Creatinine clearance is maintained in a range of wet-bulb globe temperatures and work-rest ratios during simulated occupational heat stress.

We tested the hypothesis that compliance with the National Institute for Occupational Safety and Health (NIOSH) heat stress recommendations will prevent reductions in glomerular filtration rate (GFR) across a range of wet-bulb globe temperatures (WBGTs) and work-rest ratios at a fixed work intensity. We also tested the hypothesis that noncompliance would result in a reduction in GFR compared with a work-rest matched compliant trial. Twelve healthy adults completed five trials (four NIOSH compliant and one noncompliant) that consisted of 4 h of exposure to a range of WBGTs. Subjects walked on a treadmill (heat production: approximately 430 W) and work-rest ratios (work/h: 60, 45, 30, and 15 min) were prescribed as a function of WBGT (24°C, 26.5°C, 28.5°C, 30°C, and 36°C), and subjects drank a sport drink ad libitum. Peak core temperature (TC) and percentage change in body weight (%ΔBW) were measured. Creatinine clearance measured pre- and postexposure provided a primary marker of GFR. Peak TC did not differ among NIOSH-compliant trials (P = 0.065) but differed between compliant versus noncompliant trials (P < 0.001). %ΔBW did not differ among NIOSH-compliant trials (P = 0.131) or between compliant versus noncompliant trials (P = 0.185). Creatinine clearance did not change or differ among compliant trials (P ≥ 0.079). Creatinine clearance did not change or differ between compliant versus noncompliant trials (P ≥ 0.661). Compliance with the NIOSH recommendations maintained GFR. Surprisingly, despite a greater heat strain in a noncompliant trial, GFR was maintained highlighting the potential relative importance of hydration.NEW & NOTEWORTHY We highlight that glomerular filtration rate (GFR) is maintained during simulated occupational heat stress across a range of total work, work-rest ratios, and wet-bulb globe temperatures with ad libitum consumption of an electrolyte and sugar-containing sports drink. Compared with a work-rest matched compliant trial, noncompliance resulted in augmented heat strain but did not induce a reduction in GFR likely due to an increased relative fluid intake and robust fluid conservatory responses.

The independent effects of hydrostatic pressure and hypercapnic breathing during water immersion on ventilatory sensitivity and cerebrovascular reactivity.

Head out water immersion (HOWI) induces ventilatory and hemodynamic changes, which may be a result of hydrostatic pressure, augmented arterial CO2 tension, or a combination of both. We hypothesized that the hydrostatic pressure and elevated CO2 tension that occur during HOWI will contribute to an augmented ventilatory sensitivity to CO2 and an attenuated cerebrovascular reactivity to CO2 during water immersion. Twelve subjects (age: 24±3 y, BMI: 25±3 kg/m2) completed HOWI, waist water immersion with CO2 (WWI+CO2), and WWI where a rebreathing test was conducted at baseline, 10, 30, and 60 minutes, and post. PETCO2, minute ventilation, expired gases, blood pressure, heart rate, and middle cerebral artery blood velocity were recorded continuously. PETCO2 increased throughout all visits (p£0.011), was matched during HOWI and WWI+CO2 (p³0.264), and was greater during WWI+CO2 vs. WWI at 10, 30, and 60 minutes (p<0.001). When HOWI vs. WWI+CO2 were compared, the change in ventilatory sensitivity to CO2 was different at 10 (0.59±0.34 vs. 0.06±0.23 L/min/mmHg, p<0.001), 30 (0.58±0.46 vs. 0.15±0.25 L/min/mmHg, p<0.001), and 60 minutes (0.63±0.45 vs. 0.16±0.34 L/min/mmHg, p<0.001), while there were no differences between conditions for cerebrovascular reactivity to CO2 (p³0.163). When WWI+CO2 vs. WWI were compared, ventilatory sensitivity to CO2 was not different between conditions (p³0.642), while the change in cerebrovascular reactivity to CO2 was different at 30 minutes (-0.56±0.38 vs. -0.30±0.25 cm/s/mmHg, p=0.010). These data indicate that during HOWI ventilatory sensitivity to CO2 increases due to the hydrostatic pressure, while cerebrovascular reactivity to CO2 decreases due to the combined effects of immersion.

A psychobioecological model to understand the income-food insecurity-obesity relationship.

Food insecurity, defined by unpredictable access to food that may not meet a person's nutritional needs, is associated with higher BMI (kg/m2) and obesity. People with food insecurity often have less access to food, miss meals and go hungry, which can lead to psychological and metabolic changes that favor energy conservation and weight gain. We describe a conceptual model that includes psychological (food reinforcement and delay discounting) and physiological (thermic effect of food and substrate oxidation) factors to understand how resource scarcity associated with food insecurity evolves into the food insecurity-obesity paradox. We present both animal and human translational research to describe how behavioral and metabolic adaptations to resource scarcity based on behavioral ecology theory may occur for people with food insecurity. We conclude with ideas for interventions to prevent or modify the behaviors and underlying physiology that characterize the income-food insecurity-obesity relationship.

Partial and Complete Fluid Replacement Maintains Exercise Performance in a Warm Environment Following Prolonged Cold-Water Immersion.

ABSTRACT: Wheelock, CE, Stooks, J, Schwob, J, Hess, HW, Pryor, RR, and Hostler, D. Partial and complete fluid replacement maintains exercise performance in a warm environment following prolonged cold-water immersion. J Strength Cond Res 38(2): 290-296, 2024-Special warfare operators may be exposed to prolonged immersion before beginning a land-based mission. This immersion will result in substantial hypohydration because of diuresis. This study tested the hypothesis that both partial and full postimmersion rehydration would maintain performance during exercise in the heat. Seven men (23 ± 2 years; V̇o2max: 50.8 ± 5.3 ml·kg-1·min-1) completed a control trial (CON) without prior immersion and 3 immersion (18.0°C) trials without rehydration (NO) or with partial (HALF) or full (FULL) rehydration. After immersion, subjects completed a 60-minute weighted ruck march (20.4 kg; 5.6 kph) and a 15-minute intermittent exercise protocol (iEPT) in a warm environment (30.0°C and 50.0% relative humidity). The primary outcome was distance (km) covered during the iEPT. A priori statistical significance was set to p ≤ 0.05. Immersion resulted in 2.3 ± 0.4% loss of body mass in all immersion trials (p < 0.01). Distance covered during the first 13-minute interval run portion of iEPT was reduced in the NO rehydration trial (1.59 ± 0.18 km) compared with all other conditions (CON: 1.88 ± 0.18 km, p = 0.03; HALF: 1.80 ± 0.18 km, p < 0.01; FULL: 1.86 ± 0.28 km, p = 0.01). During the final 2 minutes of the iEPT, distance in the NO rehydration trial (0.31 ± 0.07 km) was reduced compared with the FULL rehydration trial (0.37 ± 0.07 km; p < 0.01) but not compared with CON (0.35 ± 0.07 km; p = 0.09) or HALF (0.35 ± 0.07 km; p = 0.08). Both partial and full postimmersion fluid replacement maintained intermittent exercise performance and should be applied as rehydration strategies.

Diagnostic accuracy of thermal, hydration, and heart rate assessments in discriminating positive acute kidney injury risk following physical work in the heat.

Occupational heat stress increases the risk of acute kidney injury (AKI). This study presents a secondary analysis to generate novel hypotheses for future studies by investigating the diagnostic accuracy of thermal, hydration, and heart rate assessments in discriminating positive AKI risk following physical work in the heat in unacclimatized individuals. Unacclimatized participants (n = 13, 3 women, age: ∼23 years) completed four trials involving 2 h of exercise in a 39.7 ± 0.6 °C, 32 ± 3% relative humidity environment that differed by experimental manipulation of hyperthermia (i.e., cooling intervention) and dehydration (i.e., water drinking). Diagnostic accuracy was assessed via receiver operating characteristic curve analysis. Positive AKI risk was identified when the product of concentrations insulin-like growth factor binding protein 7 and tissue inhibitor of metalloproteinase-2 [IGFBP7∙TIMP-2] exceeded 0.3 (ng∙mL-1)2∙1000-1. Peak absolute core temperature had the acceptable discriminatory ability (AUC = 0.71, p = 0.009), but a relatively large variance (AUC 95% CI: 0.57-0.86). Mean body temperature, urine specific gravity, urine osmolality, peak heart rate, and the peak percent of both maximum heart rate and heart rate reserve had poor discrimination (AUC = 0.66-0.69, p ≤ 0.051). Mean skin temperature, percent change in body mass and plasma volume, and serum sodium and osmolality had no discrimination (p ≥ 0.072). A peak increase in mean skin temperature of >4.7 °C had a positive likelihood ratio of 11.0 which suggests clinical significance. These data suggest that the absolute value of peak core temperature and the increase in mean skin temperature may be valuable to pursue in future studies as a biomarker for AKI risk in unacclimatized workers.

The Impact Plant-Based Diets Have on Athletic Performance and Body Composition: A Systematic Review.

Plant-based diets have gained popularity among athletes in recent years. Some believe that plant-based diets will improve performance owing to higher intakes of carbohydrates and antioxidants. Some believe it that will harm performance due to lower intakes of complete protein and creatine. This systemic review was conducted using Covidence software. A literature search of PubMed, Embase (Elsevier), CINAHL Plus (EBSCO), and Web of Science was completed on 22 March 2022. Following the development of clear objectives and a research question that identified the population, intervention, comparison, and outcomes, initial search criteria and keywords were identified. Extracted results totaled 2249, including 797 duplicates. The initial screening resulted in 1437 articles being excluded. The remaining 15 articles proceeded to full-text screening. A final 8 articles were included in the review, with 7 excluded. This paper will review the impact plant-based diets have on athletic performance and body composition in healthy young adults aged 18 to 45 years.

Following a plant-based diet does not harm athletic performance.Plant-based diets may improve maximal oxygen consumption, vertical countermovement jumps, and relative strength.There is no evidence that plant-based diets are detrimental to athletic performance or body composition.The long-term implications and the affect following a plant-based diet has on athletic performance in professional athletes are still unknown.

Taste and Appetite at Altitude: A Comprehensive Review of Sensory and Hunger Modulation in High-Altitude Environments.

Introduction: Individuals living or working at high altitudes typically experience altered taste perceptions and reduced appetite. These changes can lead to nutritional deficiencies, affecting the energy balance and body composition. Methods: We conducted a nonsystematic review of PubMed to explore these phenomena and expound on their findings to offer additional insights. Results: Changes in taste and perception are common and typically lead to loss of mass. There are limited practical solutions to mitigate these challenges. Discussion: Gradual acclimatization and tailored nutritional strategies are required to enhance health and performance in high-altitude environments. This review provides critical insights into the intersection of altitude, nutrition, and health.

Comparing Hypothermic and Thermal Neutral Conditions to Induce Metabolic Suppression.

Suppressing metabolism in astronauts could decrease CO2 production. It is unknown whether active cooling is required to suppress metabolism in sedated patients. We hypothesized that hypothermia would have an additive effect with dexmedetomidine on suppressing metabolism. This is a randomized crossover trial of healthy subjects receiving sedation with dexmedetomidine and exposure to a cold (20°C) or thermal neutral (31°C) environment for 3 hours. We measured heart rate, blood pressure, core temperature, resting oxygen consumption (VO2), resting carbon dioxide production (VCO2), and resting energy expenditure (REE) at baseline and each hour of exposure to either environment. We also evaluated components of the Defense Automated Neurobehavioral Assessment (DANA) Brief to evaluate the effect of metabolic suppression on cognition. Six subjects completed the study. Heart rate and core temperature were lower during the cold (56 bpm) condition than the thermal neutral condition (67 bpm). VO2, VCO2, and REE decreased between baseline and the 3-hour measurement in the cold condition (Δ = 0.9 mL/min, 56.94 mL/min, 487.9 Kcal/D, respectively). DANA simple response time increased between baseline and start of recovery in both conditions (20°C 136.9 cognitive efficiency [CE] and 31°C 87.83 CE). DANA procedural reaction time increased between baseline and start of recovery in the cold condition (220.6 CE) but not in the thermal neutral condition. DANA Go/No-Go time increased between baseline and start of recovery in both conditions (20°C 222.1 CE and 31°C 122.3 CE). Sedation and cold environments are required for metabolic suppression. Subjects experienced decrements in cognitive performance in both conditions. A significant recovery period may be required after metabolic suppression before completing mission critical tasks.

Heat stress increases carbohydrate oxidation rates and oxygen uptake during prolonged load carriage exercise.

Military missions are conducted in a multitude of environments including heat and may involve walking under load following severe exertion, the metabolic demands of which may have nutritional implications for fueling and recovery planning. Ten males equipped a military pack loaded to 30% of their body mass and walked in 20°C/40% relative humidity (RH) (TEMP) or 37°C/20% RH (HOT) either continuously (CW) for 90 min at the first ventilatory threshold or mixed walking (MW) with unloaded running intervals above the second ventilatory threshold between min 35 and 55 of the 90 min bout. Pulmonary gas, thermoregulatory, and cardiovascular variables were analyzed following running intervals. Final rectal temperature (MW: p < 0.001, g = 3.81, CW: p < 0.001, g = 4.04), oxygen uptake, cardiovascular strain, and energy expenditure were higher during HOT trials (p ≤ 0.05) regardless of exercise type. Both HOT trials elicited higher final carbohydrate oxidation (CHOox) than TEMP CW at min 90 (HOT MW: p < 0.001, g = 1.45, HOT CW: p = 0.009, g = 0.67) and HOT MW CHOox exceeded TEMP MW at min 80 and 90 (p = 0.049, g = 0.60 and p = 0.024, g = 0.73, respectively). There were no within-environment differences in substrate oxidation indicating that severe exertion work cycles did not produce a carryover effect during subsequent loaded walking. The rate of CHOox during 90 minutes of load carriage in the heat appears to be primarily affected by accumulated thermal load.