Performance in the heat-physiological factors of importance for hyperthermia-induced fatigue

Squash in Los Angeles: Heat Strain and Performance Considerations at the 2028 Olympic Games

BACKGROUND

The Los Angeles 2028 Olympics will mark the debut of squash, a high-intensity sport characterized by repeated efforts, posing potential thermoregulatory challenges. The demanding nature of squash results in substantial metabolic heat production, with consequential heat strain exacerbated by the indoor environment of squash courts, where low to moderate evaporative potential limits effective cooling. Players often experience increased body-heat storage and thermal strain, with muscle cramps (an early warning sign of more severe heat-related illnesses) commonly observed during tournaments. Despite these challenges, there are limited data on the thermoregulatory responses of elite squash players during match play.

PURPOSE

We discuss the thermoregulatory challenges faced by squash players and highlight key areas for research. Additionally, practical guidelines are provided for practitioners preparing squash players for the Los Angeles 2028 Olympics.

EVIDENCE

Preliminary findings from international squash tournaments reveal that elite players endure significant physiological strain, with core temperatures rising to 39.0 °C to 40.1 °C, despite matches being played in mild wet-bulb globe temperatures of 19.4 °C (0.9 °C). Sustained heart rates exceeding 90% of maximal heart rate further compound this thermal strain. However, research on how thermal strain affects squash-specific fitness, recovery, and stroke mechanics are lacking. Such information is crucial for evaluating the need and effectiveness of tailored mitigation strategies such as heat training/exposures and precooling and midcooling during warm-up and match play.

CONCLUSION

Systematic research into the thermal demands of squash and their impact on fitness and skills is needed. These insights can inform evidence-based strategies to safeguard athlete well-being and optimize performance at Los Angeles 2028.

The psychology of thermoregulation: A coordinating mechanisms approach

Temperature is more than just the background setting of daily life-it shapes what we think, feel, and do. Drawing from the theory of emotions as coordinating mechanisms, we propose that thermal affect influences key psychological systems such as attention, memory, perception, and motivation in service of solving critical thermal challenges. Through an evolutionary task analysis, we generate a variety of testable predictions regarding the interplay of temperature, human cognition, and behavior. We hope that this manuscript contributes to the psychology of thermoregulation, a notably understudied area of research despite its importance to both basic and applied science.

The effect of dietary supplements on core temperature and sweating responses in hot environmental conditions: a meta-analysis and meta-regression

Dietary supplements are widely used among individuals exposed to hot environments, but whether their consumption confers any thermoregulatory effect is unclear. Therefore, we systematically evaluated the effect of dietary supplementation on key aspects of thermoregulation [core temperature (Tcore) and sweating responses] in the heat. Three databases were searched in April 2024. After screening, 124 peer-reviewed articles were identified for inclusion within three separate meta-analyses: 1) peak Tcore; 2) whole body sweat rate (WBSR); 3) local sweat rate (LSR). The moderating effect of several variables (e.g., training and heat acclimation status), known to influence thermoregulatory function, were assessed via subanalysis and meta-regression. There was no overall effect of the differing supplement types on WBSR (P = 0.405) and LSR (P = 0.769), despite taurine significantly increasing WBSR (n = 3, Hedges' g = 0.79, P = 0.006). Peak Tcore was significantly affected by supplement type (P = 0.011), primarily due to caffeine's "small" significant positive effect (n = 30; Hedges' g = 0.44, P < 0.001) and taurine's (n = 3, Hedges' g = -0.66, P = 0.043) and oligonol's (n = 3; Hedges' g = -0.50, P = 0.014) "medium" significant negative effects. Dietary supplements, such as amino acids (e.g., taurine), some antioxidants and anti-inflammatories (e.g., oligonol) conferred the greatest thermoregulatory benefits during heat exposure. Taurine ingestion in such conditions may lower heat strain, which is likely through its augmentation of thermal sweating. Conversely, caffeine intake may potentially pose the greatest risk in the heat due to its effect on Tcore.NEW & NOTEWORTHY The effects of dietary supplements on core temperature and sweating responses when ingested in the heat varied greatly. Some supplements demonstrated the potential to improve thermoregulatory capacity (e.g., select amino acids, anti-oxidants and anti-inflammatories), while others had no or even deleterious effects on thermal balance (e.g., caffeine). These findings have implications for those ingesting dietary supplements for their health and/or performance effects during exposure to hot environmental conditions. Certain supplements should possibly be avoided in the heat, while others may elicit a thermoregulatory benefit.

Associations Between Match-Play Characteristics and Environmental Temperatures in 4 Professional Football Leagues

This study investigated the association between environmental temperature and match-play characteristics (shooting, passing, dribbling and defending) in four professional football leagues. Twenty-seven performance indicators (PI's) were collated from 1585 matches from the German Bundesliga 1 and 2, Spanish La Liga and Australian A-League. Environmental data were obtained for dry-bulb temperature (T) and wet-bulb globe temperature (WBGT) retrospectively from public sources. For each league, linear regressions were used to determine relationships between PI's and T and WBGT and linear mixed models were used to determine those associations across all four leagues. Individual leagues showed varying associations between a collection of PI's and environmental measures. When combining the four leagues' match data, 8 of the 17 investigated parameters were associated with T and WBGT (p < 0.002). Passes, especially short passes, were reduced in higher T (-2.3 [-3.1 to -1.5] and p < 0.001) and WBGT (-3.1 [-4.0 to -2.1] and p < 0.001), alongside an increase in the success rate of passes (0.06 [0.02-0.09] and p ≤ 0.001). The number of passes into the opponent's final third was reduced for both T (-0.18 [-0.25 to -0.05] and p = 0.001) and WBGT (-0.17 [-0.28 to-0.05] and p = 0.002), but the number of key passes leading to a shot or goal was not associated with T or WBGT (p ≥ 0.67). The number of touches, take-ons and turnovers were reduced in higher T and WBGT (all p < 0.001). Accordingly, in higher heat stress, match actions, especially those performed at high volumes, are reduced. Therefore, teams should expect a possibly altered match play and may consider adapting tactical or heat-mitigating strategies to counter these effects.

Associations between injury occurrence and environmental temperatures in the Australian and German professional football leagues

A cross-sectional analysis was performed to investigate associations between environmental temperatures and injury occurrence in two professional male football (soccer) leagues. Data from seven seasons of the German Bundesliga (2142 matches) and four seasons of the Australian A-League (470 matches) were included. Injuries were collated via media reports for the Bundesliga and via team staff reports in the A-League and comprised injury incidence, mechanisms (contact, noncontact), locations (e.g., ankle, knee, and thigh), and types (e.g., muscle and tendon, joint and ligament). Weather data included ambient air temperature (temperature or T) and wet bulb globe temperature (WBGT), which were collected from online sources retrospectively. Generalized linear mixed models were analyzed to examine associations between temperature or WBGT and injury occurrence for each league, respectively. Additionally, matches were grouped into categories of 5°C temperature steps to compare for injury occurrence. Results showed no relationship existed between either temperature or WBGT and any injury occurrence, mechanisms, locations or types for the Bundesliga (P > 0.10). A trend for an increase in injury occurrence in higher WBGT existed in the A-League (P = 0.05). Comparisons between 5°C temperature categories showed no significant differences for injury occurrence for either temperature or WBGT in either League (P > 0.05). Within the observed temperature ranges (-11.2 to 37.1°C T; -12.2 to 29.6°C WBGT) environmental temperature had no relationship with the rate or type of injury occurrence in professional football. Nevertheless, the number of matches at extreme heat within this study was limited and other factors (e.g., playing intensity, season stage, ground conditions) likely co-influence the relationship with injuries.

Aerobic Energy Turnover and Exercise Economy Profile During Race Simulation in a World-Record-Breaking Male Full-Distance Triathlete

PURPOSE

To investigate metabolism and exercise economy during prolonged race simulation (>4 h) in a world-class, full-distance triathlete to help guide/adjust strategies for training, nutrition, hydration, and thermoregulation.

METHODS

Two experimental race-simulation days, designed to mimic the demands of a full-distance triathlon, were executed by a world-class male triathlete (MD; 25 y, body weight 82 kg, V˙O2max 6.2 L·min-1, blood lactate threshold ∼410 W, and 18 km · h-1 in cycling and running) who at the time ranked second in the world. Race simulation was performed 23 and 10 days prior to competing in Challenge Roth 2023, where MD won in a new world record/best time (7:24:40 h:min:s). Both test days lasted ∼4 to 5 hours with physiologic testing every ∼45 to 60 minutes in a "stationary" setting during cycling on a direct-mount trainer (∼320 W) and treadmill running (16 km · h-1), enabling gas exchange measurements (V˙O2 and respiratory exchange ratio) and other physiologic measurements of interest (ie, core temperature and heart rate). This was combined with "real activity" as repeated loops in an open-air field setting at expected race pace in swimming, biking, and running.

RESULTS

V˙O2 was maintained at ∼4.2 L·min-1, with carbohydrates being the dominant fuel for oxidation as respiratory exchange ratio values dropped from ∼1 at the start of cycling to ∼0.85 during running. Cycling economy was stable, whereas a slight impairment in running economy occurred over time.

CONCLUSION

High aerobic energy turnover and stable exercise economy can be maintained in a world-class record-breaking triathlete for prolonged period of time (+4 h), showcasing the importance of both for success in competition.

Factors Contributing to Heat Tolerance in Humans and Experimental Models

Understanding physiological mechanisms of tolerance to heat exposure, and potential ways to improve such tolerance, is increasingly important in the context of ongoing climate change. We discuss the concept of heat tolerance in humans and experimental models (primarily rodents), including intracellular mechanisms and improvements in tolerance with heat acclimation.

Effects of Precooling on Endurance Exercise Performance in the Heat: A Systematic Review and Meta-Analysis of Randomized Controlled Trials

An increasing number of studies have explored the effects of precooling on endurance exercise performance in the heat, yet the available results remain inconsistent. Therefore, this study aimed to investigate the effects of different precooling strategies on endurance exercise performance in the heat. A comprehensive search was conducted across PubMed, Web of Science, Cochrane, Scopus, and EBSCO database. The Cochrane risk assessment tool was employed to evaluate the methodological quality of the included studies. A meta-analysis was subsequently conducted to quantify the standardized mean difference (SMD) and 95% confidence interval for the effects of precooling on endurance exercise performance in the heat. Out of the initially identified 6982 search records, 15 studies were deemed eligible for meta-analysis. Our results showed that precooling significantly improved time trial (TT) performance (SMD, -0.37, p < 0.01, I2 = 0%) and time to exhaustion (TTE) performance in the heat (SMD, 0.73, p < 0.01, I2 = 50%). Further subgroup analyses revealed that external precooling is more effective in improving TT performance (SMD, -0.43, p = 0.004, I2 = 0%) and TTE performance (SMD, 1.01, p < 0.001, I2 = 48%), particularly in running-based performances (TT, SMD, -0.41, p = 0.02, I2 = 0%; TTE, SMD, 0.85, p = 0.0001, I2 = 31%). Precooling is an effective approach to improve endurance exercise performance in the heat. External precooling is more effective in improving endurance exercise performance, particularly in running-based performance.

Effects of pre-exercise glycerol supplementation on dehydration, metabolic, kinematic, and thermographic variables in international race walkers

BACKGROUND

Due to the increase in global temperature, it is necessary to investigate solutions so that athletes competing in hot conditions can perform in optimal conditions avoiding loss of performance and health problems. Therefore, this study aims to evaluate the effect of pre-exercise glycerol supplementation during a rectangular test at ambient temperature mid (28.2ºC) on dehydration variables in international race walkers.

METHODS

Eight international male race walkers (age: 28.0 years (4.4); weight: 65.6 kg (6.6); height: 180.0 cm (5.0); fat mass: 6.72% (0.66); muscle mass: 33.3 kg (3.3); VO2MAX: 66.5 ml · kg-1·min-1 (1.9)) completed this randomized crossover design clinical trial. Subjects underwent two interventions: they consumed placebo (n = 8) and glycerol (n = 8) acutely, before a rectangular test where dehydration, RPE, metabolic, kinematic, and thermographic variables were analyzed before, during and after the test.

RESULTS

After the intervention, significant differences were found between groups in body mass in favor of the placebo (Placebo: -2.23 kg vs Glycerol: -2.48 kg; p = 0.033). For other variables, no significant differences were found.

CONCLUSION

Therefore, pre-exercise glycerol supplementation was not able to improve any dehydration, metabolic, kinematic, or thermographic variables during a rectangular test at temperature mid in international race walkers. Possibly, a higher environmental temperature could have generated a higher metabolic and thermoregulatory stress, generating differences between groups like other previous scientific evidence.

Prospective heat stress risk assessment for professional soccer players in the context of the 2026 FIFA World Cup

This study investigates the risk of severe heat stress and associated potential water losses in professional soccer players, considering as well the oxygen content of the inhaled air in the context of the 2026 FIFA World Cup. For the 16 stadiums, hourly values of biometeorological indices (adjusted Universal Thermal Climate Index - UTCI, Water loss - SW and Oxygen volume - Ov) were calculated. UTCI adjustments included modifications to activity levels, movement speeds and clothing configurations to better reflect the level of thermal stress on soccer player during a match. Ten out of the sixteen sites of the 2026 FIFA World Cup are at very high risk of experiencing extreme heat stress conditions. The highest risk of uncompensable thermal stress due to very high average hourly UTCI values above 49.5 °C and excessive water loss (> 1.5 kg/h) occur in the afternoon in stadiums located in Arlington, Houston (USA) and in Monterrey (Mexico). The results of this study will enable optimization of match schedules at individual venues, taking into account the health risks associated with extreme heat stress, but also the physiological reactions to heat potentially affecting the performance of players on the pitch.

Identifying fatigue of climbing workers using physiological data based on the XGBoost algorithm

Background

High-voltage workers often experience fatigue due to the physically demanding nature of climbing in dynamic and complex environments, which negatively impacts their motor and mental abilities. Effective monitoring is necessary to ensure safety.

Methods

This study proposed an experimental method to quantify fatigue in climbing operations. We collected subjective fatigue (using the RPE scale) and objective fatigue data, including systolic blood pressure (SBP), diastolic blood pressure (DBP), blood oxygen saturation (SpO2), vital capacity (VC), grip strength (GS), response time (RT), critical fusion frequency (CFF), and heart rate (HR) from 33 high-voltage workers before and after climbing tasks. The XGBoost algorithm was applied to establish a fatigue identification model.

Results

The analysis showed that the physiological indicators of SpO2, VC, GS, RT, and CFF can effectively evaluate fatigue in climbing operations. The XGBoost fatigue identification model, based on subjective fatigue and the five physiological indicators, achieved an average accuracy of 89.75%.

Conclusion

This study provides a basis for personalized management of fatigue in climbing operations, enabling timely detection of their fatigue states and implementation of corresponding measures to minimize the likelihood of accidents.

Compromised heat loss leads to a delayed ice slurry induced reduction in heat storage

Compromised heat loss due to limited convection and evaporation can increase thermal strain. We aimed to determine the effectiveness of ice slurry ingestion to reduce thermal strain following hyperthermia in a state of compromised heat loss. Twelve healthy males (age: 25 ± 4y) underwent hot water immersion to elevate rectal temperature (Trec) by 1.82 ± 0.08°C on four occasions. In the subsequent 60-min of seated recovery, participants ingested either 6.8 g·kg-1 of ice slurry (-0.6°C) or control drink (37°C) in ambient conditions (21 ± 1°C, 39 ± 10% relative humidity), wearing either t-shirt and shorts (2 trials: ICE and CON) or a whole-body sweat suit (2 trials: ICE-SS and CON-SS). Trec and mean skin temperature (Tsk) were recorded and a two-compartment thermometry model of heat storage was calculated. Heat storage was lower in ICE compared with CON at 20-40min (p ≤ 0.044, d ≥ 0.88) and for ICE-SS compared with CON-SS at 40-60 min (p ≤ 0.012, d ≥ 0.93). Trec was lower in ICE compared with CON from 30-60min (p ≤ 0.034, d ≥ 0.65), with a trend for a reduced Trec in ICE-SS compared with CON-SS at 40min (p = 0.079, d = 0.60). A greater Tsk was found in ICE-SS and CON-SS compared with ICE and CON (p < 0.001, d ≥ 3.37). A trend for a lower Tsk for ICE compared with CON was found at 20-40min (p ≤ 0.099, d ≥ 0.53), no differences were found for ICE-SS vs CON-SS (p ≥ 0.554, d ≤ 0.43). Ice slurry ingestion can effectively reduce heat storage when heat loss through convection and evaporation is compromised, relevant to those wearing personal protective equipment or those with compromised sweat loss. Compromised heat loss delays the reduction in heat storage, possibly related to ice slurry ingestion not lowering Tsk.

Heat stress and the velocity-duration relationship in amateur runners

Tolerance to high-intensity constant power exercise can be characterized by the hyperbolic power-duration (or velocity-duration) relationship. The hyperbola is defined by the asymptote (critical power or velocity) and the curvature constant (W' or D'). The effects of thermoregulatory stress on middle-distance running performance are equivocal-possibly due to the complexities of the hyperbolic velocity-duration relationship for these relatively short duration events. We aimed to measure the effects of heat stress on the velocity-duration relationship in amateur runners. Fifteen participants (23 ± 6 years) completed a series of constant-velocity running bouts to intolerance in three heat indices (MILD: 20°C, VERY HOT: 38°C, EXTREME: 55°C). Critical velocity (CV) in MILD (3.52 ± 0.86 m/s) was higher than VERY HOT (3.39 ± 0.82 m/s) and EXTREME (3.29 ± 1.05 m/s; F[2.28] = 3.80, p < 0.035) with no effect of thermal stress on D' (F[2.28] = 2.48, p = 0.11). In amateur competitive/recreational runners, heat stress of ≥38°C heat index negatively affected CV. Thus, even during relatively short events, such as middle-distance running where fluid loss is not a primary concern, heat stress may negatively impact performance.

Assessment of the Omius™ cooling headband effectiveness during a 70-min submaximal running effort followed by a 5-km time-trial in hot/humid conditions

Exercise performed under hot/humid conditions can hinder endurance performance. The Omius™ headband (OH) is purported to reduce the perception of heat and improve performance. We examined the impact of OH on selected thermal and cardiovascular functions, subjective perceptions and running performance. Using a randomized crossover protocol, 10 trained male athletes (28 ± 4 years) completed two trials (OH and sham headband (SH), 35.0 ± 0.3 °C, 56 ± 3% relative humidity) comprising 70 min of running (60% V˙O2max) followed by a 5-km running time-trial (TT). Heart rate, perceived exertion and whole-body thermal comfort did not significantly differ between conditions during the submaximal running effort and TT. Rectal temperature was higher with OH (0.11 ± 0.16 °C, p = 0.052) than SH prior to the submaximal running effort, however, no significant differences were observed between conditions regarding the changes in rectal temperature from baseline during the submaximal running effort and TT. Forehead temperature was significantly lower with OH than SH during the submaximal running effort, but no significant differences were observed at the end of the TT. Scores of perceived forehead thermal comfort were only significantly lower with OH than SH during the submaximal running effort. TT performance did not significantly differ between OH (19.8 ± 1.2 min) and SH (20.2 ± 1.0 min). In conclusion, OH improves forehead thermal comfort and reduces forehead temperature but not rectal temperature, heart rate and perceived exertion during, nor 5-km TT performance following, 70 min of submaximal running in the heat.

The roles of ACE I/D and ACTN3 R577X gene variants in heat acclimation

Roles of genes in heat acclimation (HA, repeated exercise-heat exposures) had not been explored. ACE I/D and ACTN3 R577X genetic polymorphisms are closely associated with outstanding exercise performances. This study investigated whether the two polymorphisms influenced the response to HA. Fifty young Han nationality male subjects were selected and conducted HA for 2 weeks. Exercise indicators (5-km run, push-up and 100-m run) were tested and rest aural thermometry (RTau) was measured before and after HA. ACE gene was grouped by I homozygote and D carrier, and ACTN3 gene was grouped by R homozygote and X carrier. Results showed that there were no differences between groups in age, body mass index, exercise indicators and RTau before HA. After HA, RTau of ACE I homozygote was lower than that of D carrier [F (1, 48) = 9.12, p = 0.004, η = 0.40]. Compared with RTau before HA, that of I homozygote decreased after HA (Δ = -0.26 °C, 95 % CI -0.34-0.18, p < 0.001), while that of D carrier did not change. There was a ACE gene × HA interaction in RTau [F (1, 48) = 14.26, p < 0.001, η = 0.48]. No effect of ACTN3 gene on RTau was observed. For exercise indicators, there were no differences between groups after HA, and no gene × HA interactions were observed. There may be a strong interaction of ACE gene and HA in the change of rest core temperature. I homozygote may have an advantage on improving heat tolerance.

Implications of Heat Stress-induced Metabolic Alterations for Endurance Training

Inducing a heat-acclimated phenotype via repeated heat stress improves exercise capacity and reduces athletes̓ risk of hyperthermia and heat illness. Given the increased number of international sporting events hosted in countries with warmer climates, heat acclimation strategies are increasingly popular among endurance athletes to optimize performance in hot environments. At the tissue level, completing endurance exercise under heat stress may augment endurance training adaptation, including mitochondrial and cardiovascular remodeling due to increased perturbations to cellular homeostasis as a consequence of metabolic and cardiovascular load, and this may improve endurance training adaptation and subsequent performance. This review provides an up-to-date overview of the metabolic impact of heat stress during endurance exercise, including proposed underlying mechanisms of altered substrate utilization. Against this metabolic backdrop, the current literature highlighting the role of heat stress in augmenting training adaptation and subsequent endurance performance will be presented with practical implications and opportunities for future research.

Time-series analysis of meteorological factors and emergency department visits due to dog/cat bites in Jinshan area, China

Background

Meteorological factors play an important role in human health. Clarifying the occurrence of dog and cat bites (DCBs) under different meteorological conditions can provide key insights into the prevention of DCBs. Therefore, the objective of the study was to explore the relationship between meteorological factors and DCBs and to provide caution to avoid the incidents that may occur by DCBs.

Methods

In this study, data on meteorological factors and cases of DCBs were retrospectively collected at the Shanghai Climate Center and Jinshan Hospital of Fudan University, respectively, in 2016-2020. The distributed lag non-linear and time series model (DLNM) were used to examine the effect of meteorological elements on daily hospital visits due to DCBs.

Results

A total of 26,857 DCBs were collected ranging from 1 to 39 cases per day. The relationship between ambient temperature and DCBs was J-shaped. DCBs were positively correlated with daily mean temperature (rs = 0.588, P < 0.01). The relative risk (RR) of DCBs was associated with high temperature (RR = 1.450; 95% CI [1.220-1.722]). Female was more susceptible to high temperature than male. High temperature increased the risk of DCBs.

Conclusions

The extremely high temperature increased the risk of injuries caused by DCBs, particularly for females. These data may help to develop public health strategies for potentially avoiding the occurrence of DCBs.

Topical application of L-Menthol - Physiological and genetic considerations to assist in developing female athlete research: A narrative review

L-menthol is a cyclic monoterpene derived from aromatic plants, which gives a cooling sensation upon application. With this in mind, L-menthol is beginning to be considered as a potential ergogenic aid for exercise and sporting competitions, particularly in hot environments, however female-specific research is lacking. The aim of this narrative review is to summarize available literature relating to topical application of L-menthol and provide commentary on avenues of consideration relating to future research developments of topical L-menthol in female athletes. From available studies in male participants, L-menthol topical application results in no endurance exercise performance improvements, however decreases in thermal sensation are observed. Mixed results are observed within strength performance parameters. Several genetic variations and single nucleotide polymorphisms have been identified in relation to sweat production, fluid loss and body mass changes - factors which may influence topical application of L-menthol. More specifically to female athletes, genetic variations relating to sweat responses and skin thickness, phases of the menstrual cycle, and body composition indices may affect the ergogenic effects of L-menthol topical application, via alterations in thermogenic responses, along with differing tissue distribution compared to their male counterparts. This narrative review concludes that further development of female athlete research and protocols for topical application of L-menthol is warranted due to physiological and genetic variations. Such developments would benefit research and practitioners alike with further personalized sport science strategies around phases of the menstrual cycle and body composition indices, with a view to optimize ergogenic effects of L-menthol.

Rectal and gastrointestinal temperature differ during passive heating and subsequent recovery

We aimed to compare rectal temperature (Trec) and gastro-intestinal temperature (TGI) during passive heating and subsequent recovery with and without ice slurry ingestion. Twelve males (age: 25 ± 4 years, body mass index: 25.7 ± 2.5 kg m-2) were immersed in hot water on two occasions (Trec elevation: 1.82 ± 0.08°C). In the subsequent 60-min recovery in ambient conditions, participants ingested either 6.8 g kg-1 of ice slurry (-0.6°C, ICE) or control drink (37°C, CON). During passive heating, Trec was lower than TGI (P < 0.001), in the recovery, Trec was higher than TGI (P < 0.001). During passive heating, mean bias and 95%LoA (Limits of Agreement) were -0.10(±0.25)°C and -0.12(±0.36)°C for CON and ICE, respectively. In the recovery, mean bias and 95%LoA were 0.30(±0.60)°C and 0.42(±0.63)°C for CON and ICE, respectively. Trec and TGI differed during both heating and recovery, and less favourable agreement between Trec and TGI was found in the recovery from passive heating with or without ice slurry ingestion.

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 3: Heat and cold tolerance during exercise

In this third installment of our four-part historical series, we evaluate contributions that shaped our understanding of heat and cold stress during occupational and athletic pursuits. Our first topic concerns how we tolerate, and sometimes fail to tolerate, exercise-heat stress. By 1900, physical activity with clothing- and climate-induced evaporative impediments led to an extraordinarily high incidence of heat stroke within the military. Fortunately, deep-body temperatures > 40 °C were not always fatal. Thirty years later, water immersion and patient treatments mimicking sweat evaporation were found to be effective, with the adage of cool first, transport later being adopted. We gradually acquired an understanding of thermoeffector function during heat storage, and learned about challenges to other regulatory mechanisms. In our second topic, we explore cold tolerance and intolerance. By the 1930s, hypothermia was known to reduce cutaneous circulation, particularly at the extremities, conserving body heat. Cold-induced vasodilatation hindered heat conservation, but it was protective. Increased metabolic heat production followed, driven by shivering and non-shivering thermogenesis, even during exercise and work. Physical endurance and shivering could both be compromised by hypoglycaemia. Later, treatments for hypothermia and cold injuries were refined, and the thermal after-drop was explained. In our final topic, we critique the numerous indices developed in attempts to numerically rate hot and cold stresses. The criteria for an effective thermal stress index were established by the 1930s. However, few indices satisfied those requirements, either then or now, and the surviving indices, including the unvalidated Wet-Bulb Globe-Thermometer index, do not fully predict thermal strain.

Exposures to Elevated Core Temperatures during Football Training: The Impact on Autonomic Nervous System Recovery and Function

Exercising with elevated core temperatures may negatively affect autonomic nervous system (ANS) function. Additionally, longer training duration under higher core temperatures may augment these negative effects. This study evaluated the relationship between exercise training duration and 24 h ANS recovery and function at ≥37 °C, ≥38 °C and ≥39 °C core temperature thresholds in a sample of male Division I (D1) collegiate American football athletes. Fifty athletes were followed over their 25-week season. Using armband monitors (Warfighter MonitorTM, Tiger Tech Solutions, Inc., Miami, FL, USA), core temperature (°C) and 24 h post-exercise baseline heart rate (HR), HR recovery and heart rate variability (HRV) were measured. For HRV, two time-domain indices were measured: the root mean square of the standard deviation of the NN interval (rMSSD) and the standard deviation of the NN interval (SDNN). Linear regression models were performed to evaluate the associations between exercise training duration and ANS recovery (baseline HR and HRV) and function (HR recovery) at ≥37 °C, ≥38 °C and ≥39 °C core temperature thresholds. On average, the athletes were 21.3 (± 1.4) years old, weighed 103.0 (±20.2) kg and had a body fat percentage of 15.4% (±7.8%, 3.0% to 36.0%). The duration of training sessions was, on average, 161.1 (±40.6) min and they ranged from 90.1 to 339.6 min. Statistically significant associations between training duration and 24 h ANS recovery and function were observed at both the ≥38.0 °C (baseline HR: β = 0.10 ± 0.02, R2 = 0.26, p < 0.0000; HR recovery: β = -0.06 ± 0.02, R2 = 0.21, p = 0.0002; rMSSD: β = -0.11 ± 0.02, R2 = 0.24, p < 0.0000; and SDNN: β = -0.16 ± 0.04, R2 = 0.22, p < 0.0000) and ≥39.0 °C thresholds (β = 0.39 ± 0.05, R2 = 0.62, p < 0.0000; HR recovery: β = -0.26 ± 0.04, R2 = 0.52, p < 0.0000; rMSSD: β = -0.37 ± 0.05, R2 = 0.58, p < 0.0000; and SDNN: β = -0.67 ± 0.09, R2 = 0.59, p < 0.0000). With increasing core temperatures, increases in slope steepness and strengths of the associations were observed, indicating accelerated ANS deterioration. These findings demonstrate that exercise training under elevated core temperatures (≥38 °C) may negatively influence ANS recovery and function 24 h post exercise and progressively worsen.

A century of exercise physiology: concepts that ignited the study of human thermoregulation. Part 2: physiological measurements

In this, the second of four historical reviews on human thermoregulation during exercise, we examine the research techniques developed by our forebears. We emphasise calorimetry and thermometry, and measurements of vasomotor and sudomotor function. Since its first human use (1899), direct calorimetry has provided the foundation for modern respirometric methods for quantifying metabolic rate, and remains the most precise index of whole-body heat exchange and storage. Its alternative, biophysical modelling, relies upon many, often dubious assumptions. Thermometry, used for >300 y to assess deep-body temperatures, provides only an instantaneous snapshot of the thermal status of tissues in contact with any thermometer. Seemingly unbeknownst to some, thermal time delays at some surrogate sites preclude valid measurements during non-steady state conditions. To assess cutaneous blood flow, immersion plethysmography was introduced (1875), followed by strain-gauge plethysmography (1949) and then laser-Doppler velocimetry (1964). Those techniques allow only local flow measurements, which may not reflect whole-body blood flows. Sudomotor function has been estimated from body-mass losses since the 1600s, but using mass losses to assess evaporation rates requires precise measures of non-evaporated sweat, which are rarely obtained. Hygrometric methods provide data for local sweat rates, but not local evaporation rates, and most local sweat rates cannot be extrapolated to reflect whole-body sweating. The objective of these methodological overviews and critiques is to provide a deeper understanding of how modern measurement techniques were developed, their underlying assumptions, and the strengths and weaknesses of the measurements used for humans exercising and working in thermally challenging conditions.

Early Prediction of Impending Exertional Heat Stroke With Wearable Multimodal Sensing and Anomaly Detection

We employed wearable multimodal sensing (heart rate and triaxial accelerometry) with machine learning to enable early prediction of impending exertional heat stroke (EHS). US Army Rangers and Combat Engineers (N = 2,102) were instrumented while participating in rigorous 7-mile and 12-mile loaded rucksack timed marches. There were three EHS cases, and data from 478 Rangers were analyzed for model building and controls. The data-driven machine learning approach incorporated estimates of physiological strain (heart rate) and physical stress (estimated metabolic rate) trajectories, followed by reconstruction to obtain compressed representations which then fed into anomaly detection for EHS prediction. Impending EHS was predicted from 33 to 69 min before collapse. These findings demonstrate that low dimensional physiological stress to strain patterns with machine learning anomaly detection enables early prediction of impending EHS which will allow interventions that minimize or avoid pathophysiological sequelae. We describe how our approach can be expanded to other physical activities and enhanced with novel sensors.

The Impact of Neck Cooling on Serum Oxidant/Antioxidant Status and HSP70 Levels during High-Intensity Cycling

Numerous studies have been conducted in an attempt to discover cooling strategies that can be effective in improving exercise performance. However, the mechanism by which neck cooling relieves exercise-induced physiological stress and the optimal cooling temperature are unclear. This study aimed to investigate the effects of neck cooling at different temperatures during high-intensity cycling on body temperature, physiological variables, oxidant/antioxidant status, heat shock protein (HSP) 70 levels, and exercise performance in adolescent athletes. Seven well-trained male adolescent cyclists (age, 17.00 ± 0.76 years; athletic career, 3.86 ± 0.90 years) participated in three exercise trials involving three cooling regimens: control (CON), low-temperature (7 °C) neck cooling (LNC), and mixed-temperature (14 + 20 °C) neck cooling (MNC). The experimental condition used a cross-over design to minimize adaption to the repetitive cycling trials. Cycling consisted of a 20 km warm-up session and a two 2 km race session. Neck cooling at different temperatures was administered for 20 min during each rest period: after the warm-up, after the first 2 km race, and after the second 2 km race. Blood samples were taken to assess serum malondialdehyde (MDA), superoxide dismutase (SOD), and HSP70 levels. In addition, tympanic temperature (Tty), thermal sensation (TS), heart rate (HR), and the saturation of percutaneous oxygen (SpO2) were measured before, immediately after, and 24 h after exercise. As a measure of cycling performance, the race record and speed were measured in the first and second 2 km races. In all trials, Tty, TS, HR, MDA, SOD, and HSP70 levels significantly increased (p < 0.05), and SpO2 levels significantly decreased (p < 0.05). TS significantly decreased 24 h after exercise compared to that immediately after exercise in the LNC and MNC trials (p < 0.05). Serum HSP70 levels were significantly higher 24 h after exercise (0.87 ± 0.10 ng/mL) than immediately after exercise (0.79 ± 0.04 ng/mL) in the CON trial (p < 0.05). Twenty-four hours after exercise, the CON (0.87 ± 0.10 ng/mL) trial showed significantly higher serum HSP70 levels than the LNC (0.73 ± 0.01 ng/mL) trial (p < 0.05). There was no significant difference in cycling race record or speed between the trials (p > 0.05). Our findings suggest that neck cooling can induce a positive effect on thermal perception during recovery after cycling and that neck cooling at a relatively low temperature may be more effective in reducing exercise-induced HSP70 expression.

Core Body Temperatures in Intermittent Sports: A Systematic Review

BACKGROUND

Hyperthermia (and associated health and performance implications) can be a significant problem for athletes and teams involved in intermittent sports. Quantifying the highest thermal strain (i.e. peak core body temperature [peak Tc]) from a range of intermittent sports would enhance our understanding of the thermal requirements of sport and assist in making informed decisions about training or match-day interventions to reduce thermally induced harm and/or performance decline.

OBJECTIVE

The objective of this systematic review was to synthesise and characterise the available thermal strain data collected in competition from intermittent sport athletes.

METHODS

A systematic literature search was performed on Web of Science, MEDLINE, and SPORTDiscus to identify studies up to 17 April 2023. Electronic databases were searched using a text mining method to provide a partially automated and systematic search strategy retrieving terms related to core body temperature measurement and intermittent sport. Records were eligible if they included core body temperature measurement during competition, without experimental intervention that may influence thermal strain (e.g. cooling), in healthy, adult, intermittent sport athletes at any level. Due to the lack of an available tool that specifically includes potential sources of bias for physiological responses in descriptive studies, a methodological evaluation checklist was developed and used to document important methodological considerations. Data were not meta-analysed given the methodological heterogeneity between studies and therefore were presented descriptively in tabular and graphical format.

RESULTS

A total of 34 studies were selected for review; 27 were observational, 5 were experimental (2 parallel group and 3 repeated measures randomised controlled trials), and 2 were quasi-experimental (1 parallel group and 1 repeated measures non-randomised controlled trial). Across all included studies, 386 participants (plus participant numbers not reported in two studies) were recruited after accounting for shared data between studies. A total of 4 studies (~ 12%) found no evidence of hyperthermia, 24 (~ 71%) found evidence of 'modest' hyperthermia (peak Tc between 38.5 and 39.5 °C), and 6 (~ 18%) found evidence of 'marked' hyperthermia (peak Tc of 39.5 °C or greater) during intermittent sports competition.

CONCLUSIONS

Practitioners and coaches supporting intermittent sport athletes are justified to seek interventions aimed at mitigating the high heat strain observed in competition. More research is required to determine the most effective interventions for this population that are practically viable in intermittent sports settings (often constrained by many competing demands). Greater statistical power and homogeneity among studies are required to quantify the independent effects of wet bulb globe temperature, competition duration, sport and level of competition on peak Tc, all of which are likely to be key modulators of the thermal strain experienced by competing athletes.

REGISTRATION

This systematic review was registered on the Open Science Framework ( https://osf.io/vfb4s ; https://doi.org/10.17605/OSF.IO/EZYFA , 4 January 2021).

Key Exercise Concepts in the Rehabilitation from Severe Burns

This article presents information on the benefits of exercise in counteracting the detrimental effects of bed rest, and/or severe burns. Exercise is key for maintaining physical function, lean body mass, metabolic recovery, and psychosocial health after major burn injuries. The details of an exercise training program conducted in severely burned persons are presented, as well as information on the importance of proper regulation of body temperature during exercise or physical activity. The sections on exercise and thermoregulation are followed by a section on the role of exercise in scarring and contractures. Finally, gaps in the current knowledge of exercise, thermoregulation, and contractures are presented.

Impact of Preparticipation Hypohydration on Cognitive Performance and Concussion-like Symptoms in Recreational Athletes

BACKGROUND

Sports-related concussion is a relevant risk of contact sports, with several million cases per year worldwide. Prompt identification is crucial to prevent complications and late effects but may be impeded by an overlap with dehydration-associated impairment of cognitive function. Researchers have extensively studied the effects of pronounced dehydration in endurance sports, especially in the heat. However, little is known about the effects of isolated and mild dehydration.

METHODS

Healthy recreational athletes underwent a standardized fluid deprivation test. Hypohydration was assessed by bioelectrical impedance analysis (BIA) and laboratory testing of electrolytes and retention parameters. Participants underwent cardiopulmonary exercise testing (CPET) with a cycle ramp protocol. Each participant served as their own control undergoing CPET in a hypohydrated [HYH] and a euhydrated [EUH] state. Effects were assessed using a shortened version of Sport Concussion Assessment Tool 3 (SCAT3).

RESULTS

Fluid deprivation caused a mild (2%) reduction in body water, resulting in a calculated body mass loss of 0.8% without alterations of electrolytes, serum-osmolality, or hematocrit. Athletes reported significantly more (1.8 ± 2.2 vs. 0.4 ± 0.7; p < 0.01) and more severe (4.4 ± 6.2 vs. 1.0 ± 1.9; p < 0.01) concussion-like symptoms in a hypohydrated state. Balance was worse in HYH by trend with a significant difference for tandem stance (1.1 ± 1.3 vs. 0.6 ± 1.1; p = 0.02). No relevant differences were presented for items of memory and concentration.

CONCLUSIONS

Mild dehydration caused relevant alterations of concussion-like symptoms and balance in healthy recreational athletes in the absence of endurance exercise or heat. Further research is needed to clarify the real-life relevance of these findings and to strengthen the differential diagnosis of concussion.

Diver Underwater Cycling Endurance After Short-Term Warm and Hot Water Acclimation

INTRODUCTION

It is unclear whether immersion heat acclimation benefits exercise in warm water conditions. This study examined the effects of heat acclimation strategies on heart rate (HR), core temperature, and time to exhaustion (TTE) during cycling exercise in varying warm water conditions.

METHODS

Twenty male divers completed this study at the Navy Experimental Diving Unit. Subjects were randomly assigned to one of two 9-day heat acclimation groups. The first group (WARM; n = 10) cycled for 2 hours at 50 W in 34.4 °C water, while the second group (HOT; n = 10) cycled for 1 hour against minimal resistance in 36.7 °C water. Following acclimation, TTE was tested by underwater cycling (30 W) in 35.8 °C, 37.2 °C, and 38.6 °C water.

RESULTS

Throughout acclimation, the rate of core temperature rise in the first 30 minutes of exercise increased (P = .02), but the maximum core temperature reached was not different for either group. Time to exhaustion (TTE) was reduced, and the rate of core temperature rise during performance testing increased (both P < .001) with increasing water temperature but was not different between groups. Core temperature and HR increased throughout performance testing in each water condition and were lower in the HOT compared to the WARM acclimation group (all P < .05) with the exception of core temperature in the 37.2 °C condition.

CONCLUSIONS

Underwater exercise performance did not differ between the two acclimation strategies. This study suggests that passive acclimation to a higher water temperature may improve thermoregulatory and cardiovascular responses to exercise in warm water. Hot water immersion adaptations are dependent on exercise intensity and water temperature.

Reduced running performance and greater perceived exertion, but similar post-exercise neuromuscular fatigue in tropical natives subjected to a 10 km self-paced run in a hot compared to a temperate environment

Environmental heat stress impairs endurance performance by enhancing exercise-induced physiological and perceptual responses. However, the time course of these responses during self-paced running, particularly when comparing hot and temperate conditions, still needs further clarification. Moreover, monitoring fatigue induced by exercise is paramount to prescribing training and recovery adequately, but investigations on the effects of a hot environment on post-exercise neuromuscular fatigue are scarce. This study compared the time course of physiological and perceptual responses during a 10 km self-paced treadmill run (as fast as possible) between temperate (25°C) and hot (35°C) conditions. We also investigated the changes in countermovement jump (CMJ) performance following exercise in these two ambient temperatures. Thirteen recreational long-distance runners (11 men and 2 women), inhabitants of a tropical region, completed the two experimental trials in a randomized order. Compared to 25°C, participants had transiently higher body core temperature (TCORE) and consistently greater perceived exertion while running at 35°C (p < 0.05). These changes were associated with a slower pace, evidenced by an additional 14 ± 5 min (mean ± SD) to complete the 10 km at 35°C than at 25°C (p < 0.05). Before, immediately after, and 1 h after the self-paced run, the participants performed CMJs to evaluate lower limb neuromuscular fatigue. CMJ height was reduced by 7.0% (2.3 ± 2.4 cm) at 1 h after the race (p < 0.05) compared to pre-exercise values; environmental conditions did not influence this reduction. In conclusion, despite the reduced endurance performance, higher perceived exertion, and transiently augmented TCORE caused by environmental heat stress, post-exercise neuromuscular fatigue is similar between temperate and hot conditions. This finding suggests that the higher external load (faster speed) at 25°C compensates for the effects of more significant perceptual responses at 35°C in inducing neuromuscular fatigue.

Impact of Preparticipating Hypohydration on Cardiopulmonary Exercise Capacity in Ambitious Recreational Athletes

BACKGROUND

Heat induces a thermoregulatory strain that impairs cardiopulmonary exercise capacity. The aim of the current study is to elucidate the effect of isolated dehydration on cardiopulmonary exercise capacity in a model of preparticipating hypohydration.

METHODS

Healthy recreational athletes underwent a standardised fluid deprivation test. Hypohydration was assessed by bioelectrical impedance analysis (BIA) and laboratory testing of electrolytes and retention parameters in the blood and urine. The participants underwent cardiopulmonary exercise testing (CPET) with a cycle ramp protocol. Each participant served as their own control undergoing CPET in a hypohydrated [HYH] and euhydrated [EUH] state.

RESULTS

Fluid deprivation caused a mild (2%) but significant reduction of body water (38.6 [36.6; 40.7] vs. 39.4 [37.4; 41.5] %; p < 0.01) and an increase of urine osmolality (767 [694; 839] vs. 537 [445; 629] mosm/kg; p < 0.01). Hypohydration was without alterations of electrolytes, serum osmolality or hematocrit. The oxygen uptake was significantly lower after hypohydration (-4.8%; p = 0.02 at ventilatory threshold1; -2.0%; p < 0.01 at maximum power), with a corresponding decrease of minute ventilation (-4% at ventilatory threshold1; p = 0.01, -3.3% at maximum power; p < 0.01). The power output was lower in hypohydration (-6.8%; p < 0.01 at ventilatory threshold1; -2.2%; p = 0.01 at maximum power).

CONCLUSION

Isolated hypohydration causes impairment of workload as well as peak oxygen uptake in recreational athletes. Our findings might indicate an important role of hypohydration in the heat-induced reduction of exercise capacity.

Impact of high intensity interval exercise with and without heat stress on cardiovascular and aerobic performance: a pilot study

BACKGROUND

Heat stress during aerobic exercise training may offer an additional stimulus to improve cardiovascular function and performance in a cool-temperate environment. However, there is a paucity of information on the additive effects of high-intensity interval exercise (HIIE) and acute heat stress. We aimed to determine the effects of HIIE in combination with acute heat stress on cardiovascular function and exercise performance.

METHODS

Twelve active (peak O₂ consumption [VO_2peak]: 47 ± 8 ml·O₂/min/kg) young adults were counterbalanced to six sessions of HIIE in hot (HIIE-H, 30 ± 1 °C, 50 ± 5% relative humidity [RH]) or temperate conditions (HIIE-T, 20 ± 2 °C, 15 ± 10% RH). Resting heart rate (HR), HR variability (HRV), central (cBP) and peripheral blood pressure (pBP), peripheral mean arterial pressure (pMAP), pulse wave velocity (PWV), VO_2peak, and 5-km treadmill time-trial were measured pre- and post-training.

RESULTS

Resting HR and HRV were not significantly different between groups. However, expressed as percent change from baseline, cSBP (HIIE-T: + 0.9 ± 3.6 and HIIE-H: -6.6 ± 3.0%, p = 0.03) and pSBP (HIIE-T: -2.0 ± 4.6 and HIIE-H: -8.4 ± 4.7%, p = 0.04) were lower in the heat group. Post-training PWV was also significantly lower in the heat group (HIIE-T: + 0.4% and HIIE-H: -6.3%, p = 0.03). Time-trial performance improved with training when data from both groups were pooled, and estimated VO_2peak was not significantly different between groups (HIIE-T: 0.7% and HIIE-H: 6.0%, p = 0.10, Cohen's d = 1.4).

CONCLUSIONS

The addition of acute heat stress to HIIE elicited additive adaptations in only cardiovascular function compared to HIIE alone in active young adults in temperate conditions, thus providing evidence for its effectiveness as a strategy to amplify exercise-induced cardiovascular adaptations.

Heated environment offsets the cardiovascular responses to prolonged rowing exercise in competitive athletes

Prolonged rowing exercise sessions are often prescribed considering competitive training schedules, and under hostile environments (e.g., heated ambient). The study aimed to investigate the effect of heat stress (HS) on physical performance, Lactate concentration ([Lac]), and cardiorespiratory responses during prolonged exercise sessions in competitive rowers. Twelve rowers performed preliminary exercise tests (2-km test and five-step incremental lactate test) to assess the target workload intensity corresponding to a 2.5 mmol^.L^-1 of [Lac]. On two separate days, participants were enrolled in two exercise sessions of 12 km in a rowing machine under HS (∼30 °C) and thermal comfort (TC 22 °C) conditions. Heart rate (HR), stroke volume (SV), cardiac output (CO), oxygen uptake (VO₂), [Lac], and the rating of perceptual exertion (RPE) were obtained. From baseline, HS increased the maximum temperature of the face compared to TC. Workload and VO₂ reduced while RPE increased at 9- and 12-km of rowing exercise under HS compared to TC. From baseline to the last stage of exercise, HS shifted SV downwards and HR upwards compared to TC. Consequently, CO did not change between thermal conditions (TC vs. HS). Therefore, HS provokes a cardiovascular drift during prolonged rowing in comparison to TC. The last stages of prolonged rowing sessions under HS seem to be critical to physical performance and relative perceptual of effort in rowers.

Cold water immersion of the hand and forearm during half-time improves intermittent exercise performance in the heat

The present study aimed to investigate the effect of cold water immersion of the hand and forearm during half-time (HT) on intermittent exercise performance and thermoregulation by imitating intermittent athletic games in the heat. In a randomized crossover design, 11 physically active men performed the first half (first and second block) and second half (third and fourth block) intermittent cycling exercise protocol, which consisted of a 5-s maximal power pedalling (body weight × 0.075 kp) every minute separated by 25-s of unloaded pedalling and rest (30 s) in the heat (33°C, 50% relative humidity). The two-halves were separated by a 15-min HT. During HT, the participants were assigned to the CON (sedentary resting) or COOL (immersion of hands and forearms in cold water at 15-17°C) condition. The mean power output in the second half was significantly greater (third and fourth block: p < 0.05) in the COOL than in the CON condition. Moreover, there was a significant decrease in the rectal (0.54 ± 0.17°C, p < 0.001) and mean skin (1.86 ± 0.34°C, p < 0.05) temperatures of the COOL condition during HT. Furthermore, the heart rate (16 ± 7 bpm, p < 0.05) and skin blood flow (40.2 ± 10.5%, p < 0.001) decreased at the end of HT in the COOL condition. In the second half, thermal sensation was more comfortable in the COOL condition (p < 0.001). Cold water immersion of the hand and forearm during HT improved physiological and reduced perceived heat stress. Moreover, it prevented a reduction in intermittent exercise performance in the second half.

Heat Preparation and Knowledge at the World Athletics Race Walking Team Championships Muscat 2022

PURPOSE

To assess elite racewalkers' preparation strategies, knowledge, and general practices for competition in the heat and their health status during the World Athletics Race Walking Teams Championships (WRW) Muscat 2022.

METHODS

Sixty-six elite racewalkers (male: n = 42; mean age = 25.8 y) completed an online survey prior to WRW Muscat 2022. Athletes were grouped by sex (males vs females) and climate (self-reported) they live/trained in (hot vs temperate/cold), with differences/relationships between groups assessed. Relationships between ranking (medalist/top 10 vs nonmedalist/nontop 10) and precompetition use of heat acclimation/acclimatization (HA) were assessed.

RESULTS

All surveyed medalists (n = 4) implemented, and top 10 finishers were more likely to report using (P = .049; OR = 0.25; 95% CI, 0.06%-1%), HA before the championships. Forty-three percent of athletes did not complete specific HA training. Females (8% [males 31%]) were less likely to have measured core temperature (P = .049; OR = 0.2; 95% CI, 0.041-0.99) and more likely to not know expected conditions in Muscat (42% vs 14%; P = .016; OR = 4.3; 95% CI, 1%-14%) or what wet bulb globe temperature is (83% vs 55%; P = .024; OR = 4.1; 95% CI, 1%-14%).

CONCLUSIONS

Athletes who implemented HA before the championships tended to place better than those who did not. Forty-three percent of athletes did not prepare for the expected hot conditions at the WRW Muscat 2022, primarily attributed to challenges in accessing and/or cost of equipment/facilities for HA strategies. Further efforts to bridge the gap between research and practice in this elite sport are needed, particularly in female athletes.

A Systematic Review of Post-Work Core Temperature Cooling Rates Conferred by Passive Rest

Physical work increases energy expenditure, requiring a considerable elevation of metabolic rate, which causes body heat production that can cause heat stress, heat strain, and hyperthermia in the absence of adequate cooling. Given that passive rest is often used for cooling, a systematic search of literature databases was conducted to identify studies that reported post-work core temperature cooling rates conferred by passive rest, across a range of environmental conditions. Data regarding cooling rates and environmental conditions were extracted, and the validity of key measures was assessed for each study. Forty-four eligible studies were included, providing 50 datasets. Eight datasets indicated a stable or rising core temperature in participants (range 0.000 to +0.028 °C min^-1), and forty-two datasets reported reducing core temperature (-0.002 to -0.070 °C min^-1) during passive rest, across a range of Wet-Bulb Globe Temperatures (WBGT). For 13 datasets where occupational or similarly insulative clothing was worn, passive rest resulted in a mean core temperature decrease of -0.004 °C min^-1 (-0.032 to +0.013 °C min^-1). These findings indicate passive rest does not reverse the elevated core temperatures of heat-exposed workers in a timely manner. Climate projections of higher WBGT are anticipated to further marginalise the passive rest cooling rates of heat-exposed workers, particularly when undertaken in occupational attire.

Thermoregulatory, Cardiovascular and Perceptual Responses of Spectators of a Simulated Football Match in Hot and Humid Environmental Conditions

Major sporting events are often scheduled in thermally challenging environments. The heat stress may impact athletes but also spectators. We examined the thermal, cardiovascular, and perceptual responses of spectators watching a football match in a simulated hot and humid environment. A total of 48 participants (43 ± 9 years; n = 27 participants <50 years and n = 21 participants ≥50 years, n = 21) watched a 90 min football match in addition to a 15 min baseline and 15 min halftime break, seated in an environmental chamber (Tair = 31.9 ± 0.4 °C; RH = 76 ± 4%). Gastrointestinal temperature (Tgi), skin temperature (Tskin), and heart rate (HR) were measured continuously throughout the match. Mean arterial pressure (MAP) and perceptual parameters (i.e., thermal sensation and thermal comfort) were scored every 15 min. Tri (37.3 ± 0.4 °C to 37.4 ± 0.3 °C, p = 0.11), HR (76 ± 15 bpm to 77 ± 14 bpm, p = 0.96) and MAP (97 ± 10 mm Hg to 97 ± 10 mm Hg, p = 0.67) did not change throughout the match. In contrast, an increase in Tskin (32.9 ± 0.8 °C to 35.4 ± 0.3 °C, p < 0.001) was found. Further, 81% of participants reported thermal discomfort and 87% a (slightly) warm thermal sensation at the end of the match. Moreover, the thermal or cardiovascular responses were not affected by age (all p-values > 0.05). Heat stress induced by watching a football match in simulated hot and humid conditions does not result in substantial thermal or cardiovascular strain, whereas a significant perceptual strain was observed.

The neural pathway of the hyperthermic response to antagonists of the transient receptor potential vanilloid-1 channel

We identified the neural pathway of the hyperthermic response to TRPV1 antagonists. We showed that hyperthermia induced by i.v. AMG0347, AMG 517, or AMG8163 did not occur in rats with abdominal sensory nerves desensitized by pretreatment with a low i.p. dose of resiniferatoxin (RTX, TRPV1 agonist). However, neither bilateral vagotomy nor bilateral transection of the greater splanchnic nerve attenuated AMG0347-induced hyperthermia. Yet, this hyperthermia was attenuated by bilateral high cervical transection of the spinal dorsolateral funiculus (DLF). To explain the extra-splanchnic, spinal mediation of TRPV1 antagonist-induced hyperthermia, we proposed that abdominal signals that drive this hyperthermia originate in skeletal muscles - not viscera. If so, in order to prevent TRPV1 antagonist-induced hyperthermia, the desensitization caused by i.p. RTX should spread into the abdominal-wall muscles. Indeed, we found that the local hypoperfusion response to capsaicin (TRPV1 agonist) in the abdominal-wall muscles was absent in i.p. RTX-desensitized rats. We then showed that the most upstream (lateral parabrachial, LPB) and the most downstream (rostral raphe pallidus) nuclei of the intrabrain pathway that controls autonomic cold defenses are also required for the hyperthermic response to i.v. AMG0347. Injection of muscimol (inhibitor of neuronal activity) into the LPB or injection of glycine (inhibitory neurotransmitter) into the raphe blocked the hyperthermic response to i.v. AMG0347, whereas i.v. AMG0347 increased the number of c-Fos cells in the raphe. We conclude that the neural pathway of TRPV1 antagonist-induced hyperthermia involves TRPV1-expressing sensory nerves in trunk muscles, the DLF, and the same LPB-raphe pathway that controls autonomic cold defenses.

The effect of cold water immersion on the recovery of physical performance revisited: A systematic review with meta-analysis

This review evaluated the effect of CWI on the temporal recovery profile of physical performance, accounting for environmental conditions and prior exercise modality. Sixty-eight studies met the inclusion criteria. Standardised mean differences were calculated for parameters assessed at <1, 1-6, 24, 48, 72 and ≥96 h post-immersion. CWI improved short-term recovery of endurance performance (p = 0.01, 1 h), but impaired sprint (p = 0.03, 1 h) and jump performance (p = 0.04, 6h). CWI improved longer-term recovery of jump performance (p < 0.01-0.02, 24 h and 96 h) and strength (p < 0.01, 24 h), which coincided with decreased creatine kinase (p < 0.01-0.04, 24-72 h), improved muscle soreness (p < 0.01-0.02, 1-72 h) and perceived recovery (p < 0.01, 72 h). CWI improved the recovery of endurance performance following exercise in warm (p < 0.01) and but not in temperate conditions (p = 0.06). CWI improved strength recovery following endurance exercise performed at cool-to-temperate conditions (p = 0.04) and enhanced recovery of sprint performance following resistance exercise (p = 0.04). CWI seems to benefit the acute recovery of endurance performance, and longer-term recovery of muscle strength and power, coinciding with changes in muscle damage markers. This, however, depends on the nature of the preceding exercise.

A 6-year retrospective review of injuries sustained during the Singapore Cricket Club International Rugby Sevens tournament

There are limited studies looking at injury statistics for Rugby Sevens. This study aims to assess injury patterns among amateur players participating in the annual Singapore Cricket Club Rugby Sevens International tournament from 2012 to 2017, by performing a retrospective review of their injury data. Outcome measures include injury incidence rate, injury site, and comparative injury incidence between successive days of competition. A total of 343 injuries were recorded over 6 tournaments, with an injury incidence of 348.0 per 1000 player hours. The lower limb was the most commonly injured site (45.8%), and there was greater incidence of injuries on day 3 of competition compared to day 1 in 2013 and 2016. This study reports a higher level of background risk to Rugby Sevens than is reported in literature. A well designed-prospective injury surveillance study will be necessary to confirm these findings and to investigate risk factors to guide injury prevention programmes.

The effectiveness of heat preparation and alleviation strategies for cognitive performance: A systematic review

A range of occupational and performance contexts (e.g. military personnel operations, emergency services, sport) require the critical maintenance of cognitive performance in environmentally challenging environments. Several reviews exist which evaluate the effectiveness of heat preparation strategies to facilitate physical performance. To date, no review has explored the usefulness of heat preparation strategies for cognitive performance. Therefore, this systematic review aimed to evaluate a range of interventions for the maintenance of cognitive performance, during or following active or passive heat exposure. Studies to be included were assessed by two authors reviewing title, abstract, and full-text. Forty articles were identified which met the inclusion criteria. Interventions were categorised into chronic (i.e. acclimation/acclimatisation) and acute strategies (i.e. hydration, cooling, supplementation, psychological). The results indicate that medium-term consecutive heat acclimation may mitigate some cognitive deficits under heat stress, although heat acclimation effectiveness could be influenced by age. Further, pre-cooling appears the most effective cooling method for maintaining cognitive performance under heat stress, although results were somewhat ambiguous. The hydration literature showed that the most effective hydration strategies were those which individualised electrolyte fortified fluid volumes to match for sweat loss. Limited research exploring psychological interventions indicates that motivational self-talk could be facilitative for maintaining cognitive skills following exercise in hot conditions. These findings can be used to help inform strategies for maintaining critical cognitive and decision-making skills in hot environments.

Fatigue and Human Performance: An Updated Framework

Fatigue has been defined differently in the literature depending on the field of research. The inconsistent use of the term fatigue complicated scientific communication, thereby limiting progress towards a more in-depth understanding of the phenomenon. Therefore, Enoka and Duchateau (Med Sci Sports Exerc 48:2228-38, 2016, [3]) proposed a fatigue framework that distinguishes between trait fatigue (i.e., fatigue experienced by an individual over a longer period of time) and motor or cognitive task-induced state fatigue (i.e., self-reported disabling symptom derived from the two interdependent attributes performance fatigability and perceived fatigability). Thereby, performance fatigability describes a decrease in an objective performance measure, while perceived fatigability refers to the sensations that regulate the integrity of the performer. Although this framework served as a good starting point to unravel the psychophysiology of fatigue, several important aspects were not included and the interdependence of the mechanisms driving performance fatigability and perceived fatigability were not comprehensively discussed. Therefore, the present narrative review aimed to (1) update the fatigue framework suggested by Enoka and Duchateau (Med Sci Sports Exerc 48:2228-38, 2016, [3]) pertaining the taxonomy (i.e., cognitive performance fatigue and perceived cognitive fatigue were added) and important determinants that were not considered previously (e.g., effort perception, affective valence, self-regulation), (2) discuss the mechanisms underlying performance fatigue and perceived fatigue in response to motor and cognitive tasks as well as their interdependence, and (3) provide recommendations for future research on these interactions. We propose to define motor or cognitive task-induced state fatigue as a psychophysiological condition characterized by a decrease in motor or cognitive performance (i.e., motor or cognitive performance fatigue, respectively) and/or an increased perception of fatigue (i.e., perceived motor or cognitive fatigue). These dimensions are interdependent, hinge on different determinants, and depend on body homeostasis (e.g., wakefulness, core temperature) as well as several modulating factors (e.g., age, sex, diseases, characteristics of the motor or cognitive task). Consequently, there is no single factor primarily determining performance fatigue and perceived fatigue in response to motor or cognitive tasks. Instead, the relative weight of each determinant and their interaction are modulated by several factors.

Comparison of the effects of high and low levels of solar radiations on exercise capacity in hot outdoor environments

BACKGROUND

High solar radiation from the sun in the heat outdoor may be impaired exercise capacity. This study aimed to compare the effects of different levels of solar radiation on exercise capacity and evaluate skin temperature responses in the heat.

METHODS

Seven male participants performed cycling exercise at 60% of their maximal oxygen uptake until volitional exhaustion in hot outdoor environments (approximately 33-35°C, 40-50% relative humidity) under both clear sky (high solar radiation trial: 1062±50 W/m²) and under thick clouds (low solar radiation trial: 438±52 W/m²).

RESULTS

The time to exhaustion of the participants was shorter in the high solar radiation trial (32.0±12.4 min) than in the low solar radiation trial (39.2±18.0 min: P=0.045). Mean skin temperature was significantly higher in the high solar radiation trial than that in the low solar radiation trial (P<0.05); however, the rectal temperature did not differ significantly between the two trials. The high solar radiation trial had narrower core-to-skin temperature gradient, greater the body heat gain from the sun, and higher rating of perceived exertion than the low solar radiation trial.

CONCLUSIONS

These results indicate that high solar radiation during outdoor exercise in the heat causes a greater increase in skin temperature and body heat gain from the sun than low solar radiation and consequently impairs exercise capacity.

Responses of soccer players performing repeated maximal efforts in simulated conditions of the FIFA World Cup Qatar 2022: A holistic approach

This study aimed to assess the capacity for repeated maximal effort (RME) of soccer players in the thermo-natural conditions (NC) and in simulated conditions for the 2022 FIFA World Cup in Qatar (QSC). Twenty-four semi-professional soccer players participated in the study. The exercise test consisted of ten 6-second maximal efforts on a cycloergometer. A 90-second passive rest interval was used. The test was performed in a Weiss Technik WK-26 climate test chamber in two different conditions: 1) thermo-neutral conditions (NC-20.5°C; 58.7% humidity); and 2) simulated conditions for the 2022 World Cup in Qatar (QSC-28.5 ± 1.92°C; 58.7 ± 8.64% humidity). Power-related, physiological, psychomotor, blood, and electrolyte variables were recorded. Results showed that (1) players achieved higher peak power (max 1607,46 ± 192,70 [W] - 3rd rep), needed less time to peak power (min 0,95 ± 0,27 [s] - 3rd rep), and had a higher fatigue slope (max 218,67 ± 59,64 [W/sek] - 7th rep) in QSC than in NC (in each repetition of study protocol); (2) between the 1st repetition and subsequent repetitions a number of significants in among physiological, blood-related, and electrolyte variables were noted, but their direction was similar in both simulated conditions (e.g. V'O2/kg 37,59 ± 3,96 vs 37,95 ± 3,17 [ml/min/kg] - 3rd rep, LAC 13,16 ± 2,61 vs 14,18 ± 3,13 [mg/dl] - 10th rep or K 4,54 ± 0,29 vs 4,79 ± 0,36 [mmol/l] - 2nd rep when compare QCS and NC respectively); (3) an 8°C of temperature difference between the climatic conditions did not significantly affect the soccer players' physical and physiological responses in RME. The study results can be used in the design of training programs aimed to increase players' physiological adaptations by simulating soccer-specific conditions of play in terms of anaerobic capacity, in particular, repetitive maximal efforts. These findings will be useful during the upcoming 2022 World Cup in Qatar and in locations where high ambient temperatures are customary.

Effect of cold ambient temperature on heat flux, skin temperature, and thermal sensation at different body parts in elite biathletes

Introduction

When exercising in the cold, optimizing thermoregulation is essential to maintain performance. However, no study has investigated thermal parameters with wearable-based measurements in a field setting among elite Nordic skiers. Therefore, this study aimed to assess the thermal response and sensation measured at different body parts during exercise in a cold environment in biathletes.

Methods

Thirteen Swiss national team biathletes (6 females, 7 males) performed two skiing bouts in the skating technique on two consecutive days (ambient temperature: -3.74 ± 2.32 °C) at 78 ± 4% of maximal heart rate. Heat flux (HF), core (Tcore) and skin (Tskin) temperature were measured with sensors placed on the thigh, back, anterior and lateral thorax. Thermal sensation (TS) was assessed three times for different body parts: in protective winter clothing, in a race suit before (PRE) and after exercise (POST).

Results

HF demonstrated differences (p < 0.001) between sensor locations, with the thigh showing the highest heat loss (344 ± 37 kJ/m2), followed by the back (269 ± 6 kJ/m2), the lateral thorax (220 ± 47 kJ/m2), and the anterior thorax (192 ± 37 kJ/m2). Tcore increased (p < 0.001). Tskin decreased for all body parts (p < 0.001). Thigh Tskin decreased more than for other body parts (p < 0.001). From PRE to POST, TS of the hands decreased (p < 0.01).

Conclusion

Biathletes skiing in a race suit at moderate intensity experience significant heat loss and a large drop in Tskin, particularly at the quadriceps muscle. To support the optimal functioning of working muscles, body-part dependent differences in the thermal response should be considered for clothing strategy and for race suit design.

Taking the plunge: When is best for hot water immersion to complement exercise in heat and hypoxia

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

Amateur runners more influenced than elite runners by temperature and air pollution during the UK's Great North Run half marathon

The short- and long-term impacts of air pollution on human health are well documented and include cardiovascular, neurological, immune system and developmental damage. Additionally, the irritant qualities of air pollutants can cause respiratory and cardiovascular distress. This can be heightened during exercise and especially so for those with respiratory conditions such as asthma. Meteorological conditions have also been shown to adversely impact athletic performance; but research has mostly examined the impact of pollution and meteorology on marathon times or running under laboratory settings. This study focuses on the half marathon distance (13.1 miles/21.1 km) and utilises the Great North Run held in Newcastle-upon-Tyne, England, between 2006 and 2019. Local meteorological (temperature, relative humidity, heat index and wind speed) and air quality (ozone, nitrogen dioxide and PM_2.5) data is used in conjunction with finishing times of the quickest and slowest amateur participants, along with the elite field, to determine the extent to which each group is influenced in real-world conditions. Results show that increased temperatures, heat index and ozone concentrations are significantly detrimental to amateur half marathon performances. The elite field meanwhile is influenced by higher ozone concentrations. It is thought that the increased exposure time to the environmental conditions contributes to this greater decrease in performance for the slowest participants. For elite athletes that are performing closer to their maximal capacity (VO₂ max), the higher ozone concentrations likely results in respiratory irritation and decreased performance. Nitrogen dioxide and PM_2.5 pollution showed no significant relationship with finishing times. These results provide additional insight into the environmental effects on exercise, which is particularly important under the increasing effects climate change and regional air pollution. This study can be used to inform event organisation and start times for both mass participation and major elite events with the aim to reduce heat- and pollution-related incidents.

Effect of 3 min whole-body and lower limb cold water immersion on subsequent performance of agility, sprint, and intermittent endurance exercise

The aim of this study was to investigate the effects of whole-body cold-water immersion (WCWI) and lower-limb cold-water immersion (LCWI) employed during a 15-min recovery period on the subsequent exercise performance as well as to determine the physiological and perceptual parameters in the heat (39°C). Eleven males performed team-sports-specific tests outdoors. The exercise program consisted of two identical exercise protocols (1 and 2) separated by a 15-min recovery period. The participants completed the same tests in each exercise protocol, in the following order: agility t test (t-test), 20-m sprint test (20M-ST), and Yo-Yo Intermittent Endurance Test Level 1 (Yo-Yo). During the recovery period, a 3-min recovery intervention of a passively seated rest (control, CON), WCWI, or LCWI was performed. The t-test and 20M-ST for the CON group were significantly longer during exercise protocol 2, but they were not significantly different between the two exercise protocols for the WCWI and LCWI groups. The completed Yo-Yo distance for the CON and LCWI groups was shorter during exercise protocol 2, but it was not significantly different between the two exercise protocols for the WCWI group. The chest temperature (Tchest), upper arm temperature (Tarm), thigh temperature (Tthigh), mean skin temperature (Tskin), and thermal sensation (TS) values were lower for the WCWI group than for the CON group; but only the Tthigh, Tskin, and TS values were lower for the LCWI group compared to the CON group. The Tchest, Tarm, Tskin, and TS values after the intervention were lower for the WCWI group than for the LCWI group. None of the three intervention conditions affected the core temperature (Tcore), heart rate (HR), or rating of perceived exertion (RPE). These results suggest that WCWI at 15°C for 3 min during the 15-min recovery period attenuates the impairment of agility, sprint, and intermittent-endurance performance during exercise protocol 2, but LCWI only ameliorates the reduction of agility and sprint performance. Furthermore, the ergogenic effects of WCWI and LCWI in the heat are due, at least in part, to a decrease of the Tskin and improvement of perceived strain.

Human temperature regulation under heat stress in health, disease, and injury

The human body constantly exchanges heat with the environment. Temperature regulation is a homeostatic feedback control system that ensures deep body temperature is maintained within narrow limits despite wide variations in environmental conditions and activity-related elevations in metabolic heat production. Extensive research has been performed to study the physiological regulation of deep body temperature. This review focuses on healthy and disordered human temperature regulation during heat stress. Central to this discussion is the notion that various morphological features, intrinsic factors, diseases, and injuries independently and interactively influence deep body temperature during exercise and/or exposure to hot ambient temperatures. The first sections review fundamental aspects of the human heat stress response, including the biophysical principles governing heat balance and the autonomic control of heat loss thermoeffectors. Next, we discuss the effects of different intrinsic factors (morphology, heat adaptation, biological sex, and age), diseases (neurological, cardiovascular, metabolic, and genetic), and injuries (spinal cord injury, deep burns, and heat stroke), with emphasis on the mechanisms by which these factors enhance or disturb the regulation of deep body temperature during heat stress. We conclude with key unanswered questions in this field of research.

Effects of pre-exercise H2 inhalation on physical fatigue and related prefrontal cortex activation during and after high-intensity exercise

Objective: In this study, we examined the effects of pre-exercise H₂ gas inhalation on physical fatigue (PF) and prefrontal cortex (PFC) activation during and after high-intensity cycling exercise.

Methods: Twenty-four young men completed four study visits. On the first two visits, the maximum workload (W_max) of cycling exercise of each participant was determined. On each of the other two visits, participants inhaled 20 min of either H₂ gas or placebo gas after a baseline test of maximal voluntary isometric contraction (MVIC) of thigh. Then participants performed cycling exercise under their maximum workload. Ratings of perceived exertion (RPE), heart rate (HR) and the PFC activation by using functional near-infrared spectroscopy (fNIRS) was measured throughout cycling exercise. The MVIC was measured again after the cycling.

Results: It was observed that compared to control, after inhaling H₂ gas, participants had significantly lower RPE at each workload phase (p < 0.032) and lower HR at 50% W_max, 75% W_max, and 100% W_max during cycling exercise (p < 0.037); the PFC activation was also significantly increased at 75 and 100% W_max (p < 0.011). Moreover, the H₂-induced changes in PF were significantly associated with that in PFC activation, that is, those who had higher PFC activation had lower RPE at 75% W_max (p = 0.010) and lower HR at 100% W_max (p = 0.016), respectively.

Conclusion: This study demonstrated that pre-exercise inhalation of H₂ gas can alleviate PF, potentially by maintaining high PFC activation during high-intensity exercise in healthy young adults.

Assessing climatic, travel, and methodological influences on whole-match and worst-case scenario locomotor demands of international men's rugby sevens match-play

AbstractThis study assessed the influence of environmental factors, air travel, and epoch estimation method on locomotor demands of international men's rugby sevens match-play. Eighteen men's rugby sevens players wore 10 Hz Global Positioning Systems (STATsport) during 52 international matches over nine global tournaments (418 observations). Whole-match average speed was recorded, whilst average speed and relative high-speed distance (>5.0 m·s^-1) were quantified using FIXED and ROLL methods over 60-420 s epochs (60 s increments) to establish worst-case scenario demands. Linear mixed models compared FIXED versus ROLL estimation methods and assessed whether temperature, humidity, travel duration, number of time-zones crossed, and travel direction were associated with locomotor responses. Temperature and humidity were positively associated with overall and worst-case scenario average speed (effect estimates; b: 0.18 to 0.54), whilst worst-case scenario high-speed distance at 300 s was also related to temperature (b: 0.19). Easterly air travel compromised overall and 180 and 300 s worst-case scenario average speed (b: -8.31 to-7.39), alongside high-speed distance over 300 s (b: -4.54). For worst-case scenario average speed and high-speed distance, FIXED underestimated ROLL at all epoch lengths (∼9.9 to 18.4%, p≤0.001). This study indicated that international rugby sevens match-play locomotor responses were greater as air temperature increased but reduced following eastward air travel. Underestimation of demands in FIXED vs ROLL over 60-420 s epochs was confirmed. Such climatic and travel influences warrant the adoption of strategies targeted at maximising performance and safety according to the tournament conditions. Knowing the most demanding periods of match-play facilitates training specificity.