat [Na+], [Cl-] and [lactate] decreased after heat acclimation (50% p<0.05, 51% p<0.05 and 49% p<0.05 respectively) and re-acclimation (46% p<0.05, 47% p<0.05 and 38% p<0.05 respectively) for a given sweat rate. Average sweat [K+] did not change significantly after heat acclimation (18% p>0.05) nor after re-acclimation (12% p>0.05) for a given sweat rate. Conclusions: Exercise induced heat acclimation and re-acclimation by controlled hyperthermia improved reabsorption of sweat constituents in the eccrine sweat gland and possibly whole-body losses of ions and small organic molecules.

ABSTRACT. Introduction: Local skin heating to 42ºC causes cutaneous vasodilatation, known as cutaneous thermal hyperaemia. This response is widely employed to diagnose microvascular dysfunction or to evaluate whether interventions improve microvascular function. Nitric oxide (NO) synthase (NOS) is a major player in mediating cutaneous thermal hyperaemia. We recently reported that ATP-sensitive K+ (KATP) channels are involved in cutaneous vasodilatation occurring during whole-body heating, though it remains to be determined if these channels also contribute to cutaneous thermal hyperaemia. In the present study, we tested the hypothesis that the NOS-mediated elevation in NO activates KATP channels, partly mediating the cutaneous thermal hyperaemia response during local heating to 42ºC in young adults. Method: In thirteen young adults (7 men and 6 women), cutaneous vascular conductance (CVC, laser-Doppler signal/mean arterial pressure) was measured at four intradermal microdialysis sites that were continuously perfused with either 1) lactated Ringer (Control), 2) 5 mM glybenclamide (KATP channel blocker), 3) 20 mM Nω-Nitro-L-arginine methyl ester (NOS inhibitor), or 4) a combination of glybenclamide and Nω-Nitro-L-arginine methyl ester. Local skin heating to 42ºC and subsequent administration of 1.25 mM Pinacidil (KATP channel opener) or 25 mM sodium nitroprusside (NO donor) were applied to all four skin sites. Results: Glybenclamide attenuated the local-heating induced increase in CVC relative to the Control site, but this response was not observed in the presence of NOS inhibition. Pinacidil caused an elevation in CVC, but this response was abolished at the skin site treated with glybenclamide, demonstrating the effectiveness of glybenclamide as a KATP channel blocker. The pinacidil induced increase in CVC was unaffected by NOS inhibition, whereas the increase in CVC elicited by sodium nitroprusside was partly inhibited by glybenclamide. Conclusions: We show that the NOS mediated increase in NO activates KATP channels, partly underlying the cutaneous thermal hyperaemia response in young adults.

ABSTRACT. Introduction: Human eccrine sweat glands respond to intradermal administration of alpha adrenergic receptor agonists. However, whether alpha adrenergic receptors functionally contribute to sweating during exercise remains to be determined. Method: Twelve endurance trained men performed two incremental cycling until exhaustion on separate days. Bilateral forearm sweat rates (ventilated capsule) were measured at two skin sites that were transdermally administered via iontophoresis with either 1% terazosin (alpha1 adrenergic receptor antagonist, visit 1) or 1% phentolamine (alpha1 and alpha2 adrenergic receptors antagonist, visit 2) as well as saline (Control) at the opposite arm. Follwoing 10-20 min of postexercise recovery period wherein increased sweat rate returned back to baseline level, 0.25% phenylephrine (alpha1 adrenergic receptor agonist) was iontophoretically administered to confirm the blockade of alpha1 adrenergic receptor. Results: Administration of terazosin did not affect sweat rate relative to the Control site during incremental exercise (interaction, P = 0.848). Postexercise administration of phenylephrine increased sweat rate at the Control site (0.07±0.08 mg cm-2 min-1), which was suppressed by 81% at the terazosin-treated site (0.01±0.02 mg cm-2 min-1) (P = 0.026). Sweat rate was increased at the phentolamine-treated site at the end of incremental exercise relative to the Control site (0.85±0.35 vs. 0.68±0.36 mg cm-2 min-1, P = 0.033). Phenylephrine-induced sweating was attenuated by 87% at the phentolamine-treated site relative to the Control site after the exercise (0.06±0.06 vs. 0.01±0.01 mg cm-2 min-1, P = 0.008). Conclusions: alpha1 adrenergic receptors located at sweat glands do not contribute to sweating during incremental exercise in habitually trained men. Results from phentolamine administration combined witht the fact that alpha1 adrenergic receptos do not modulate sweating during exercise, implied that alpha2 adrenergic receptors located at the noradrenergic nerve terminals may suppress sweating during exercise (e.g., inhibits the release of noradrenaline).

ABSTRACT. Typical liquid moisture management property tests of textiles such as vertical wicking test (AATCC 197) and moisture management test (AATCC 195) are conducted with infinite reservoirs or limited, but large amounts of liquid. Therefore, those methods may not represent human sweating circumstances with continuous microfluidic flow from sweat pores. Even though a fabric received a favourable evaluation from these typical wicking tests, we cannot be sure the fabric would remove sweat well in realistic physiological sweating conditions. In terms of textile structures, typical wicking tests could not explain how yarn-level wicking plays a role within the fabric, even though liquid transport in the void space between the fibers within a yarn (or between yarns) is known as the most critical phenomenon in fabric wicking. For this reason, we developed a new method called ‘Single Point Source Wicking within Fabric’ to investigate how liquid is transported in fabrics based on within-yarn and yarn-to-yarn transfer wicking. This measurement system was conducted by supplying continuous liquid flow to a single yarn within the fabric at a similar flow rates to a single sweat gland (approximately 50 nl/min/gland). In order to mimic the sweating phenomenon, this single point source method avoided the flooding liquid stage by controlling flow rate and choosing a diameter of liquid source similar to sweat gland pore size. From microscope video analysis, we quantitatively evaluated the wicking phenomena of fabrics. We successfully measured directional wicking rates and individual yarn wicking performance, which has not previously been shown. The realistic point source sweat rates provided very different wicking results than were observed from standardized tests. A better understanding of wicking performance with this new method promises to provide a predictive model of textile wicking and should allow to improve physiological comfort of fabrics for sportswear, military apparel and personal protective equipment.

*This project was funded by Eastman Chemical Company.

ABSTRACT. Introduction: Posture-induced reductions in sweating from the lower, along with concurrent sweating elevations from the upper skin surfaces, have been described during lateral recumbency. This is known as the hemihidrotic reflex, which is also reported to accompany localised, lateral pressure applications. Since sudomotor inhibition in heated individuals elevates heat storage, then more pronounced sweating from untreated regions would be expected. Therefore, we examined that reflex in isothermally clamped, but mildly hyperthermic individuals. Method: Pre-heated, thermally clamped males participated in supine (N=12) and seated trials (N=12). In each trial, pressures were applied (5 min, 10 cm2) to the left side of the chest (6 N.cm-2) and the left heel (3 N.cm-2). Sudomotor activity was measured (ventilated capsules) from the left forehead, left dorsal hand, left and right medial chest, left and right lateral abdomen and the left calf. Results: Sweating was reduced at the ipsilateral forehead, hand and chest during the supine pressure application to the chest (P<0.05). However, sudomotor enhancement was not observed from any contralateral surface (P>0.05). Heel-pressure applications when seated did not elicit any ipsilateral responses (P>0.05), but when supine, excitatory effects were seen across all spinal segments (P<0.05). Conclusions: As a consequence, the universal acceptance of the hemihidrotic reflex can no longer be sustained, although pressure-induced inhibitory influences were apparent. That inhibition is believed to result from a spinal reflex that commences with cutaneous mechanoreceptor activation. The resulting sensory feedback enters the spinal cord (dorsal root ganglia) and ascends ipsilaterally (dorsal columns). Segmental variations in the pressure-dependent sudomotor inhibition are possibly mediated by interactions between those afferents and descending sympathetic neurones. However, unilateral inhibition was only apparent upstream of the pressure application, possibly as a segment-specific reflex. That mechanism cannot explain the heel-pressure responses, which might have arisen as an adaptation to bipedal locomotion.

ABSTRACT. Introduction: In this presentation, three sources of evidence will be reviewed to evaluate the possibility that the mammalian thermoeffectors (thermogenesis, cutaneous vasomotor activity and thermolysis) are under independent, central nervous system control. Method: The first, perhaps circumstantial, evidence will be drawn from the evolution of reptiles, monotremes and the Old World monkeys, apes and humans. Secondly, neurological evidence gathered from rodents will be presented, commencing with the early hypothalamic ablation experiments. Finally, a comprehensive series of human experiments will be described, in which the critical temperature (threshold) for each thermoeffector was determined in thermoneutral and thermally pre-conditioned (pre-heated and pre-cooled) individuals. Results: The phylogenetic evidence revealed a sequential acquisition of those effectors across the animal phyla, over millions of years. Ablation studies first demonstrated that hypothalamic microcuts could deactivate one thermoeffector, whilst the others remained effective. Recent human experiments revealed that the lower and upper critical temperatures for the vasomotor zone differed from those of the inter-threshold zone. Moreover, those thresholds were found to move independently of one another following thermal pre-conditioning. Conclusions: Critical (mean) body temperatures for the activation of human thermoeffectors were neither unitary points, nor were they fixed. Instead, they represented unique and adjustable thresholds. Shifts in the vasomotor and thermogenic thresholds appeared to depend upon changes in mean body temperature. Following whole-body pre-cooling, the vasomotor and sudomotor thresholds varied independently, and in opposite directions. Those outcomes are interpreted to signify the presence of independent central controllers for the vasomotor and sudomotor responses, and possibly also for thermogenesis. Such a conclusion is consistent with the phylogenetic acquisition of those thermoeffectors, and also with neurological evidence obtained from animal studies.