Primary Hyperhidrosis and Sensitive Skin: Exploring the Link with Predictive Machine Learning-Based Classification Models.

BACKGROUND: Primary hyperhidrosis (PHH) is a disorder of excessive sweating caused by aberrant cholinergic signaling. Sensitive skin (SS) is a condition of subjective cutaneous hyperreactivity to innocuous stimuli, impacting 40% to 70% of the population. SS is exacerbated by sweat, stress, and heat, suggesting that cholinergic stimulation may contribute to SS flares. OBJECTIVE: To survey PHH sufferers to assess hyperhidrosis (HH) and SS symptom burden. METHODS: An International Review Board (IRB)-exempt survey was disseminated by the International Hyperhidrosis Society. A predictive classification model for SS was built using random forest machine learning algorithms. RESULTS: Of the 637 respondents with PHH, 89% reported SS; and there was a significant association between HH and SS severity scores. Importantly, SS occurred on body sites affected and unaffected by HH. Predictive modeling designated Sensitive Scale-10 (SS-10), a validated questionnaire to gauge SS severity, to be the most helpful in predicting SS in this cohort. LIMITATIONS: Self-reported data. CONCLUSION: These data are the first to propose and support a relationship between SS and HH. SS occurred with greatest frequency at HH-afflicted body sites, but also occurred on unaffected sites, suggesting that sweat is not the sole causative link. Future work can explore cholinergic signaling as a potential link between these conditions. Screening HH patients for SS may be warranted. J Drugs Dermatol. 2024;23(10):882-888. doi:10.36849/JDD.8461.

A Double-Layer Polyurethane Electrospun Membrane with Directional Sweat Transport Ability for Use as a Soft Strain Sensor.

Wearable electronics for long-term monitoring of physiological signals should be capable of removing sweat generated during daily motion, which significantly impacts signal stability, human comfort, and safety of the electronics. In this study, we developed a double-layer polyurethane (PU) membrane with sweat-directional transport ability that can be applied for monitoring strain signals. The PU membrane was composed of a hydrophilic, conductive layer and a relatively hydrophobic layer. The double-layer PU composite membrane exhibited varied pore size and opposite hydrophilicity on its two sides, enabling the spontaneous pumping of sweat from the hydrophobic side to the hydrophilic side, i.e., the directional transport of sweat. The membrane can be used as a strain sensor to monitor motion strain over a broad working range of 0% to 250% with high sensitivity (GF = 4.11). The sensor can also detect simple human movements even under sweating conditions. We believe that the strategy demonstrated here will provide new insights into the design of next-generation strain sensors.

The Effect of a Synthetic-Grass Sport Surface on Physiology and Perception During Intermittent Exercise in Hot Conditions.

PURPOSE: The current study aimed to determine the effect of a synthetic-grass sport surface on core body temperature, skin temperature, heart rate, thermal sensation, thermal comfort, and rating of perceived exertion (RPE) during intermittent exercise in hot conditions. METHODS: Using a randomized crossover design, 13 trained/developmental team-sport athletes completed two 50-minute standardized intermittent running protocols on a synthetic and a natural-grass surface, on separate days (control-condition air temperature 32.6 °C [1.3 °C], relative humidity 43.2% [5.3%]). RESULTS: Final skin temperature was significantly higher on synthetic compared with natural grass at the calf (40.1 °C [2.5 °C] vs 33.4 °C [0.6 °C]; P < .001), shoulder (36.6 °C [1.7 °C] vs 33.7 °C [0.7 °C]; P < .001), and chest (33.2 °C [1.1 °C] vs 31.8 °C [1.2 °C]; P = .02). Thermal sensation (median: 2.3; interquartile range [0.5] vs 2.2 [0.5], P = .03) and sweat rate (1.5 [0.4] L·h-1 vs 1.2 [0.3] L·h-1; P = .02) were also significantly higher on synthetic grass. While final core body temperature was significantly higher on the natural than synthetic grass (38.4 °C [0.3 °C] vs 38.2 °C [0.4 °C]), there were no significant differences in delta core temperature, as well as heart rate, thermal comfort, or RPE. CONCLUSIONS: Higher skin temperatures, thermal sensation, and sweat rates suggest that exercising on synthetic grass in hot conditions may increase some markers of heat strain during exercise. However, delta core body temperature, heart rate, thermal comfort, and RPE remained unaffected.

Mild dehydration does not alter acute changes in sweat electrolyte concentrations during exercise.

The purpose of this study was to determine the effect of hydration status on the change in sweat sodium (Na+), chloride (Cl-), and potassium (K+) concentrations during exercise-heat stress. Fifteen subjects (Six female, nine male; 29 ± 9 y; 71 ± 14 kg) completed 90 min of cycling (81% HRmax) in the heat (~33°C, 42% rh) with fluid replacement to maintain euhydration (EUH) or without fluid to dehydrate to 2.4 ± 0.4% body mass loss (DEH). Sweat was collected from the forehead (FH), right scapula (SCAP), and left (LVFA) and right (RVFA) ventral forearms using the absorbent pad technique at the beginning (0-30 min) and end of exercise (60-90 min). Sweat was analyzed for Na+, Cl-, and K+ concentrations using ion chromatography. Data are reported as mean ± SD or median ± IQR. There were no differences (Paired t-tests or Wilcoxon signed-rank tests) between EUH and DEH in the change in sweat Na+ (FH: 24.3 ± 21.5 vs. 30.8 ± 22.4 mmol/L; SCAP: 9.7 ± 6.2 vs. 9.6 ± 8.2 mmol/L; LVFA: 7.5 ± 6.0 vs. 5.6 ± 5.9 mmol/L; RVFA: 8.2 ± 8.6 vs. 7.8 ± 5.2 mmol/L), sweat Cl-, or sweat K+ at any site (p = 0.07-0.99). The change in sweat electrolyte concentrations during 90 min of exercise in the heat was not significantly influenced by mild dehydration in recreational to moderately-trained male and female athletes.

Whole body sweat rate prediction: indoor treadmill and cycle ergometer exercise.

This article describes the development and validation of accurate whole body sweat rate prediction equations for individuals performing indoor cycle ergometer and treadmill exercise, where power output can be measured or derived from simple inputs. For cycle ergometry, 112 trials (67 participants) were used for model development and another 56 trials (42 participants) for model validation. For treadmill exercise, 171 trials (67 participants) were used for model development and another 95 trials (63 participants) for model validation. Trials were conducted over a range of dry-bulb temperature (20°C to 40°C), relative humidity (14% to 60%), and exercise intensity (∼40% to 85% of peak aerobic power) conditions, which were matched between model development and model validation. Whole body sweat rates were measured, and proprietary prediction models were developed (accounting for all relevant biophysical factors) and then validated. For model validation, mean absolute error for predicted sweating rate was 0.01 and 0.02 L·h-1 for cycle and treadmill trials, respectively. The 95% confidence intervals were modest for cycle ergometer (+0.25 and -0.22 L·h-1) and treadmill exercise (+0.33 and -0.29 L·h-1). The accounted for variance between predicted and measured values was 92% and 78% for cycle and treadmill exercise, respectively. Bland-Altman analysis indicated that zero and one predicted value exceeded the a priori acceptable level of agreement (equivalent to ±2% of total body mass in 3 h) for cycle and treadmill exercise, respectively. There were fewer trials with female subjects, but their values did not differ from those expected for males. This is the foremost study to develop and validate whole body sweat rate prediction equations for indoor treadmill and cycle ergometer exercise of moderate to high intensity. These prediction equations are publicly available for use (https://sweatratecalculator.com).NEW & NOTEWORTHY This study presents the development of new proprietary whole body sweat rate prediction models for people exercising indoors on a cycle ergometer or treadmill using simple input parameters and delivered through a publicly available online calculator: https://sweatratecalculator.com. In an independent validation group, the predictive models for both indoor cycling and treadmill exercise were accurate across moderate to high exercise intensities in temperate to hot conditions. These equations will enable individualized hydration management during physical training and exercise physiology experiments.

Efficacy of the FIFA cooling break heat policy during an intermittent treadmill football simulation in hot conditions in trained males.

OBJECTIVE: To evaluate the efficacy of the Fédération Internationale de Football Association (FIFA) cooling break policy against alternative cooling configurations in attenuating thermal strain during simulated football in the heat. METHODS: 12 males (age: 27±6 years, V̇O2peak: 61±7 mL/kg/min) completed five 90 min intermittent treadmill football match simulations in 40°C and 41% relative humidity (32°C wet-bulb globe temperature) with different cooling configurations: regular match without cooling breaks (REG), 3 min breaks without cooling (BRKno-cool), 3 min breaks with cooling (BRKcool: current FIFA policy; chilled fluid ingestion and ice towel across neck and shoulders), 5 min extended half-time without cooling breaks (ExtHTonly) and 3 min cooling breaks with 5 min ExtHT (ExtHTcool). Rectal temperature (Tre), heart rate, whole-body sweat rate (WBSR) and rating of perceived exertion (RPE) were recorded. Data are presented as mean (95% CIs). RESULTS: Final Tre was lower in BRKno-cool (0.20°C (0.01, 0.39), p=0.038), BRKcool (0.39°C (0.21, 0.57), p<0.001) and ExtHTcool (0.40°C (0.22, 0.58), p<0.001) than REG (39.1°C (38.8, 39.3)). Mean Tre was lower in ExtHTcool (38.2°C (38.0, 38.4)) than BRKcool (38.3°C (38.1, 38.5), p=0.018), BRKno-cool and ExtHTonly (38.4°C (38.2, 38.6), p<0.001) and REG (38.5°C (38.3, 38.7), p<0.001). Mean heart rate was lower during BRKcool (6 beats/min (4, 7), p<0.001) and ExtHTcool (7 beats/min (6, 8), p<0.001) compared with REG. WBSR was comparable across trials (p≥0.07) and RPE was attenuated during BRKcool (0.4 (0.1, 0.7), p=0.004) and ExtHTcool (0.5 (0.2, 0.7), p=0.002), compared with REG. CONCLUSION: BRKcool and ExtHTcool attenuated thermal, cardiovascular and perceptual strain during a simulated football match in the heat. Additional strategies may be required in field settings or under harsher conditions.

Questions and questionnaires about acute climacteric syndrome.

The acute climacteric syndrome has a large scale of symptoms. Main symptoms are hot flashes and night sweats. Each symptom could be presented alone or commonly in combination with other symptoms. The acute climacteric syndrome is induced by decrease and fluctuations of estrogen and neurosteroids levels. Therapy could be focused on hormone replacement. Changes of quality of life and especially effects of the therapy could be measured by standardized questionaries.

Involvement of TRPV4 in temperature-dependent perspiration in mice.

Reports indicate that an interaction between TRPV4 and anoctamin 1 (ANO1) could be widely involved in water efflux of exocrine glands, suggesting that the interaction could play a role in perspiration. In secretory cells of sweat glands present in mouse foot pads, TRPV4 clearly colocalized with cytokeratin 8, ANO1, and aquaporin-5 (AQP5). Mouse sweat glands showed TRPV4-dependent cytosolic Ca2+ increases that were inhibited by menthol. Acetylcholine-stimulated sweating in foot pads was temperature-dependent in wild-type, but not in TRPV4-deficient mice and was inhibited by menthol both in wild-type and TRPM8KO mice. The basal sweating without acetylcholine stimulation was inhibited by an ANO1 inhibitor. Sweating could be important for maintaining friction forces in mouse foot pads, and this possibility is supported by the finding that wild-type mice climbed up a slippery slope more easily than TRPV4-deficient mice. Furthermore, TRPV4 expression was significantly higher in controls and normohidrotic skin from patients with acquired idiopathic generalized anhidrosis (AIGA) compared to anhidrotic skin from patients with AIGA. Collectively, TRPV4 is likely involved in temperature-dependent perspiration via interactions with ANO1, and TRPV4 itself or the TRPV4/ANO 1 complex would be targeted to develop agents that regulate perspiration.

Stress, spicy foods and elevated temperatures can all trigger specialized gland cells to move water to the skin ­ in other words, they can make us sweat. This process is one of the most important ways by which our bodies regulate their temperature and avoid life-threatening conditions such as heatstroke. Disorders in which this function is impaired, such as AIGA (acquired idiopathic generalized anhidrosis), pose significant health risks. Finding treatments for sweat-related diseases requires a detailed understanding of the molecular mechanisms behind sweating, which has yet to be achieved. Recent research has highlighted the role of two ion channels, TRPV4 and ANO1, in regulating fluid secretion in glands that produce tears and saliva. These gate-like proteins control how certain ions move in or out of cells, which also influences water movement. Once activated by external stimuli, TRPV4 allows calcium ions to enter the cell, causing ANO1 to open and chloride ions to leave. This results in water also exiting the cell through dedicated channels, before being collected in ducts connected to the outside of the body. TRPV4, which is activated by heat, is also present in human sweat gland cells. This prompted Kashio et al. to examine the role of these channels in sweat production, focusing on mice as well as AIGA patients. Probing TRPV4, ANO1 and AQP5 (a type of water channel) levels using fluorescent antibodies confirmed that these channels are all found in the same sweat gland cells in the foot pads of mice. Further experiments highlighted that TRPV4 mediates sweat production in these animals via ANO1 activation. As rodents do not regulate their body temperature by sweating, Kashio et al. explored the biological benefits of having sweaty paws. Mice lacking TRPV4 had reduced sweating and were less able to climb a slippery slope, suggesting that a layer of sweat helps improve traction. Finally, Kashio et al. compared samples obtained from healthy volunteers with those from AIGA patients and found that TRPV4 levels are lower in individuals affected by the disease. Overall, these findings reveal new insights into the underlying mechanisms of sweating, with TRPV4 a potential therapeutic target for conditions like AIGA. The results also suggest that sweating could be controlled by local changes in temperature detected by heat-sensing channels such as TRPV4. This would depart from our current understanding that sweating is solely controlled by the autonomic nervous system, which regulates involuntary bodily functions such as saliva and tear production.

Chasing Gold: Heat Acclimation in Elite Handcyclists with Spinal Cord Injury.

Thermoregulation is impaired in individuals with a spinal cord lesion (SCI), affecting sweat capacity, heat loss, and core temperature. This can be particularly problematic for athletes with SCI who exercise in hot and humid conditions, like those during the Tokyo 2020 Paralympic Games. Heat acclimation can support optimal preparation for exercise in such challenging environments, but evidence is limited in endurance athletes with SCI. We evaluated whether seven consecutive days of exercise in the heat would result in heat acclimation. Five elite para-cycling athletes with SCI participated (two females, three males, median (Q1-Q3) 35 (31-51) years, four with paraplegia and one with tetraplegia). All tests and training sessions were performed in a heat chamber (30°C and 75% relative humidity). A time-to-exhaustion test was performed on day 1 (pretest) and day 7 (posttest). On days 2-6, athletes trained daily for one hour at 50-60% of individual peak power (PPeak). Comparing pretest and posttest, all athletes increased their body mass loss (p=0.04), sweat rate (p=0.04), and time to exhaustion (p=0.04). Effects varied between athletes for core temperature and heart rate. All athletes appeared to benefit from our heat acclimation protocol, helping to optimize their preparation for the Tokyo 2020 Paralympic Games.

A case report on the physiological responses to extreme heat during Sicily's July 2023 heatwave.

July 2023 has been confirmed as Earth's hottest month on record, and it was characterized by extraordinary heatwaves across southern Europe. Field data collected under real heatwave periods could add important evidence to understand human adaptability to extreme heat. However, field studies on human physiological responses to heatwave periods remain limited. We performed field thermo-physiological measurements in a healthy 37-years male undergoing resting and physical activity in an outdoor environment in the capital of Sicily, Palermo, during (July 21; highest level of local heat-health alert) and following (August 10; lowest level of local heat-health alert) the peak of Sicily's July 2023 heatwave. Results indicated that ~40 min of outdoor walking and light running in 33.8°C Wet Bulb Globe Temperature (WBGT) conditions (July 21) resulted in significant physiological stress (i.e., peak heart rate: 209 bpm; core temperature: 39.13°C; mean skin temperature: 37.2°C; whole-body sweat losses: 1.7 kg). Importantly, significant physiological stress was also observed during less severe heat conditions (August 10; WBGT: 29.1°C; peak heart rate: 190 bpm; core temperature: 38.48°C; whole-body sweat losses: 2 kg). These observations highlight the physiological strain that current heatwave conditions pose on healthy young individuals. This ecologically-valid empirical evidence could inform more accurate heat-health planning.

Single Session Intermittent Heat Exposure With More Frequent and Shorter Cooling Breaks Facilitates Greater Training Intensity and Elicits Physiological Responses Comparable to Continuous Heat Exposure.

PURPOSE: To investigate the influence of shorter, more frequent rest breaks with per-cooling as an alternative heat-acclimation session on physiological, perceptual, and self-paced maximal cycling performance, compared with continuous heat exposure. METHODS: Thirteen participants completed 1 continuous and 3 intermittent-heat-exposure (IHE) maximal self-paced cycling protocols in a random order in heat (36 °C, 80% relative humidity): 1 × 60-minute exercise (CON), 3 × 20-minute exercise with 7.5-minute rest between sets (IHE-20), 4 × 15-minute exercise with 5-minute rest between sets (IHE-15), and 6 × 10-minute exercise with 3-minute rest between sets (IHE-10). Mixed-method per-cooling (crushed-ice ingestion and cooling vest) was applied during rest periods of all IHE protocols. RESULTS: Total distance completed was greater in IHE-10, IHE-15, and IHE-20 than in CON (+11%, +9%, and +8%, respectively), with no difference observed between IHE protocols. Total time spent above 38.5 °C core temperature was longer in CON compared with IHE-15 and IHE-20 (+62% and +78%, respectively) but similar to IHE-10 (+5%). Furthermore, a longer time above 38.5 °C core temperature occurred in IHE-10 versus IHE-15 and IHE-20 (+54% and +69%, respectively). Sweat loss did not differ between conditions. CONCLUSION: IHE with per-cooling may be a viable alternative heat-acclimation protocol in situations where training quality takes precedence over thermal stimulus or when both factors hold equal priority.

The effect of female breast surface area on heat-activated sweat gland density and output.

Female development includes significant morphological changes across the breast. Yet, whether differences in breast surface area (BrSA) modify sweat gland density and output remains unclear. The present study investigated the relationship between BrSA and sweat gland density and output in 22 young to middle-aged women (28 ± $\ \pm \ $ 10 years) of varying breast sizes (BrSA range: 147-561 cm2) during a submaximal run in a warm environment (32  ± $ \pm \ $ 0.6°C; 53  ± $ \pm \ $ 1.7% relative humidity). Local sweat gland density and local sweat rate (LSR) above and below the nipple and at the bra triangle were measured. Expired gases were monitored for the estimation of evaporative requirements for heat balance (Ereq, in W/m2). Associations between BrSA and (i) sweat gland density; (ii) LSR; and (iii) sweat output per gland for the breast sites were determined via correlation and regression analyses. Our results indicated that breast sweat gland density decreased linearly as BrSA increased (r = -0.76, P < 0.001), whereas sweat output per gland remained constant irrespective of BrSA (r = 0.29, P = 0.28). This resulted in LSR decreasing linearly as BrSA increased (r = -0.62, P = 0.01). Compared to the bra triangle, the breast had a 64% lower sweat gland density (P < 0.001), 83% lower LSR (P < 0.001) and 53% lower output per gland (P < 0.001). BrSA (R2 = 0.33, P = 0.015) explained a greater proportion of variance in LSR than Ereq (in W/m2) (R2 = 0.07, P = 0.538). These novel findings extend the known relationship between body morphology and sweat gland density and LSR, to the female breast. This knowledge could innovate user-centred design of sports bras by accommodating breast size-specific needs for sweat management, skin wetness perception and comfort.

Nature-Inspired Superhydrophilic Biosponge as Structural Beneficial Platform for Sweating Analysis Patch.

Perspiration plays a pivotal role not only in thermoregulation but also in reflecting the body's internal state and its response to external stimuli. The up-to-date skin-based wearable platforms have facilitated the monitoring and simultaneous analysis of sweat, offering valuable physiological insights. Unlike conventional passive sweating, dynamic normal perspiration, which occurs during various activities and rest periods, necessitates a more reliable method of collection to accurately capture its real-time fluctuations. An innovative microfluidic patch incorporating a hierarchical superhydrophilic biosponge, poise to significantly improve the efficiency capture of dynamic sweat is introduced. The seamlessly integrated biosponge microchannel showcases exceptional absorption capabilities, efficiently capturing non-sensitive sweat exuding from the skin surface, mitigating sample loss and minimizing sweat volatilization. Furthermore, the incorporation of sweat-rate sensors alongside a suite of functional electrochemical sensors endows the patch of uninterrupted monitoring and analysis of dynamic sweat during various activities, stress events, high-energy intake, and other scenarios.

Autonomic impairment in primary lateral sclerosis.

PURPOSE: Prior studies reported evidence of autonomic involvement in motor neuron disease and suggested more severe dysfunction in upper motor neuron predominant syndromes. Hence, we sought to characterize autonomic impairment in primary lateral sclerosis. METHODS: Neurological evaluations, thermoregulatory sweat tests, and autonomic reflex screens were analyzed retrospectively in 34 primary lateral sclerosis patients (28 definite and 6 probable). Patients with other potential causes of autonomic failure and patients with autonomic testing results compromised by artifact were excluded. RESULTS: A total of 17 patients reported autonomic symptoms. Orthostatic lightheadedness was most frequent (8 patients), followed by bladder (7), bowel (5), and erectile dysfunction (3). The autonomic reflex screens of 33 patients were reviewed; 20 patients had abnormal studies. The thermoregulatory sweat tests of 19 patients were reviewed; 11 patients had abnormal studies. Composite Autonomic Severity Score was calculated for 33 patients and found abnormal in 20/33 patients (60.6%): 15/20 patients (75%) had mild impairment, and 5/20 patients (25%) had moderate impairment. The frequencies of testing abnormalities were: sudomotor 18/20 (90%), cardiovagal 9/20 (45%), and adrenergic 6/20 (30%). Sweat loss pattern analysis showed global, regional, and mixed patterns to be more common than length-dependent and distal patterns. CONCLUSION: We found evidence of frequent autonomic dysfunction in primary lateral sclerosis, which is generally of modest severity akin to prior reports for amyotrophic lateral sclerosis, but more commonly in a pattern consistent with preganglionic/ganglionic localization. This suggests that primary lateral sclerosis, as with amyotrophic lateral sclerosis, is a multisystem disease that affects the autonomic nervous system.

Sleep effects of psychological therapies for menopausal symptoms in women with hot flashes and night sweats: A systematic review.

Sleep disturbance is frequently reported by women during the menopausal transition due to various physiological changes and environmental factors. Insomnia is a critical treatment target for its deleterious effects on daytime functioning and quality of life and increased risk of developing a depressive disorder. Due to medication side effects and patient preferences, there is increased interest in the use of psychological treatments that address the myriad of menopausal symptoms, including cognitive-behavioural therapy, clinical hypnosis and mindfulness-based therapies. The objective of this article is to review the effects of psychological treatments for menopausal symptoms on sleep disturbance in peri-/postmenopausal women. We conducted a systematic review of the literature using PubMed and reference lists from inception until May 2023, including 12 studies that evaluated sleep as a secondary outcome. Most studies found that group and self-help (guided and unguided) cognitive-behavioural therapies and clinical hypnosis for menopausal symptoms have positive effects on sleep among women with significant vasomotor symptoms. There was preliminary support for mindfulness-based stress reduction. Future research including more diverse samples and women with sleep disorders is needed. Evaluating the implementation of psychological therapies in clinics where menopausal women seek care is an important next step.

Personalized Hydration Strategy to Improve Fluid Balance and Intermittent Exercise Performance in the Heat.

Sweat rate and electrolyte losses have a large inter-individual variability. A personalized approach to hydration can overcome this issue to meet an individual's needs. This study aimed to investigate the effects of a personalized hydration strategy (PHS) on fluid balance and intermittent exercise performance. Twelve participants conducted 11 laboratory visits including a VO2max test and two 5-day trial arms under normothermic (NOR) or hyperthermic (HYP) environmental conditions. Each arm began with three days of familiarization exercise followed by two random exercise trials with either a PHS or a control (CON). Then, participants crossed over to the second arm for: NOR+PHS, NOR+CON, HYP+PHS, or HYP+CON. The PHS was prescribed according to the participants' fluid and sweat sodium losses. CON drank ad libitum of commercially-available electrolyte solution. Exercise trials consisted of two phases: (1) 45 min constant workload; (2) high-intensity intermittent exercise (HIIT) until exhaustion. Fluids were only provided in phase 1. PHS had a significantly greater fluid intake (HYP+PHS: 831.7 ± 166.4 g; NOR+PHS: 734.2 ± 144.9 g) compared to CON (HYP+CON: 369.8 ± 221.7 g; NOR+CON: 272.3 ± 143.0 g), regardless of environmental conditions (p < 0.001). HYP+CON produced the lowest sweat sodium concentration (56.2 ± 9.0 mmol/L) compared to other trials (p < 0.001). HYP+PHS had a slower elevated thirst perception and a longer HIIT (765 ± 452 s) compared to HYP+CON (548 ± 283 s, p = 0.04). Thus, PHS reinforces fluid intake and successfully optimizes hydration status, regardless of environmental conditions. PHS may be or is an important factor in preventing negative physiological consequences during high-intensity exercise in the heat.

Whole body sweat rate prediction: outdoor running and cycling exercise.

Our aim was to develop and validate separate whole body sweat rate prediction equations for moderate to high-intensity outdoor cycling and running, using simple measured or estimated activity and environmental inputs. Across two collection sites in Australia, 182 outdoor running trials and 158 outdoor cycling trials were completed at a wet-bulb globe temperature ranging from ∼15°C to ∼29°C, with ∼60-min whole body sweat rates measured in each trial. Data were randomly separated into model development (running: 120; cycling: 100 trials) and validation groups (running: 62; cycling: 58 trials), enabling proprietary prediction models to be developed and then validated. Running and cycling models were also developed and tested when locally measured environmental conditions were substituted with participants' subjective ratings for black globe temperature, wind speed, and humidity. The mean absolute error for predicted sweating rate was 0.03 and 0.02 L·h-1 for running and cycling models, respectively. The 95% confidence intervals for running (+0.44 and -0.38 L·h-1) and cycling (+0.45 and -0.42 L·h-1) were within acceptable limits for an equivalent change in total body mass over 3 h of ±2%. The individual variance in observed sweating described by the predictive models was 77% and 60% for running and cycling, respectively. Substituting measured environmental variables with subjective assessments of climatic characteristics reduced the variation in observed sweating described by the running model by up to ∼25%, but only by ∼2% for the cycling model. These prediction models are publicly accessible (https://sweatratecalculator.com) and can guide individualized hydration management in advance of outdoor running and cycling.NEW & NOTEWORTHY We report the development and validation of new proprietary whole body sweat rate prediction models for outdoor running and outdoor cycling using simple activity and environmental inputs. Separate sweat rate models were also developed and tested for situations where all four environmental parameters are not available, and some must be subsequently estimated by the user via a simple rating scale. All models are freely accessible through an online calculator: https://sweatratecalculator.com. These models, via the online calculator, will enable individualized hydration management for training or recreational cycling or running in an outdoor environment.

Biological sex does not independently influence core temperature change and sweating of children exercising in uncompensable heat stress.

The purpose of this study was to investigate the influence of biological sex, independent of differences in aerobic fitness and body fatness, on the change in gastrointestinal temperature (ΔTgi) and whole body sweat rate (WBSR) of children exercising under uncompensable heat stress. Seventeen boys (means ± SD; 13.7 ± 1.3 yr) and 18 girls (13.7 ± 1.4 yr) walked for 45 min at a fixed rate of metabolic heat production per kg body mass (8 W·kg-1) in 40°C and 30% relative humidity. Sex and peak oxygen consumption (V̇o2peak) were entered into a Bayesian hierarchical general additive model (HGAM) for Tgi. Sex, V̇o2peak, and the evaporative requirement for heat balance (Ereq) were entered into a Bayesian hierarchical linear regression for WBSR. For 26 (12 M and 14 F) of the 35 children with measured body composition, body fat percentage was entered in a separate HGAM and hierarchical linear regression for Tgi and WBSR, respectively. Conditional on sex-specific mean V̇o2peak, ΔTgi was 1.00°C [90% credible intervals (Crl): 0.84, 1.16] for boys and 1.17°C [1.01, 1.33] for girls, with a difference of 0.17°C [-0.39, 0.06]. When sex differences in V̇o2peak were accounted for, the difference in ΔTgi between boys and girls was 0.01°C [-0.25, 0.22]. The difference in WBSR between boys and girls was 0.03 L·h-1 [-0.02, 0.07], when isolated from differences in Ereq. The difference in ΔTgi between boys and girls was -0.10°C [-0.38, 0.17] when sex differences in body fat (%) were accounted for. Biological sex did not independently influence the ΔTgi and WBSR of children exercising under uncompensable heat stress.NEW & NOTEWORTHY Limited studies have investigated the thermoregulatory responses of boys and girls exercising under uncompensable heat stress. Boys and girls often differ in physiological characteristics other than biological sex, such as aerobic fitness and body fat percentage, which may confound interpretations. We investigated the influence of biological sex on exercise thermoregulation in children, independent of differences in aerobic fitness and body fatness.

Caffeine ingestion compromises thermoregulation and does not improve cycling time to exhaustion in the heat amongst males.

PURPOSE: Caffeine is a commonly used ergogenic aid for endurance events; however, its efficacy and safety have been questioned in hot environmental conditions. The aim of this study was to investigate the effects of acute caffeine supplementation on cycling time to exhaustion and thermoregulation in the heat. METHODS: In a double-blind, randomised, cross-over trial, 12 healthy caffeine-habituated and unacclimatised males cycled to exhaustion in the heat (35 °C, 40% RH) at an intensity associated with the thermoneutral gas exchange threshold, on two separate occasions, 60 min after ingesting caffeine (5 mg/kg) or placebo (5 mg/kg). RESULTS: There was no effect of caffeine supplementation on cycling time to exhaustion (TTE) (caffeine; 28.5 ± 8.3 min vs. placebo; 29.9 ± 8.8 min, P = 0.251). Caffeine increased pulmonary oxygen uptake by 7.4% (P = 0.003), heat production by 7.9% (P = 0.004), whole-body sweat rate (WBSR) by 21% (P = 0.008), evaporative heat transfer by 16.5% (P = 0.006) and decreased estimated skin blood flow by 14.1% (P < 0.001) compared to placebo. Core temperature was higher by 0.6% (P = 0.013) but thermal comfort decreased by - 18.3% (P = 0.040), in the caffeine condition, with no changes in rate of perceived exertion (P > 0.05). CONCLUSION: The greater heat production and storage, as indicated by a sustained increase in core temperature, corroborate previous research showing a thermogenic effect of caffeine ingestion. When exercising at the pre-determined gas exchange threshold in the heat, 5 mg/kg of caffeine did not provide a performance benefit and increased the thermal strain of participants.

The effect of 8-day oral taurine supplementation on thermoregulation during low-intensity exercise at fixed heat production in hot conditions of incremental humidity.

PURPOSE: To determine the effect of taurine supplementation on sweating and core temperature responses, including the transition from compensable to uncompensable heat stress, during prolonged low-intensity exercise of a fixed-heat production (~ 200W/m2) in hot conditions (37.5 °C), at both fixed and incremental vapour-pressure. METHODS: Fifteen females (n = 3) and males (n = 12; 27 ± 5 years, 78 ± 9 kg, V ˙ O2max 50.3 ± 7.8 mL/kg/min), completed a treadmill walking protocol (~ 200W/m2 heat production [Hprod]) in the heat (37.5 ± 0.1 °C) at fixed-(16-mmHg) and ramped-humidity (∆1.5-mmHg/5-min) following 1 week of oral taurine supplementation (50 mg/kg/bm) or placebo, in a double-blind, randomised, cross-over design. Participants were assessed for whole-body sweat loss (WBSL), local sweat rate (LSR), sweat gland activation (SGA), core temperature (Tcore), breakpoint of compensability (Pcrit) and calorimetric heat transfer components. Plasma volume and plasma taurine concentrations were established through pre- and post-trial blood samples. RESULTS: Taurine supplementation increased WBSL by 26.6% and 5.1% (p = 0.035), LSR by 15.5% and 7.8% (p = 0.013), SGA (1 × 1 cm) by 32.2% and 29.9% (p < 0.001) and SGA (3 × 3 cm) by 22.1% and 17.1% (p = 0.015) during the fixed- and ramped-humidity exercise periods, respectively. Evaporative heat loss was enhanced by 27% (p = 0.010), heat-storage reduced by 72% (p = 0.024) and Pcrit was greater in taurine vs placebo (25.0-mmHg vs 21.7-mmHg; p = 0.002). CONCLUSION: Taurine supplementation increased sweating responses during fixed Hprod in hot conditions, prior to substantial heat strain and before the breakpoint of compensability, demonstrating improved thermoregulatory capacity. The enhanced evaporative cooling and reduced heat-storage delayed the subsequent upward inflection in Tcore-represented by a greater Pcrit-and offers a potential dietary supplementation strategy to support thermoregulation.