Heat Exposure Research Articles

Digestive Enzyme Activities in Mussel Mytilus californianus Endure Acute Heat Exposure in Air.

The mussel Mytilus californianus is an ecosystem engineer forming beds along the coastlines of Northeastern Pacific shores. As sessile organisms, they modulate their energy balance through valve movements, feeding, and digestive functionality. A recent study observed that activity of the digestive enzyme cellulase was higher than predicted in mussels high on the shore, where temperatures are characteristically high and food availability is limited compared to low-shore habitats. In the current study, we predicted that this scavenging behavior is induced to mitigate energy losses related to heat-shock responses-that cellulase and amylase will display hyperactivity for limited recourses in the face of aerial heating. In the laboratory, we acclimated mussels to three complex diets that differed in starch and cellulose composition, followed by two acute heat shocks (+8°C) in the laboratory. Results showed no hyperactivity of amylase and cellulase in heated mussels. These results differ from previous studies that showed lowered amylase activity following heat acclimation. This difference in amylase activity across heat-stress exposure time is important when analyzing mussel bed disturbances following heat waves that compromise energy balance or cause death within adult populations.

Influence of head-mounted virtual reality (VR) on psychological and physiological responses in the heat

Evidence suggests that vision may play a role in the perception of temperature in humans (Mayes et al., 2023, J Therm Bio, 112, 103488). Virtual reality (VR) has garnered attention for its potential applications in various domains, including sports training and rehabilitation. However, the psychophysiological effects of using VR in hot environments remain relatively unexplored. The present study tested the hypothesis that a ‘cold’ visual environment would decrease thermal perception when compared to a ‘hot’ visual environment during passive heat exposure. Twelve healthy participants (2 females) [mean ± SD, age: 24 ± 5 years; stature: 174 ± 9 cm; mass: 72 ± 8 kg] provided their written informed consent to participate in this study. Ethical approval was obtained from the Faculty of Science and Health’s Ethics Committee at The University of Portsmouth. In a within-participant, randomised, controlled crossover design participants completed a familiarisation visit followed by three experimental sessions in 40°C (50% r.h.). The three conditions were: no virtual reality (NoVR), virtual reality displaying an arid landscape (HotVR), and virtual reality displaying a snow-covered landscape (ColdVR). Thermal sensation, thermal comfort, skin wetness, heart rate, rectal temperature, and four-site skin temperature were recorded. Mean skin temperature and mean body temperature were subsequently calculated. Data were analysed using a 3 (Condition [NoVR, VRHot, VRCold]) × 7 (Time [Pre, 5-, 10-, 15-, 20-, 25-, 30-min post-VR exposure]) repeated measures ANOVA. The main effects of condition, time, and their interaction were explored, with statistical significance accepted at P < 0.05. The use of VR in the heat resulted in increased thermal sensation, skin wetness, mean skin temperature, mean body temperature, and heart rate over time (all P < 0.05). However, the manipulation of the visual environment did not alter perceptual or physiological variables (all P > 0.05). Significant interaction effects were observed for mean skin temperature and mean body temperature; however, these minimal differences were considered not meaningful. In conclusion, these novel data indicate that using VR to manipulate the virtual environment in the heat does not meaningfully alter perceptual or physiological responses. These findings also suggest that VR may be used within settings such as the military and elite-sport without any deleterious effects. Future work should look to examine the effects of using VR whilst exercising on perceptual and physiological measures.

Effects of short-term high temperature at different life stages on reproductive fitness in Mythimna separata (Lepidoptera: Noctuidae).

Extreme heat events commonly occur under climate warming. All life stages of insects may experience the occurrence of extremely high temperatures. However, the effects of short-term extreme heat events on life-history traits remain unclear in most migratory pests. Here, we investigated the biological effects of short-term heat exposure (35 °C for 4 h) at different life stages on Mythimna separata Walker (Lepidoptera: Noctuidae), a typical migratory pest. We found that the reproductive sensitivity of pupae and adults was higher than that of 3rd-instar larvae. Increasing the frequency of heat exposure decreased the reproductive performance of M. separata at all life stages. Parental short-term heat exposures could cause transgenerational damage to offspring survival and reproductive fitness when the exposure frequency reached 3 times. Our results suggest that short-term exposure to extreme temperatures could impact reproductive fitness across different life stages in M. separata. This should be taken into consideration in the population prediction of migratory pests under climate change.

The Impact of Hydration Level on Groundhandling Officer at Bandara Soekarno Hatta

Background: Groundhandling workers are workers who are exposed to heat for quite a long time. A work environment that exceeds tolerance limits can cause health problems such as dehydration and fatigue. Lestari (2016) in his research stated that a hot work environment that exceeds the Threshold Limit Value (TLV) can increase the risk of dehydration. Purpose: This research focuses on fatigue and the risk factors of fatigue, especially those caused by dehydration, without disregarding other risk factors among ground handling workers at Soekarno-Hatta Airport. Method: The method used in this research is an observational analytic approach with a cross-sectional design. The sampling technique employed random sampling with a sample size of 219 respondents consisting of ground handling workers working both inside buildings and on the apron. The measuring instruments used were specific gravity urine tests to determine hydration status and IFRC questionnaires to assess workers' physical fatigue status. Result: From the existing data it was found that the majority of respondenst experienced mild fatigue, namely 36,5% of the 219 respondents and others experienced severe fatigue 63,5%. With hydration status, most workers have good hydration status (euhydration), namely 70,3% and and some others experienced dehydration, namely 29,7%. The result of the analysis between hydration status and level fatigue showed 35,4% of respondents who werw dehydrated experienced severe fatigue, while 37% of respondents who were euhydrated/normohydrated experirienced severe fatgue. The results of the analysis test obtained was no relationship between hydratin status and fatigue level. The OR (Odd Ratio) shows a result or 0,932 meaning that respondents withs dehyration are protective factor of 0,93 times agains severe fatigue. Conclusion: The conclusion of this research is that good hydraton status can prevent fatigue in workers, especially those who work with direct heat exposure.

Mitigating Heat Exposure Inside Sherman Traps: Efficacies of Various Techniques

Mitigating Heat Exposure Inside Sherman Traps: Efficacies of Various Techniques

Microencapsulation of peanut skin polyphenols for shelf life improvement of sunflower seeds.

Derived from industrial processing waste, peanut skins contain polyphenols that delay oxidative food spoilage. However, these compounds are susceptible to light, heat, and oxygen exposure. Microencapsulation provides a solution by offering protection from these factors. The aim of this study was to evaluate the protective effect of peanut skin extract microcapsules on the chemical, microbiological, and sensory property and shelf life of sunflower seeds during storage. Five roasted sunflower seed samples were prepared: control (S-C); added with butylhydroxytoluene (S-BHT); coated with carboxymethyl cellulose (S-CMC); coated with CMC and the addition of peanut skin crude extract (S-CMC-CE); coated with CMC and the addition of microcapsules (S-CMC-M20). Sensory acceptability was determined using hedonic testing. Chemical (peroxide value, conjugated dienes, hexanal and nonanal content, and fatty acid profile), microbiological, and descriptive analyses were carried out on samples stored for 45 days at room temperature. Shelf life was calculated using a simple linear regression. All samples were microbiologically fit for human consumption and accepted by consumer panelists, scoring above five points on the nine-point hedonic scale. S-CMC-M20 exhibited the lowest peroxide value (6.59meqO2/kg) and hexanal content (0.4µg/g) at the end of the storage. Estimated shelf life showed that S-MC-M20 (76.3 days) extended its duration nearly ninefold compared to S-C (8.3 days) and doubled that of S-CMC-CE (37.5 days). This indicates a superior efficacy of microencapsulated extract compared to its unencapsulated form, presenting a promising natural strategy for improving the shelf life of analogous food items. PRACTICAL APPLICATION: Incorporating peanut skin extract microcapsules in coating sunflower seeds presents a promising strategy to extend the shelf life of lipid-rich foods, capitalizing on the antioxidant properties of polyphenols. This innovative approach not only enhances nutritional quality but also addresses sustainability concerns by repurposing agro-industrial byproducts, such as peanut skins. By meeting consumer demand for functional foods with added health benefits, this technique offers potential opportunities for the development of novel, value-added food products while contributing to circular economy principles and waste management efforts.

Exploring the contribution of inter-individual factors to the development of physiological heat strain in older adults exposed to simulated indoor overheating.

Older adults are at elevated risk of heat-related mortality due to age-associated declines in thermoregulatory and cardiovascular function. However, the inter-individual factors that exacerbate physiological heat strain during heat exposure remain unclear, making it challenging to identify more heat-vulnerable subgroups. We therefore explored factors contributing to inter-individual variability in physiological responses of older adults exposed to simulated hot weather. Thirty-seven older adults (61-80 years, 16 females) rested for 8 h in 31 and 36 °C (45% relative humidity). Core (rectal) temperature, heart rate (HR), HR variability, mean arterial pressure (MAP), and cardiac autonomic responses to standing were measured at baseline and end-exposure. Bootstrapped least absolute shrinkage and selection operator regression was used to evaluate whether variation in these responses was related to type 2 diabetes (T2D, n=10), hypertension (n=18), age, sex, body morphology, habitual physical activity levels, and/or heat-acclimatization. T2D was identified as a predictor of end-exposure HR (with vs. without: 13 beats/min (bootstrap 95% confidence interval: 6, 23)), seated MAP (-7mmHg (-18, 1)), and the systolic pressure response to standing (20mmHg (4, 36)). HR was also influenced by sex (female vs. male: 8 beats/min (1, 16)). No other predictors were identified. The inter-individual factors explored did not meaningfully contribute to the variation in body temperature responses in older adults exposed to simulated indoor overheating. By contrast, cardiovascular responses were exacerbated in females and individuals with T2D. These findings improve understanding of how inter-individual differences contribute to heat-induced physiological strain in older persons.

Experimental Analysis of Palm-Oil Biodiesel Oxidation Stability on the Aging Characteristics of Diesel-Biodiesel Blends

Abstract The utilization of biodiesel-diesel blends has gained significant momentum in recent years. However, the unique properties of palm oil biodiesel demand careful handling compared to conventional diesel fuel whereas the most important is the preservation of oxidation stability. It is related to the resistance of biodiesel and its blends against heat and oxygen-induced oxidation reactions. This study focuses on the aging characteristics of palm oil biodiesel-diesel blends (B10 to B50) which were impacted by varying pristine biodiesel oxidation stability by aging with air and heat exposure. The experiment of biodiesel and its blend aging was set up using the Accelerated method (EN 14112 / EN 15751) and Rapid Smale Scale Oxidation Test method (ASTM D7545). Furthermore, the effects of diesel fuel aging on high and low biodiesel oxidation stability were examined, including density, kinematic viscosity, water content, acid number, and lubricity. Based on the results, it was found that the aging time of palm oil biodiesel significantly influences the oxidative parameters of the biodiesel-diesel blends (B10 to B50). Moreover, prolonged aging resulted in decreased oxidation stability and increased viscosity, total acid number, and lubricity. These outcomes highlight how crucial it is to handle and store palm oil biodiesel properly in order to maintain the quality of biodiesel-diesel blends.

Eccentric muscle-damaging exercise in the heat lowers cellular stress prior to and immediately following future exertional heatexposure.

Muscle-damaging exercise (e.g., downhill running [DHR]) or heat exposure bouts potentially reduce physiological and/or cellular stress during future exertional heat exposure; however, the true extent of their combined preconditioning effects is unknown. Therefore, this study investigated the effect of muscle-damaging exercise in the heat on reducing physiological and cellular stress during future exertional heat exposure. Ten healthy males (mean±Standard Definition; age, 23±3years; body mass, 78.7±11.5kg; height, 176.9±4.7cm) completed this study. Participants were randomly assigned into two preconditioning groups: (a) DHR in the heat (ambient temperature [Tamb], 35°C; relative humidity [RH], 40%)and (b) DHR in thermoneutral (Tamb, 20°C; RH, 20%). Seven days following DHR, participants performed a 45-minflat run in the heat (FlatHEAT [Tamb, 35°C; RH, 40%]). During exercise, heart rate and rectal temperature (Trec) were recorded at baseline and every 5-min. Peripheral blood mononuclear cells were isolated to assess heat shock protein 72 (Hsp72) concentration between conditions at baseline, immediately post-DHR, and immediately pre-FlatHEAT and post-FlatHEAT. Mean Trec during FlatHEAT between hot (38.23±0.38°C) and thermoneutral DHR (38.26±0.38°C) was not significantly different (P=0.68), with no mean heart rate differences during FlatHEAT between hot (172±15beatsmin-1) and thermoneutral conditions (174±8beatsmin-1; P=0.58). Hsp72 concentration change from baseline to immediately pre-FlatHEAT was significantly lower in hot (-51.4%) compared to thermoneutral (+24.2%; P=0.025) DHR, with Hsp72 change from baseline to immediately post-FlatHEAT also lower in hot (-52.6%) compared to thermoneutral conditions (+26.3%; P=0.047). A bout of muscle-damaging exercise in the heat reduces cellular stress levels prior to and immediately following future exertional heat exposure.

Optimizing Athletic Performance and Health: Strategies for Training in Hot Environments

This review article explores the physiological effects of heat exposure on athletic performance, offering practical advice for athletes and coaches to optimize training and competition in hot environments. It addresses endurance exercise capacity, anaerobic power, and health concerns associated with heat exposure.

Extreme heat exposure of host plants indirectly reduces solitary bee fecundity and survival.

Extreme heat poses a major threat to plants and pollinators, yet the indirect consequences of heat stress are not well understood, particularly for native solitary bees. To determine how brief exposure of extreme heat to flowering plants affects bee behaviour, fecundity, development and survival we conducted a no-choice field cage experiment in which Osmia lignaria were provided blueberry (Vaccinium corymbosum), phacelia (Phacelia tanacetifolia) and white clover (Trifolium repens) that had been previously exposed to either extreme heat (37.5°C) or normal temperatures (25°C) for 4 h during early bloom. Despite a similar number of open flowers and floral visitation frequency between the two treatments, female bees provided with heat-stressed plants laid approximately 70% fewer eggs than females provided with non-stressed plants. Their progeny received similar quantities of pollen provisions between the two treatments, yet larvae consuming pollen from heat-stressed plants had significantly lower survival as larvae and adults. We also observed trends for delayed emergence and reduced adult longevity when larvae consumed heat-stressed pollen. This study is the first to document how short, field-realistic bursts of extreme heat exposure to flowering host plants can indirectly affect bee pollinators and their offspring, with important implications for crop pollination and native bee populations.

Leveraging data science and machine learning for urban climate adaptation in two major African cities: a HE2AT Center study protocol

IntroductionAfrican cities, particularly Abidjan and Johannesburg, face challenges of rapid urban growth, informality and strained health services, compounded by increasing temperatures due to climate change. This study aims to understand...

Substantial increase of heat-induced labor and economic loss in China under rapid economic and environmental temperature growth

Exposure to heat stress causes diminished work performance and leads to economic loss. In the last two decades, China has experienced both rapid economic development and environmental warming; however, the spatiotemporal variations of association between environmental heat and labor loss have been rarely investigated behind this double impact. Here, we evaluated the variation in China's heat-induced labor productivity loss and related economic cost from 2001 to 2019 and investigated the effect of economic development and regional warming. We found that decline in labor productivity because of heat stress increased significantly (p < 0.05 for heavy-intensity work), and the corresponding economic loss also exhibited a drastic increase by 6- to 9-fold. The relative economic loss showed a slight but nonsignificant increase with an average value of 0.54% of the annual total earnings. At the sub-regional and sectoral level, adverse effects were more prominent in the southeast region, and the secondary industry sectors, such as construction and manufacturing, contributed to larger proportions of economic losses. The transformation of industrial structure made economic sectors more vulnerable to heat exposure, and increasingly preventive effects of air-conditioning use were noted on economic damage due to heat-induced productivity decline (36.0% relative economic benefits in 2019 compared to 9.7% in 2001). Our findings could provide a deep insight into heat burden on occupational health and heat adaptation strategies regionally under climate change, especially in developing areas with higher temperature and humidity environment.

Physiological high temperatures alter the amino acid metabolism of bovine early antral follicles.

Heat stress reduces the developmental competence of bovine oocytes during the growth phase; however, the detailed mechanisms remain unclear. Amino acids play various critical roles in follicular development, including protein synthesis and as energy sources. We performed in vitro growth (IVG) culture of oocyte-cumulus-granulosa complexes (OCGCs) to assess the amino acid metabolism of small follicles at high temperatures. We isolated OCGCs from early antral follicles (0.5-1.0 mm) and subjected them to IVG culture for 12 days. OCGCs in the heat shock group were cultured under a temperature cycle of (38.5°C: 5 h, 39.5°C: 5 h, 40.5°C: 5 h, and 39.5°C: 9 h) to reproduce the body temperature of lactating cows under a hot environment. OCGCs in the control group were cultured at a constant temperature of 38.5°C for 24 h. Of the surviving OCGCs, those showing similar morphology and size between the groups were selected for amino acid analysis. We analyzed the free amino acids and their metabolites in the culture medium and calculated the depletion or appearance of molecular species. The depletion of three essential amino acids (isoleucine, leucine, and valine), two non-essential amino acids (aspartic acid and glycine), and ornithine was higher in the heat shock group (P < 0.05). Alanine depletion was lower in the heat shock group (P < 0.05). We concluded that heat exposure alters the amino acid metabolism of OCGCs isolated from early antral follicles, which might be involved with the diminished developmental potential of oocytes during summer.

Maternity Nurses’ Competences regarding the Potential Consequences of Heat Exposure on the Mothers and Newborns in the Face of Climate Change

Maternity Nurses’ Competences regarding the Potential Consequences of Heat Exposure on the Mothers and Newborns in the Face of Climate Change

Heatwave frequency and disability status: Thermal inequities in the U.S. South

BackgroundAlthough extreme heat has been found to be disproportionately distributed with respect to socially disadvantaged and marginalized groups, persons with disabilities have received limited attention in previous research on heat exposure disparities. ObjectiveThis gap is addressed by analyzing the relationship between local heatwave frequency and the percentages of people with a disability and specific disability types in the U.S. South—a region characterized by extremely high summer temperatures and greater disability prevalence. MethodsCensus tract level values of heatwave annualized frequency from the U.S. Federal Emergency Management Agency's National Risk Index are linked to relevant disability variables from the latest American Community Survey five-year estimates. Statistical analyses are based on bivariate correlations and multivariable generalized estimating equations that consider spatial clustering of tracts based on climate zone and county. ResultsThe overall percentage of civilian noninstitutionalized persons with a disability and more than one disability are significantly greater (p < 0.001) in census tracts with higher heatwave frequency, after controlling for clustering, race/ethnicity, socioeconomic status, older age, population density, and metropolitan status. Heatwave frequency is also positively and significantly associated (p < 0.01) with the percentages of people with hearing, vision, cognitive, ambulatory, self-care, and independent living difficulties. ConclusionsThese heat-related distributive injustices in the U.S. South demonstrate an urgent need to: (1) include disability status in future research on social disparities in heatwave exposure; (2) conduct more detailed investigations in other regions, states, and nations; and (3) develop disability-inclusive policies and interventions that provide equitable protection during extreme weather events.

Passive and low-energy strategies to improve sleep thermal comfort and energy resilience during heat waves and cold snaps

Sleep is a pillar of human health and wellbeing. In high- and middle-income countries, there is a great reliance on heating, ventilation, and air conditioning systems (HVAC) to control the interior thermal environment in the bedroom. However, these systems are expensive to buy, maintain, and operate while being energy and environmentally intensive—problems that may increase due to climate change. Easily-accessible passive and low-energy strategies, such as fans and electrical heated blankets, address these challenges but their comparative effectiveness for providing comfort in sleep environments has not been studied. We used a thermal manikin to experimentally show that many passive and low-energy strategies are highly effective in supplementing or replacing HVAC systems during sleep. Using passive strategies in combination with low-energy strategies that elevate air movement like ceiling or pedestal fans enhances the cooling effect by three times compared to using fans alone. We extrapolated our experimental findings to estimate heating and cooling effects in two historical case studies: the 2015 Pakistan heat wave and the 2021 Texas power crisis. Passive and low-energy strategies reduced sleep-time heat or cold exposure by 69–91%. The low-energy strategies we tested require one to two orders of magnitude less energy than HVAC systems, and the passive strategies require no energy input. These strategies can also help reduce peak load surges and total energy demand in extreme temperature events. This reduces the need for utility load shedding, which can put individuals at risk of hazardous heat or cold exposure. Our results may serve as a starting point for evidence-based public health guidelines on how individuals can sleep better during heat waves and cold snaps without relying on HVAC.

Cyclical heat stress during lactation influences the microstructure of the bovine mammary gland

This study aimed to evaluate the impact of heat stress on mammary epithelial cell (MEC) losses into milk, secretory mammary tissue structure, and mammary epithelial cell activity. Sixteen multiparous Holstein cows (632 ± 12 kg BW) approximately 100 d in milk housed in climate-controlled rooms were paired by body weight and randomly allocated to one of 2 treatments, heat stress (HS) or pair feeding thermoneutral (PFTN) using 2 cohorts. Each cohort was subjected to 2 periods of 4 d each. In period 1, both treatments had ad libitum access to a common total mixed ration and were exposed to a controlled daily temperature-humidity index (THI) of 64. In period 2, HS cows were exposed to controlled cyclical heat stress (THI: 74 to 80), while PFTN cows remained at 64 THI and daily dry matter intake was matched to HS. Cows were milked twice daily, and milk yield was recorded at each milking. Individual milk samples on the last day of each period were used to quantify MEC losses by flow cytometry using butyrophilin as a cell surface marker. On the final day of period 2, individual bovine mammary tissue samples were obtained for histomorphology analysis, assessment of protein abundance, and evaluation of gene expression of targets associated with cellular capacity for milk and milk component synthesis, heat response, cellular proliferation, and autophagy. Statistical analysis was performed using the GLIMMIX procedure of SAS. Milk yield was reduced by 4.3 kg by HS (n = 7) compared with PFTN (n = 8). Independent of treatment, MEC in milk averaged 174 cells/mL (2.9% of total cells). There was no difference between HS vs. PFTN cows for MEC shed or concentration in milk. Alveolar area was reduced 25% by HS, and HS had 4.1 more alveoli than PFTN. Total number of nucleated MEC per area were greater in HS (389 ± 1.05) compared with PFTN (321 ± 1.05); however, cell number per alveolus was similar between groups (25 ± 1.5 vs. 26 ± 1.4). There were no differences in relative fold expression for GLUT1, GLUT8, CSN2, CSN3, LALBA, FASN, HSPA5, and HSPA8 in HS compared with PFTN. Immunoblotting analyses showed a decrease abundance for phosphorylated STAT5 and S6K1, and an increase in LC3 II in HS compared with PFTN. These results suggest that even if milk yield differences and histological changes occur in the bovine mammary gland after 4 d of heat exposure, MEC loss into milk, nucleated MEC number per alveolus, and gene expression of nutrient transport, milk component synthesis, and heat stress related targets are unaffected. In contrast, the abundance of proteins related to protein synthesis and cell survival decreased significantly, while an upregulation of proteins associated with autophagy in HS compared with PFTN.

Exposure to teflubenzuron reduces drought tolerance of collembolans

Chitin synthesis inhibitors (CSIs) are commonly used insecticides compromising cuticle formation and structure in arthropods. Arthropods rely on intact cuticles to maintain water balance and cellular homeostasis to survive in different weather conditions. We hypothesized that physiological impacts of CSIs may make arthropods more vulnerable to harsh environmental conditions, such as extreme heat, cold or drought. The aim of this study was to investigate if pre-exposure to teflubenzuron (a common CSI) would influence Folsomia candida's (Collembola: Isotomidae) sensitivity to natural stressors. Here, we exposed adult collembolans to teflubenzuron through food for two weeks, then survivors were immediately divided into three groups for subsequent acute heat, cold, and drought exposure. After acute exposure to these natural stressors, the collembolans were moved to optimal conditions for a one-week recovery period during which their survival, time to regain reproduction, and egg production were examined. We analyzed the interaction between effects of teflubenzuron and natural stressors using a multiplicative model. No interaction between effects of teflubenzuron and heat was observed in any test endpoints. A synergistic interaction between effects of teflubenzuron and cold was observed in the time to regain reproduction. Both survival and egg production, on the other hand, showed synergistic interaction between effects of teflubenzuron and drought, as well as a tendency for longer reproduction recovery times. Our results suggest that pre-exposure to teflubenzuron reduces drought tolerance in F. candida, while its impact on heat or cold tolerance is minor or absent. This study is among the first to explore the combined effects of CSI and natural stressors on soil arthropods, providing more insight on potential risks posed by such chemicals in the environment.

Effects of heat exposure from late sowing on agronomic traits and the technological quality of hexaploid wheat

Heat stress reduces wheat grain yield and affects quality traits relevant to trading and end use. In this study, 98 landraces and 152 elite hexaploid wheat varieties and breeding lines were trialled at two irrigated field sites in southern NSW to better understand heat stress responses and identify promising genotypes for heat tolerance breeding. Potential heat tolerance was defined using performance in heat-exposed late-sown (LS) plots relative to normal-sown (NS) plots, using a regression approach to calculate response indices uncorrelated with awn emergence time and performance per se in NS. The best individual responders for grain yield included genotypes from both Australia and Mexico. On average, lines selected in CIMMYT's High Temperature Wheat Yield Trials (HTWYT) performed well for yield per se in NS as well as for yield response to LS. CIMMYT lines previously selected for large grains under heat stress conditions performed well for grain size in NS and for LS responses of grain size and test weight. Dough peak resistance and time to peak resistance in a mixograph were increased by LS and these traits were positively correlated with grain protein and the occurrence of the Glu-D1d high molecular weight glutenin locus allele, respectively.