Body Water Loss Research Articles

Development of heat stress charts for older people under indoor environmental conditions

It has been acknowledged that as outdoor temperature and relative humidity increase past threshold values, so do older people mortality and morbidity rates. Similarly, there exist indoor conditions of temperature (Tamb) and relative humidity (RH) that would pose a health-risk to older people when they are exposed to these conditions for extended periods. However, these indoor conditions need to be identified to set protective measures for this vulnerable population. The aim of this work is to develop heat stress indices for older people similar to the standard effective temperature (SET) for a wide range of indoor conditions, activity levels and clothing insulation. A robust and validated bioheat model for older people was used to predict thermal responses and deduce the limits of Tamb and RH that would present a heat-related health risk when the core temperature exceeds 38 °C, or percentage of body water loss exceeds 2%, or when skin wettedness and SET exceed given thresholds. The results were consistent with published experimental data. At relatively cool ambient conditions, Tamb < 21 °C, older people have higher mean skin temperatures and feel cooler than younger people. At Tamb ≥ 25 °C, older people have lower mean skin temperatures and SET values become greater than younger ones, indicating that older people would rate their indoor conditions more stressful than younger people.

Nutritional Requirements for Sustaining Health and Performance During Exposure to Extreme Environments.

Dietary guidelines are formulated to meet minimum nutrient requirements, which prevent deficiencies and maintain health, growth, development, and function. These guidelines can be inadequate and contribute to disrupted homeostasis, lean body mass loss, and deteriorated performance in individuals who are working long, arduous hours with limited access to food in environmentally challenging locations. Environmental extremes can elicit physiological adjustments that alone alter nutrition requirements by upregulating energy expenditure, altering substrate metabolism, and accelerating body water and muscle protein loss. The mechanisms by which the environment, including high-altitude, heat, and cold exposure, alters nutrition requirements have been studied extensively. This contemporary review discusses physiological adjustments to environmental extremes, particularly when those adjustments alter dietary requirements.

Aestivation Motifs Explain Hypertension and Muscle Catabolism in Experimental Chronic Renal Failure

Chronic renal failure leads to muscle mass loss and hypertension, which according to textbook teaching occur secondary to an inability of the kidneys to excrete solutes and water. We found instead that rats with experimental chronic renal failure constantly lost body water, because their kidneys could not sufficiently concentrate the urine. Physiological adaptation to body water loss, termed aestivation, is an evolutionary conserved survival strategy that relies on complex physiologic-metabolic adjustment across multiple organs to prevent otherwise lethal dehydration. We show that rats with chronic renal failure utilize these ancient water conservation motifs to successfully stabilize their body water. Metabolic aestivation responses to chronic renal failure require nitrogen-rich organic osmolyte production. Continuous endogenous energy and nitrogen supply from skeletal muscle in support of this metabolic requirement explains “renal” muscle mass loss. Accompanying circulatory aestivation responses are designed to limit skin water loss. This process requires vasoconstriction, which explains “renal” hypertension.

DI-5-CUFFS: Venoconstrictive Thigh Cuffs Limit Body Fluid Changes but Not Orthostatic Intolerance Induced by a 5-Day Dry Immersion.

Venoconstrictive thigh cuffs are used by cosmonauts to ameliorate symptoms associated with cephalad fluid shift. A ground simulation of microgravity, using the dry immersion (DI) model, was performed to assess the effects of thigh cuffs on body fluid changes and dynamics, as well as on cardiovascular deconditioning. Eighteen healthy men (25–43 years), randomly divided into two groups, (1) control group or (2) group with thigh cuffs worn 10 h/day, underwent 5-day DI. Cardiovascular responses to orthostatic challenge were evaluated using the lower body negative pressure (LBNP) test; body fluid changes were assessed by bio-impedance and hormonal assay; plasma volume evolution was estimated using hemoglobin-hematocrit; subjective tolerance was assessed by questionnaires. DI induced a decrease in plasma volume of 15–20%. Reduction in total body water of 3–6% stabilized toward the third day of DI. This reduction was derived mostly from the extracellular compartment. During the acute phase of DI, thigh cuffs limited the decrease in renin and the increase in N-terminal prohormone of brain natriuretic peptide (NT-proBNP), the loss in total body water, and tended to limit the loss in calf volume, extracellular volume and plasma volume. At the later stable phase of DI, a moderate protective effect of thigh cuffs remained evident on the body fluids. Orthostatic tolerance time dropped after DI without significant difference between groups. Thigh cuff countermeasure slowed down and limited the loss of body water and tended to limit plasma loss induced by DI. These observed physiological responses persisted during periods when thigh cuffs were removed. However, thigh cuffs did not counteract decreased tolerance to orthostatic challenge.

MicroRNA expression in the heart of Xenopus laevis facilitates metabolic adaptation to dehydration

Xenopus laevis survive severe dehydration during the summer months in their natural range. MicroRNA regulate translation of target mRNAs and have shown to be differentially expressed in response to dehydration in X. laevis. During dehydration, heart rate is elevated which appears to compensate for the reduced oxygen delivery capability due to increased hematocrit. We hypothesized that microRNAs would be differentially expressed in the heart to modulate gene expression levels in response to dehydration. The present study assessed changes in the microRNAome of X. laevis heart in response to severe dehydration (30% loss of body water) using microRNA-seq. We show that target genes are enriched for RNA, DNA, and transcription factor binding activities, cardiac muscle contraction, and glycolysis/gluconeogenesis. These results suggest that microRNAs contribute to gene expression reorganization in the heart in response to dehydration, putatively supporting the increased physiological demands and ATP production needs by the heart under these conditions.

The influence of biological sex and fitness status on markers of recovery optimisation in response to prolonged high intensity interval exercise

This study aimed to characterise recovery outcomes and repeated performance following 2h high-intensity interval training (HIIT) exercise, followed by consumption of 1.2g/kg body mass (BM) and 0.4g/kgBM of carbohydrate and protein, respectively, between biological sex and fitness status categories. Venous blood samples, muscle biopsies, BM, body water, and breath samples were collected, and gastrointestinal symptoms (GIS) were measured, pre-exercise, and throughout 4h recovery. The following morning, participants returned to assess performance outcomes. Significantly greater body water losses were experienced by high (BM loss: 2.3%) vs. moderate fitness athletes (1.8%; P=0.009), but there were no differences between sexes (1.9%). Intestinal injury, carbohydrate malabsorption, and GIS occurred amongst all groups, with no differences. Phosphorylation of mTOR (P<0.001) and Akt (P=0.031), but not rpS6, increased from 0-2 h recovery in both fitness groups. Greater overall phosphorylation of GSK-3β was observed amongst high fitness (P=0.033). There were no group differences for glucose, insulin, cortisol, leukocyte or cytokine markers. A decline in neutrophil functional responses (36%) occurred for all groups. The following day, rates of carbohydrate oxidation were greater amongst males at all intensities. Rates of fat oxidation rates were greater at 50% and 60% VO2max, and carbohydrate oxidation were greater at 70% and 80% VO2max amongst high compared to moderate fitness athletes. Absolute performance was greater amongst high vs. moderate fitness; however, there were no differences in relative performance between groups. Recovery optimisation markers following a 2h HIIT exercise protocol and consumption of carbohydrate and protein at 1.2g/kgBM and 0.4g/kgBM, respectively, are similarly achieved by male and female athletes of moderate and high fitness status. Registration: This sub-group analysis was part of a larger study that was prospectively registered with ANZCTR (reference number 375090).

Estimation of Time-Course Core Temperature and Water Loss in Realistic Adult and Child Models with Urban Micrometeorology Prediction.

Ambient conditions may change rapidly and notably over time in urban areas. Conventional indices, such as the heat index and wet bulb globe temperature, are useful only in stationary ambient conditions. To estimate the risks of heat-related illness, human thermophysiological responses should be followed for ambient conditions in the time domain. We develop a computational method for estimating the time course of core temperature and water loss by combining micrometeorology and human thermal response. We firstly utilize an urban micrometeorology prediction to reproduce the environment surrounding walkers. The temperature elevations and sweating in a standard adult and child are then estimated for meteorological conditions. With the integrated computational method, we estimate the body temperature and thermophysiological responses for an adult and child walking along a street with two routes (sunny and shaded) in Tokyo on 7 August 2015. The difference in the core temperature elevation in the adult between the two routes was 0.11 °C, suggesting the necessity for a micrometeorology simulation. The differences in the computed body core temperatures and water loss of the adult and child were notable, and were mainly characterized by the surface area-to-mass ratio. The computational techniques will be useful for the selection of actions to manage the risk of heat-related illness and for thermal comfort.

Variation in field body temperature and total evaporative water loss along an environmental gradient in a diurnal ectotherm

AbstractThe maintenance of optimal body temperatures has profound consequences on all aspects of ectotherms life history, like fitness and performance, and has been the subject of research for decades. In contrast, for reptiles, comparatively less is known on the potential effects of water balance on physiology, ecology and behaviour. In recent years, several recent studies are pointing out the importance of studying thermoregulation and water balance within the same framework. Here, we used a Mediterranean lizard, Psammodromus algirus, to investigate how field body temperature and water loss rates may vary among populations, between sexes and along an altitudinal gradient. We found little variation in field body temperatures among populations, while within each population, field body temperature may change daily, seasonally and differ between sexes. On the contrary, water loss rates decreased with elevation and showed no seasonal trend or difference between sexes. Microclimatic data indicated that highland lizards experienced more fluctuating conditions, a factor that may explain their lower water loss rates. Other factors, like inter‐population differences in ectoparasite intensity, might also contribute in explaining the observed patterns. We present here the first data for a lacertid lizard on the inter‐population variability and sexual difference in water loss rates and point out that water balance may play a fundamental role in regulating lizard activity during the hottest and driest period of the year.

CHALLENGES TO ANIMAL WELFARE ASSOCIATED WITH CAPTURE AND LONG ROAD TRANSPORT IN BOMA-ADAPTED BLACK (DICEROS BICORNIS) AND SEMI-CAPTIVE WHITE (CERATOTHERIUM SIMUM) RHINOCEROSES

Capture and transport are part of translocation and expose animals to a variety of stressors that can lead to morbidity and mortality. We aimed to establish a better understanding of the physiologic responses to capture and transport in black (Diceros bicornis) and white (Ceratotherium simum) rhinoceroses in Southern Africa. Fourteen adult black rhinoceroses were transported 600 km by vehicle and 32 white rhinoceroses (24 adults and 8 juveniles) were transported 1,300 km by vehicle. The black rhinoceroses had been wild-caught and boma-adapted over 6 wk prior to the translocation and were only sedated to allow for loading into the transport crates. The white rhinoceroses originated from a game farm and were chemically immobilized from a helicopter and then loaded. Paired blood samples were collected from animals at loading (capture) and after transport and evaluated for changes in clinical chemistry analytes, acute phase reactants, and oxidative stress biomarkers. The Wilcoxon rank sum test was used to compare changes in measured analytes from capture and after transport. All rhinoceroses survived capture and transport. Rhinoceroses experienced total body water loss, mobilization of energy reserves, and muscular damage. Alterations in acute phase reactants suggested that animals mounted a stress response. Oxidative stress was observed in black rhinoceroses. We identified the following challenges to animal welfare during transport: hydration status, energy balance, skeletal muscle fatigue, and stress-induced immunomodulation. Measures to mitigate these challenges, such as administration of fluids, need to be included in the planning of future translocations.

P5407Body-composition analysis of patients with acute heart failure - preliminary results from the SCALE HF trial

Abstract Background Guidance for intensified diuretic therapy in acute heart failure (AHF) is mainly based on body weight measurement, frequently leading to a short episode of dehydration with kidney failure after recompensation. In addition, patients often present immobilized due to severe health issues making weight measurement stressful. Purpose Bioelectrical impedance analysis (BIA) may be a more direct approach to guide intensified diuretic therapy analysing patient's body composition. We hypothesized that patient's weight loss during therapy correlates with loss of body water measured by BIA. Therefore, we tested if this method could be an alternative to daily weight measurement. Methods We conducted an observational, single-centre study to evaluate and monitor body composition of patients hospitalised with AHF, adjudicated according to current ESC/HFA guidelines by a cardiologist. We used an eight-electrode, segmental, multi-frequency body composition analyser, previously validated against air displacement plethysmography, whole body MRI, deuterium and sodium bromide dilution. We investigated patients until hospital discharge or latest one day after ending intensified diuretic therapy. Disease specific properties, BIA and weight measurement were assessed daily. Furthermore, we investigated BIA raw data. Results 390 BIA were applied on 76 patients (47 men; 29 women; mean age 76±11 years; mean weight 75.6±15.7 kg). 34 patients presented with global, 27 with left-heart, 8 with right-heart and 7 with not specified AHF. 44 patients presented with pleural effusion. Pearson correlations showed that total body water (r=0.737, p≤0.001) and extracellular water (r=0.69, p≤0.001) correlated each with total body weight. Changes in total body water accurately (within a range of ± 1kg) reflected changes in total body weight in 40.28% of the patients and changes in extracellular water showed a similarly accurate reflection of total body weight change in 68.06% of the patients. BIA raw-data analysis showed significant changes using Wilcoxon test between measurements at the beginning of intensified diuretic therapy and at its end. We found a significant increase of resistance (mean from 334.6±67.5 to 362.8±69.5 Ohm/m; p=0.021) and reactance (mean from 21.3±7.1 to 24.1±6.2 Ohm/m; p=0.009) standardized to patients height and a non-significant increase of phase angle (mean from 3.6±0.9 to 3.8±0.8 °; p=0.149) during hospitalisation. Conclusion BIA is able to estimate changes in total body weight by analysing changes in extracellular body water in patients under intensified diuretic therapy and raw data analysis seems even more accurate and promising. This data derive from a heterogeneous AHF patient group, needing further investigation. Once validated, wearable BIA connected to an automated device monitoring system would enable an easy to use diuretic therapy monitoring for impaired patients or outpatients and could help reducing care efforts.

Intermittent Fasting During Ramadan and Its Effects in Individuals With Metabolic Syndrome

This study evaluated the effect of intermittent fasting during Ramadan, the Muslim religious season of fasting, on body composition among 95 adults (65 male adults) with a mean age of 45.4 years with metabolic syndrome in Iran. The individuals were classified retrospectively into fasting and nonfasting groups based on fasting for a minimum of 10 days during Ramadan. Body composition, physical activity, and dietary intake were assessed both at baseline before the fast began and after Ramadan. Those who fasted a minimum of 10 days had significant reductions in body weight (−1.5 kg) and body mass index, body fat mass (−1.2 kg), fat free mass (−0.4 kg), skeletal muscle mass (−0.3 kg), and visceral fat area (−5.7 cm2). Also, they showed significant decreases in the total body water, intracellular water, 50-kHz whole-body phase angle (−0.13 degrees), and total physical activity. Fasting resulted in a 1.5-kg weight loss, of which the percentage losses were loss in body fat mass, 76%; body water loss, 18%; and protein loss, 6%, and also decrease in daily dietary intake during fasting in those who fasted. Fasting during Ramadan, which restricts the time of eating and caloric restriction, may be effective as dietary interventions in patients with metabolic syndrome to reduce body weight, fat mass, and visceral fat while retaining lean mass.

Validation of the Predicted Heat Strain Model in Hot Underground Mines

Heat-related illnesses (HRI) are relatively common in both hot surface and underground mining operations. When workers are exposed to extreme heat or strenuous work in a hot environment, they become prone to heat stress. Heat strain is the result of the body’s response to external and internal heat stress. It is therefore vital for the conditions leading to heat strain be detected and treated in a timely manner. Heat-related illnesses are manifested by exhaustion and heat stroke. The predicted heat strain (PHS) [ISO 7933 (2004)] model has been developed to predict the health condition of the worker in terms of core body temperature and water loss. The PHS model tested in this study is based on eight physical parameters that are measured at different intervals during a work shift. They include air temperature, humidity, radiation, air velocity, metabolic rate, clothing insulation, posture, and acclimatization. The model predictions are then compared with a direct physiological measurement, such as core body temperature. We present the results of an extensive study that monitored and predicted body’s response to heat stress under different environmental and working conditions. The PHS model provided reliable results in most instances in comparison with other prediction methods currently in use in the field.

Tolerance and response of two honeybee species Apis cerana and Apis mellifera to high temperature and relative humidity.

The ambient temperature and relative humidity affect the metabolic and physiological responses of bees, thus affecting their life activities. However, the physiological changes in bee due to high temperature and high humidity remain poorly understood. In this study, we explored the effects of higher temperature and humidity on the epiphysiology of bees by evaluating the survival, tolerance and body water loss in two bee species (Apis cerana and Apis mellifera). We also evaluated the changes in the activity of antioxidant and detoxification enzymes in their body. We observed that under higher temperature and humidity conditions, the survival rate of A. mellifera was higher than that of A. cerana. On the other hand, a comparison of water loss between the two species revealed that A. mellifera lost more water. However, under extremely high temperature conditions, A. cerana was more tolerant than A. mellifera. Moreover, under higher temperature and humidity conditions, the activity of antioxidant and detoxification enzymes in bees was significantly increased. Overall, these results suggest that high temperatures can adversely affect bees. They not only affect the survival and water loss, but also stimulate oxidative stress in bees. However, unlike our previous understanding, high humidity can also adversely affect bees, although its effects are lower than that of temperature.

Effect of ultrafiltration on extravascular lung water assessed by lung ultrasound in children undergoing cardiac surgery: a randomized prospective study

BackgroundIncreased lung water and the resultant atelectasis are significant pulmonary complications after cardiopulmonary bypass (CPB) in children undergoing cardiac surgery; these complications are observed after CPB than after anaesthesia alone. Ultrafiltration has been shown to decrease total body water and postoperative blood loss and improve the alveolar to arterial oxygen gradient and pulmonary compliance. This study investigated whether conventional ultrafiltration during CPB in paediatric heart surgeries influences post-bypass extravascular lung water (EVLW) assessed by lung ultrasound (LUS).MethodsThis randomized controlled study included 60 patients with congenital heart disease (ASA II-III), aged 1 to 48 months, with a body weight > 3 kg. Conventional ultrafiltration targeting a haematocrit (HCT) level of 28% was performed on the ultrafiltration group, while the control group did not receive ultrafiltration. LUS scores were recorded at baseline and at the end of surgery. The PaO2/FiO2 ratio (arterial oxygen tension divided by the fraction of inspired oxygen), urine output, and haemodynamic parameters were also recorded.ResultsLUS scores were comparable between the two groups both at baseline (p = 0.92) and at the end of surgery (p = 0.95); however, within the same group, the scores at the end of surgery significantly differed from their baseline values in both the ultrafiltration (p = 0.01) and non-ultrafiltration groups (p = 0.02).The baseline PaO2/FiO2 ratio was comparable between both groups. at the end of surgery, The PaO2/FiO2 ratio increased in the ultrafiltration group compared to that in the non-ultrafiltration group, albeit insignificant (p = 0.16). no correlation between the PaO2/FiO2 ratio and LUS score was found at baseline (r = − 0.21, p = 0.31). On the other hand, post-surgical measurements were negatively correlated (r = − 0.41, p = 0.045).ConclusionConventional ultrafiltration did not alter the EVLW when assessed by LUS and oxygenation state. Similarly, ultrafiltration did not affect the urea and creatinine levels, intensive care unit (ICU) stays, ventilation days, or mortality.Trial registrationClinicaltrials.gov Identifier: NCT03146143 registered on 29-April-2017.

Changes in precipitation may alter food preference in an ecosystem engineer, the black land crab, Gecarcinus ruricola.

Gecarcinid land crabs are ecosystem engineers playing an important role in nutrient recycling and seedling propagation in coastal forests. Given a predicted future decline in precipitation for the Caribbean, the effects of dehydration on feeding preferences of the black land crab Gecarcinus ruricola were investigated. G. ruricola were offered novel food items of lettuce, apple, or herring to test for food choice based on water and nutritional (energetic) content in single and multiple choice experimental designs. The effect of dehydration was incorporated by depriving crabs of water for 0, 4, or 8 days, leading to an average body water loss of 0%, 9%, and 17%, respectively, (crabs survived a body water loss of 23% + 2% and 14–16 days without access to water). The results were consistent between the single and multiple choice experiments: crabs consumed relatively more apple and fish and only small amounts of lettuce. Overall, no selective preferences were observed as a function of dehydration, but crabs did consume less dry food when deprived of water and an overall lower food intake with increasing dehydration levels occurred. The decrease in feeding was likely due to loss of water from the gut resulting in the inability to produce ample digestive juices. Future climatic predictions suggest a 25–50% decline in rainfall in the Caribbean, which may lead to a lower food intake by the crabs, resulting in compromised growth. The subsequent reduction in nutrient recycling highlights possible long-term effects on coastal ecosystems and highlights the importance of future work on climate relative behavioral interactions that influence ecosystem function.

Glucose and urea metabolic enzymes are differentially phosphorylated during freezing, anoxia, and dehydration exposures in a freeze tolerant frog

Vertebrate freeze tolerance requires multiple adaptations underpinned by specialized biochemistry. Freezing of extracellular water leads to intracellular dehydration as pure water is incorporated into growing ice crystals and also results in the cessation of blood supply to tissues, creating an anoxic cellular environment. Hence, the freeze tolerant wood frog, Rana sylvatica, must endure both dehydration and anoxia stresses in addition to freezing. The metabolic responses to freezing, dehydration and anoxia involve both protein/enzyme adaptations and the production of metabolites with metabolic or osmotic functions, particularly glucose and urea. The present study uses a phosphoproteome analysis to examine the differential phosphorylation of metabolic enzymes involved in the production of these two metabolites in liver in response to freezing, anoxia, or dehydration exposures. Our results show stress-specific responses in the abundance of phosphopeptides retrieved from nine glycolytic enzymes and three urea cycle enzymes in liver of wood frogs exposed to 24 h freezing, 24 h anoxia, or dehydration to 40% of total body water loss, as compared with 5 °C acclimated controls. Data show changes in the abundance of phosphopeptides belonging to glycogen phosphorylase (GP) and phosphofructokinase 2 (PFK2) that were consistent with differential phosphorylation control of glycogenolysis and a metabolic block at PFK1 that can facilitate glucose synthesis as the cryoprotectant during freezing. Anoxia-exposed animals showed similar changes in GP phosphorylation but no changes to PFK2; changes that would facilitate mobilization of glycogen as a fermentative fuel for anaerobic glycolysis. Urea is commonly produced as a compatible osmolyte in response to amphibian dehydration. Selected urea cycle enzymes showed small changes in phosphopeptide abundance in response to dehydration, but during freezing differential phosphorylation occurred that may facilitate this ATP expensive process when energy resources are sparse. These results add to the growing body of literature demonstrating the importance and efficiency of reversible protein phosphorylation as a regulatory mechanism allowing animals to rapidly respond to environmental stress.

Purification and characterization of a urea sensitive lactate dehydrogenase from skeletal muscle of the African clawed frog, Xenopus laevis.

The African clawed frog, Xenopus laevis endures whole body dehydration which can increase its reliance on anaerobic glycolysis for energy production. This makes the regulation of the terminal enzyme of glycolysis, lactate dehydrogenase (LDH), crucial to stress survival. We investigated the enzymatic properties and posttranslational modification state of purified LDH from the skeletal muscle of control and dehydrated (30% total body water loss) X. laevis. LDH from the muscle of dehydrated frogs showed a 93% reduction in phosphorylation on threonine residues and an 80% reduction of protein nitrosylation. LDH from dehydrated muscle also showed a 74% lower Vmax in the pyruvate oxidizing direction and a 78% decrease in Vmax in the lactate reducing direction along with a 33% lower Km for pyruvate and a 40% higher Km for lactate. In the presence of higher levels of urea and molecular crowding by polyethylene glycol, used to mimic conditions in the cells of dehydrated animals, the Km values of control and dehydrated LDH demonstrated opposite responses. In the pyruvate oxidizing direction, control muscle LDH was unaffected by these additives, whereas the affinity for pyruvate dropped further for LDH from dehydrated muscle. The opposite effect was more pronounced in the lactate reducing direction as control LDH showed an increased affinity for lactate, whereas LDH from dehydrated animals showed a further reduction in affinity. The physiological consequences of dehydration-induced LDH regulation appear to poise the enzyme towards lactate production when urea levels are high and lactate catabolism when urea levels are low, perhaps helping to maintain glycolysis under dehydrating conditions whilst providing for the ability to recycle lactate upon rehydration.

Factors influencing hydration status during a National Collegiate Athletics Association division 1 soccer preseason

ObjectivesTo investigate the roles that training load and environmental conditions have on fluid balance during a collegiate men’s soccer preseason. DesignObservational study. MethodsTwenty-eight male collegiate soccer players (mean±SD; age, 20±1.7y; body mass (BM), 79.9±7.3kg; height, 180.9±6.8cm; body fat, 12.7±3.1%; VO2max, 50.7±4.3ml·kg−1·min−1) participated in this study. Prior to (PRE) and following (POST) each team session, BM, percent BM loss (%BML) and hydration status was measured. Participants donned a heart rate and GPS enabled monitor to measure training load. For all team activities, ambient temperature (TAMB) and relative humidity (RH) were obtained from the nearest local weather station. Participants consumed 500mL of water as part of the team-based hydration strategy before and after training session. Stepwise linear regression was used to identify the variables that predicted %BML. Significance was set a-priori p<0.05. ResultsTotal distance covered predicted %BML during all preseason activities (r2=0.253, p<0.001), with TAMB and RH further adding to the model (r2=0.302, p<0.001). %BML never exceeded 2% of BM during any one session and daily variation in BM was <1% from baseline measures. Urine specific gravity was greater than 1.020 on 12/15days and UCOL was above 4 on 13/15days, indicating a state of hypohydration. ConclusionsTotal distance covered was the best predictor for the extent of body water losses during a collegiate preseason. While the team-based hydration strategy during preseason was successful in minimizing fluid losses during activity, participants arrived hypohydrated 80% of the time, necessitating a greater focus on daily fluid needs.

Ad libitum drinking adequately supports hydration during 2h of running in different ambient temperatures.

To examine if ad libitum drinking will adequately support hydration during exertional heat stress. Ten endurance-trained runners ran for 2h at 60% of maximum oxygen uptake under different conditions. Participants drank water ad libitum during separate trials at mean ambient temperatures of 22°C, 30°C and 35°C. Participants also completed three trials at a mean ambient temperature of 35°C while drinking water ad libitum in all trials, and with consumption of programmed glucose or whey protein hydrolysate solutions to maintain euhydration in two of these trials. Heart rate, oxygen uptake, rectal temperature, perceived effort, and thermal sensation were monitored, and nude body mass, hemoglobin, hematocrit, and plasma osmolality were measured before and after exercise. Water and mass balance equations were used to calculate hydration-related variables. Participants adjusted their ad libitum water intake so that the same decrease in body mass (1.1-1.2kg) and same decrease in body water (0.8-0.9kg) were observed across the range of ambient temperatures which yielded significant differences (p < .001) in sweat loss. Overall, water intake and total water gain replaced 57% and 66% of the water loss, respectively. The loss in body mass and body water associated with ad libitum drinking resulted in no alteration in physiological and psychophysiological variables compared with the condition when hydration was nearly fully maintained (0.3L body water deficit) relative to pre-exercise status from programmed drinking. Ad libitum drinking is an appropriate strategy for supporting hydration during running for 2h duration under hot conditions.

Effect of rehydration schedule after four-hour head-out water immersion on running performance and recovery

Head-out water immersion (HOWI) results in diuresis, which could potentially limit performance after egress to land. We examined the effect of rehydration on endurance, cardiovascular stability, and overnight recovery following a four-hour thermoneutral HOWI on 12 subjects. Twelve males completed a crossover design consisting of no hydration, replacement of fluid loss during immersion (RD), and replacement of fluid after the immersion period (RA). Sixty minutes following immersion, subjects ran to exhaustion at ~80% maximum heart rate. After completing the run, each subject submitted to a head-up tilt test (HUTT). Vital signs and ECG were monitored overnight. HOWI resulted in a transient diuresis in NH and RA, while it was sustained throughout immersion in the RD protocol, resulting in greater urine [l] output (1.27 ± 0.48 (NH), 1.18 ± 0.43 (RA), 2.32 ± 0.77 (RD) (p ⟨ 0.001). Body mass change (%) was greater in NH than RD, but not RA (-1.58 ± 0.56 (NH), -0.66 ± 0.47 (RD), and -0.92 ± 0.76 (RA)). Run times were 17% versus 20% in NH compared to RD and RA, respectively, but were not statistically different. Time to orthostasis during the HUTT did not differ by condition. Overnight heart rate variability and blood pressures were not different. Rehydration during water immersion resulted in a large, sustained diuresis without improving performance or recovery after exiting the water. Loss of body water during thermoneutral HOWI was modest, and both rehydration strategies minimally affected aerobic performance and overnight recovery in young, healthy males.