Samuel N. Cheuvront’s research while affiliated with AT Sciences LLC and other places

Objective The primary aim of this study was to assess the efficacy of the weight, urine, 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 days; Study 2, 35 participants for 7 days). Phase 2 entailed a two-hour passive heating protocol, where participants from Study 2 were randomly assigned to one of three groups that manipulated total body water over 24-hours 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-hour 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 change 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.

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 (D2O). Blood samples were collected pre-, 2-min, 5-min, and every 5-min until 60-min post-ingestion to quantify maximal D2O 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: D2O 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.

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.

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.

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 Tcorecritical 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, 8km time-trial) and soldiers in fully encapsulating personal protective equipment (PPE, N=8 male, 2km 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) with higher Tcore=40.1±0.4°C for ELITE vs 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 vs 9.0±2.5 vs; 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.

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.

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.