Exercise and Fluid Replacement

Impact of carbohydrate timing on glucose metabolism and substrate oxidation following high-intensity evening aerobic exercise in athletes: a randomized controlled study

OBJECTIVE

The study aimed to investigate the impact of nutrient timing in relation to evening exercise. Specifically, it examined the effects of pre- or post-exercise carbohydrate (CHO) ingestion on glucose metabolism, glucose regulation, and overall substrate oxidation in well-trained athletes during and after physical exercise (PE), spanning the nocturnal period and the subsequent morning.

METHODS

Ten male endurance cyclists participated in the study. The initial assessments included body composition measurements and an incremental cycle test to determine maximal oxygen uptake (V ˙ O2 max) and maximum power output (Wmax). Following this, participants underwent a control (rest previous day) oral glucose tolerance test (OGTT) and a familiarization exercise trial that had two objectives: (1) to establish the appropriate amount of CHO to use in the pre- or post-exercise drink during the experimental trials, and (2) to familiarize participants with the equipment and study protocol. In the three days prior to both the control and experimental trials, participants followed a standardized, individualized diet designed to meet their energy needs. During the experimental trials, participants completed two separate evening exercise sessions (50 min@70%Wmax +  ~24 min time-trial (TT)) with either pre- or post-exercise CHO ingestion (253 ± 52 g), matching the CHO oxidized during exercise. The CHO drink and a volume-matched placebo (PLA) drink (containing no energy) were randomly assigned to be consumed two hours before and directly after the experimental exercise sessions. Post-exercise nocturnal interstitial glucose levels (24:00-06:00) were continuously monitored, and a 120-min OGTT was conducted the following morning to assess substrate oxidation rates and glucose control.

RESULTS

Pre-exercise CHO intake significantly lowered capillary glucose levels during steady-state exercise (mean difference 0.41 ± 0.27 mmol/L, p = 0.001) without affecting perceived exertion and TT-performance. No difference was observed in nocturnal glucose regulation (00:00-06:00) regardless of whether CHO was consumed before or after exercise. Post-exercise CHO ingestion reduced glucose tolerance during the OGTT compared to the iso-caloric pre-exercise CHO intake (mean difference 0.76 ± 0.21 mmol/L, p = 0.017). However, a post-exercise CHO intake improved respiratory exchange ratio/metabolic flexibility (MetF) significantly. Enhanced MetF during the first OGTT hour after post-exercise CHO ingestion resulted in 70% and 91% higher CHO oxidation compared to pre-exercise CHO and control, respectively (p ≤ 0.029). Average 120-min OGTT fat oxidation rates were higher with both pre- and post-exercise CHO ingestion compared to control (p ≤ 0.008), with no difference between pre- and post-exercise CHO intake.

CONCLUSION

Morning glucose tolerance was markedly reduced in healthy athletes when CHO was ingested after evening exercise. However, the observed improvements in MetF during the OGTT compared to placebo post-exercise suggest a potential for enhanced athletic performance in subsequent exercise sessions. This opens exciting possibilities for future research to explore whether enhanced MetF induced by CHO-timing can translate to improved athletic performance, offering new avenues for optimizing training and performance.

Association between objectively assessed physical activity and kidney function among female agricultural workers in hot environments in Spain

BACKGROUND

Physical activity in hot environments has been associated with impaired kidney function. We aimed to quantify the association between occupational physical activity and kidney function over one work shift in female agricultural workers exposed to environmental heat.

METHODS

We measured occupational physical activity in female berry pickers in Huelva, Spain, using movement intensity, based on vector magnitude units (VMU), and heart rate (HR). For both, we calculated the mean (VMU_mean; HR_mean), standard deviation (VMU_sd; HR_sd), and 3-min 95th percentile (VMU_p95; HR_p95). Environmental heat in greenhouses was estimated using wet bulb globe temperature (WBGT). Kidney function and injury were quantified using pre- and post-shift differences in serum creatinine (SCr_dif), Cystatin C (Cystatin C_dif) and neutrophil gelatinase associated lipocalin (NGAL_dif), respectively. Acute Kidney Injury (AKI) was defined as an increase in post-shift serum creatinine of ≥0.3 mg/dl, or ≥1.5 times pre-shift levels. Heat strain was estimated using the ISO 7933:2004 index. We used linear and logistic regressions.

RESULTS

Ninety women aged 37.4 ± 5.7 years were exposed to a mean WBGT of 25.2 (±3.6)°C and light intensity physical activity (HR_mean of 94 (±9)bpm). Of those, 26 % experienced heat strain, 68 % were dehydrated, and 7 % presented with AKI at the end of the shift. Higher VMU_sd was associated with higher Scr_dif (β: 0.029 (95 % CI: 0.00; 0.058) and meeting the threshold for AKI (OR: 1.6 (95 % CI: 0.8; 3.2)). We observed higher NGAL_dif with higher VMU_mean (β: 1.944 (95 % CI: 0.139; 3.748)) per 100 VMU_mean increase. The positive association between HR_mean and SCr_dif was stronger among women with heat strain (interaction p = 0.033).

CONCLUSIONS AND RELEVANCE

In female harvest workers, high means and variations in VMU over a single one shift worked under hot conditions were associated with kidney injury, as assessed by urinary biomarkers, though there is limited evidence for any change in kidney function. Precautiously, large changes in physical activity intensity over one work shift should be avoided to protect from renal injury.

Electric fan-based cooling strategies to mitigate heat strain during prolonged heat exposure in young males

Prolonged exposure to hot-humid environments can elevate core temperature and induce severe cardiovascular strain, potentially triggering an inflammatory response. Electric fan use and cold water consumption are common cooling strategies to reduce core temperature, but it remains unclear whether combining these two can effectively alleviate heat strain during daylong exposure. This study aimed to evaluate the efficacy of combining fan use with cold drink or ice slurry intake in mitigating physiological responses and thermal perceptions during 8 h of heat exposure (36.5 °C, 57 % RH). Fourteen male participants were exposed to four conditions: (i) limited fluid intake (2.5 mL/kg/hour, Con), (ii) fan use with limited fluid intake (2.5 mL/kg/hour, Fan), (iii) fan use with full fluid intake (6 mL/kg/hour, Fan + Fluid), and (iv) fan use with full ice slurry intake (6 mL/kg/hour, Fan + Ice slurry). Body temperature, heart rate, blood pressure, sweat loss, blood immune cell counts, and thermal perceptions were measured. Fan significantly reduced core temperature, cardiovascular strain and immune cell counts after exposure compared to Con (all P < 0.05), but led to a higher dehydration rate (P < 0.001). Fan + Fluid exhibited significantly greater cooling effects across all measured parameters than Fan (all P < 0.01). Except for a lower skin temperature in Fan + Fluid (P < 0.01), no significant differences were found in the improvement of other parameters between Fan + Fluid and Fan + Ice slurry (all P > 0.05). This study demonstrates the effectiveness of fan use combined with full fluid intake in mitigating physiological strain during heatwaves, providing practical implications for public health policy.

The Addition of Glycerol and Sodium Chloride to a Hyperhydration Protocol Does Not Improve Half-Marathon Time-Trial Performance in Trained Runners in Warm Conditions

PURPOSE

We examined the effect of glycerol- and sodium-induced hyperhydration on a field-based half-marathon in warm conditions.

METHODS

Endurance runners (N = 13) completed a 180-minute hyperhydration (HYP) and control (CON) protocol before a maximal-effort half-marathon time trial (∼24 °C wet-bulb globe temperature) in a randomized crossover order. HYP involved ingesting 25 mL·kg body mass (BM)-1 fluid with glycerol (1.2 g·kg BM-1) and sodium chloride (7.5 g·L-1) in 4 equal boluses across 60 minutes, with CON matching fluid ingestion for volume and timing. Every 20 minutes, urine samples were analyzed for volume (UVol; in milliliters) and fluid retention (fluid ingested minus UVol; in milliliters), while gastrointestinal symptoms were recorded using a questionnaire. Changes in plasma volume were calculated from hematocrit and hemoglobin at baseline and every 60 minutes. Core temperature (gastrointestinal temperature) and heart rate were recorded during the half-marathon. Intervention effects were estimated using linear mixed models and are presented as mean differences with 95% CIs.

RESULTS

HYP increased fluid retention compared with CON by 1189 mL, 95% CI 987-1391 (P < .001), and plasma volume by 9.0%, 95% CI 3.6-14.4 (P = .001). However, there were no statistically significant differences in exercise performance, gastrointestinal symptoms, gastrointestinal temperature, and heart rate (P > .05 for mean values and at all time points).

CONCLUSIONS

Glycerol- and sodium-induced hyperhydration improved hydration status without changing gastrointestinal symptoms prior to endurance exercise in warm conditions but did not improve half-marathon performance. This strategy requires further investigation in environments with greater heat stress.

Effect of On-Duty Resistance Training Fatigue on Neuromuscular Function in Structural Firefighters

BACKGROUND

Participation in on-duty exercise is critical to enhance firefighter safety and readiness. However, these sessions are often interrupted with emergency responses and require firefighters to work in a fatigued state that may increase injury risk.

OBJECTIVE

To assess the impact of on-duty resistance training on neuromuscular function.

METHODS

A sample of 18 firefighters (Age: 38.8 ± 8.0 y; Body fat: 24.9 ± 7.0%) completed three testing sessions, separated by at least 72 h to compare the effects of circuit (CT) versus heavy resistance training (HRT) fatigue on neuromuscular function. During Session 1, anthropometrics and familiarization trials of balance and neuromuscular function were completed, which included single-leg drop landing (SLDL), postural sway (PS), and modified Functional Balance Test (mFBT). Sessions 2 and 3 were randomized, where participants completed either HRT or CT. Isometric midthigh pull (IMTP), long jump (LJ), and lower body power (LBP) tests were conducted pre- and immediately post exercise, whereas static and dynamic balance assessments were conducted pre- and 10 min post exercise to simulate an emergency response time course. Repeated measures ANOVA, effect sizes, and difference scores were used to analyze the effects of condition and time. The level of significance was set at p < 0.05.

RESULTS

CT decreased IMTP, LJ, and LBP, whereas HRT decreased LJ and LBP (p ≤ 0.001, ES ≥ 0.476). Despite several significant condition by time interaction effects on balance outcomes, there were no differences within CT or HRT over time (p ≥ 0.066).

CONCLUSIONS

These findings suggest that on-duty resistance training reduces firefighters' power and/or strength immediately post exercise but does not influence most firefighters' balance 10 min post exercise. Thus, firefighters are recommended to perform resistance training on-duty during low emergency call volume times.

Prolonged Humid Heat Triggers Systemic Inflammation and Stress Signaling: Fluid Intake Modulates NF-κB, p38, JNK2, and STAT3α Pathways

Prolonged exposure to extreme humid heat can induce systemic inflammation, organ stress, and hormonal imbalance. While fluid replacement is commonly recommended, its mechanistic efficacy under humid heat stress remains unclear. This study investigated the impact of fluid intake on thermoregulation, inflammation, organ function, and stress signaling during 8 h of humid heat exposure (ambient temperature: 40 °C, relative humidity: 55%) in 32 healthy young adults (20 males and 12 females). Participants completed two randomized trials: limited fluid intake (LFI, 125 mL/h) and full fluid intake (FFI, 375 mL/h). Core temperature (Tcore), inflammatory cytokines (IL-6, IL-1β, IFN-γ, TNF-α), organ stress markers (ALT, BUN), oxidative stress indices (MDA, SOD), and cortisol were assessed pre- and post-exposure. FFI significantly reduced post-exposure Tcore (37.8 ± 0.3 °C vs. 38.1 ± 0.3 °C, p = 0.046), mitigated cytokine elevations, and decreased BUN (blood urea nitrogen), ALT (alanine aminotransferase), and cortisol levels. Western blot analysis of PBMCs revealed that LFI activated NF-κB p65, JNK2, p38, and STAT3α phosphorylation, whereas FFI suppressed these responses. These findings demonstrate that adequate hydration attenuates heat-induced systemic and molecular stress responses. Our results highlight hydration as a key modulator of inflammatory signaling pathways during prolonged heat stress, offering insights into preventive strategies for populations vulnerable to climate-induced extreme heat events.

Prior SARS-CoV-2 infection does not increase heat stress during one hour of exercise in a hot and moderately humid environment

PURPOSE

Prior viral infection has been suggested to increase exertional heatstroke (EHS) risk. This study examined physiological and immune responses in persons with prior clinical diagnosis of SARS-CoV-2 infection, who were challenged with 1 h of cycling exercise in hot, moderately humid ambient conditions.

METHODS

Fourteen men and six women (age: 21 ± 1 years, stature: 1.7 ± 0.1 m, mass: 70.7 ± 2.6 kg, VO2 max: 47 ± 1 mL kg lbm-1 min-1) completed 1 h of cycling exercise at an intensity that elicited 7.0 W/kg of metabolic heat production in an environmental chamber (35 °C/35% RH). Ten participants had been previously diagnosed with SARS-CoV-2 and ten participants served as CONTROL. Physiological parameters including heart rate (HR), esophageal temperature (Tc), mean body temperature (Tb), minute ventilation (VE), and oxygen consumption (VO2) were measured throughout exercise. Blood samples collected at Pre, Post, 1 h-Post, and 3 h-Post exercise were assayed for immune markers including Interleukin 1 receptor antagonist (IL-1RA) and interferon gamma (IFN-γ).

RESULTS

As compared to CONTROL, prior SARS-CoV-2 infection did not cause greater elevations in HR, Tc, Tb, VE or VO2 during 1 h of cycling exercise [all p > 0.05]. The increase in IL-1RA at 1 h-Post exercise in SARS-CoV-2 (195 ± 104%, p = 0.012) was greater than the increase in CONTROL (44 ± 18%, p = 0.002). IFN-y was elevated at 1 h-Post exercise in SARS-CoV-2 (105 ± 50%, p = 0.021) but did not increase following exercise in CONTROL (p > 0.05).

CONCLUSIONS

Prior SARS-CoV-2 infection did not alter metabolic responses or increase the rate of rise in HR, Tc or Tb during matched workload cycling exercise under hot, moderately humid ambient conditions. IL-1RA is an anti-inflammatory cytokine and IFN-y exhibits direct anti-viral activity, suggesting that immunocompetence was maintained during exertional heat stress.

Edward F. Adolph, PhD: A Preeminent Physiologist Who Studied Human Exposure to Desert Heat

During combat with German Nazis in the deserts of North Africa, it became imperative for the United States Army to research to ascertain the physiological limits of military ground troops subjected to extreme desert heat exposure. In the 1940s, Edward F. Adolph, PhD, from the University of Rochester School of Medicine & Dentistry (URSMD), was funded through a contract with the government to initiate research on human tolerance to the extremes of desert heat. Consequently, Adolph and his associates established the university's Desert Research Unit in the California desert. In the 1930s, a team from Harvard University's Fatigue Laboratory established the "Harvard Desert Expedition" for field research in the Nevada desert. Notably, both Harvard and Rochester research teams investigated human metabolic responses in desert heat, with Dr Adolph participating in both desert locations. These field studies were conducted during Adolph's time as a faculty member in the Department of Physiology at the URSMD, which spanned over 62 years. Adolph's research interests encompassed investigations into the physiological responses of humans in desert environments, including regulation of water and heat metabolism, sweat formation, dehydration, thirst, physiological adaptations to extreme heat, and survival without water. Adolph authored or co-authored a substantial body of work, including 155 articles and 4 books, culminating in the seminal text Physiology of Man in the Desert (1947). We aim to provide some pertinent lessons learned and practical applications derived from the research conducted by Adolph and his associates in the desert.

Far from Home: Heat-Illness Prevention and Treatment in Austere Environments

Austere environments present unique challenges concerning the prevention and treatment of exertional heat-illness patients that may greatly increase the risks of morbidity and mortality. For athletes, occupational groups, and others who may work, train, or compete in austere environments, proper preparation and planning may be lifesaving. The roles of acclimatization and hydration are often emphasized in the literature, but other important risk factors may be overlooked. Work capacity, especially aerobic work capacity, will always be reduced in hot environments, and individuals should understand that simply slowing down, to reduce metabolic heat production, can be considered the universal precaution to mitigate heat stress and strain. Conversely, appropriate rehydration alone does not mitigate other risk factors, such as metabolic heat production, high ambient temperature, or inadequate physical fitness. Risk factor-specific mitigation recommendations are provided, and areas where additional research is needed are identified. The ability to recognize the signs and symptoms of heat illness early in the progression of illness is especially important in austere environments due to the possibility of delayed access to higher levels of medical care. Treatment considerations in austere environments include knowledge of availability and effectiveness of cooling modalities such as natural bodies of water. Medications such as antipyretics, dantrolene, and nonsteroidal anti-inflammatory drugs are not recommended to treat a suspected heat casualty. Aggressive cooling, with the objective of reducing core temperature to <39°C within 30-min, is the treatment priority.

Customizing individual heat mitigation strategies to optimize performance in elite athletes

The aim of this review is twofold: 1) provide a brief discussion surrounding the interindividual variability that has been observed within the context of heat acclimation/acclimatization, body cooling, and hydration strategies, and 2) provide the reader with a practitioner-focused approach for creating individualized heat mitigation strategies. Considering individual variability for heat acclimation and heat acclimatization, various body cooling strategies, and hydration assessment/fluid replacement is important to maximize effects of these strategies, which lead to better performance and health outcomes. There are many factors to consider, and comprehensive approaches are required. The evidenced-informed decision is critical when making an individual approach, and data will help to make decisions effectively. It is important to keep adjusting the approach based on observed data as data is useful information to check if the approach is effective. Specific considerations to individualize the plan are discussed in this review.

Is It Required to Abstain From Fluid Consumption in the 10 Min Before Collection of a Saliva Sample?

The noninvasive and reliable saliva collection method for stress-related endocrine biomarkers analysis has become common in field- and laboratory-based research in the last 15 years. Current guidelines recommend interrupting water consumption 10 min before saliva sampling to avoid inaccurate, diluted concentrations of the biomarkers being examined. However, the impact of saliva dilution on salivary cortisol and testosterone levels has not been examined yet. This was a randomized, crossover experiment. Fourteen active healthy males completed three separate cycle-bout trials, where a set volume of water (250 ml) was consumed 10, 5, or 1 min before saliva sampling. Saliva was collected pre-, post-, and 30 min postexercise. No differences were observed in resting samples in any of the trials (p < .05). However, salivary cortisol increased from pre- to postexercise in the 10 (+52%, p = 0.022) and 5-min trial (+36%, p = .005) only. Salivary testosterone also increased in 10 (+34%, p = .005), 5 (+37%, p < .001), and 1-min trials (+24%, p < .035). This study proposes that consuming water up to 1 min before providing a saliva sample will not dilute the sample, allowing for an accurate determination of salivary cortisol and testosterone concentration levels. Practically, the 10-min fluid abstinence required before saliva sampling in the previous guidelines could be reduced to 1 min; however, if examining the response of salivary cortisol to an exercise trail, a fluid abstinence of 5 min may be more appropriate. This conclusion will allow for less restriction on researchers and participants alike.

No hyponatremia despite continuous plasma sodium decline in female runners during a seven stage ultramarathon

The role of sodium supplements and sex in the occurrence of exercise-associated hyponatremia (EAH) remains controversial. This study investigated hydration status in ultrarunners (19 males and 9 females) who completed seven marathons over seven consecutive days. Due to the limited number of female participants, no statistical comparison between sexes was performed. Plasma sodium concentration ([Na+]) and multiple hydration markers were assessed before, during, and after the race. Reported sodium supplement consumption showed no association with plasma [Na+]. An overall decline in plasma [Na+] was observed in females (regression slope = -1.278, p = 0.02) across the event, whereas no significant change was detected in males (slope = -0.325, p = 0.57). Additionally, no significant associations were found between plasma [Na+] and other monitored variables, including sodium supplement intake, pre-race hydration strategy, body mass, total body water, plasma osmolality, hematocrit, hemoglobin, urine specific gravity, urinary [Na+], thirst rating, or fluid intake reported pre-, during, and post-stage. No cases of symptomatic or asymptomatic hyponatremia were identified, suggesting that total fluid and sodium intake were adequate to maintain fluid-electrolyte balance and prevent EAH in both sexes.

The impact of a two-hour endurance run on brain activity monitored over 24 h

Acute exercise has been shown to enhance cognitive abilities, particularly those governed by the prefrontal cortex, such as executive function. However, the effects of prolonged exercise on cognition and brain activity, especially over extended recovery periods, remain underexplored. This pilot study investigated the effects of two hours of moderate-intensity running on oscillatory brain activity and working memory performance, monitored across a 24-hour recovery period-an interval not previously studied. Using electroencephalography (EEG) and a 2-back task, resting-state brain activity and task-specific frontal theta power were assessed. While task accuracy and reaction times showed no significant changes, frontal theta power increased one hour post-exercise, reflecting heightened cognitive effort. Resting-state EEG demonstrated a sustained increase in high-alpha power, which persisted until the 24-hour mark and indicated cortical recovery processes. While limited by the lack of a control group, these findings suggest that prolonged moderate-intensity exercise may elicit complex and delayed neurophysiological responses, supporting recovery and neural resilience in trained individuals. Therefore, our research offers new insights into the interplay between exercise, cognition, and recovery, with implications for optimizing performance in physically demanding contexts.

Nutritional Intake and Timing of Marathon Runners: Influence of Athlete's Characteristics and Fueling Practices on Finishing Time

BACKGROUND

Endurance athletes' competitions have increased over the decades and marathon races are becoming increasingly popular. Proper nutrition is critical for optimal performance and long-term health in marathon athletes. This study aimed to investigate runners' nutritional intake, especially fluids, food, and supplements, competing in the Seville Marathon. A descriptive and cross-sectional study was carried out to obtain information on the consumption of liquids, food, and supplements. A total of 160 runners (aged 42.2 ± 7.3 years) who were primarily men (87.5%) who participated in the 2022 Seville marathon took part in the study.

RESULTS

There was no significant difference (p > 0.050) between marathon finish time (from 2 h 12 min to 5 h) or sports experience and fluid, carbohydrates (CHO), sodium, and caffeine intake pre- and post-competition. However, according to the results obtained, the athletes who met CHO intake recommendations during the competition (60-90 g/h) were more likely to finish the marathon in less than 180 min (p = 0.035).

CONCLUSIONS

The intake of CHO (35 ± 17 g/h), sodium (192 ± 150 mg/h) and caffeine (57 ± 49 mg/h) was low compared to the current recommendations during the competition. The intake of fluids (466 ± 279 mL/h) was at the lower limit of recommendations. Most athletes did not receive nutritional counselling by a sport dietitian, which may explain why athletes failed to meet specific nutrient recommendations. Future investigations with a larger sample size are warranted to assess the relationship between dietary intake and finish time.

Returning to the Basics: Embracing Oral Rehydration Therapy During an Intravenous Fluid Shortage After Hurricane Helene

In developed countries, the use of intravenous (IV) fluid for fluid resuscitation and other routine medical or surgical indications has become standard practice, with its availability often taken for granted. However, natural disasters can disrupt supply chains, leading to shortages. In September 2024, Hurricane Helene rendered the Baxter Healthcare facility in North Carolina inoperable, halting production and disrupting the supply of IV fluid in the U.S. In contrast, countries with limited access to IV fluid have long relied on oral rehydration therapy (ORT) as the cornerstone of fluid resuscitation and replacement. The well-documented efficacy of ORT provided a viable alternative to IV fluid for managing volume and electrolyte loss in the aftermath of the hurricane. This case series presents two patients, one with nephrogenic diabetes insipidus and the other with acute tubular necrosis due to dehydration, who were successfully treated with ORT, reinforcing its potential role as a practical solution during IV fluid shortages.

Plasma and serum volume remain unchanged following a 12-h fast from food and drink despite changes in blood and urinary hydration markers

BACKGROUND/OBJECTIVES

The effect of mild dehydration on plasma and serum volume has not been well established. Furthermore, the ability of urinary and blood biomarkers to monitor small hydration changes have not been solidified. There were two objectives of this research: 1. Determine if mild dehydration affects plasma and serum volume; 2. Determine if mild dehydration can be detected better by urinary or blood biomarkers.

SUBJECTS/METHODS

47 subjects were recruited; 10 subjects were removed from the study and 37 subjects (27% male) completed the study. This was a crossover study design such that each subject underwent all protocols in a counterbalanced order. Protocols consisted of 12-h dehydration, 12-h hydration, and control.

RESULTS

Neither plasma volume (p = 0.914), plasma volume status (p = 0.649), nor serum volume (p = 0.273) were different among protocols. Body mass (p < 0.001) was lower following the dehydration protocol. Urine color (p < 0.001), urine osmolality (p < 0.001), urine specific gravity (p < 0.001), serum osmolality (p < 0.001), and plasma osmolality (p < 0.001) were all lower following the hydration protocol. Hematocrit (p = 0.842) and hemoglobin concentration (p = 0.558) were not different among protocols.

CONCLUSIONS

Dehydration did not affect plasma or serum volume. Therefore, a 12-h fast from food and water as done in this study will not likely affect laboratory test results of biomarker concentration. All 3 urinary measures were able to detect changes in hydration status, whereas only 2 blood measures were able to detect changes in hydration status. This may indicate that urinary measures are best at detecting small changes in hydration status.

Determinants of Health and Performance in Wildland Firefighters: A Narrative Review

BACKGROUND/OBJECTIVES

Wildland firefighters (WFFs) are subjected to significant physical and physiological demands that expose them to substantial occupational risks, including thermal stress, prolonged physical exertion, and exposure to harmful substances. These factors not only affect their immediate performance but also have long-term implications for their health. This narrative review seeks to analyze the main factors influencing the health and performance of WFFs, with a particular focus on physical, environmental, and psychological challenges.

METHODS

A narrative review was performed, synthesizing data from diverse sources. The analysis centered on studies addressing the physiological, environmental, and psychological aspects of WFF performance. Specific topics included physical workload, exposure to environmental stressors, use of protective equipment, hydration, sleep patterns, and mental health.

RESULTS

The review highlights several critical challenges faced by WFFs, including the extreme physical demands of carrying heavy equipment during extended interventions, elevated physiological strain induced by protective gear, and significant health risks associated with smoke inhalation and dehydration. Additionally, inadequate sleep and heightened mental stress were found to impair both cognitive and physical performance. Variations in injury prevalence and patterns of chronic pain were observed, often influenced by factors such as sex, age, and professional experience.

CONCLUSION

To mitigate these risks and enhance the health and performance of WFFs, targeted interventions are essential. These include tailored physical training programs, heat acclimatization strategies, and improved resource management. Future research should aim to integrate these measures comprehensively and address existing knowledge gaps to ensure the long-term well-being of these professionals.

Heat strain in road construction workers during the summer in New Mexico: a preliminary study

In the summer season, road construction workers perform physically demanding tasks outdoors, placing them at greater risk for exertional heat illness conditions. Assessing core temperature (Tcore) is critical as it serves as a key indicator of heat strain and helps to estimate the risk of heat-related illness. Despite the increased risk of hyperthermia, previous research has not assessed Tcore in road construction workers in the United States during summer work.

PURPOSE

To report heat strain and environmental heat stress in a pilot study of road construction workers during work in the summer.

METHODS

Seven male road construction workers in New Mexico were observed performing physically demanding work during a summer work shift. Environmental heat stress (heat index [HI], dry/wet bulb temperature, and relative humidity), Tcore, and skin temperature (Tskin) were measured continuously at a single job site throughout the workday. Hydration was assessed pre- and post-shift via measurements of urine specific gravity (USG) and changes in body weight.

RESULTS

The peak HI recorded throughout the workday was 34.1 °C, corresponding to a "warning" heat risk level according to the Occupational Safety and Health Administration Heat Safety Tool App. Two of seven (29%) workers reached a peak Tcore of greater than 38.0 °C, and 4 (57%) began the work shift dehydrated, indicated by a USG >1.020.

CONCLUSIONS

Findings from this pilot study suggest that road construction workers may begin their shifts dehydrated and some experience moderate hyperthermia while performing physically demanding work in hot environmental conditions.

Work rate adjustments needed to maintain heart rate and RPE during high-intensity interval training in the heat

Introduction

Higher work rates may be sustainable when maintaining target rating of perceived exertion (RPE) compared to maintaining target heart rate (THR) during high-intensity interval training (HIIT) exercise in hot conditions, but may also result in greater thermal strain and cardiovascular drift, as well as greater decrements in maximal oxygen uptake (V ˙ O2max).

Purpose

To test the hypotheses that maintaining target RPE compared to THR during HIIT in the heat results in 1) smaller work rate adjustments, 2) greater thermal and cardiovascular strain, and 3) larger decreases inV ˙ O2max.

Methods

Eight adults (4 women) completed a graded exercise test on a cycle ergometer in 22°C and then 4 cycling trials in 35°C, consisting of an 8-min warm-up at 70% maximal heart rate (HRmax) or 12 RPE followed by 1 (15HR and 15RPE) or 5 (43HR and 43RPE) rounds of HIIT (1 round = 4 min work at 90% HRmax or 17 RPE and 3 min recovery at 70% HRmax or 12 RPE) totaling 15 min or 43 min of exercise, respectively. Each trial ended with a GXT to measureV ˙ O2max.

Results

In the 43-min trials work rate decreased from the first to the fifth work interval in both conditions, but by a non-significant, yet moderately larger (ES = 0.53) amount during 43HR (46 ± 29 W) compared to 43RPE (30 ± 28 W). From the first to fifth work interval HR increased over time by 12 b⋅min-1 in 43RPE (p < 0.001), but did not increase during 43HR (p = 0.36). Rectal temperature increases were not different between conditions (43HR = 0.7°C, p < 0.001; 43RPE = 0.8°C, p < 0.001).V ˙ O2max decreased 15.6% (ES = 0.41) between 15RPE and 43RPE (p = 0.005), but it was not different over time during the HR-based trials [6.5%, ES = 0.16 (α adjusted for multiple comparisons = 0.0125) p = 0.03].

Conclusion

Maintaining target RPE and THR require considerable declines in work rate during HIIT in the heat, with ∼53% larger declines needed to maintain THR. The mitigation of cardiovascular drift in the THR trial may have contributed to the preservation ofV ˙ O2max.

The Impact of a Commercial Electrolyte Beverage on the Hydration Status of Active Men and Women

BACKGROUND/OBJECTIVES

Hypo-hydration is a major health concern that affects performance and is associated with increasing morbidity and growing health care costs. There is an emerging interest in optimizing hydration and identifying how factors such as ingestion rate and beverage composition affect hydration. This study examined three beverages with varying ingestion rates and measured markers of hydration.

METHODS

Thirty healthy, active participants between the ages of 18 and 45 years were given three different beverages on three separate days. The beverages were of identical volumes (1 L), but differed in the rate of ingestion, carbohydrate content and electrolyte content. Beverage 1 and water alone were both consumed at a metered rate of one liter over four hours, whereas Beverage 2 was used as a positive control and was consumed at a bolus rate of one liter in 30 min.

RESULTS

After six hours, Beverage 1 significantly improved markers of hydration compared to water alone or Beverage 2. Beverage 1 decreased cumulative urine output vs. water alone by 32% (absolute difference -0.33 L; CI ± -0.16 to -0.51) and vs. Beverage 2 by 26% (absolute difference -0.26 L; CI ± -0.13 to -0.38). Beverage 1 increased the beverage hydration index vs. water alone by 64% (absolute difference +0.64 L; CI ± 0.36 to 0.92) and vs. Beverage 2 by 48% (absolute difference +0.53 L; CI ± 0.30 to 0.76).

CONCLUSIONS

Beverage 1 is superior to water alone at improving hydration when it is ingested at similar rates. Moreover, metered ingestion of Beverage 1 improved hydration compared to a bolus ingestion of Beverage 2, this could be due to the dissimilar ingestion rates and/or beverage composition.

Health on the Pitch: Dietary Habits of Football Referees in Poland

BACKGROUND

Football referees are pivotal to match regulation, requiring both cognitive and physical abilities comparable to players. Proper nutrition is essential to sustain their intense activity levels, yet dietary habits among referees in Poland are under-researched.

OBJECTIVE

This study aimed to evaluate the dietary habits of football referees in Poland, focusing on identifying beneficial and detrimental practices and assessing their impact on professional performance.

MATERIAL AND METHODS

A survey-based study was conducted with 258 football referees from Poland between December 2022 and January 2023. The questionnaire assessed demographic data, professional experience, and dietary habits, including meal frequency, food choices, and hydration. Statistical analysis was performed using the chi-squared test, with significance set at p < 0.05.

RESULTS

Most referees consumed 4-5 meals daily (63.7%), but irregular meal timing (45.2%) was common, particularly among less-experienced referees. Consumption of fruits and vegetables was limited, with significant age-related differences. Water intake was generally adequate, but hydration strategies during matches varied. Cooking practices revealed a preference for frying (48.1%), reflecting limited awareness of healthier alternatives. Dietary education was highlighted as a key need, especially among referees with lower professional experience.

CONCLUSIONS

The results of the study clearly indicate significant deficiencies in meal regularity and healthy cooking practices among Polish soccer referees. The findings underscore the need for targeted educational programs that could help improve the health and professional performance of this group, especially in the context of increasing fruit and vegetable consumption and promoting healthier food processing methods.

Post-training breakdown: acute effects of different training types on body hydration status and performance

Objective

Wrestling is a complex sport that requires a combination of strength, endurance, and wrestling-specific technical training. Endurance activities, such as running, are commonly performed for rapid weight reduction before competition. However, these activities can severely disrupt recovery and lead to significant declines in performance. This study aimed to examine the acute effects of endurance, strength, and wrestling training sessions on hydration status and performance parameters in young wrestlers, providing insights to guide more effective hydration and recovery strategies.

Method

A total of 14 experienced young wrestlers participated in a crossover design, completing endurance, strength, and wrestling training sessions on separate days. The hydration status was assessed through urine specific gravity (USG) before and after each session. The performance measures included hand grip strength, back and leg strength tests, anaerobic power (vertical and horizontal jumps), respiratory muscle strength (maximal inspiratory pressure, MIP), and reaction time assessments.

Results

The endurance training caused the most significant acute reductions in the hydration (USG increase: 0.016 ± 0.005 g/cm3, p < 0.05) and body mass (BM; -1.89 ± 0.4%, p < 0.05), along with immediate performance decrements in the back strength (-7.02 ± 1.2%, p < 0.001), right-hand grip strength (-8.79 ± 2.1%, p < 0.001), jump height (-7.26 ± 1.8%, p < 0.001), and MIP (-9.01 ± 2.3%, p < 0.001). The hydration levels in the endurance group did not fully recover by the next day (USG post-training vs. before the next day's training: p < 0.05). In contrast, the strength training improved the reaction time before the next day's session (+5.6 ± 1.3%, p < 0.05), while the attention remained unaffected across all training types.

Conclusion

Endurance training-commonly used for rapid weight loss-can acutely compromise hydration and reduce key performance measures, with recovery taking more time compared to strength or wrestling sessions. Given these findings, endurance sessions should be strategically scheduled before rest days or low-intensity technical training to minimize their negative effects on subsequent performance. Implementing enhanced hydration strategies during endurance-focused sessions may also help mitigate these acute impacts and optimize recovery and performance in young wrestlers.

Gastrointestinal symptoms and nutritional intake among participants in a non-professional cycling event

PURPOSE

To determine the occurrence of gastrointestinal (GI) symptoms in different settings among cyclists participating in a non-professional cycling event. The nutritional intake during the event and the association between GI symptoms and both nutritional and non-nutritional factors were also analyzed.

METHODS

A descriptive correlational study was performed among participants in the 2023 'Mallorca 312-Milestone Series' cycling event. A pre-race questionnaire was completed by 247 participants (37 women) while a post-race questionnaire was completed by 138 participants (24 women).

RESULTS

The prevalence of GI symptoms in training sessions and in previous cycling events were 22-26%. GI complaints during the race were reported by 38.4% of participants. GI symptoms during training (p = 0.003), in previous cycling events (p = 0.012) and in the Mallorca 312 event (during: p = 0.010; after p = 0.014) were associated with rest GI symptoms. Furthermore, GI symptoms during the Mallorca 312 event were associated with an immediately previous more nervous feeling (p = 0.016). Participants with shorter previous experience in similar events reported a more nervous feeling (p = 0.023). On average, participants in the Mallorca 312 achieved the recommended carbohydrate intake (59.2 g/h; recommended 30-60 g/h) and the fluid intake (500 ml; recommended 400-800 ml/h) rates. No association was found between GI symptoms and nutritional parameters or food intake.

CONCLUSION

GI symptoms at rest could be considered the main factor associated with GI symptoms in cyclists. GI symptoms during the event were also associated with a more nervous feeling, which could be explained, at least in part, by shorter previous experience.

Change in interleukin (IL)-6, 8, and 10 and its association with an increase in core temperature following a 7-mile running race in the warm weather

The purposes of this study were 1) to investigate if cytokines were increased following a running road-race, and 2) to examine associations between cytokines and hyperthermia. Seventy-seven recreational runners participated in this study which occurred at the 7-mile race in the heat (ambient temperature, 25.0-26.7°C; %RH, 56.7-79.0 ± 5.0%). Before and following the race, blood draws were performed to measure circulating inflammatory cytokines. Core temperature was measured using an ingestible thermistor throughout the race. Core temperature was significantly higher at post-race (39.5 ± 0.7°C) than pre-race (36.9 ± 0.4°C, p < 0.001). IL-6, IL-8, and IL-10 significantly increased at post-race (IL-6, 48.0 ± 22.3 pg⋅ml-1; IL-8, 63.8 ± 23.9 pg⋅ml-1; IL-10, 29.2 ± 20.0 pg⋅ml-1) compared to pre-race (IL-6, 28.4 ± 13.6 pg⋅ml-1; IL-8, 53.2 ± 19.4 pg⋅ml-1; IL-10, 18.6 ± 11.9 pg⋅ml-1, p < 0.001). A greater increase in core temperature pre- to post-race was predicted by the faster finish time, a greater increase in IL-6, and greater body mass loss during the race (r2 = 0.298, p < 0.001). Small associations were found between IL-8 and core temperature at post-race (r = 0.255, p = 0.025). In conclusion, cytokines concentrations and core temperature increased following the race. Moreover, post-race hyperthermia is associated with increased IL-6, faster finish times, and higher body mass losses.

The Effect of Fluid Restriction and Intake Conditions on the Shooting Performance of Competitive Adolescent Handball Players

(1) Background: This study aimed to investigate the effects of fluid restriction and intake (water vs. sports drink) on shooting accuracy and speed in adolescent handball players, a population with high sensitivity to hydration levels yet understudied in this context. (2) Methods: A total of 47 adolescent competitive handball players (15.04 ± 1.5 years) were included in this study, and the participants were divided into low, average, and high performance according to their shooting performance in the familiarization session. All participants were exposed to fluid restriction and intake conditions during handball training on different days. Before and after the training sessions, changes in shooting accuracy and speed were evaluated. (3) Results: The training protocol resulted in body mass loss in the Average Performer group (p = 0.001). Compared to fluid restriction, fluid intake (water intake and sports drink intake) post-training had a positive main effect on shooting accuracy, F(2, 88) = 34.32, p < 0.001, ηp2 = 0.44, and shooting speed, F(1, 61) = 4.05, p = 0.35, ηp2 = 0.84. (4) Conclusions: Hydration level plays an important role in shooting accuracy and speed performance in adolescent handball players. Therefore, fluid intake integrated into training or match sessions may contribute to the maintenance and improvement of shooting performance.

Nutrition and Golf Performance: A Systematic Scoping Review

BACKGROUND

Golf is played both recreationally and professionally by approximately 66.6 million people worldwide. Despite the potential for nutrition to influence golf performance, research in this area is somewhat limited.

OBJECTIVE

To identify the existing literature regarding nutrition and golf and where the current research gaps lie.

DESIGN

Scoping review. Online databases were used to retrieve data from 2003 to the present day.

DATA SOURCES

A three-step search strategy identified relevant primary and secondary articles as well as grey literature. Published and unpublished articles in the English language, identified by searching electronic databases (ProQuest Central, Web of Science, Scopus, SPORTDiscus and PubMed) and reference searching.

REVIEW METHODS

Relevant identified studies were screened for final inclusion. Data were extracted using a standardised tool to create a descriptive analysis and a thematic summary. In summary, studies were included if they focused on nutrition, hydration, energy requirements, supplements, or body composition in relation to golf.

RESULTS AND DISCUSSION

Our initial search found 3616 relevant articles. Eighty-two of these articles were included for the scoping review. Nutrition has the potential to impact golf performance in areas including the maintenance of energy levels, cognitive function, and body composition. Currently, there is limited research available discussing the effects of nutrition interventions related specifically to golf performance.

CONCLUSION

This scoping review highlights that more work is needed to provide golfers and practitioners with golf-specific nutrition research. The key areas for future golf-specific nutrition research include nutrition on cognitive performance, body composition, energy requirements, supplementation, and the potential role of nutrition for the travelling golfer. Systematic reviews could also be used to identify future priorities for nutrition and golf research.

Assessment of Perceived Effort Through On-Field Hydration Monitoring: A Case Analysis

This case report examines the correlation between hydration, weight variation, and perceived effort in a 43-year-old amateur athlete during a self-supported 81.5 km crossing of Death Valley, completed over 3 days with significant elevation changes. Studies have shown that a body mass loss greater than 2-3% can lead to an increased perception of effort and a decline in performance. Specifically, during passive and active heat exposures, the average body mass loss was found to be 1.4 ± 0.3% and 4.1 ± 0.7%, respectively. Salivary osmolarity has demonstrated a sensitivity of 86% and specificity of 91% in diagnosing dehydration of ≥ 2%, suggesting its potential as a non-invasive indicator of hydration status. The subject monitored their own body weight, hydration (via salivary osmolarity), and perceived effort using a rate of perceived exertion (RPE) scale. Nutritional intake included isocaloric meals and nutritional bars, and hydration was managed using water and a hydroelectrolytic solution. Key bioimpedance parameters were measured to assess body composition and hydration status. A progressive decrease in body weight correlated with an increase in perceived effort (RPE score) and salivary osmolarity. Resistance (Rx) remained stable, while reactance (Xc) showed a biphasic trend and was inversely correlated with the sodium/potassium ratio (NAK). There were significant linear correlations between perceived effort and both weight loss and salivary osmolarity, indicating that salivary osmolarity is a potential early predictor of these changes. The findings highlight a linear correlation between weight loss, perceived effort, and salivary osmolarity, suggesting that monitoring salivary osmolarity would be useful for the field assessment of hydration and exertion. Further research with larger populations is necessary to validate these observations.

Influence of sustained mild dehydration on thermoregulatory and cognitive functions during prolonged moderate exercise

PURPOSE

The current study investigated whether sustained mild dehydration affects thermoregulatory function and cognitive performance during prolonged exercise.

METHODS

Twelve young adults performed a test consisting of three sets of 20-min exercise with 2-min intervals under euhydrated (control, CON) and mildly dehydrated conditions (MDEH) at an ambient temperature of 30 °C and 60% relative humidity. MDEH was established by restricting water intake for 24 h, resulting in urine specific gravity of ≥ 1.020. Heart rate (HR), mean arterial blood pressure (MAP), skin blood flow (SkBF), sweat rate (SR) on the chest and forearm, and ear canal and mean skin surface temperatures (Tear and mean Tskin, respectively) were continuously recorded. For each exercise set, thermal and humid sensations and thermal discomfort were assessed using visual analog scales (VAS), and the rating of perceived exertion (RPE) was estimated. Cognitive performance on the Go/No-Go (easy) and incongruent Stroop (difficult) tasks was assessed before and after the test.

RESULTS

No differences were observed in HR, MAP, SkBF, SR, Tear, and mean Tskin between the CON and MDEH. Thermal and humidity sensations, thermal discomfort, and RPE were higher in MDEH than in CON. Moreover, response time to the Stroop task was prolonged in MDEH.

CONCLUSION

These findings suggest that sustained mild dehydration does not affect autonomic thermoregulation during exercise. Augmented thermal perception and perceived exertion, which are necessary for behavioral thermoregulation, were noted; however, cognitive function may be attenuated under MDEH.

Perceptual Health and Wellbeing, Self-Reported Sleep, and Hydration Status in Youth Soccer Players During Competition

Introduction: The aim of this study was to assess match time courses on hydration, wellness, and sleep as well as the interrelationship between these variables in youth national soccer players. Materials and Methods: Under-17 and under-19 youth national soccer players (age range: 16.96 ± 1.17 years) completed a perceptual wellness questionnaire, self-reported their sleep, and carried out hydration assessments each morning during a period of competitive match play. Results: Players reported having significantly more sleep leading into the day of a match (MD) compared to both the evening after a match (MD-2; p < 0.001; CI = 7.972 and 8.212) and the evening before a match (MD-1; p < 0.001; CI = 7.996 and 8.174). Furthermore, players reported better health and wellbeing scores on MD compared to both MD-1 (p < 0.001; CI = 19.231 and 19.692) and MD-2 (p < 0.001; CI = 18.911 and 19.489). When self-reported sleep was correlated with the individual components of health and wellbeing, it was highlighted that there were significant effects for fatigue (r = 0.304, p < 0.001; CI = 0.250 and 0.383), mood (r = 0.170, p < 0.001; CI = 0.112 and 0.243), general muscle soreness (r = 0.225, p < 0.001; CI = 0.162 and 0.306), and stress (r = 0.203, p < 0.001; CI = 0.147 and 0.274). Conclusion: It is important to consider sleep strategies to mitigate the potential impact of lack of sleep following match play. Self-reported sleep seems to be appropriate for estimating individual components of health and wellbeing, and therefore may be a suitable replacement for perceptual wellness questionnaires.

A Review on In Vivo Research Dehydration Models and Application of Rehydration Strategies

Background: Dehydration, a common condition where the amount water lost from the body exceeds intake, disrupts metabolic processes and negatively impacts health and performance. Rehydration, the process of restoring body fluids and electrolytes to normal levels, is crucial for maintaining physiological health. In vivo dehydration models are experimental systems used to study the effects of dehydration on living organisms. However, a comprehensive summary of in vivo models and the application of human rehydration strategies is lacking. Methods: This review provides a comprehensive overview of various in vivo models and rehydration strategies. Results: In vivo models, stimulated by fluid restriction, exercise, thermal exposure, and chemicals, have been used to study dehydration. Importantly, the principles, characteristics, and limitations of the in vivo models are also discussed, along with rehydration administration methods, including oral, intestinal, intravenous, subcutaneous, and intraperitoneal routes. Additionally, rehydration strategies and the application for managing different dehydration conditions both in daily life and clinical settings have been summarized. Conclusions: Overall, this review aims to enhance the understanding of the conditions in which in vivo dehydration models and rehydration strategies are applicable, thereby advancing research into the physiological and pathological mechanisms of dehydration and supporting the development of effective rehydration therapies.

Training, environmental and nutritional practices in indoor cycling: an explorative cross-sectional questionnaire analysis

Introduction

Indoor cycling at home has grown rapidly in recent years facilitated by advances in technology and gamification. However, there is limited data on individual's training practices when cycling indoors.

Methods

Using a single-time point, cross-sectional questionnaire, we gathered information on equipment, environmental considerations, training practices and nutrition during indoor cycling.

Results

Following 492 responses, external variables (weather; 88.4%, lack of daylight; 56.3%), time efficiency (81.9%) and general fitness (70.9%) were most frequently cited as reasons to engage in indoor cycling. "Smart" turbo trainers linked to a mixed-reality cycling software were most frequently reported in equipment set-up. 78% of participants attempted to control temperature with 96% of these participants using at least 1 fan to control airflow. The volume of indoor training differed between seasons (winter: 6h10 ± 3 h 30, summer 2h52 ± 2h57, p < 0.001), and structured (61.9%) and unstructured work-outs (64.7%) were completed more than once a week with fewer participants engaging in competitive/racing events (20.9%). 98% percent of participants consumed fluids with an average fluid intake of 0.74 ± 0.28 L/h. Dependent on type of work-out, participants reported less planning of carbohydrate and protein intake during short-duration work-outs (∼40%-60%) relative to longer-duration work-outs (∼56%-80%). Caffeine use was the most frequently reported ergogenic aid.

Conclusion

Together we report indoor cycling practices with respect to training equipment, considerations of environmental and nutritional strategies and training habits. Our findings could be used to support the development of future research and indoor training guidelines.

Cognitive, Psychophysiological, and Perceptual Responses to a Repeated Military-Specific Load Carriage Treadmill Simulation

BACKGROUND

Dismounted military operations require soldiers to complete cognitive tasks whilst undertaking demanding and repeated physical taskings.

OBJECTIVE

To assess the effects of repeated fast load carriage bouts on cognitive performance, perceptual responses, and psychophysiological markers.

METHODS

Twelve civilian males (age, 28 ± 8 y; stature, 186 ± 6 cm; body mass 84.3 ± 11.1 kg; V̇O2max, 51.5 ± 6.4 mL·kg-1·min-1) completed three ∼65-min bouts of a Fast Load Carriage Protocol (FLCP), each interspersed with a 65-min recovery period, carrying a representative combat load of 25 kg. During each FLCP, cognitive function was assessed using a Shoot/Don't-Shoot Task (SDST) and a Military-Specific Auditory N-Back Task (MSANT), along with subjective ratings. Additional psychophysiological markers (heart rate variability, salivary cortisol, and dehydroepiandrosterone-sulfate concentrations) were also measured.

RESULTS

A main effect of bout on MSANT combined score metric (p < .001, Kendall's W = 69.084) and for time on the accuracy-speed trade-off parameter of the SDST (p = .025, Ѡ2 = .024) was evident. These likely changes in cognitive performance were coupled with subjective data indicating that participants perceived that they increased their mental effort to maintain cognitive performance (bout: p < .001, Ѡ2 = .045; time: p < .001, Ѡ2 = .232). Changes in HRV and salivary markers were also evident, likely tracking increased stress.

CONCLUSION

Despite the increase in physiological and psychological stress, cognitive performance was largely maintained; purportedly a result of increased mental effort.

APPLICATION

Given the likely increase in dual-task interference in the field environment compared with the laboratory, military commanders should seek approaches to manage cognitive load where possible, to maintain soldier performance.

Impact of a simulated multiday heatwave on nocturnal physiology, behavior, and sleep: a 10-day confinement study

This study investigated the impact of a multiday heatwave on nocturnal physiology, behavior, and sleep under controlled conditions with comprehensive monitoring of environmental factors and participant activities. Seven young healthy males were confined for 10 days in controlled conditions that ranged between hot-to-warm (day: 35.4 °C, night: 26.3 °C) during nights 4-6 and temperate (day: 25.4 °C, night: 22.3 °C) before (nights 1-3) and after (nights 7-10) the heatwave. Measurements included core and skin temperatures, heart rate, sympathovagal balance, vasomotion indicators, urine samples, blanket coverage, subjective sleep assessments, and partial polysomnography. The average nocturnal core temperature was 0.2 °C higher during and after the heatwave compared to the pre-heatwave period, with this difference being more pronounced (+0.3 °C) in the first 2 h of sleep (p < 0.001). For every 0.1 °C rise in overnight core temperature, the total sleep time decreased by 14 min (pseudo-R2 = 0.26, p = 0.01). The elevated core temperatures occurred despite the participants exhibiting evident thermoregulatory behavior, as they covered 30% less body surface during the heatwave compared to pre- and post-heatwave periods (p < 0.001). During the heatwave, mean skin temperature at bedtime was 1.3 °C higher than pre-heatwave and 0.8 °C higher than post-heatwave periods (p < 0.001). No differences in other responses, including heart rate and vasomotion indicators, were observed. The paper details a 20-min sleepwalking episode that was coupled with marked changes in sleepwalker's thermophysiological responses. In conclusion, the simulated heatwave resulted in higher overnight core temperature which was associated with reduced total sleep time. Behavioral thermoregulation during sleep may serve as a defense against these effects, though more research is needed.

Whole body sweat rate prediction: indoor treadmill and cycle ergometer exercise

This article describes the development and validation of accurate whole body sweat rate prediction equations for individuals performing indoor cycle ergometer and treadmill exercise, where power output can be measured or derived from simple inputs. For cycle ergometry, 112 trials (67 participants) were used for model development and another 56 trials (42 participants) for model validation. For treadmill exercise, 171 trials (67 participants) were used for model development and another 95 trials (63 participants) for model validation. Trials were conducted over a range of dry-bulb temperature (20°C to 40°C), relative humidity (14% to 60%), and exercise intensity (∼40% to 85% of peak aerobic power) conditions, which were matched between model development and model validation. Whole body sweat rates were measured, and proprietary prediction models were developed (accounting for all relevant biophysical factors) and then validated. For model validation, mean absolute error for predicted sweating rate was 0.01 and 0.02 L·h-1 for cycle and treadmill trials, respectively. The 95% confidence intervals were modest for cycle ergometer (+0.25 and -0.22 L·h-1) and treadmill exercise (+0.33 and -0.29 L·h-1). The accounted for variance between predicted and measured values was 92% and 78% for cycle and treadmill exercise, respectively. Bland-Altman analysis indicated that zero and one predicted value exceeded the a priori acceptable level of agreement (equivalent to ±2% of total body mass in 3 h) for cycle and treadmill exercise, respectively. There were fewer trials with female subjects, but their values did not differ from those expected for males. This is the foremost study to develop and validate whole body sweat rate prediction equations for indoor treadmill and cycle ergometer exercise of moderate to high intensity. These prediction equations are publicly available for use (https://sweatratecalculator.com).NEW & NOTEWORTHY This study presents the development of new proprietary whole body sweat rate prediction models for people exercising indoors on a cycle ergometer or treadmill using simple input parameters and delivered through a publicly available online calculator: https://sweatratecalculator.com. In an independent validation group, the predictive models for both indoor cycling and treadmill exercise were accurate across moderate to high exercise intensities in temperate to hot conditions. These equations will enable individualized hydration management during physical training and exercise physiology experiments.

Associations between urine specific gravity and race/ethnicity at the population level: Implications for hydration status categorization

OBJECTIVE

We aimed to evaluate how urine specific gravity (USG) and rates of supposed hypohydration vary by race/ethnicity, and to examine how adjustment for several important factors impacts estimated USG.

METHODS

Using the National Health and Nutrition Examination Survey, this cross-sectional study evaluated a total of 4195 (2098 female, 2097 male) Americans and categorized them as supposedly hypohydrated (USG≥1.020) or not using spot urine samples. USG and prevalence of supposed hypohydration were compared across racial/ethnic groups, separately by gender. The analyses considered the impact of urine creatinine, body composition, age, dietary nutrients, and physical activity.

RESULTS

Differences in supposed hypohydration prevalence were observed by race/ethnicity in men (p = .030) and women (p < .001). In unadjusted models, Black women's USG (1.0189) was higher (p < .05) than all the other race/ethnicity groups' USG (1.0142-1.0171). In men, Blacks' USG (1.0197) was higher (p < .05) than the USG of Whites (1.0177) and other/multi-racial (1.0176) but not Mexican Americans (1.0196) or other Hispanics (1.0192). Adjustments for age, arm circumference, nutrients (protein, sodium, potassium, and moisture), and physical activity minimally influenced USG estimates. Further adjustment for urine creatinine lowered USG for Black women and men by 0.003 and 0.0023, respectively, with no notable lowering of USG in the other races/ethnicities. Supplemental analyses matching Whites and Blacks on age, moisture intake, and poverty-to-income ratio confirmed racial differences in urine creatinine and USG, though the effects were most pronounced in women.

CONCLUSIONS

Using a USG≥1.020 to identify hypohydration in all races/ethnicities may be inappropriate due to, among other factors, differences in urinary creatinine.

Chasing Gold: Heat Acclimation in Elite Handcyclists with Spinal Cord Injury

Thermoregulation is impaired in individuals with a spinal cord lesion (SCI), affecting sweat capacity, heat loss, and core temperature. This can be particularly problematic for athletes with SCI who exercise in hot and humid conditions, like those during the Tokyo 2020 Paralympic Games. Heat acclimation can support optimal preparation for exercise in such challenging environments, but evidence is limited in endurance athletes with SCI. We evaluated whether seven consecutive days of exercise in the heat would result in heat acclimation. Five elite para-cycling athletes with SCI participated (two females, three males, median (Q1-Q3) 35 (31-51) years, four with paraplegia and one with tetraplegia). All tests and training sessions were performed in a heat chamber (30°C and 75% relative humidity). A time-to-exhaustion test was performed on day 1 (pretest) and day 7 (posttest). On days 2-6, athletes trained daily for one hour at 50-60% of individual peak power (PPeak). Comparing pretest and posttest, all athletes increased their body mass loss (p=0.04), sweat rate (p=0.04), and time to exhaustion (p=0.04). Effects varied between athletes for core temperature and heart rate. All athletes appeared to benefit from our heat acclimation protocol, helping to optimize their preparation for the Tokyo 2020 Paralympic Games.

What About Water? Implications for Body Composition Assessment in Military Personnel

ABSTRACT

Sergi, TE, Roberts, BM, and Heileson, JL. What About Water? Implications for Body Composition Assessment in Military Personnel. J Strength Cond Res 38(9): e534-e540, 2024-Body composition standards ensure service members maintain physical fitness, wellness, and support mission readiness. Anthropometric techniques (i.e., height/mass, circumference-based "tape test") have been the primary screening and percent body fat (%BF) assessment method in military personnel for about 4 decades. Recently, the Army and Marine Corps have implemented more advanced body composition assessment methods, such as air displacement plethysmography (ADP), multifrequency bioelectrical impedance analysis (MF-BIA), and dual-energy x-ray absorptiometry (DXA), to serve as supplemental %BF assessment after failing the tape test. Although supplemental assessments are intended to improve on the accuracy and precision of the tape test, preassessment standardization, specifically regarding acute water ingestion (AWI), is lacking. Thus, the purpose of this narrative review was to (a) summarize the available literature regarding the influence of AWI on body composition estimates derived from ADP, MF-BIA, and DXA and (b) provide evidence-based recommendations for researchers and practitioners. Studies indicate that AWI increases %BF estimates with ADP (4 of 6 [4/6] observations) and MF-BIA (6/7), whereas AWI increases muscle mass (6/6) and likely decreases %BF (2/3) when obtained by DXA. In conclusion, ADP, MF-BIA, and DXA are susceptible to confounding from AWI, leading to inaccurate body composition estimates that may negatively affect the careers of military personnel. Based on the findings from this narrative review, military practitioners and researchers should (a) follow manufacturer guidelines for calorie intake [food and fluid] and exercise avoidance, (b) conduct urine-specific gravity testing [if possible], and (c) limit AWI to <250 ml before assessment.

Nourishing Physical Productivity and Performance On a Warming Planet - Challenges and Nutritional Strategies to Mitigate Exertional Heat Stress

PURPOSE OF REVIEW: Climate change is predicted to increase the frequency and severity of exposure to hot environments. This can impair health, physical performance, and productivity for active individuals in occupational and athletic settings. This review summarizes current knowledge and recent advancements in nutritional strategies to minimize the impact of exertional-heat stress (EHS). RECENT FINDINGS: Hydration strategies limiting body mass loss to < 3% during EHS are performance-beneficial in weight-supported activities, although evidence regarding smaller fluid deficits (< 2% body mass loss) and weight-dependent activities is less clear due to a lack of well-designed studies with adequate blinding. Sodium replacement requirements during EHS depends on both sweat losses and the extent of fluid replacement, with quantified sodium replacement only necessary once fluid replacement > 60-80% of losses. Ice ingestion lowers core temperature and may improve thermal comfort and performance outcomes when consumed before, but less so during activity. Prevention and management of gastrointestinal disturbances during EHS should focus on high carbohydrate but low FODMAP availability before and during exercise, frequent provision of carbohydrate and/or protein during exercise, adequate hydration, and body temperature regulation. Evidence for these approaches is lacking in occupational settings. Acute kidney injury is a potential concern resulting from inadequate fluid replacement during and post-EHS, and emerging evidence suggests that repeated exposures may increase the risk of developing chronic kidney disease. Nutritional strategies can help regulate hydration, body temperature, and gastrointestinal status during EHS. Doing so minimizes the impact of EHS on health and safety and optimizes productivity and performance outcomes on a warming planet.

Skimmed, Lactose-Free Milk Ingestion Postexercise: Rehydration Effectiveness and Gastrointestinal Disturbances Versus Water and a Sports Drink in Physically Active People

Postexercise hydration is fundamental to replace fluid loss from sweat. This study evaluated rehydration and gastrointestinal (GI) symptoms for each of three beverages: water (W), sports drink (SD), and skimmed, lactose-free milk (SLM) after moderate-intensity cycling in the heat. Sixteen college students completed three exercise sessions each to lose ≈2% of their body mass. They drank 150% of body mass loss of the drink assigned in randomized order; net fluid balance, diuresis, and GI symptoms were measured and followed up for 3 hr after completion of fluid intake. SLM showed higher fluid retention (∼69%) versus W (∼40%; p < .001); SD (∼56%) was not different from SLM or W (p > .05). Net fluid balance was higher for SLM (-0.26 kg) and SD (-0.42 kg) than W (-0.67 kg) after 3 hr (p < .001), resulting from a significantly lower diuresis with SLM. Reported GI disturbances were mild and showed no difference among drinks (p > .05) despite ingestion of W (1,992 ± 425 ml), SD (1,999 ± 429 ml), and SLM (1,993 ± 426 ml) in 90 min. In conclusion, SLM was more effective than W for postexercise rehydration, showing greater fluid retention for the 3-hr follow-up and presenting with low-intensity GI symptoms similar to those with W and SD. These results confirm that SLM is an effective option for hydration after exercise in the heat.

Compromised heat loss leads to a delayed ice slurry induced reduction in heat storage

Compromised heat loss due to limited convection and evaporation can increase thermal strain. We aimed to determine the effectiveness of ice slurry ingestion to reduce thermal strain following hyperthermia in a state of compromised heat loss. Twelve healthy males (age: 25 ± 4y) underwent hot water immersion to elevate rectal temperature (Trec) by 1.82 ± 0.08°C on four occasions. In the subsequent 60-min of seated recovery, participants ingested either 6.8 g·kg-1 of ice slurry (-0.6°C) or control drink (37°C) in ambient conditions (21 ± 1°C, 39 ± 10% relative humidity), wearing either t-shirt and shorts (2 trials: ICE and CON) or a whole-body sweat suit (2 trials: ICE-SS and CON-SS). Trec and mean skin temperature (Tsk) were recorded and a two-compartment thermometry model of heat storage was calculated. Heat storage was lower in ICE compared with CON at 20-40min (p ≤ 0.044, d ≥ 0.88) and for ICE-SS compared with CON-SS at 40-60 min (p ≤ 0.012, d ≥ 0.93). Trec was lower in ICE compared with CON from 30-60min (p ≤ 0.034, d ≥ 0.65), with a trend for a reduced Trec in ICE-SS compared with CON-SS at 40min (p = 0.079, d = 0.60). A greater Tsk was found in ICE-SS and CON-SS compared with ICE and CON (p < 0.001, d ≥ 3.37). A trend for a lower Tsk for ICE compared with CON was found at 20-40min (p ≤ 0.099, d ≥ 0.53), no differences were found for ICE-SS vs CON-SS (p ≥ 0.554, d ≤ 0.43). Ice slurry ingestion can effectively reduce heat storage when heat loss through convection and evaporation is compromised, relevant to those wearing personal protective equipment or those with compromised sweat loss. Compromised heat loss delays the reduction in heat storage, possibly related to ice slurry ingestion not lowering Tsk.

Metabolic, cardiovascular, neuromuscular and perceptual responses to repeated military-specific load carriage treadmill simulations

Bouts of military load carriage are rarely completed in isolation; however, limited research has investigated the physiological responses to repeated load carriage tasks. Twelve civilian men (age, 28 ± 8 years; stature, 185.6 ± 5.8 cm; body mass 84.3 ± 11.1 kg and maximal oxygen uptake, 51.5 ± 6.4 mL·kg-1 min-1) attended the laboratory on two occasions to undertake a familiarisation and an experimental session. Following their familiarisation session, participants completed three bouts of a fast load carriage protocol (FLCP; ∼65 min), carrying 25 kg, interspersed with a 65-min recovery period. Physiological strain (oxygen uptake [V̇O2] and heart rate [HR]) was assessed during the FLCP bouts, and physical performance assessments (weighted counter-movement jump [wCMJ], maximal isometric voluntary contraction of the quadriceps [MIVC] and seated medicine ball throw [SMBT]) was measured pre and post each FLCP bout. A main effect for bout and measurement time was evident for V̇O2 and HR (both p < 0.001 and Ѡ2 = 0.103-0.816). There was no likely change in SMBT distance (p = 0.201 and Ѡ2 = 0.004), but MIVC peak force reduced by approximately 25% across measurement points (p < 0.001 and Ѡ2 = 0.133). A mean percentage change of approximately -12% from initial values was also evident for peak wCMJ height (p = 0.001 and Ѡ2 = 0.028). Collectively, these data demonstrate that repeated FLCP bouts result in an elevated physiological strain for each successive bout, along with a substantial reduction in lower body power (wCMJ and MIVC). Therefore, future research should investigate possible mitigation strategies to maintain role-related capability.

Nicotine exacerbates exertional heat strain in trained men: a randomized, placebo-controlled, double-blind study

To determine whether using nicotine exacerbates exertional heat strain through an increased metabolic heat production (Hprod) or decreased skin blood flow (SkBF), 10 nicotine-naïve trained males [37 ± 12 yr; peak oxygen consumption (V̇o2peak): 66 ± 10 mL·min-1·kg-1] completed four trials at 20°C and 30°C following overnight transdermal nicotine (7 mg·24 h-1) and placebo use in a crossover, double-blind design. They cycled for 60 min (55% V̇o2peak) followed by a time trial (∼75% V̇o2peak) during which measures of gastrointestinal (Tgi) and mean weighted skin ([Formula: see text]sk) temperatures, SkBF, Hprod, and mean arterial pressure (MAP) were made. The difference in ΔTgi between nicotine and placebo trials was greater during 30°C (0.4 ± 0.5°C) than 20°C (0.1 ± 0.7°C), with [Formula: see text]sk higher during nicotine than placebo trials (0.5 ± 0.5°C, P = 0.02). SkBF became progressively lower during nicotine than placebo trials (P = 0.01) and progressively higher during 30°C than 20°C trials (P < 0.01); MAP increased from baseline (P < 0.01) and remained elevated in all trials. The difference in Hprod between 30°C and 20°C trials was lower during nicotine than placebo (P = 0.01) and became progressively higher during 30°C than 20°C trials with exercise duration (P = 0.03). Mean power output during the time trial was lower during 30°C than 20°C trials (24 ± 25 W, P = 0.02), and although no effect of nicotine was observed (P > 0.59), two participants (20%) were unable to complete their 30°C nicotine trials as one reached the ethical limit for Tgi (40.0°C), whereas the other withdrew due to "nausea and chills" (Tgi = 39.7°C). These results demonstrate that nicotine use increases thermal strain and risk of exertional heat exhaustion by reducing SkBF.NEW & NOTEWORTHY In naïve participants, acute nicotine use exerts a hyperthermic effect that increases the risk of heat exhaustion during exertional heat strain, which is driven by a blunted skin blood flow response. This has implications for 1) populations that face exertional heat strain and demonstrate high nicotine use (e.g., athletes and military, 25%-50%) and 2) study design whereby screening and exclusion for nicotine use or standardization of prior use (e.g., overnight abstinence) is encouraged.

Parade safety and planning: A heat balance case study of marching band artists

Marching band (MB) artists are subject to exertional heat illnesses (EHIs) similar to other active groups like laborers and athletes. Yet, they are an understudied population with no evidence-based heat safety guidelines. Presented here is a case study of the 233rd annual Bristol, RI Independence Day Parade in 2018 that resulted in over 50 EHIs, including 25 from the Saint Anthony Village marching band (MB) from suburban Minneapolis, MN. This research aims to identify the contributing factors that led to the large number of EHIs, as well as guide ensuring the safety of MB artists in future events. A human heat balance model in conjunction with local weather data was used to simulate heat stress on MB artists. Three modeling scenarios were used to isolate the roles of clothing (band uniform vs. t-shirt and shorts), weather (July 4, 2018 vs. 30-year climatology), and metabolic rate (slow, moderate, and brisk marching pacing) on heat stress. The results identify several key factors that increased heat stress. The meteorological conditions were unusually hot, humid, and sunny for Bristol, resulting in reduced cooling from evaporation and convection, and increased radiant heating. Behavioral factors also affect heat stress. The full marching band uniforms reduced evaporative cooling by 50% and the activity levels of marching 4 km over several hours without breaks resulted in conditions that were uncompensable. Finally, it is speculated that a lack of acclimatization for participants from cooler regions may have exacerbated heat-related impacts. These findings highlight several recommendations for MB directors and race organizers, including the use of summer uniforms for anticipated hot conditions, and advance parade planning that includes providing shade/hydration before and after the parade for participants, considering cooler routes that reduce radiant heating and preparing for anticipated heat-related health impacts appropriate for anticipated hot conditions.

New Zealand blackcurrant extract modulates the heat shock response in men during exercise in hot ambient conditions

PURPOSE

To determine if 7d of New Zealand blackcurrant (NZBC) extract alters the heat shock, inflammatory and apoptotic response during prolonged exertional-heat stress.

METHODS

Ten men (Age: 29 ± 2 years, Stature: 1.82 ± 0.02 m, Mass: 80.3 ± 2.7 kg, V̇O2max: 56 ± 2 mL·kg-1·min-1) ingested two capsules of CurraNZ™ (NZBC extract: 210 mg anthocyanins·day-1) or PLACEBO for 7d prior to 1 h treadmill run (65% V̇O2max) in hot ambient conditions (34 °C/40% RH). Blood samples were collected before (Pre), immediately after (Post), 1 h after (1-Post), and 4 h after (4-Post) exercise. Heat shock proteins (HSP90, HSP70, HSP32) were measured in plasma. HSP and protein markers of inflammatory capacity (TLR4, NF-κB) and apoptosis (BAX/BCL-2, Caspase 9) were measured in peripheral blood mononuclear cells (PBMC).

RESULTS

eHSP32 was elevated at baseline in NZBC(+ 31%; p < 0.001). In PLACEBO HSP32 content in PBMC was elevated at 4-Post(+ 98%; p = 0.002), whereas in NZBC it fell at Post(- 45%; p = 0.030) and 1-Post(- 48%; p = 0.026). eHSP70 was increased at Post in PLACEBO(+ 55.6%, p = 0.001) and NZBC (+ 50.7%, p = 0.010). eHSP90 was increased at Post(+ 77.9%, p < 0.001) and 1-Post(+ 73.2%, p < 0.001) in PLACEBO, with similar increases being shown in NZBC (+ 49.0%, p = 0.006 and + 66.2%, p = 0.001; respectively). TLR4 and NF-κB were both elevated in NZBC at PRE(+ 54%, p = 0.003 and + 57%, p = 0.004; respectively). Main effects of study condition were also shown for BAX/BCL-2(p = 0.025) and Caspase 9 (p = 0.043); both were higher in NZBC.

CONCLUSION

7d of NZBC extract supplementation increased eHSP32 and PBMC HSP32 content. It also increased inflammatory and apoptotic markers in PBMC, suggesting that NZBC supports the putative inflammatory response that accompanies exertional-heat stress.

Role of nutrition in human performance in military populations

The role of nutrition and performance is well established. Service members' physical and cognitive performance, sleep and mood are impacted by nutritional choices. Although many eating patterns have emerged, consensus among experts recommend a dietary pattern focused on predominantly whole plant-based foods. Adequate intakes of fruits, vegetables, whole grains, beans, legumes, nuts and seeds should be prioritised. Implementation of strategic and intentional fuelling strategies around times of activity maintain adequate energy stores, enhance recovery and protect against training injuries. Carbohydrates are prioritised before, during and after activity or a mission, although the type and amount will vary based on duration and intensity of activity. Protein is generally the focus after activity or a mission and may be included before activity depending on individual tolerance. There are no specific recommendations for fat consumption before, during and after exercise that will improve performance. That said, Service members generally tolerate low-fat meals/snacks prior to exercise, limit fat intake during exercise, may include fat as part of the post exercise meal/snack, and generally consume most fat during the maintenance and growth phase. Careful consideration and planning for food and fluid requirements should be made when Service members are exposed to heat, cold and/or altitude. Operational rations are formulated to meet the nutritional needs of all Service members across a variety of diverse climates, environments and altitudes. Service members may use dietary supplements to improve their performance and need to be aware of available resources to help them make informed decisions.

Reliability and validity of the MX3 portable sweat sodium analyser during exercise in warm conditions

PURPOSE

Accurately measuring sweat sodium concentration ([Na+]) in the field is advantageous for coaches, scientists, and dieticians looking to tailor hydration strategies. The MX3 hydration testing system is a new portable analyser that uses pre-calibrated biosensors to measure sweat [Na+]. This study aimed to assess the validity and reliability of the MX3 hydration testing system.

METHODS

Thirty-one (11 females) recreationally active participants completed one experimental trial. During this trial, participants exercised at a self-selected pace for 45 min in a warm environment (31.5 ± 0.8 °C, 63.2 ± 1.3% relative humidity). Sweat samples were collected from three measurement sites using absorbent patches. The samples were then analysed for sweat [Na+] using both the MX3 hydration testing system and the Horiba LAQUAtwin-NA-11. The reliability of the MX3 hydration testing system was determined following two measurements of the same sweat sample.

RESULTS

The mean difference between measurements was 0.1 mmoL·L-1 (95% limits of agreement (LoA): - 9.2, 9.4). The analyser demonstrated a coefficient of variation (CV) of 5.6% and the standard error of measurement was 3.3 mmoL·L-1. When compared to the Horiba LAQUAtwin-NA-11, there was a mean difference of - 1.7 mmoL·L-1 (95% LoA: - 0.25 X ¯ , 0.25 X ¯ ) and the CV was 9.8%.

CONCLUSION

The MX3 hydration testing system demonstrated very good single-trial reliability, moderate agreement and a very good CV relative to the Horiba LAQUAtwin-Na-11. To further validate its performance, the MX3 hydration testing system should be compared with analytical techniques known for superior reliability and validity.

Trehalose Improved 20-min Cycling Time-Trial Performance After 100-min Cycling in Amateur Cyclists

Carbohydrate (CHO) supplementation during endurance exercise can improve performance. However, it is unclear whether low glycemic index (GI) CHO leads to differential ergogenic and metabolic effects compared with a standard high GI CHO. This study investigated the ergogenic and metabolic effects of CHO supplementation with distinct GIs, namely, (a) trehalose (30 g/hr), (b) isomaltulose (30 g/hr), (c) maltodextrin (60 g/hr), and (d) placebo (water). In this double-blind, crossover, counterbalanced, placebo-controlled study, 13 male cyclists cycled a total of 100 min at varied exercise intensity (i.e., 10-min stages at 1.5, 2.0, and 2.5 W/kg; repeated three times plus two 5-min stages at 1.0 W/kg before and after the protocol), followed by a 20-min time trial on four separated occasions. Blood glucose and lactate (every 20 min), heart rate, and ratings of perceived exertion were collected throughout, and muscle biopsies were taken before and immediately after exercise. The results showed that trehalose improved time-trial performance compared with placebo (total work done 302 ± 39 vs. 287 ± 48 kJ; p = .01), with no other differences between sessions (all p ≥ .07). Throughout the 100-min protocol, blood glucose was higher with maltodextrin compared with the other supplements at all time points (all p < .05). Heart rate, ratings of perceived exertion, muscle glycogen content, blood glucose, and lactate were not different between conditions when considering the 20-min time trial (all p > .05). Trehalose supplementation throughout endurance exercise improved cycling performance and appears to be an appropriate CHO source for exercise tasks up to 2 hr. No ergogenic superiority between the different types of CHO was established.

Health Claims for Sports Drinks-Analytical Assessmentaccording to European Food Safety Authority's Scientific Opinion

In Europe, sports food supplements (SSFs) are subject to specific laws and regulations. Up to 70% of athletes are highly influenced by the information on the label or the advertisement of the SSF, which often does not correspond to the scientific evidence, such as health claims. The aim is to analyze such claims relating to sports drinks (SDs) in commercial messages. To this end, an observational and cross-sectional study was conducted based on the analysis of the content and degree of adequacy of the health claims indicated on the labelling or technical data sheet of the SDs with those established by the European legislation in force according to the European Food Safety Authority (EFSA). The SSFs were searched for via Amazon and Google Shopping. A total of 114 health claims were evaluated. No claim fully conformed with the recommendations. A total of 14 claims (n = 13 products) almost conformed to the recommendations; they were "Maintain endurance level in exercises requiring prolonged endurance", "Improve water absorption during physical exercise", and "Improved physical performance during high intensity, high duration physical exercise in trained adults", representing 12.3% of the total (n = 114). The vast majority of the claims identified indicated an unproven cause-effect and should be modified or eliminated, which amounts to food fraud towards the consumer.

Whole body sweat rate prediction: outdoor running and cycling exercise

Our aim was to develop and validate separate whole body sweat rate prediction equations for moderate to high-intensity outdoor cycling and running, using simple measured or estimated activity and environmental inputs. Across two collection sites in Australia, 182 outdoor running trials and 158 outdoor cycling trials were completed at a wet-bulb globe temperature ranging from ∼15°C to ∼29°C, with ∼60-min whole body sweat rates measured in each trial. Data were randomly separated into model development (running: 120; cycling: 100 trials) and validation groups (running: 62; cycling: 58 trials), enabling proprietary prediction models to be developed and then validated. Running and cycling models were also developed and tested when locally measured environmental conditions were substituted with participants' subjective ratings for black globe temperature, wind speed, and humidity. The mean absolute error for predicted sweating rate was 0.03 and 0.02 L·h-1 for running and cycling models, respectively. The 95% confidence intervals for running (+0.44 and -0.38 L·h-1) and cycling (+0.45 and -0.42 L·h-1) were within acceptable limits for an equivalent change in total body mass over 3 h of ±2%. The individual variance in observed sweating described by the predictive models was 77% and 60% for running and cycling, respectively. Substituting measured environmental variables with subjective assessments of climatic characteristics reduced the variation in observed sweating described by the running model by up to ∼25%, but only by ∼2% for the cycling model. These prediction models are publicly accessible (https://sweatratecalculator.com) and can guide individualized hydration management in advance of outdoor running and cycling.NEW & NOTEWORTHY We report the development and validation of new proprietary whole body sweat rate prediction models for outdoor running and outdoor cycling using simple activity and environmental inputs. Separate sweat rate models were also developed and tested for situations where all four environmental parameters are not available, and some must be subsequently estimated by the user via a simple rating scale. All models are freely accessible through an online calculator: https://sweatratecalculator.com. These models, via the online calculator, will enable individualized hydration management for training or recreational cycling or running in an outdoor environment.

Recommendations for management of diabetes and its complications during Hajj (Muslim Pilgrimage) - 2024 update

Hajj is an obligatory duty for all healthy adult Muslims once in the lifetime subjected to the ability. Considering the 10.5 % global prevalence of diabetes coupled with the numbers of Muslims performing the Hajj, ∼ 1.8 million in 2023, it is estimated that Muslims with diabetes performing Hajj may exceed 340,000 this year. During Hajj the pattern and amount of their meal, fluid intake and physical activity are markedly altered. Many people with diabetes insist on doing the Hajj duty, thereby creating a medical challenge for themselves and their health care providers. It is therefore important that medical professionals be aware of the potential risks that may be associated with Hajj. People with diabetes may face many health hazards during Hajj including but not limited to the killer triad which might occur during Hajj: Hypoglycemia, Foot injury and Infections. Many precautions should be taken to prevent and treat these potentially serious complications. Risk stratification, medication adjustments, proper clinical assessment, and education before doing Hajj are crucial.