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Claims that ENDUROX enhances performance by altering metabolic responses to exercise were tested. In a double-blind crossover design, 10 male subjects were randomly assigned to consume 400 mg of placebo or 800 mg ENDUROX for 7 days. Cycle ergometry was performed for 30 minutes at 25%, followed by 10 min at 65% of peak oxygen consumption. After a 1-week washout period, subjects performed the identical exercise protocol following 7 days of reciprocal supplemental conditions. Expired gases were collected and analyzed continuously for oxygen consumption, minute ventilation, and respiratory exchange ratio. Heart rate, blood pressure, rating of perceived exertion, blood lactate, and serum glycerol data were also collected at regular intervals. A two-way ANOVA with repeated measures revealed no significant main or interaction effects involving group differences (p > 0.05) between trials for any variable during rest, 25% or 65% (VO2 peak), or recovery. Our findings do not support the ergogenic claims for ENDUROX. [ABSTRACT FROM AUTHOR]

Exercise alone or in combination with environmental heat stress can elevate blood S-100beta protein concentrations. However, the explanatory power of exercise with marked environmental heat stress on the appearance of S-100beta is questionable. It is possible that the process of heat acclimation might afford additional insight. PURPOSE:: Determine the S-100beta response to moderate-intensity exercise with heat strain before and after heat acclimation. METHODS:: Nine healthy male volunteers completed 10 consecutive days of heat acclimation consisting of up to 100 min of treadmill walking (1.56 m.s, 4% grade) in the heat (45 degrees C, 20% relative humidity). Changes in HR, rectal temperature (Tre), and sweat rate (SR) were examined to determine successful acclimation. Area under the curve (AUC) for Tre greater than 38.5 degrees C was calculated to assess cumulative hyperthermia. Blood samples were taken before and after exercise on days 1 and 10 and were analyzed for serum osmolality and S-100beta concentration. RESULTS:: All subjects displayed physiological adaptations to heat acclimation including a significant (P < 0.05) reduction in final HR (161 to 145 bpm) and Tre (39.0 to 38.4 degrees C), as well as a modest ( 10%) increase in SR (1.10 to 1.20 L.h; P = 0.09). No differences were observed in pre- to postexercise serum S-100beta concentrations on day 1 or 10, and no differences were observed in S-100beta values between days 1 and 10. No significant correlations were found between S-100beta values and any variable of interest. CONCLUSIONS:: S-100beta concentrations do not necessarily increase in response to exercise-heat strain, and no effect of heat acclimation on S-100beta could be observed despite other quantifiable physiological adaptations. [ABSTRACT FROM AUTHOR]

The effectiveness of intermittent, microclimate cooling for men who worked in US Army chemical protective clothing (modified mission-oriented protective posture level 3; MOPP 3) was examined. The hypothesis was that intermittent cooling on a 2 min on-off schedule using a liquid cooling garment (LCG) covering 72% of the body surface area would reduce heat strain comparably to constant cooling. Four male subjects completed three experiments at 30 degrees C, 30% relative humidity wearing the LCG under the MOPP 3 during 80 min of treadmill walking at 224 +/- 5 W . m(-2). Water temperature to the LCG was held constant at 21 degrees C. The experiments were; 1) constant cooling (CC); 2) intermittent cooling at 2-min intervals (IC); 3) no cooling (NC). Core temperature increased (1.6 +/- 0.2 degrees C) in NC, which was greater than IC (0.5 +/- 0.2 degrees C) and CC (0.5 +/- 0.3 degrees C) ( p < 0.05). Mean skin temperature was higher during NC (36.1 +/- 0.4 degrees C) than IC (33.7 +/- 0.6 degrees C) and CC (32.6 +/- 0.6 degrees C) and mean skin temperature was higher during IC than CC ( p < 0.05). Mean heart rate during NC (139 +/- 9 b . min(-1)) was greater than IC (110 +/- 10 b . min(-1)) and CC (107 +/- 9 b . min(-1)) ( p < 0.05). Cooling by conduction (K) during NC (94 +/- 4 W . m(-2)) was lower than IC (142 +/- 7 W . m(-2)) and CC (146 +/- 4 W . m(-2)) ( p < 0.05). These findings suggest that IC provided a favourable skin to LCG gradient for heat dissipation by conduction and reduced heat strain comparable to CC during exercise-heat stress in chemical protective clothing. [ABSTRACT FROM AUTHOR]

PURPOSE: Serious heat illness has received considerable recent attention due to catastrophic heat waves in the United States and Europe, the deaths of high-profile athletes, and military deployments. METHODS: This study documents heat illness hospitalizations and deaths for the U.S. Army from 1980 through 2002. Hospitalization data were obtained from the Total Army Injury Health Outcomes Database (TAIHOD) coded according to the International Classification of Diseases, Ninth Revision, Clinical Modification (ICD-9-CM). North Atlantic Treaty Organization Standardization Agreement codes were searched for heat injuries in an effort to detect cases that were not found during the ICD-9-CM search. RESULTS: Five-thousand two-hundred forty-six soldiers were hospitalized, and 37 died due to heat illness. Our results indicate: 1) approximately 60% reduction in hospitalization rates (fewer heat exhaustion cases) over the 22-yr period; 2) fivefold increase in heat stroke hospitalization rates (1.8 per 100,000 in 1980 to 14.5 per 100,000 in 2001); 3) heat stroke cases were associated with dehydration (17%), rhabdomyolysis (25%), and acute renal failure (13%); 4) lower hospitalizations rates among African and Hispanic Americans compared with Caucasians (incidence density ratio, 0.76 [95% confidence interval, 0.71-0.82]; 5) greater rates of hospitalizations and heat strokes among recruits from northern than southern states (incidence density ratio, 1.69 [95% confidence interval, 1.42-1.90]; and 6) greater rates of hospitalizations and heat strokes among women than men (incidence density ratio, 1.18 [95% confidence interval, 1.09-1.27]). CONCLUSIONS: Exertional heat illness continues to be a military problem during training and operations. Whereas the hospitalization rate of heat illness is declining, heat stroke has markedly increased. [ABSTRACT FROM AUTHOR]

The Zone Diet is an eating plan claiming to maintain an 'ideal' hormone balance and improve health through the manipulation of dietary carbohydrate and protein. Although popular, the diet's health claims are based on dubious information and misinterpreted scientific facts, and it ultimately remains unsubstantiated. [ABSTRACT FROM AUTHOR]

Objective: The primary aim of this study was to assess the efficacy of the weight, urine, and thirst (WUT) framework in predicting dehydration after a body water manipulation protocol, while concurrently determining the individual and interactive contributions of the model components., Methods: The total study sample was 93 participants (female, n = 47), recruited from two institutions. Phase 1 involved collecting daily hydration measures from free-living participants (study 1, 58 participants for 3 d; study 2, 35 participants for 7 d). Phase 2 entailed a 2-h passive heating protocol, where participants from study 2 were randomly assigned to one of three groups that manipulated total body water over 24 h using passive heating and fluid restriction. During each phase, participants provided urine samples, underwent body mass measurements, and completed questionnaires pertaining to thirst perception. Morning and 24-h urine samples were assessed for color, osmolality, and specific gravity. Differences between intervention groups, based on the probability of hydration status, were examined (ANOVA), and ridge regression analysis assessed the relative importance of variables within the WUT model., Results: The study revealed significant differences among the intervention groups for predicted probability of dehydration, as determined by changes in body mass ( P = 0.001), urine color ( P = 0.044), and thirst perception ( P < 0.001). Binomial ridge regression indicated that changes in body mass (58%) and thirst perception (26%) were the most influential predictors of dehydration., Conclusions: These data support use of an enhanced version of the WUT model, underscoring the significance of changes in body mass and thirst perception in the assessment of hydration status., (Copyright © 2024 by the American College of Sports Medicine.)

Objectives: The primary aim was to explore the impact of exertional-heat stress (EHS) promoted exercise-associated bacteraemia. A secondary aim was to examine if an amino acid beverage (AAB) intervention may mitigate exercise-associated bacteraemia., Design: Counterbalanced randomised control trial., Methods: Twenty endurance trained male participants completed two randomised EHS trials. On one occasion, participants consumed a 237 mL AAB twice daily for 7 days prior, immediately before and every 20 min during EHS (2 h running at 60 % V̇O 2max in 35 °C). On the other occasion, a water volume control (CON) equivalent was consumed. Whole blood samples were collected pre- and immediately post-EHS, and were analysed for plasma DNA concentration by fluorometer quantification after microbial extraction, and bacterial relative abundance by next generation 16s rRNA gene sequencing., Results: Increased concentration of microbial DNA in plasma pre- to post-EHS was observed on CON (pre-EHS 0.014 ng/μL, post-EHS 0.039 ng/μL) (p < 0.001) and AAB (pre-EHS 0.015 ng/μL, post-EHS 0.031 ng/μL) (p < 0.001). The magnitude of change from pre- to post-exercise on AAB was 40 % lower, but no significant difference was observed versus CON (p = 0.455). Predominant bacterial groups identified included: phyla-Proteobacteria (88.0 %), family-Burkholderiaceae (59.1 %), and genus-Curvibacter (58.6 %). No significant variation in absolute and relative change in α-diversity and relative abundance for phyla, family, and genus bacterial groups was observed in AAB versus CON., Conclusions: The increased presence of microbial-bacterial DNA in systemic circulation in response to EHS appears positive in all participants. An amino acid beverage supplementation period prior to and consumption during EHS did not provide significant attenuation of EHS-associated bacteraemia., Competing Interests: Declaration of interest statement Apart from the industry funded aspect of this research study, KH, RC, RH, SG, RA, AM, and CR have no conflicts of interest to declare regarding the development, undertaking and reporting of this research study. SC, PB, and RK are employees of Entrinsic Bioscience, LLC., (Copyright © 2024 The Authors. Published by Elsevier Ltd.. All rights reserved.)

Purpose: Rapid gastric emptying and intestinal absorption of beverages is essential for rapid rehydration, and certain amino acids (AA) may augment fluid delivery. Three sugar-free beverages, containing differing AA concentrations (AA + PZ), were assessed for fluid absorption kinetics against commercial sugar-free (PZ, GZ) and carbohydrate-containing (GTQ) beverages., Methods: Healthy individuals (n = 15-17 per study) completed three randomised trials. Three beverages (550-600 mL) were ingested in each study (Study 1: AA + PZ [17.51 g/L AA], PZ, GZ; Study 2: AA + PZ [6.96 g/L AA], PZ, GZ; Study 3: AA + PZ [3.48 g/L AA], PZ, GTQ), containing 3.000 g deuterium oxide (D 2 O). Blood samples were collected pre-, 2-min, 5-min, and every 5-min until 60-min post-ingestion to quantify maximal D 2 O enrichment (Cmax), time Cmax occurred (Tmax) and area under the curve (AUC)., Results: Study 1: AUC (AA + PZ: 15,184 ± 3532 δ‰ vs. VSMOW; PZ: 17,328 ± 3153 δ‰ vs. VSMOW; GZ: 17,749 ± 4204 δ‰ vs. VSMOW; P ≤ 0.006) and Tmax (P ≤ 0.005) were lower for AA + PZ vs. PZ/GZ. Study 2: D 2 O enrichment characteristics were not different amongst beverages (P ≥ 0.338). Study 3: Cmax (AA + PZ: 440 ± 94 δ‰ vs. VSMOW; PZ: 429 ± 83 δ‰ vs. VSMOW; GTQ: 398 ± 81 δ‰ vs. VSMOW) was greater (P = 0.046) for AA + PZ than GTQ, with no other differences (P ≥ 0.106)., Conclusion: The addition of small amounts of AA (3.48 g/L) to a sugar-free beverage increased fluid delivery to the circulation compared to a carbohydrate-based beverage, but greater amounts (17.51 g/L) delayed delivery., (© 2024. The Author(s).)

Background: Amino-acid based medical foods have shown promise in alleviating symptoms of drug induced gastrointestinal side effects; particularly, diarrhea-predominant symptoms. Irritable bowel syndrome (IBS) is a gastrointestinal disorder that affects up to 9% of people globally, with diarrhea predominant IBS (IBS-D) being the most prevalent subtype. Further trials are needed to explore potential added benefits when integrated into standard care for IBS-D., Aim: To assess the effectiveness of an amino acid-based medical food as an adjunct to standard of care for adults with IBS-D., Methods: This is a pragmatic, real world, open label, single arm study comparing a 2-week baseline assessment to a 2-week intervention period. One hundred adults, aged 18 to 65 years, with IBS-D, according to Rome IV criteria, were enrolled after completing a 2-week baseline assessment period and received a 2-week supply of an amino acid based medical food which was consumed at home twice daily on top of their standard of care. The primary outcome was an assessment of tolerability after 2-weeks of consumption, while secondary outcomes included changes in stool consistency (Bristol Stool Form Scale), severity of abdominal pain & discomfort, symptoms of urgency, Global Improvement Survey (GIS), and the IBS severity scoring system (IBS-SSS)., Results: The test product was well-tolerated as each participant successfully completed the full 14-day trial, and there were no instances of dropouts or discontinuation of the study product reported. Forty percent of participants achieved a 50% or more reduction in the number of days with type 6-7 bowel movements (IBS-D stool consistency responders). Fifty-three percent of participants achieved a clinically meaningful reduction of 30% in mean weekly pain scores, and 55% experienced the same for mean weekly discomfort scores (IBS-D pain and discomfort responders). Participants experienced a mean -109.4 (95% confidence interval: -130.1, -88.8) point reduction on the IBS-SSS and 52% experienced a minimally clinically important difference of > 95 points. An IBS-SSS category shift from severe to moderate or mild occurred in 69% of participants. For functional symptoms, 76% of participants reported symptom relief on the GIS., Conclusion: The amino acid-based medical food was well-tolerated, when added to the standard of care, and demonstrated improvements in both overall IBS symptom severity and IBS-D symptoms within just 2 wk., Competing Interests: Conflict-of-interest statement: All authors are employees of Entrinsic Bioscience LLC (EBS) and EBS was the research sponsor. Patent 174821-011205/PCT (PCT/US11/53265) is issued to EBS Holdings, and patent 174821-012001/PCT (PCT/US13/25294) is issued to EBS Holding., (©The Author(s) 2023. Published by Baishideng Publishing Group Inc. All rights reserved.)

Introduction: Recent success in predicting individual sweat losses from air temperature and energy expenditure measurements suggests a potential for forecasting individual sweat losses for future combinations of environment and exercise. The purpose of this study is to determine the plausibility of accurately forecasting exercise sweat losses from meteorological air temperature forecasts and individual running energy expenditure forecasts. The potential impact on plasma sodium is also estimated when setting drinking rates equal to forecast sweat losses., Materials and Methods: Individual exercise sweat losses (equated to water needs) and energy expended while running were measured in 33 participants along with air temperature and compared with forecasts of the same. Forecast inputs were used in a web app to forecast exercise sweat losses for comparison with observed values. The bias between forecast and observed exercise sweat losses was used to calculate the potential drinking impact on plasma sodium., Results: The concordance correlation coefficient between forecast and observed values was 0.95, 0.96, and 0.91 for air temperature, energy expenditure, and exercise sweat losses, respectively, indicating excellent agreement and no significant differences observed via t -test. Perfect matching of water intake to sweat losses would lower plasma sodium concentrations from 140 to 138 mmol/L; calculations using the 95% limits of agreement for bias showed that drinking according to forecast exercise sweat losses would alter plasma sodium concentrations from 140 to between 136 and 141 mmol/L., Conclusions: The outcomes support the strong potential for accurately forecasting exercise sweat losses from commonly available meteorological air temperature forecasts and energy expenditure from forecast running distance., Competing Interests: SC is the owner of Sports Science Synergy, LLC and the creator of the patented H2Q™ algorithm (U.S. Patent No. 11,219,410 B2) used in this study. RK was employed by entrinsic bioscience, LLC. The remaining author declares that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2023 Cheuvront, Sollanek and Kenefick.)

Introduction: The importance of providing wet bulb globe temperature (WBGT) heat stress flag category measurements in real time is well recognized by road race directors, and it is bound to become even more important with the rise of extreme weather and pandemic outbreaks. The purpose of this paper is to describe the WBGT index and its components measured during the 125th running of the Boston Marathon on October 11, 2021, for qualitative comparison to measurements made similarly on its traditional April date, 2014 to 2019., Methods: Monitoring occurred at the 7 km, 18 km, and 32 km marks of the race in the towns of Ashland, Natick-Wellesley, and Newton. The outdoor WBGT index was calculated from direct hourly measurements of the dry bulb, black globe, and natural wet bulb temperatures from 0900 to 1500 h., Results: The WBGT index was not different among towns; thus, the average hourly values for the 3 towns were compared to historical data averaged identically. Although the black globe temperature fluctuated considerably in response to changing cloud cover, on average, partly cloudy skies kept the solar load comparable to what has been observed in April. Dry bulb and wet bulb temperatures were higher than those on most April dates shown, which resulted in a yellow (or amber) flag day for most of the race., Conclusions: The historic October Boston Marathon was among the warmest in recent history. Like the impact of COVID-19 on the 2021 Boston Marathon, future climate challenges around outdoor activities could necessitate rescheduling; they underscore the importance of real-time WBGT index measures., (Copyright © 2023 Wilderness Medical Society. Published by Elsevier Inc. All rights reserved.)

Objective . Exercise-heat strain estimation approaches often involve combinations of body core temperature (Tcore), skin temperature (Tsk) and heart rate (HR). A successful existing measure is the 'Physiological Strain Index' (PSI), which combines HR and Tcore values to estimate strain. However, depending on variables such as aerobic fitness and clothing, the equation's 'maximal/critical' Tcore must be changed to accurately represent the strain, in part because high Tsk (small Tcore-Tsk) can increase cardiovascular strain and thereby negatively affect performance. Here, an 'adaptive PSI' (aPSI) is presented where the original PSI Tcore critical value is 'adapted' dynamically by the delta between Tcore and Tsk. Approach . PSI and aPSI were computed for athletes (ELITE, N = 11 male and 8 female, 8 km time-trial) and soldiers in fully encapsulating personal protective equipment (PPE, N = 8 male, 2 km approach-march). While these were dissimilar events, it was anticipated given that the clothing and work rates would elicit similar very-high exercise-heat strain values. Main results . Mean end HR values were similar (∼180 beats min -1 ) with higher Tcore = 40.1 ± 0.4 °C for ELITE versus PPE 38.4 ± 0.6 °C ( P < 0.05). PSI end values were different between groups ( P < 0.01) and appeared 'too-high' for ELITE (11.4 ± 0.8) and 'too-low' for PPE (7.6 ± 2.0). However, aPSI values were not different (9.9 ± 1.4 versus 9.0 ± 2.5 versus; p > 0.05) indicating a 'very high' level of exercise-heat strain for both conditions. Significance . A simple adaptation of the PSI equation, which accounts for differences in Tcore-to-Tsk gradients, provides a physiological approach to dynamically adapt PSI to provide a more accurate index of exercise-heat strain under very different working conditions., (© 2023 Institute of Physics and Engineering in Medicine.)

The study aimed to determine the effects of two differing amino acid beverage interventions on biomarkers of intestinal epithelial integrity and systemic inflammation in response to an exertional-heat stress challenge. One week after the initial assessment, participants (n = 20) were randomly allocated to complete two exertional-heat stress trials, with at least 1 week washout. Trials included a water control trial (CON), and one of two possible amino acid beverage intervention trials (VS001 or VS006). On VS001 (4.5 g/L) and VS006 (6.4 g/L), participants were asked to consume two 237-ml prefabricated doses daily for 7 days before the exertional-heat stress, and one 237-ml dose immediately before, and every 20 min during 2-hr running at 60% maximal oxygen uptake in 35 °C ambient conditions. A water volume equivalent was provided on CON. Whole blood samples were collected pre-, immediately post-, 1 and 2 hr postexercise, and analyzed for plasma concentrations of cortisol, intestinal fatty acid protein, soluble CD14, and immunoglobulin M (IgM) by ELISA, and systemic inflammatory cytokines by multiplex. Preexercise resting biomarker concentrations for all variables did not significantly differ between trials (p > .05). A lower response magnitude for intestinal fatty acid protein (mean [95% CI]: 249 [60, 437] pg/ml, 900 [464, 1,336] pg/ml), soluble CD14 (-93 [-458, 272] ng/ml, 12 [-174, 197] ng/ml), and IgM (-6.5 [-23.0, 9.9] MMU/ml, -10.4 [-16.2, 4.7] MMU/ml) were observed on VS001 and V006 compared with CON (p < .05), respectively. Systemic inflammatory response profile was lower on VS001, but not VS006, versus CON (p < .05). Total gastrointestinal symptoms did not significantly differ between trials. Amino acid beverages' consumption (i.e., 4.5-6.4 g/L), twice daily for 7 days, immediately before, and during exertional-heat stress ameliorated intestinal epithelial integrity and systemic inflammatory perturbations associated with exercising in the heat, but without exacerbating gastrointestinal symptoms.

Introduction: This study compared the efficacy of three commercial oral rehydration solutions (ORS) for restoring fluid and electrolyte balance, after exercise-induced dehydration., Method: Healthy, active participants ( N  = 20; ♀ = 3; age ∼27 y, V ˙ O 2 peak ∼52 ml/kg/min) completed three randomised, counterbalanced trials whereby intermittent exercise in the heat (∼36°C, ∼50% humidity) induced ∼2.5% dehydration. Subsequently, participants rehydrated (125% fluid loss in four equal aliquots at 0, 1, 2, 3 h) with a glucose-based (G-ORS), sugar-free (Z-ORS) or amino acid-based sugar-free (AA-ORS) ORS of varying electrolyte composition. Urine output was measured hourly and capillary blood samples collected pre-exercise, 0, 2 and 5 h post-exercise. Sodium, potassium, and chloride concentrations in urine, sweat, and blood were determined., Results: Net fluid balance peaked at 4 h and was greater in AA-ORS (141 ± 155 ml) and G-ORS (101 ± 195 ml) than Z-ORS (-47 ± 208 ml; P  ≤ 0.010). Only AA-ORS achieved positive sodium and chloride balance post-exercise, which were greater for AA-ORS than G-ORS and Z-ORS ( P  ≤ 0.006), as well as for G-ORS than Z-ORS ( P  ≤ 0.007) from 1 to 5 h., Conclusion: when provided in a volume equivalent to 125% of exercise-induced fluid loss, AA-ORS produced comparable/superior fluid balance and superior sodium/chloride balance responses to popular glucose-based and sugar-free ORS., Competing Interests: LJ has current funding from Entrinsic Beverage Company LLC, Entrinsic Bioscience, LLC, Herbalife Europe Ltd, Bridge Farm Nurseries and Decathlon SA, and has previously received funding from PepsiCo Inc., Volac International and British Summer Fruits; has performed consultancy for PepsiCo Inc. and Lucozade, Ribena Suntory, and has received conference fees from PepsiCo Inc. and Danone Nutricia. In all cases, monies have been paid to LJ's institution and not to LJ. The funders were involved in the study design, but were not involved in the collection or analyses of data; or the decision to publish the results. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (© 2023 Peden, Funnell, Reynolds, Kenefick, Cheuvront, Mears and James.)

Employing a methodology reported in a recent theoretical study on male astronauts, this study estimated the effects of body size and aerobic countermeasure (CM) exercise in a four-person, all-female crew composed of individuals drawn from a stature range (1.50- to 1.90-m) representative of current space agency requirements (which exist for stature, but not for body mass) upon total energy expenditure (TEE), oxygen (O 2 ) consumption, carbon dioxide (CO 2 ) and metabolic heat (H prod ) production, and water requirements for hydration, during space exploration missions. Assuming geometric similarity across the stature range, estimates were derived using available female astronaut data (mean age: 40-years; BMI: 22.7-kg·m -2 ; resting VO 2 and VO 2max : 3.3- and 40.5-mL·kg -1 ·min -1 ) on 30- and 1080-day missions, without and with, ISS-like countermeasure exercise (modelled as 2 × 30-min aerobic exercise at 75% VO 2max , 6-day·week -1 ). Where spaceflight-specific data/equations were not available, terrestrial equivalents were used. Body size alone increased 24-h TEE (+ 30%), O 2 consumption (+ 60%), CO 2 (+ 60%) and H prod (+ 60%) production, and water requirements (+ 17%). With CM exercise, the increases were + 25-31%, + 29%, + 32%, + 38% and + 17-25% across the stature range. Compared to the previous study of theoretical male astronauts, the effect of body size on TEE was markedly less in females, and, at equivalent statures, all parameter estimates were lower for females, with relative differences ranging from -5% to -29%. When compared at the 50th percentile for stature for US females and males, these differences increased to - 11% to - 41% and translated to larger reductions in TEE, O 2 and water requirements, and less CO 2 and H prod during 1080-day missions using CM exercise. Differences between female and male theoretical astronauts result from lower resting and exercising O 2 requirements (based on available astronaut data) of female astronauts, who are lighter than male astronauts at equivalent statures and have lower relative VO 2max values. These data, combined with the current move towards smaller diameter space habitat modules, point to a number of potential advantages of all-female crews during future human space exploration missions., (© 2023. The Author(s).)

When will women run a sub-4-minute mile? The answer seems to be a distant future given how women's progress has plateaued in the mile, or its better studied metric placeholder, the 1500 m. When commonly accepted energetics principles of running, along with useful field validation equations of the same, are applied to probe the physiology underpinning the 10 all-time best women's mile performances, insights gained may help explain the present 12.34-second shortfall. Insights also afford estimates of how realistic improvements in the metabolic cost of running could shrink the difference and bring the women's world record closer to the fabled 4-minute mark. As with men in the early 1950s, this might stir greater interest, excitement, participation, and depth in the women's mile, the present absence of which likely contributes to more pessimistic mathematical modeling forecasts. The purpose of this invited commentary is to provide a succinct, theoretical, but intuitive explanation for how women might get closer to their own watershed moment in the mile.

This study sought to (a) estimate how the duration of running influences sweat losses and contributes to the daily fluid requirement, and (b) empirically estimate the drinking rates required to prevent significant dehydration (≥2% body weight as body water). Individual sweating data and running duration were obtained from male (n = 83) and female (n = 36) runners (n = 146 total observations) performing under highly heterogeneous conditions and over a range of exercise durations (33-280 min). Running <60 min/day increased daily fluid needs by a factor of 1.3, whereas running >60 min/day increased the daily fluid need by a factor of 1.9-2.3. Running <60 min/day generally required no fluid intake to prevent significant dehydration before run completion (31/35 runners). In contrast, running >60 min/day required more than 50% replacement of sweating rates to prevent the same (65/111 runners). Overall sweat losses ranged from ∼0.2 to ∼5.0 L/day, whereas the drinking rates required to prevent significant dehydration ranged from 0 to 1.4 L/hr. The characterization of sweat losses, sweat rate, and required drinking among runners in this study indicate wide individual variability that warrants personalized hydration practices, particularly when running is prolonged (>60 min) and performance is important. This study may serve as a useful guidepost for sports dietitians when planning and communicating fluid needs to athletes, as well as complement guidance related to both personalized programmed and thirst-driven drinking strategies.

Background: A historical turning point occurred in the treatment of diarrhea when it was discovered that glucose could enhance intestinal sodium and water absorption. Adding glucose to salt water (oral rehydration solution, ORS) more efficiently replaced intestinal water and salt losses., Aim: Provide a novel hypothesis to explain why mainstream use of ORS has been strongly recommended, but weakly adopted., Methods: Traditional (absorptive) and novel (secretory) physiological functions of glucose in an ORS were reviewed., Results: Small amounts of glucose can stimulate both intestinal absorption and secretion. Glucose can exacerbate a net secretory state and may aggravate pathogen-induced diarrhea, particularly for pathogens that affect glucose transport., Conclusion: A hypothesis is made to explain why glucose-based ORS does not appreciably reduce diarrheal stool volume and why modern food science initiatives should focus on ORS formulations that replace water and electrolytes while also reducing stool volume and duration of diarrhea.

Purpose: This study aimed to compare the wet bulb globe temperature (WBGT) index and other environmental parameters between early and late Boston Marathon race start times from 1995 to 2016., Methods: Environmental data from 1995 to 2016 (excluding 1996) were used to compare two identical time frames using the 0900-1300 h start versus the 1100-1500 h start. This included the WBGT, dry bulb (Tdb), black globe (Tbg), wet bulb (Twb), solar radiation, relative humidity, and air water vapor pressure. To make comparisons between start times, the difference in the area under the curve (AUC) for each environmental variable was compared within each year with a Wilcoxon signed rank test with a Holm-Bonferroni correction., Results: AUC exposures for WBGT (P = 0.027), Twb (P = 0.031), Tdb (P = 0.027), Tbg (P = 0.055), and solar radiation (P = 0.004) were reduced with an earlier start, whereas those for relative humidity and air water vapor pressure were not. Overall, an earlier race start time by 2 h (0900 vs 1100 h) reduced the odds of experiencing a higher flag category 1.42 times (β = 0.1744, P = 0.032)., Conclusions: The 2007 decision to make the Boston Marathon start time earlier by 2 h has reduced by ~1.4 times the odds that runners will be exposed to environmental conditions associated with exertional heat illness., (Copyright © 2021 by the American College of Sports Medicine.)

It is well appreciated that a loss of body water (dehydration) can impair endurance performance and that the effect is magnified by environmental heat stress. A majority of professional sports medicine and nutrition organizations recommend drinking during exercise to replace sweat losses and prevent dehydration, while also avoiding frank over-hydration. Knowledge of sweating rate, which is highest in the heat for any given metabolic rate, is therefore considered key to developing a sound drinking strategy. Exercise duration and the provision of liquid fuel interacts with required drink volumes in important ways that are infrequently discussed but are of utmost practical concern. This review details some challenges related to the optimized coupling of fluid and fuel needs during prolonged exercise in the heat and the need for personalization., (Copyright © 2021. Published by Elsevier Ltd.)

This study tested the accuracy of a novel, limited-availability web application (H 2 Q™) for predicting sweat rates in a variety of sports using estimates of energy expenditure and air temperature only. The application of predictions for group water planning was investigated for soccer match play. Fourteen open literature studies were identified where group sweat rates were reported (n = 20 group means comprising 230 individual observations from 179 athletes) with fidelity. Sports represented included: walking, cycling, swimming, and soccer match play. The accuracy of H 2 Q™ sweat rates was tested by comparing to measured group sweat rates using the concordance correlation coefficient (CCC) with 95% confidence interval [CI]. The relative absolute error (RAE) with 95% [CI] was also assessed, whereby the mean absolute error was expressed relative to an acceptance limit of 0.250 L/h. The CCC was 0.98 [0.95, 0.99] and the RAE was 0.449 [0.279, 0.620], indicating that the prediction error was on average 0.112 L/h. The RAE was < 1.0 for 19/20 observations (95%). Drink volumes modeled as a proxy for sweat losses during soccer match play prevented dehydration (< 1% loss of body mass). The H 2 Q™ web application demonstrated high group sweat prediction accuracy for the variety of sports activities tested. Water planning for soccer match play suggests the feasibility of easily and accurately predicting sweat rates to plan group water needs and promote optimal hydration in training and/or competition., Competing Interests: Author SNC is the owner of Sports Science Synergy, LLC and creator of the H2Q™ web application (patent pending). Author LBB is employed by PepsiCo, Inc. The soccer pilot study was funded by the Gatorade Sports Science Institute, a division of PepsiCo, Inc. The views expressed in this article are those of the authors and do not necessarily reflect the position or policy of PepsiCo, Inc., (Copyright © Biology of Sport 2021.)

Background: Neuroendocrine tumors, although relatively rare in incidence, are now the second most prevalent gastrointestinal neoplasm owing to indolent disease biology. A small but significant sub-group of neuroendocrine tumor patients suffer from diarrhea. This is usually secondary to carcinoid syndrome but can also be a result of short gut syndrome, bile acid excess or iatrogenic etiologies. Recently, an amino acid based oral rehydration solution (enterade® Advanced Oncology Formula) was found to have anti-diarrheal properties in preclinical models., Methods: A retrospective chart review of all NET patients treated with enterade® AO was performed after IRB approval., Results: Ninety-eight NET patients who had received enterade® AO at our clinic from May 2017 through June 2019 were included. Patients (N = 49 of 98) with follow up data on bowel movements (BMs) were included for final analysis. Eighty-four percent of patients (41/49) had fewer BMs after taking enterade® AO and 66% (27/41) reported more than 50% reduction in BM frequency. The mean number of daily BMs was 6.6 (range, 3-20) at baseline before initiation of therapy, while the mean number of BMs at 1 week time point post enterade® AO was 2.9 (range, 0-11)., Conclusions: Our retrospective observations are encouraging and support prospective validation with appropriate controls in NET patients. This is first published report of the potential anti-diarrheal activity of enterade® AO in NET patients.

Purpose: This study aimed to characterize HTT specificity and to determine any effect of HA on the outcome., Methods: Thirteen unacclimatized, healthy men (V˙O2peak, 43.0 ± 4.8 mL·kg-1⋅min-1) with no previous history of heat illness completed 8 d of HA using the HTT protocol (40°C/40% RH; 120 min; 5 km·h-1 and 2% grade). Heart rate (HR) and core temperature (Tcore) recorded every 5 min during exercise and at the end of 120 min (terminal value) were compared between days 1 and 8. Test specificity (given no previous history of heat illness, the probability of being heat tolerant) was calculated on days 1 and 8., Results: There was a significant reduction in HR and Tcore between days 1 and 8, indicating successful HA. All volunteers successfully completed 120 min of walking on all days. HTT specificity ranged between 54% and 85% on day 1 and between 77% and 92% on day 8, depending on the HTT criteria used., Conclusion: Young healthy men without any previous heat illness experienced a 15% to 46% false-positive fail rate for the HTT without HA. After HA, the false-positive fail rate decreased to between 8% and 13%. Outcomes of the HTT are significantly affected by the criteria used and by HA status. The use of HTT for RTA decisions should be done with the recognition of these effects., (Copyright © 2020 by the American College of Sports Medicine.)

High-dose chemotherapy frequently causes injury to the gastrointestinal mucosa, resulting in diarrhea. The purpose of the current study was to assess the tolerability and efficacy of enterade® in reducing ≥ grade 2 diarrhea (G2D) in association with high-dose melphalan followed by autologous stem cell transplantation (ASCT). We conducted a prospective, double blinded, multi-center trial in which 114 subjects were randomized to receive enterade® or placebo twice daily during the transplant hospitalization. Gastrointestinal toxicities (nausea, vomiting, oral mucositis and dysphagia) resulted in poor study compliance in both arms. Among subjects who were able to complete planned therapy (13%), the incidence of G2D was lower for those receiving enterade® as compared to placebo (16% vs 86%, p <0.03). Twice daily oral administration of enterade® and placebo following high-dose chemotherapy and ASCT was not feasible due to significant gastrointestinal toxicities.  Future explorations of enterade® should be conducted in populations capable of reasonable oral intake., .

This proof-of-concept study used a web application to predict runner sweat losses using only energy expenditure and air temperature. A field study (FS) of n = 37 runners was completed with n = 40 sweat loss observations measured over 1 h (sweat rate, SR). Predictions were also compared with 10 open literature (OL) studies in which individual runner SR was reported ( n = 82; 109 observations). Three prediction accuracy metrics were used: for FS, the mean absolute error (MAE) and concordance correlation coefficient (CCC) were calculated to include a 95% confidence interval [CI]; for OL, the percentage concordance (PC) was examined against calculation of accumulated under- and over-drinking potential. The MAE for FS runners was 0.141 kg [0.105, 0.177], which was less than estimated scale weighing error on 85% of occasions. The CCC was 0.88 [0.82, 0.93]. The PC for OL was 96% for avoidance of both under- and over-drinking and 93% overall. All accuracy metrics and their CIs were below acceptable error tolerance. Input errors of ±10% and ±1 °C for energy expenditure and air temperature dropped the PC to between 84% and 90%. This study demonstrates the feasibility of accurately predicting SR from energy expenditure and air temperature alone. Novelty Results demonstrate that accurate runner SR prediction is possible with knowledge of only energy expenditure and air temperature. SR prediction error was smaller than scale weighing error in 85% of observations. Accurate runner SR prediction could help mitigate the common risks of over- and under-drinking.

Purpose: It is often assumed that a person with a higher mean skin temperature (Tsk) will sweat more during exercise. However, it has not yet been demonstrated whether Tsk describes any individual variability in whole-body sweat rate (WBSR) independently of the evaporative requirement for heat balance (Ereq)., Methods: One hundred forty bouts of 2-h treadmill walking completed by a pool of 21 participants (23 ± 4 yr, 174 ± 8 cm, 76 ± 11 kg, 1.9 ± 0.2 m) under up to nine conditions were analyzed. Trials employed varying rates of metabolic heat production (Hprod; 197-813 W), and environmental conditions (15°C, 20°C, 25°C, 30°C; all 50% relative humidity), yielding a wide range of Ereq (86-684 W) and Tsk values (26.9°C-34.4°C)., Results: The individual variation observed in WBSR was best described using Ereq (in watts; R = 0.784) as a sole descriptor, relative to Ereq (in watts per meter squared; R = 0.735), Hprod (in watts; R = 0.639), Hprod (in watts per meter squared; R = 0.584), ambient air temperature (Ta) (R = 0.263), and Tsk (R = 0.077; all, P < 0.001). A multiple stepwise linear regression included only Ereq (in watts; adjusted R = 0.784), with Tsk not significantly correlating with the residual variance (P = 0.285), independently of Ereq (in watts). Hprod (in watts) had similar predictive strength to Ereq (in watts) at a fixed air temperature, explaining only 5.2% at 30°C, 4.9% at 25°C, 2.7% at 20°C, and 0.5% at 15°C (all, P < 0.001) less variance in WBSR compared with Ereq. However, when data from all ambient temperatures were pooled, Hprod alone was a markedly worse predictor of WBSR than Ereq (R = 0.639 vs 0.784; P < 0.001)., Conclusions: Ereq (in watts) explained approximately four-fifths of the individual variation in WBSR over a range of ambient temperatures and exercise intensities, whereas Tsk did not explain any residual variance independently of Ereq.

Selecting the most appropriate performance test is critical in detecting the effect of an intervention. In this investigation we 1 ) used time-trial (TT) performance data to estimate sample size requirements for test selection and 2 ) demonstrated the differences in statistical power between a repeated-measures ANOVA (RM-ANOVA) and analysis of covariance (ANCOVA) for detecting an effect in parallel group design. A retrospective analysis of six altitude studies was completed, totaling 105 volunteers. We quantified the test-retest reliability [i.e., intraclass correlation coefficient (ICC) and standard error of measurement (SEM)] and then calculated the standardized effect size for a 5-20% change in TT performance. With these outcomes, a power analysis was performed and required sample sizes were compared among performance tests. Relative to TT duration, the 11.2-km run had the lowest between-subject variance, and thus greatest statistical power (i.e., required smallest sample size) to detect a given percent change in performance. However, the 3.2-km run was the most reliable test (ICC: 0.89, SEM: 81 s) and thus better suited to detect the smallest absolute (i.e., seconds) change in performance. When TT durations were similar, a running modality (11.2-km run; ICC: 0.83, SEM: 422 s) was far more reliable than cycling (720-kJ cycle; ICC: 0.77, SEM: 480 s). In all scenarios, the ANCOVA provided greater statistical power than the RM-ANOVA. Our results suggest that running tests (3.2 km and 11.2 km) using ANCOVA analysis provide the greatest likelihood of detecting a significant change in performance response to an intervention, particularly in populations unaccustomed to cycling. NEW & NOTEWORTHY This is the first investigation to utilize time-trial (TT) data from previous studies in simulations to estimate statistical power. We developed an easy-to-use decision aid detailing the required sample size needed to detect a given change in TT performance for the purpose of test selection. Furthermore, our detailed methods can be applied to any scenario in which there is an impact of a stressor and the desire to detect a treatment effect.

The purpose of this theoretical study was to estimate the effects of body size and countermeasure (CM) exercise in an all-male crew composed of individuals drawn from a height range representative of current space agency requirements upon total energy expenditure (TEE), oxygen (O 2 ) consumption, carbon dioxide (CO 2 ) and metabolic heat (H prod ) production, and water requirements for hydration, during space exploration missions. Using a height range of 1.50- to 1.90-m, and assuming geometric similarity across this range, estimates were derived for a four-person male crew (age: 40-years; BMI: 26.5-kg/m 2 ; resting VO 2 and VO 2max : 3.3- and 43.4-mL/kg/min) on 30- to 1,080-d missions, without and with, ISS-like CM exercise (modelled as 2 × 30-min aerobic exercise at 75% VO 2max , 6-d/week). Where spaceflight-specific data/equations were not available, terrestrial data/equations were used. Body size alone increased 24-h TEE (+ 44%), O 2 consumption (+ 60%), CO 2 (+ 60%) and H prod (+ 60%) production, and water requirements (+ 19%). With CM exercise, the increases were + 29 to 32%, + 31%, + 35%, + 42% and + 23 to 33% respectively, across the height range. Compared with a 'small-sized' (1.50-m) crew without CM exercise, a 'large-sized' (1.90-m) crew exercising would require an additional 996-MJ of energy, 52.5 × 10 3 -L of O 2 and 183.6-L of water, and produce an additional 44.0 × 10 3 -L of CO 2 and 874-MJ of heat each month. This study provides the first insight into the potential implications of body size and the use of ISS-like CM exercise upon the provision of life-support during exploration missions. Whilst closed-loop life-support (O 2 , water and CO 2 ) systems may be possible, strategies to minimize and meet crew metabolic energy needs, estimated in this study to increase by 996-MJ per month with body size and CM exercise, are required.

In order to inform the Athlete Biological Passport (ABP), this study determined whether the elevation in hemoglobin (Hb) following intracellular or extracellular dehydration would trigger an atypical passport finding (ATPF). Seven male and three female volunteers (age: 23 ± 4 y; height: 170 ± 8 cm; body mass: 78 ± 12 kg) were carefully euhydrated (EUH) to determine baseline Hb levels. Volunteers then completed both an exercise-induced sweating dehydration (SW) protocol and a diuretic-induced dehydration (DI) protocol. Dehydration was assessed via body mass changes and Hb was measured via a bench-top automated hematology analyzer. Using the ABP module, the expected baseline range for each individual was determined using EUH trials, and the impact of each dehydration protocol was then assessed in comparison with these thresholds. Volunteers lost on average 3.1% and 3.7% body mass in the SW and DI trials, respectively. While only one subject exceeded the upper threshold following DI dehydration, six additional subjects demonstrated highly unusual ABP profiles; this was not the case for SW. Sweating is not a feasible explanation for elevated Hb during ABP testing; however, recent illness such as secretory diarrhea, which is mimicked by diuretic administration, may be capable of producing elevated Hb in athletes' biological passports., (© 2020 John Wiley & Sons, Ltd.)

Purpose: There is growing interest in the measurement of plasma levels of arginine vasopressin (AVP) for the assessment of mild dehydration. However, the principles of biological variation have not been applied to the study of AVP and understanding biological variation of AVP may provide insights regarding measurement thresholds. The purpose of this investigation was to determine the biological variation of AVP in healthy euhydrated individuals to understand the potential for establishing both static and/or change thresholds of importance., Methods: We studied 29 healthy volunteers (24 men and 5 women) while controlling for hydration and pre-analytical factors. All subjects completed between 2-8 trials where biological variation was determined using widely published methods. We determined the intraindividual, interindividual, and analytical coefficients of variation (CV I , CV G , and CV A , respectively) and subsequently the index of individuality and heterogeneity (II and IH, respectively)., Results: AVP did not reach the IH threshold required to be considered useful in the dynamic assessment of physiological deviations from normal. AVP levels approached the II threshold required to be considered useful in the static assessment of physiological deviations from normal., Conclusions: This analysis demonstrates that AVP assessment is unlikely to yield useful information about hydration status.

Purpose: Resting measures of ventilation and gas exchange are impacted by a variety of physiological stressors, such as those resulting from a research intervention or an extreme environment. However, the biological variation of these parameters, an important statistical consideration for identifying a meaningful physiological change, has not been quantified., Methods: We performed a retrospective analysis of 21 studies completed by the U.S. Army Research Institute of Environmental Medicine (USARIEM) from 1985 to present, totaling 411 healthy volunteers. First, we determined the intraindividual, interindividual, and analytic coefficients of variation (CV I , CV G , and CV A , respectively) and subsequently the index of individuality and heterogeneity (II and IH, respectively). Second, when deemed appropriate via these outcomes, we defined the accompanying static and dynamic thresholds, beyond which a significant deviation from normal is indicated., Results: End-tidal partial pressure of oxygen (P ET O 2 ) and the respiratory exchange ratio (RER) approached the II threshold required to be considered useful in the static assessment of physiological deviations from normal. P ET O 2 and peripheral oxygen saturation (SpO 2 ) approached the IH threshold required to be considered useful in the dynamic assessment of physiological deviations from normal., Conclusions: This analysis identifies RER and P ET O 2 as parameters that might be most useful when aiming to identify a meaningful ventilatory change following a research intervention or stressor. Alternatively, other parameters of ventilation and gas exchange, such as P ET CO 2 and V E , may be less useful for observing an anticipated physiological change.

Introduction: Precipitating factors that contribute to the severity of exertional heat stroke (EHS) are unclear. The purpose of this study was to determine the effect of prior illness (PI) on EHS severity., Methods: We performed a retrospective clinical record review of 179 documented cases of EHS at the Marine Corps Base in Quantico, Virginia., Results: Approximately 30% of EHS cases had a medically documented PI. Anthropometrics (height, weight, body mass index) and commonly associated risk factors for EHS (age, number of days in training, wet bulb globe temperature, sleep patterns) did not differ between PI and no illness (NI) groups. PI patients presented with higher maximal rectal core temperatures (40.6 ± 1.0°C vs. 40.3 ± 1.2°C; P = 0.0419), and elevated pulse rates (118.1 ± 16.7 bpm vs. 110.5 ± 24.2 bpm; P = 0.0397). At the point of care, biomarker values were similar between PI and NI groups, with the exception of a trend toward elevated monocytes in those with PI (7.9 ± 2.9% vs 6.7± 2.7%; P = 0.0521). Rate and duration of cooling were similar between PI and NI patients., Conclusion: This study indicates that PI has a minimal effect on the patient presentation, severity and treatment outcome of EHS. The results of this study have important implications for military, civilian, and occupational populations who are at risk for EHS., Competing Interests: The authors have declared that no competing interests exist.

Oral rehydration solutions (ORS) are specifically formulated with an osmolality to optimize fluid absorption. However, it is unclear how many ORS products comply with current World Health Organization (WHO) osmolality guidelines and the osmotic shelf-life stability is not known. Therefore, the purpose of this investigation was to examine the within and between ORS product osmolality variation in both pre-mixed and reconstituted powders. Additionally, the osmotic stability was examined over time. The osmolality of five different pre-mixed solutions and six powdered ORS products were measured. Pre-mixed solutions were stored at room temperatures and elevated temperatures (31 °C) for two months to examine osmotic shelf stability. Results demonstrated that only one pre-mixed ORS product was in compliance with the current guidelines both before and after the prolonged storage. Five of the six powdered ORS products were in compliance with minimal inter-packet variation observed within the given formulations. This investigation demonstrates that many commercially available pre-mixed ORS products do not currently adhere to the WHO recommended osmolality guidelines. Additionally, due to the presence of particular sugars and possibly other ingredients, the shelf-life stability of osmolality for certain ORS products may be questioned. These findings should be carefully considered in the design of future ORS products.

The average environmental and occupational physiologist may find statistics are difficult to interpret and use since their formal training in statistics is limited. Unfortunately, poor statistical practices can generate erroneous or at least misleading results and distorts the evidence in the scientific literature. These problems are exacerbated when statistics are used as thoughtless ritual that is performed after the data are collected. The situation is worsened when statistics are then treated as strict judgements about the data (i.e., significant versus non-significant) without a thought given to how these statistics were calculated or their practical meaning. We propose that researchers should consider statistics at every step of the research process whether that be the designing of experiments, collecting data, analysing the data or disseminating the results. When statistics are considered as an integral part of the research process, from start to finish, several problematic practices can be mitigated. Further, proper practices in disseminating the results of a study can greatly improve the quality of the literature. Within this review, we have included a number of reminders and statistical questions researchers should answer throughout the scientific process. Rather than treat statistics as a strict rule following procedure we hope that readers will use this review to stimulate a discussion around their current practices and attempt to improve them. The code to reproduce all analyses and figures within the manuscript can be found at https://doi.org/10.17605/OSF.IO/BQGDH., (© 2019 Informa UK Limited, trading as Taylor & Francis Group.)

Background: The beverage hydration index (BHI) is a composite measure of fluid balance after consuming a test beverage relative to water. BHI is a relatively new measure that has been explored in young, but not yet older, adults., Objective: The aim of this study was to investigate potential differences in BHI between euhydrated younger and older adults after drinking 4 different commercial beverages. We hypothesized that 1) older subjects would remain in positive fluid balance longer than young subjects after ingestion of each test beverage due to decreased urinary excretion rates, 2) glucose (glu)- and amino acid (AA)-based hydration beverages with sodium would have a BHI greater than water in both groups, and 3) the traditional 2-h postingestion BHI may be inappropriate for older adults., Methods: On 5 separate visits, 12 young (23 ± 3 yr, 7 M/5F) and 12 older (67 ± 6 yr, 5 M/7F) subjects consumed 1 L of distilled water, G-20 (6% CHO, 20 mmol/L Na+), G-45 (2.5% CHO, 45 mmol/L Na+), AA-30 (5 AAs, 30 mmol/L Na+), or AA-60 (8 AAs, 60 mmol/L Na+) over 30 min. Blood and urine samples were collected before ingestion and at 0, 60, 120, 180, and 240 min postingestion with additional venous blood sampling at 5, 10, 15, and 30 min postingestion., Results: In young subjects, BHI increased with increasing beverage Na+ concentration, and AA-60 had the highest BHI (AA-60 = 1.24 ± 0.10 compared with water = 1.00, P = 0.01). For older subjects, BHI was highest in AA-30 (AA-30; 1.20 ± 0.13 compared with water, P < 0.01) and was still in flux beyond 2 h in AA-60 (P < 0.05)., Conclusions: Beverage Na+ content progressively increased BHI in young adults independent of glucose or AA content. For older adults, the AA-30 beverage had the highest BHI. A 4-h BHI may be more appropriate for older adults due to attenuated urine excretion rates. This trial was registered at clinicaltrials.gov as NCT03559101., (Copyright © American Society for Nutrition 2019.)

Water planning is an important risk management concern for road race event organizers., Purpose: To compare water and cup prediction outputs from a mobile application (app) planning tool against: 1) measured group sweat losses, 2) documented event water and cup usage, and 3) traditional mathematical planning solutions., Methods: Group mean sweating rates (L·h) from 12 published outdoor running studies were each compared to 12 composite averages using the Road Race Water Planner© (RRWP) app. Estimated water (gallons) and cup (number) needs were also compared with documented usage at a large marathon event and to traditional mathematical solutions., Results: Thirteen group mean sweating rates from 286 runners were compared to composite RRWP estimates. Predicted sweating rate accuracy was 92% for RRWP and ranged from 0% to 69% for traditional mathematical solutions. The 2017 Boston marathon included 27,222 runners on a day averaging 21.5°C. Water and cup usage was 31,740 gallons and 1,036,003 cups, respectively. The RRWP estimates were 33,505 gallons and 1,072,160 cups, respectively. The difference in gallons expressed as liters was 0.236 L per person. For an approximately 4-h marathon, the difference per person as a rate was <60 mL·h. The difference in cups was a 3.5% error. All traditional solutions gave inferior estimates to RRWP due to large errors related to fluctuations in weather, as well as complications related to water station numbers., Conclusions: The results of the RRWP analysis indicate that it can provide event organizers with a valid, quantitative way to narrow the uncertainties of water planning related to changes in participant numbers, race distance, and weather. "Rule of thumb" alternatives are also discussed.

Aging is associated with altered water, electrolyte, and glucose handling. Alternative beverages to those containing carbohydrate (CHO) should be considered for older adults. We hypothesized that reduced sodium (CNa + ) and/or water (CH 2 O) clearance would underlie greater beverage retention in older compared with young adults, secondary to reduced glomerular filtration rate (GFR). We further hypothesized that amino acid (AA)- and CHO-based beverages would promote retention better than water. Over five visits, 12 young (23 ± 3 yr; 7 men, 5 women) and 12 older (67 ± 6 yr; 5 men, 7 women) subjects consumed 1 liter of distilled water or beverages with 6% CHO, 0.46 g/l Na + [Gatorade (GAT)]; 2.5% CHO, 0.74 g/l Na + [Pedialyte (PED)]; 5 AA, 1.04 g/l Na + [enterade (ENT)-5]; or 8 AA, 1.38 g/l Na + (ENT-8) over 30 min. Blood and urine were collected every hour for 4 h after ingestion; retention, CH 2 O, and CNa + were calculated at 2 and 4 h. Additional calculations adjusted CH 2 O and CNa + for estimated GFR (eGFR). Water yielded the lowest retention in both groups ( P ≤ 0.02). Retention was higher in older vs. young adults except for ENT-8 at 4 h ( P = 0.73). CH 2 O was higher for older vs. young adults for GAT at 2 h ( P < 0.01) and GAT and PED at 4 h ( P < 0.01) after ingestion but was otherwise similar between groups. CNa + was lower in older vs. young adults except for ENT-8 ( P ≥ 0.19). Adjusting for eGFR resulted in higher CH 2 O for all beverages in older vs. young adults ( P < 0.05) but did not influence CNa + . Older adults may better retain beverages with less Na + than young adults because of reduced CNa + . AA- and CHO-based electrolyte-rich beverages may similarly promote beverage retention. NEW & NOTEWORTHY Commercially available amino acid (AA)-containing beverages may provide an alternative to traditional carbohydrate (CHO)-containing beverages, particularly for older adults with attenuated water, electrolyte, and glucose handling. We compared beverage retention and free water and sodium clearance between young and older adults after ingestion of water, two CHO-based beverages, and two AA-based beverages. Our data suggest that older adults better retain beverages with less sodium compared with young adults and that AA-based and CHO-based electrolyte-containing beverages similarly promote retention.

The 2019 International Amateur Athletics Federation Track-and-Field World Championships will take place in Qatar in the Middle East. The 2020 Summer Olympics will take place in Tokyo, Japan. It is quite likely that these events may set the record for hottest competitions in the recorded history of both the Track-and-Field World Championships and Olympic Games. Given the extreme heat in which track-and-field athletes will need to train and compete for these games, the importance of hydration is amplified more than in previous years. The diverse nature of track-and-field events, training programs, and individuality of athletes taking part inevitably means that fluid needs will be highly variable. Track-and-field events can be classified as low, moderate, or high risk for dehydration based on typical training and competition scenarios, fluid availability, and anticipated sweat losses. This paper reviews the risks of dehydration and potential consequences to performance in track-and-field events. The authors also discuss strategies for mitigating the risk of dehydration.

Background: Small sample volumes may artificially elevate plasma osmolality (Posm) measured by freezing point depression. The purpose of this study was to compare two widely different sample volumes of measured Posm (mmol/kg) to each other, and to calculated osmolarity (mmol/L), across a physiological Posm range (~50 mmol/kg)., Methods: Posm was measured using freezing point depression and osmolarity calculated from measures of sodium, glucose, and blood urea nitrogen. The influence of sample volume was investigated by comparing 20 and 250 μL Posm samples (n = 126 pairs). Thirty-two volunteers were tested multiple times while EUH (n = 115) or DEH (n = 11) by -4.0% body mass. Protinol™ (240, 280, and 320 mmol/kg) and Clinitrol™ (290 mmol/kg) reference solutions were compared similarly (n = 282 pairs)., Results: The 20 μL samples of plasma showed a 7 mmol/kg positive bias compared to 250 μL samples and displayed a nearly constant proportional error across the range tested (slope = 0.929). Calculated osmolarity was lower than 20 μL Posm by the same negative bias (-6.9 mmol/kg) but not different from 250 μL Posm (0.1 mmol/kg). The differences between 20 and 250 μL samples of Protinol™ were significantly higher than Clinitrol™., Conclusions: These results demonstrate that Posm measured by freezing point depression will be ~7 mmol/kg higher when using 20 μL vs 250 μL sample volumes. Approximately half of this effect may be due to plasma proteins. Posm sample volume should be carefully considered when calculating the osmole gap or assessing hydration status., (© 2018 The Authors Journal of Clinical Laboratory Analysis Published by Wiley Periodicals, Inc.)

Exercise or work in hot environments increases susceptibility to exertional heat illnesses such as exertional heat stroke (EHS). EHS occurs when body heat gain exceeds body heat dissipation, resulting in rapid body heat storage and potentially life-threatening consequences. EHS poses a dangerous threat for athletes, agriculture workers, and military personnel, as they are often exposed to hot environmental conditions that restrict body heat loss or contribute to body heat gain. Currently, there is limited guidance on return to activity (RTA) after an episode of EHS. While examining biomarkers in the blood is thought to be beneficial for determining RTA, they are not sensitive or specific enough to be a final determining factor as organ damage may persist despite blood biomarkers returning to baseline levels. As such, additional assessment tests to more accurately determine RTA are desired. One method used for determining RTA is the heat tolerance test (HTT, 120 minutes treadmill walking; 40°C, 40% relative humidity). Unfortunately, the HTT provides even less information about EHS recovery since it offers no test sensitivity or specificity even after years of implementation. We provide an overview of the HTT and the controversy of this test with respect to assessment criteria, applicability to tasks involving high metabolic workloads, and the lack of follow-up analyses to determine its accuracy for determining recovery in order to diminish the likelihood of a second EHS occurrence.

Background: The efficacy of different commercial beverage compositions for meeting oral rehydration therapy (ORT) goals in the treatment of acute dehydration in healthy humans has not been systematically tested. The objective of the study was to compare fluid retention, plasma volume (PV), and interstitial fluid (ISF) volume restoration when using 1 popular glucose-based and 1 novel amino acid-based (AA) commercial ORT beverage following experimental hypertonic or isotonic dehydration., Methods: Twenty-six healthy adults (21 males, 5 females) underwent either a controlled bout of hypertonic (n = 13) or isotonic (n = 13) dehydration (3%-4% body mass) via eccrine or renal body water and electrolyte losses induced using exercise-heat stress (EHS) or Lasix administration (LAS), respectively. Rehydration was achieved over 90 minutes by matching fluid intake to water losses (1:1) using a sports drink (SP) or AA commercial ORT beverage. Fluid retention (water and electrolytes), PV, and ISF volume changes were tracked for 180 minutes., Results: AA produced significantly (P <0.05) greater fluid retention (75% vs 57%), ISF volume restoration, and tended (P = 0.06) to produce greater PV restoration in trial EHS. In trial LAS, neither beverage exceeded 65% retention, but AA replaced electrolytes and preserved ISF volume better than SP (P <0.05)., Conclusion: The results of this study demonstrate superior rehydration when using AA compared with SP for both hypertonic and isotonic dehydration., (© 2018 American Society for Parenteral and Enteral Nutrition.)

Background: Fluid intake during military training is prescribed based on the interactions among work rates, environmental conditions, and uniform configurations. The efficacy of this guidance has not been empirically assessed in over a decade. To determine the acceptability of the fluid intake guidance, sweat losses were measured in a variety of conditions with modern uniform/body armor configurations and were then compared to prescribed fluid intakes for each condition (workload, environment, clothing)., Methods: Whole body sweat losses of 324 Soldiers and 14 model simulations were measured under a variety of work intensities ((Watts) easy, moderate, hard), work durations (2-25 h), environmental conditions (White-Black flag), and uniform configurations (including Army Combat Uniform and body armor). Whole body sweat losses were then calculated relative to 4 h drinking guidance and in accordance with TB MED 507 recommended work/rest ratios. The differences between the prescribed fluid intake and sweat loss were calculated and expressed as a percent loss or gain of body weight. Values within a threshold of ±2% body water flux (BWF) were deemed an acceptable conservative starting point for performance and health concerns., Findings: Values within ±2% BWF numbered 309/338; 25 of 338 observations exceeded the +2% BWF while 4 of 338 observations exceeded the -2% BWF. When total fluid restriction was simulated, all experienced body weight loss with 151 of 338 observations exceeding the -2% BWF., Discussion: When calculated using actual measured sweating rates from the laboratory and model simulations, current fluid intake guidance appears to predict with 91.4% accuracy the volume of fluid required to maintain a proper euhydrated state (±2%) during 4 h of exercise. Simulations of total fluid restriction support the necessity for fluid intake guidance so that the Warfighter's performance does not degrade. It is recommended that the current military fluid intake guidance focuses on methods for accurately tracking fluid intakes., (Published by Oxford University Press on behalf of Association of Military Surgeons of the United States 2018.)

Heat acclimation is the best strategy to improve performance in a hot environment. Many athletes seeking the benefits of heat acclimation lack access to a hot environment for exercise and, thus, rely on overdressing to simulate environmental heat stress. It is currently unknown whether this approach produces the requisite thermoregulatory strain necessary for heat acclimation in trained men and women., Purpose: To compare physiological and cellular responses to exercise in a hot environment (HOT; 40°C, 30% RH) with minimal clothing (clo = 0.87) and in a temperate environment (CLO; 15°C, 50% RH) with overdressing (clo = 1.89) in both men and women., Methods: HR, rectal temperature (Tre), mean skin temperature (Tsk), sweating rate (SR), and extracellular heat shock protein (eHSP)72 were measured in 13 (7 males, 6 females) well-trained runners (V˙O2max: 58.7 ± 10.7 mL·kg·min) in response to ~60 min of treadmill running at 50%-60% V˙O2max in HOT and CLO., Results: Tre increased in both conditions, but the increase was greater in HOT (ΔTre HOT: 2.6°C ± 0.1°C; CLO 2.0°C ± 0.1°C; P = 0.0003). SR was also higher in HOT (1.41 ± 0.1 L h; CLO: 1.16 ± 0.1 L·h; P = 0.0001). eHSP72 increased in HOT (% change: 59% ± 11%; P = 0.03) but not in CLO (6% ± 2%; P = 0.31). Mean Tsk and HR were not different between HOT and CLO in men but were higher in HOT for women., Conclusion: These data support the idea that overdressing during exercise in a temperate environment may produce the high Tre, Tsk, HR, and SR necessary for adaptation, but these responses do not match those in hot, dry environments. It is possible that greater exercise stimulus, warmer environment, or more clothing may be required to allow for a similar level of acclimation.

Background: The beverage hydration index (BHI) assesses the hydration potential of any consumable fluid relative to water. The BHI is a relatively new metric, and the impact of body mass, sex, and reproducibility has yet to be investigated., Objectives: To assess the independent impact of body mass and sex on BHI using beverages not previously assessed, including an amino acid-based oral rehydration solution (AA-ORS), a glucose-containing ORS (G-ORS), and a sports drink (SpD), compared with water (control). The reproducibility of the results was examined using statistical modeling (bootstrap analysis)., Design: Using a repeated-measures design, 40 euhydrated and fasted subjects (17 male, 23 female; urine specific gravity <1.025) were studied on 4 separate occasions. During each trial, subjects ingested 1 L of each beverage, and urine output was measured immediately postingestion and at 1-h intervals for the next 4 h. The BHI was calculated as a ratio of each individual's cumulative urine output after drinking 1 L of water over their cumulative urine output after drinking each of the test beverages., Results: The calculated mean ± SD BHIs of the beverages were as follows: water (1.0 ± 0.0), AA-ORS (1.15 ± 0.28), G-ORS (1.21 ± 0.28), and SpD (1.09 ± 0.26). The BHI for both AA-ORS and G-ORS was greater than that for water (P < 0.05). Despite overall differences in body mass, neither body mass nor sex independently affected BHI. Based upon statistical modeling, our results demonstrate excellent reproducibility of outcomes and external validity., Conclusions: Our results suggest that the BHI may be used and interpreted with confidence independently of body mass or sex. Furthermore, a novel carbohydrate-free AA-ORS and a traditional commercially available G-ORS were superior to water in optimizing hydration, whereas SpD was not. This trial was registered at clinicaltrials.gov as NCT03262597.

Purpose: This study aimed to investigate the effect of increasing external loads on 5-km treadmill time trial (TT) performance in 20°C and 40°C environmental conditions and to construct an ecologically relevant performance prediction decision aid., Methods: Twenty-six male and four female volunteers (age, 23.5 ± 6.9 yr; weight, 76.0 ± 8.9 kg; height, 1.75 ± 0.07 m; V˙O2peak, 50.7 ± 4.5 mL·kg·min) participated in a counterbalanced, mixed-model design, with each subject assigned to a load group (20%, 30%, or 50% body mass (BM); n = 10 per group). Volunteers performed three, self-paced 5-km familiarization TT (treadmill) without external load. Each volunteer then performed a 5-km TT in each environment with loads of either 20% (n = 10), 30% (n = 10), or 50% (n = 10) of BM., Results: 1) Loads of (20%, 30%, and 50% of BM) impaired 5-km TT performance compared with that when unloaded (P < 0.05); 2) the time penalties of the 20% and 30% load were <50% load (P < 0.05); 3) in all trials, the addition of heat exposure reduced 5-km TT performance beyond the penalty of load itself (P < 0.05); and 4) the combination of heat and 50% load resulted in a substantial penalty such that continuous work was not sustainable for all of the volunteers., Conclusions: Relative to prediction models using fixed or constant workload exercise trials, an ecologically valid decision aid was developed from self-paced data, in which pace (km·h) can be predicted for individual levels of heat, load, or heat + load in combination.