Heat Production Research Articles

Influence of work intensity on acute kidney injury risk during simulated occupational heat stress.

Violation of the National Institute of Occupational Safety and Health (NIOSH) heat stress recommendations by exceeding the allowable wet bulb globe temperature (WBGT) for a given work intensity and work-rest ratio augments acute kidney injury (AKI) risk. Here we tested the hypothesis that exceeding the allowable work intensity at a given WBGT and work-rest ratio would also worsen AKI risk. Twelve healthy adults completed two NIOSH recommendation compliant trials and one noncompliant trial consisting of a 4 h (half workday) exposure. Work-rest ratio was fixed at 30 min of walking and 30 min of rest each hour. Work intensity (metabolic heat production) was prescribed as a function of WBGT- 412±51 W (27.3±0.3°C; high intensity compliant [Chigh]), 290±75 W (31.6±0.2°C; low intensity compliant [Clow]), and 410±61 W (31.7±0.2°C; high intensity noncompliant [NChigh]). AKI risk was quantified by the product of urinary insulin-like growth factor-binding protein 7 and tissue inhibitor of metalloproteinase 2 normalized to urine specific gravity ([IGFBP7•TIMP-2]USG). Peak core temperature was higher in NChigh trial (38.3±0.4°C) compared to the compliant trials (Chigh: 38.0±0.3°C; Clow: 37.8±0.4°C; p≤0.0095). [IGFBP7•TIMP-2]USG increased from pre- to immediately postexposure in all trials (time effect: p=0.0454) but the peak increase was not different between trials (Chigh: 0.89±1.7 [ng/mL]2/1000; Clow: 0.78±1.7 [ng/mL]2/1000; NChigh: 1.0±1.4 [ng/mL]2/1000; p=0.7811). Violating the NIOSH recommendations by exceeding either the allowable work intensity (i.e., NChigh versus Clow) or WBGT (i.e., NChigh versus Chigh) resulted in a modest elevation in peak core temperature but did not modify AKI risk.

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

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. 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. 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. 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.

Effect of gamma dose rate on the public from soil samples collected from industrial areas of Tamil Nadu.

The present work is the first and foremost radiological study of soil samples collected from industrial estates in Tamil Nadu. The magnetic susceptibility measurement revealed that 74.19% of the samples have medium %χFD, which denotes a commixture of coarser grains or the SP grains with a size of <0.005μm. The range of measured activities of 210Po and 210Pb were 3±0.3-38±2.6Bqkg-1 and 16±1.5-48±2.9Bqkg-1. The mean activity concentrations of 238U (33Bqkg-1) and 40K (467Bqkg-1) marginally exceeded the Indian recommended values of 28.67 and 400Bqkg-1, respectively, whereas 232Th (47Bqkg-1) did not exceed 63.83Bqkg-1. The 238U and 232Th are the significant contributors to the production of radiogenic heat in the study area. Pearson correlation analysis confirmed the prime role of 232Th in radiation hazards and the insignificant relation between magnetic minerals and natural radioactivity.

Short-Term Warm-Water Immersion for Improving Whole-Body Heat Loss in Older Men.

Exercise-induced heat acclimation can mitigate age-related reductions in heat-loss capacity, though performing repeated bouts of strenuous exercise in the heat may be untenable for many older adults. While short-term passive heat acclimation (e.g., ≤7 days of warm-water immersion) enhances whole-body heat loss in young adults, evidence of its efficacy in older adults is lacking. Thus, we examined whether 7-days warm-water immersion would improve whole-body heat loss in older adults. Twelve habitually active older men (median [IQR] age: 68 [64-73] years; peak oxygen uptake (V̇O2peak): 34.1 [29.4-36.1] mLO2·kg-1·min-1) completed 7 consecutive days of ~90-minutes warm-water immersion (~40 °C) with core (rectal) temperature clamped at ~38.5 °C for the final 60 minutes. Before and after the warm-water immersion intervention, whole-body total (evaporative + dry) heat loss was measured via direct calorimetry during three, 30-minute bouts of cycling at increasing fixed rates of metabolic heat production (150, 200, 250 W·m-2), each separated by 15-minutes rest, in a hot-dry environment (40 °C, ~13% relative humidity). Rectal temperature and heart rate were measured continuously. Following 7 days of warm-water immersion, whole-body total heat loss was elevated by 23 [95% confidence interval: 14, 31] W·m-2 across exercise bouts (acclimation-effect: P < 0.001; interaction: P = 0.598). This was paralleled by reductions in core temperature and heart rate of 0.3 [0.2, 0.4] °C and 11 [8, 14] beats·min-1 (both, acclimation-effect: P < 0.001; interaction: P = 0.288), respectively. Seven consecutive days of warm-water immersion improved whole-body heat loss and reduced core temperature and cardiovascular strain across light-to-vigorous intensity exercise in habitually active older men. Passive heat acclimation may be an efficacious alternative to exercise-heat acclimation to improve heat-loss capacity. Studies are warranted to assess effectiveness in more heat-vulnerable populations.

Boosting Thermal Generation in Cation-Exchanged Transparent MXene Composite Films with Hierarchical Wrinkled Structure.

Efficient thermal generation from solar/electric energy in transparent films remains challenging due to the limited toolbox of high-performance thermal generation materials and methods for microstructure engineering. Here, we proposed a two-step strategy to introduce hierarchical wrinkles to the MXene composite films with high transparency, leading to upgraded photo/electrothermal conversion efficiency. Specifically, the thin film contains protic acid-treated MXene layers assembled with Ag nanowires (H-MXene/Ag NWs). The hydrogen-bonding interaction between MXene and Ag NWs in a MXene-based thin film forms the first-level wrinkles, while the cation-exchanged method is then developed to enhance conductivity and form the second-level wrinkles. The H-MXene/Ag NWs composite transparent film is observed to achieve a surface temperature rise of 40 °C relative to an ambient environment under 1.0 sun illumination and 70 °C at 1 V voltage in the dark, along with notable photo/electrothermal production stability under ambient conditions. Moreover, experimental and theoretical results show that the improved heat production capability is mainly due to low reflectivity led by the wrinkles and high conductivity led by the cation-exchange process. On the basis of the excellent photothermal generation capability of the H-MXene/Ag NWs composite transparent film, we applied it to biomimetic soft robots and flexible wearable devices. This work paves a novel strategy for the generation of thermal production devices that achieve high-performance photo/electroconversion.

UCP variants are linked to hypercholesterolemia and abdominal obesity in metabolically unhealthy women.

It has been reported that even with the same body mass index (BMI), there are subjects with metabolically healthy or unhealthy phenotype. The main determinants of the unhealthy phenotype are the type and distribution of fat, ectopic fat accumulation, genetics, and lifestyle factors. Uncoupling proteins (UCPs) disengage mitochondrial respiration from ATP synthesis and result in heat production, which in turn is related to energy expenditure and, thus, to fat mass accumulation. The association of the UCP1 -3826A/G (rs1800592), UCP2 Ala55Val (rs660339), and UCP3 -55C/T (rs1800849) variants with metabolic variables was evaluated according to metabolic phenotype in Mexican women. Women aged 18 to 65 years classified as normal weight (NW) or excessive weight (EW) according to their BMI (from 18.5 to <25 kg/m2 for NW, and from 25 to <40 kg/m2 for EW), were included. Participants were classified into two metabolic phenotypes: metabolically healthy or metabolically unhealthy (MH or MUH, respectively) based on ATP-III criteria and the homeostasis model assessment of insulin resistance (HOMA-IR). The genetic variants were determined by allelic discrimination using TaqMan® probes. In participants with the UCP1 -3826A/G variant, an increased risk of hypercholesterolemia was observed in those with the NW-MUH phenotype (OR=5.09, CI=1.03-25.12, p=0.017). The UCP2 Ala55Val variant in EW-MUH subjects was associated with higher abdominal obesity risk (OR=3.23, CI=1.21-8.60, p=0.019), while no associations were found with the UCP3 -55C/T variant. UCP1 and UCP2 variants are related with hypercholesterolemia and visceral fat accumulation in women with MUH phenotype.

The Surface Heat Flow of Mars at the Noachian–Hesperian Boundary

The time period around the Noachian–Hesperian boundary, 3.7 billionyears ago, was an epoch when great geodynamical and environmental changes occurred on Mars. Currently available remote sensing data are crucial for understanding the Martian heat loss pattern and its global thermal state in this transitional period. We here derive surface heat flows in specific locations based on the estimations of the depth of five large thrust faults in order to constrain both surface and mantle heat flows. Then, we use heat-producing element (HPE) abundances mapped from orbital measurements by the Gamma-Ray Spectrometer (GRS) onboard the Mars Odyssey 2001 spacecraft and geographical crustal thickness variations to produce a global model for the surface heat flow. The heat loss contribution of large mantle plumes beneath the Tharsis and Elysium magmatic provinces is also considered in our final model. We thus obtain a map of the heat flow variation across the Martian surface at the Noachian–Hesperian boundary. Our model also predicts an average heat flow between 32 and 50 mW m−2, which implies that the heat loss of Mars at that time was lower than the total radioactive heat production of the planet, which has profound implications for the thermal history of Mars.

Minimally invasive measurement of carotid artery and brain temperature in the mouse.

Brain temperature is tightly regulated and reflects a balance between cerebral metabolic heat production and heat transfer between the brain, blood, and external environment. Blood temperature and flow are critical to the regulation of brain temperature. Current methods for measuring in vivo brain and blood temperature are invasive and impractical for use in small animals. This work presents a methodology to measure both brain and arterial blood temperature in anesthetized mice by MRI using a paramagnetic lanthanide complex: thulium tetramethyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid (TmDOTMA-). A phase-based imaging approach using a multi-TE gradient echo sequence was used to measure the temperature-dependent chemical shift difference between thulium tetramethyl-1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid methyl protons and water, and from this calculate absolute temperature using calibration data. In a series of mice in which core body temperature was held stable but at different values within the range of 33° to 37°C, brain temperature away from the midline was independent of carotid artery blood temperature. In contrast, midline voxels correlated with carotid artery blood temperature, likely reflecting the preponderance of larger arteries and veins in this region. These results are consistent with brain temperature being actively regulated. A limitation of the present implementation is that the spatial resolution in the brain is coarse relative to the size of the mouse brain, and further optimization is required for this method to be applied for finer spatial scale mapping or to characterize focal pathology.

Roles of perivascular adipose tissue in the pathogenesis of atherosclerosis - an update on recent findings.

Lifestyle-related diseases, such as atherosclerosis and diabetes, are now considered to be a series of diseases caused by chronic inflammation. Adipose tissue is considered to be an endocrine organ that not only plays a role in lipid storage, heat production, and buffering, but also produces physiologically active substances and is involved in chronic inflammation. Perivascular adipose tissue (PVAT) surrounding blood vessels similarly produces inflammatory and anti-inflammatory physiologically active substances that act on blood vessels either directly or via the bloodstream. Epicardial adipose tissue (EAT), which is in direct contact with the coronary arteries inside the pericardium, is thought to have a direct effect on the coronary arteries as well. The presence and inflammatory status of these adipose tissues can be evaluated by imaging tests, and has been shown to be associated with the presence of current cardiovascular disease (CVD) and to be a prognostic factor. It is also expected to become a new diagnostic and therapeutic target for CVD.

Enhanced thermogenesis in PAS Kinase-deficient male mice.

PAS domain-containing serine/threonine-protein kinase (PASK) is a nutrient and energy sensor regulated by fasting/refeeding conditions in hypothalamic areas involved in controlling energy balance. In this sense, PASK plays a role in coordinating the activation/inactivation of AMP-activated protein kinase (AMPK) and mechanistic target of rapamycin (mTOR) in response to fasting. PASK deficiency protects against the development of diet-induced obesity. This has prompted an investigation into the potential role of PASK on energy expenditure through thermogenesis in adipose tissue. Our results indicate that PASK-deficient male mice exhibited higher brown adipose tissue (BAT) thermogenic activity and heat production. The inhibition of PASK function induces the expression of Uncoupling Protein 1 (UCP1) and the adipogenic marker peroxisome proliferator-activated receptor gamma (PPARγ) in BAT. In addition, PASK deficiency promotes the expression of UCP1 and other browning markers such as PR/SET Domain 16 (PRDM16) in inguinal white adipose tissue (WAT). PASK-deficient mice record an enhanced thermogenic response, even under stimuli such as β-3adrenergic receptor agonist or cold. This evidence reveals PASK as a new mechanism modulating BAT thermogenesis.

Probing the water adsorption and stability under steam flow of Zr-based metal-organic frameworks using 91Zr solid-state NMR spectroscopy.

The stability of metal-organic frameworks (MOFs) in the presence of water is crucial for a wide range of applications, including the production of freshwater, desiccation, humidity control, heat pumps/chillers and capture and separation of gases. In particular, their stability under steam flow is essential since most industrial streams contain water vapor. Nevertheless, to the best of our knowledge, the stability under steam flow of Zr-based MOFs, which are among the most widely studied MOFs, has not been investigated so far. We explore it herein for three UiO-like Zr-based MOFs built from the same Zr cluster but distinct organic linkers at temperature ranging from 80 to 200 °C. We demonstrate the possibility of acquiring their 91Zr NMR spectra using high magnetic field (18.8 T) and low temperature (140 K) and of interpreting them by comparing experimental data with NMR parameters calculated by DFT. NMR observation of this challenging isotope combined with more conventional techniques, such as N2 adsorption, X-ray diffraction, IR, and 1H and 13C solid-state NMR spectroscopies, provides information not only on the possible collapse of the MOF framework but also on the adsorption of molecules into the pores. We notably show that UiO-66(Zr) and UiO-66-Fum(Zr) built from terephthalate and fumarate linkers, respectively, are stable over 24 h (and even over 7 days for UiO-66(Zr)) under steam flow at all investigated temperatures, whereas UiO-67-NH2 containing a 2-amino-[1,1'-biphenyl]-4,4'-dicarboxylate linker degrades under steam flow at temperatures ranging from 80 to 150 °C but is preserved at 200 °C. The lower stability of UiO-67-NH2 stems from its larger pores and its weaker Zr-O coordination bonds, whereas its preservation at 200 °C results from a more limited condensation of water in the pores.

Exploring diverse pathways for low-carbon production of hydrogen, methanol, power and heat with enhanced solid carbon utilization efficiency

Exploring diverse pathways for low-carbon production of hydrogen, methanol, power and heat with enhanced solid carbon utilization efficiency

Numerical study on heat storage and production effects of the aquifer thermal energy storage (ATES) system based on reservoir reconstruction

Numerical study on heat storage and production effects of the aquifer thermal energy storage (ATES) system based on reservoir reconstruction

Characteristics of low-temperature oxidative heating and gas production in coal storage under forced convection: Influencing factors and mechanisms.

Slow oxidation of coal during storage and transportation poses significant risks, making it essential to identify hot spots and understand the heat generation and gas production patterns in coal stockpiles. This study leverages the advantages of adiabatic oxidation experiments, which account for time effects, to accurately describe the low-temperature oxidation process of coal through warming and gas production dimensions. Additionally, the warming and gas production patterns of three-dimensional coal stockpiles with varying stacking parameters were investigated. The results indicate that activation energy for heat generation increases linearly with particle size. In anthracite and bituminous coals, the activation energy for gas production was lower than that for heat generation below 70°C, but higher above 70°C. Lignite showed a general trend of lower activation energy for heat generation compared to gas production. Under forced convection, airflow paths within the three-dimension coal stockpile became more complex, resulting in 3 distinct flow patterns. As external wind speed increased, the dominant factor in coal oxidation shifted from oxygen concentration control to heat dissipation control. Maintaining porosity below 0.15, particle size under 5mm, height under 8m, and slope angle below 40° can effectively delay the oxidation process. The factors influencing coal storage efficiency, ranked by importance, are wind speed, porosity, geometry, and particle size. This study offers theoretical insights for optimizing coal storage and transportation processes.

Waste Heat and Habitability: Constraints from Technological Energy Consumption.

Waste heat production represents an inevitable consequence of energy conversion as per the laws of thermodynamics. Based on this fact, by using simple theoretical models, we analyze constraints on the habitability of Earth-like terrestrial planets hosting putative technological species and technospheres characterized by persistent exponential growth of energy consumption and waste heat generation. In particular, we quantify the deleterious effects of rising surface temperature on biospheric processes and the eventual loss of liquid water. Irrespective of whether these sources of energy are ultimately stellar or planetary (e.g., nuclear, fossil fuels) in nature, we demonstrate that the loss of habitable conditions on such terrestrial planets may be expected to occur on timescales of ≲1000 years, as measured from the start of the exponential phase, provided that the annual growth rate of energy consumption is of order 1%. We conclude with a discussion of the types of evolutionary trajectories that might be feasible for industrialized technological species, and we sketch the ensuing implications for technosignature searches.

Effect of different cold acclimation methods on the exercise capacity of mice in low-temperature environments.

This study aimed to evaluate the effects of different cold acclimation strategies on exercise performance in male mice exposed to low-temperature environments. Male mice were subjected to five distinct acclimation regimens over 8 weeks: immersion at 10°C (10 °CI) or 20°C (20 °CI), swimming at 10°C (10 °CS), 20°C (20 °CS), or 34°C (34 °CS). During the first 2 weeks, the acclimation time progressively decreased from 30min to 3min per day, and the water temperatures were lowered from 34°C to the target levels, followed by 6 weeks of consistent exposure. Body weight, food intake, and rectal temperature were monitored throughout the study. Post-acclimation assessments included low-temperature exhaustion exercise ability testing; 16S rDNA sequencing of gut microbiota; and quantification of gene expression related to brown adipose thermogenesis, skeletal muscle synthesis, and degradation. (1) After 8 weeks of acclimation, neither serum adrenaline nor angiotensin II levels significantly increased in mice exposed to 10°C or 20°C water. (2) Cold acclimation extended the endurance time under low-temperature conditions, notably in the 20 °CI, 10 °CS, and 20°CS groups. (3) Compared with the control (C) group, the 20 °CI and 10°CS groups showed significantly increased UCP1, IGF-1, AKT, and mTOR gene expression levels (P<0.05). The expression levels of MAFbx and MuRF1 genes in the 10°CS and 20°CS groups significantly decreased compared with those in the C group (P<0.05). (4) Compared with the C group, the 20 °CI, 10 °CS, and 20°CS groups demonstrated significant changes in intestinal microbiota diversity. Specifically, the abundance of Akkermansia strains significantly increased in the 20 °CI and 10°CS groups. The abundance of Ruminococcus and Prevotellaceae_UCG-001 significantly increased in the 20°CS group. Exercise in cold environments can activate genes related to heat production and skeletal muscle synthesis and increase the abundance of beneficial bacteria producing short-chain fatty acids, thereby modulating host metabolism, accelerating the formation of cold acclimation, and enhancing exercise capacity in low-temperature environments.

The Addition of Felsic Sediments to the Lower Continental Crust During the Variscan Orogeny

AbstractLower crustal metasedimentary xenoliths (garnet‐sillimanite granulites) from the Bournac breccia pipe in the Massif Central, France, provide a robust example of sediments transported to depth and incorporated into stable lower continental crust during a collisional orogeny. Dates for detrital igneous zircon range from the Archean (up to 3,300 Ma) to the Devonian and record sedimentation prior to the onset of the collisional phase of the Variscan orogeny. Metamorphic zircon and monazite document the presence of the metasediments in the lower crust by ca. 330 Ma during the later phase of Variscan collision. Zircon and monazite crystallization continued within the lower crust until ca. 265 Ma, corresponding to a period of slow cooling following an episode of ultra‐high temperature (UHT) metamorphism that peaked at 313 Ma. Zr‐in‐rutile thermometry and GASP barometry applied to these samples record conditions of 0.63–0.77 GPa and 830–910°C, which correspond to Ti‐in‐zircon temperatures from the latter part of the Variscan orogeny and geotherms in excess of typical continent‐continent collisions. Rutile in these samples remained open to Pb loss until their eruption at ca. 11.6 Ma, providing an indirect date of the Bournac eruption. These rocks record the incorporation of felsic sedimentary material into the stable deep continental crust during a collisional orogen and their residence there for over 300 Ma. More broadly, the addition of sediments to stable lower crust contributes to changes in crustal composition and has significant implications for the heterogeneity of the deep continental crust, as well as overall crustal heat production and mantle heat flow.

Early quality control of stabilised dredged material by correlating heat production with strength

This study explores the use of isothermal calorimetry to assess heat release during the initial phases of dredged sediment (DS) stabilisation with the primary goal of predicting the 28-day unconfined compressive strength (UCS) and enhancing the stabilisation process’ quality control. The study was performed on DS samples collected from Göta river, Gothenburg, Sweden. The water content of the raw DS was set to 138%, 185%, and 291%, and mixing was performed with water-to-binder ratios 4, 5, 6, 7, and 8 using a binder consisting of 40% Portland limestone cement and 60% slag. The heat release measurements were conducted during the first 7 days of hydration, non-destructive free–free resonance tests were performed at 7, 14, and 28 days of hydration, and the 28-day UCS was done to assess the compressive strength of stabilised DS. For each water content, a statistical analysis was performed to determine the strength of the relationship, specifically using linear regression, to assess how well early calorimetric data could predict the UCS, and a correlation was found between the 28-day compressive strength and heat release of stabilised DS after 48 h of hydration. By measuring water content and heat release in the early stages of stabilisation, it is thus possible to assess the binder content and predict the ultimate compressive strength of a treated DS.

Use of Biogas in Gas Turbines for the Production of Heat and Electricity

In the modern developed countries of the world, the main part of the extracted fuel and energy resources is spent on the production of electricity and heat of low and medium potential. In Ukraine, the biomethane production potential is estimated at 7.8 billion m3/year, which is 25 % of the current natural gas consumption in the country. The infrastructure of Ukraine is ready for transportation and energy use of biomethane, as biomethane is a complete analogue of natural gas. When storing organic waste ("bio-waste") – for example, the organic part of household waste - biogas, a mixture of methane and carbon dioxide, is released. This gas is a high-quality fuel for gas engines or gas turbines - just like methane gas produced from biomass in sewage treatment plants. Biogas can replace fossil fuels and is also characterized by its CO2 neutrality. Biogas can be burned on-site with little to no processing to heat buildings and power boilers or even the reactor itself. Biogas can be used for combined heat and power generation, can be simply converted to electricity using an internal combustion engine, fuel cells or gas turbine, with the resulting electricity being used on-site or sold into the electricity grid. Taking into account the advantages of using biogas, as well as the price policy for natural gas, the study carried out a calculation of the thermal scheme of the state district power plant. Natural gas is used as the main fuel, biogas was chosen for comparison. The specific heat of combustion of biogas is almost half that of natural gas. When operating on biogas, the efficiency of a gas turbine installation is 8.5 % lower, and that of a steam-gas installation is 7.5 % lower than on natural gas. Since 1000 m³ of natural gas is equivalent to 1,00 m³ of biogas, a biogas accounting factor has been introduced. On the basis of the relevant research, conclusions were drawn regarding the use of biogas as an alternative to natural gas. The relevance of the use of biogas for the production of heat and electricity is to provide a promising source of electricity and reduce carbon dioxide emissions.

Sex differences in cardiac energetics in the rat ventricular muscle

Cardiac sex-difference functional studies have centred on measurements of twitch force and Ca2+ dynamics. The energy expenditures from these two cellular processes: activation (Ca2+ handling) and contraction (cross-bridge cycling), have not been assessed, and compared, between sexes. Whole-heart studies measuring oxygen consumption do not directly measure the energy expenditure of these activation-contraction processes. In this study, we directly quantified these energy expenditures in terms of heat production. Left-ventricular trabeculae were dissected from rats aged 9–13 weeks. Mechano-energetics of trabeculae were characterized using our work-loop calorimeter under various conditions including varying muscle lengths, stimulus frequencies, and afterloads. Each trabecula was subjected to protocols that allowed it to contract either isometrically or shorten to perform work-loops. Force production, length change, and heat output were simultaneously measured. We extracted various metrics: twitch kinetics, shortening kinetics, mechanical work, and heat associated with cross-bridge cycling and Ca2+ cycling, and quantified mechanical efficiency. Results show no sex differences in any of the metrics. Peak mechanical efficiency was not affected by sex (10.25 ± 0.57% in female trabeculae; 10.93 ± 0.87% in male trabeculae). We conclude that cardiac mechanics and energetics are not affected by sex at the muscle level, within the rat age range studied.