Dehydration Impairs Cognitive Performance: A Meta-analysis

The Cognitive Function and Taekwondo-Specific Kick Performance of Taekwondo Athletes at Different Hydration Statuses

PURPOSE

Successful participation in taekwondo (TKD) requires athletes to possess quick decision-making abilities and demonstrate technical proficiency during competition. Dehydration, occurring during both training and competition, is widely recognized to have various negative effects.

METHODS

This study investigated the impact of different levels of dehydration on cognitive function, as measured by the Vienna Test System, and the specific performance of kicking techniques among TKD athletes. Using a randomized crossover design, 12 participants were involved in the study. Before and after 1 hour of training at 80% of maximal heart rate, participants were weighed and provided urine samples. All participants were randomly assigned to 3 different hydration conditions: the euhydrated (EUH) group had unrestricted access to fluid consumption, while the hypohydrated (HYP) and severely HYP (S-HYP) groups experienced reductions of 2.0% and 4.0% of their initial body weight, respectively.

RESULTS

The EUH group exhibited better reaction speed in reaction-time test-form S1 than the HYP and S-HYP groups. Notably, the EUH group demonstrated a significantly higher success rate in the front-side kick (EUH 98%, HYP 90%, S-HYP 88%; P < .05). However, the success rates of back roundhouse kick and free head kick were similar among the 3 statuses. Furthermore, postexercise heart rates were found to be significantly higher in the HYP and S-HYP groups compared with the EUH group.

CONCLUSIONS

This study provides insight into the negative effects of dehydration on cognitive function and TKD-specific performance. It is recommended that TKD athletes maintain optimal hydration levels during training and competition to ensure optimal performance.

All-in-One, Wireless, Multi-Sensor Integrated Athlete Health Monitor for Real-Time Continuous Detection of Dehydration and Physiological Stress

Athletes are at high risk of dehydration, fatigue, and cardiac disorders due to extreme performance in often harsh environments. Despite advancements in sports training protocols, there is an urgent need for a non-invasive system capable of comprehensive health monitoring. Although a few existing wearables measure athlete's performance, they are limited by a single function, rigidity, bulkiness, and required straps and adhesives. Here, an all-in-one, multi-sensor integrated wearable system utilizing a set of nanomembrane soft sensors and electronics, enabling wireless, real-time, continuous monitoring of saliva osmolality, skin temperature, and heart functions is introduced. This system, using a soft patch and a sensor-integrated mouthguard, provides comprehensive monitoring of an athlete's hydration and physiological stress levels. A validation study in detecting real-time physiological levels shows the device's performance in capturing moments (400-500 s) of synchronized acute elevation in dehydration (350%) and physiological strain (175%) during field training sessions. Demonstration with a few human subjects highlights the system's capability to detect early signs of health abnormality, thus improving the healthcare of sports athletes.

Ad libitum dehydration is associated with poorer performance on a sustained attention task but not other measures of cognitive performance among middle-to-older aged community-dwelling adults: A short-term longitudinal study

OBJECTIVE

Hydration status and water intake are critical to physiological health. Despite a popular narrative that dehydration impairs cognitive performance, results are mixed in the literature. Therefore, we tested how hydration status was associated with cognitive performance in an ad libitum state over the course of 3 months.

METHODS

Data come from a short-term longitudinal study among middle-to-older aged US adults (n = 78) measured three times (207 observations). All participants were scheduled for 8:00 a.m. visits for the baseline, two-week, and 3-month examinations where they completed surveys, neuropsychological tests to measure cognitive performance, anthropometrics, and a blood draw for biomarker analysis. Serum osmolality (Sosm) was measured as a biomarker of hydration status using osmometry. Four cognitive performance tasks were assessed, including inhibition, working memory, cognitive flexibility, and sustained attention.

RESULTS

Panel random effects linear regressions demonstrate that there was an inverse association between dehydration and sustained attention, whereas there were no significant relationships between dehydration and inhibition, working memory, and cognitive flexibility. Adults who were dehydrated (defined as Sosm >300 mOsm/kg) performed substantially worse (B = 0.65 z-score; SE = 0.28; p = .020) on the sustained attention task than those who were not dehydrated adjusting for time fixed effects, age, body mass index, sex, and educational attainment.

CONCLUSION

This short-term longitudinal study found that dehydration was only associated with poorer performance on a cognitive performance task that required sustained attention. Maintaining adequate hydration may be increasingly important for middle-to-older aged adults to ensure proper cognitive function, particularly as water needs increase in future climatic scenarios.

Differences in urine creatinine and osmolality between black and white Americans after accounting for age, moisture intake, urine volume, and socioeconomic status

Urine osmolality is used throughout research to determine hydration levels. Prior studies have found black individuals to have elevated urine creatinine and osmolality, but it remains unclear which factors explain these findings. This cross-sectional, observational study sought to understand the relationship of self-reported race to urine creatinine and urine osmolality after accounting for age, socioeconomic status, and fluid intake. Data from 1,386 participants of the 2009-2012 National Health and Nutrition Examination Survey were utilized. Age, poverty-to-income ratio (PIR), urine flow rate (UFR), fluid intake, estimated lean body mass (LBM), urine creatinine, and urine osmolality were measured. In a sex-specific manner, black and white participants were matched on age, dietary moisture, UFR, and PIR. Urine creatinine was greater in black men (171 mg/dL) than white men (150 mg/dL) and greater in black women (147 mg/dL) than white women (108 mg/dL) (p < .001). Similarly, urine osmolality was greater in black women than white women (723 vs. 656 mOsm/kg, p = .001), but no difference was observed between white and black men (737 vs. 731 mOsm/kg, p = .417). Estimated LBM was greater in black men (61.8 kg) and women (45.5 kg) than in white men (58.9 kg) and women (42.2 kg) (p≤.001). The strongest correlate of urine osmolality in all race-sex groups was urine creatinine (Spearman ρ = .68-.75). These results affirm that individuals identifying as black produce higher urine creatinine concentrations and, in women, higher urine osmolality after matching for age, fluid intake, and socioeconomic status. The findings suggest caution when comparing urine hydration markers between racial groups.

Fluid and electrolyte balance following consumption of skimmed milk and a plant-based soya beverage at rest in euhydrated males

PURPOSE

Cow's milk is one of the most hydrating beverages, but many individuals choose not to consume dairy in their diet due to intolerance, allergy, or dietary preference. Milk is commonly replaced with plant-based beverages, including soya which has the most comparable protein content, but little is known about their hydration potential. This study compared fluid and electrolyte balance responses between a soya beverage and skimmed cow's milk.

METHODS

Ten healthy males [age 27 (6) y; body mass index 24.6 (2.3) kg/m2] completed two randomised counterbalanced trials, involving consuming 1000 mL water from approximately isocaloric amounts of skimmed cow's milk (MILK) or a sweetened soya beverage (SOYA), in four aliquots over 30 min in a euhydrated fasted state. Volume, specific gravity, and electrolyte (sodium, potassium, chloride) concentrations were determined in total-void urine samples collected pre-/post-beverage ingestion, and hourly for 180 min thereafter. Hunger, thirst, nausea and stomach fullness were rated proximal to urine samples.

RESULTS

Total urine mass (MILK, 986 ± 254 g; SOYA, 950 ± 248 g; P = 0.435) and urine specific gravity (P = 0.156) did not differ between trials. Potassium balance was greater in SOYA 0-180 min post-beverage (P ≤ 0.013), whilst chloride balance was greater in MILK 0-120 min post-beverage (P ≤ 0.036). Sodium balance (P = 0.258), total electrolyte balance (P = 0.258), and subjective measures (P ≥ 0.139) were not different between trials.

CONCLUSION

Replacing cow's milk with a soya beverage did not negatively impact fluid balance in healthy young males, making it a viable option for those who choose not to consume dairy in their diet.

Plain Water Intake, Sleep Quality, and Hydration Status of Pregnant Woman in Hainan, China: A Cross-Sectional Study

OBJECTIVE

Both short and long sleep durations are associated with decreased kidney function; however, few studies have examined the relationship between sleep, hydration status, and plain water intake. This study aimed to assess the relationship between sleep quality, hydration status, and plain water intake in pregnant women.

METHODS

A cross-sectional study method was used to collect data from 380 pregnant women with regular examinations at the hospital between May 2019 and February 2021.

RESULTS

There were statistically significant differences in daily plain water intake (x2 = 14.118, p = 0.001), PSQI score (x2 = 77.708, p < 0.001), sleep duration (x2 = 67.569, p > 0.001), subjective sleep quality (x2 = 67.441, p = 0.001), time to fall asleep (x2 = 64.782, p < 001), sleep disorders (x2 = 70.853, p < 0.001), and daytime dysfunction (x2 = 38.441, p < 0.001) among different hydration status groups. Ordinal logistic regression results indicated that the intake of plain water ≥1500 mL/d (OR = 0.40, 95% CI = 0.24~0.67), good subjective sleep quality (OR = 0.15, 95% CI = 0.07~0.32), short time to fall asleep (OR = 0.32, 95% CI = 0.14~0.70), 8 h of sleep (OR = 0.06, 95% CI = 0.02~0.17), 6-7 h of sleep (OR = 0.19, 95% CI = 0.07~0.54), no sleep disturbance (OR = 0.31, 95% CI = 0.11~0.89), and high sleep efficiency (OR = 0.46, 95% CI = 0.03~0.79) were factors that were correlated with optimal hydration status. Sleep duration and daytime dysfunction partially mediated the effect of plain water intake on hydration status. The mediating effect of sleep duration was -0.036, accounting for 14.006% of the overall effect. The mediating effect of daytime dysfunction was -0.024, accounting for 9.459% of the overall effect.

CONCLUSION

The hydration status in pregnant women may be affected by daily plain water intake and sleep quality.

Factors affecting the psychomotor vigilance of nurses working night shift

BACKGROUND

Shifts and long working hours decrease the psychomotor vigilance of healthcare workers especially when working night shifts. Working night shifts adversely affects nurses' health and impacts patient safety.

AIM

The purpose of this study is to identify factors affecting the psychomotor vigilance of nurses working night shift.

METHODS

This descriptive cross-sectional study was carried out with 83 nurses who were working in a private hospital in Istanbul and voluntarily participated in this study between April 25 and May 30, 2022. Data were collected using "Descriptive Characteristics Form," "Psychomotor Vigilance Task," "Pittsburgh Sleep Quality Index," and "Epworth Sleepiness Scale." The "STROBE checklist" for cross-sectional studies was utilized in order to report the findings of the study.

RESULTS

When time-dependent variation of the nurses' psychomotor vigilance task performances on the night shift was examined, it was observed that the nurses' mean reaction time and number of lapses increased at the end of the night shift. Age, smoking, physical activity, daily water consumption, daytime sleepiness, and sleep quality were found as the factors affecting nurses' psychomotor vigilance.

CONCLUSION

The psychomotor vigilance task performances of nurses working night shift are affected by age and a variety of behavioral factors.

IMPLICATIONS FOR NURSING AND HEALTH POLICY

Suggestions for nursing policy include the implementation of workplace health promotion programs in order to increase the attention level of nurses in order to ensure employee and patient health and safety and create a healthy working environment.

Shifting focus: Time to look beyond the classic physiological adaptations associated with human heat acclimation

Planet Earth is warming at an unprecedented rate and our future is now assured to be shaped by the consequences of more frequent hot days and extreme heat. Humans will need to adapt both behaviorally and physiologically to thrive in a hotter climate. From a physiological perspective, countless studies have shown that human heat acclimation increases thermoeffector output (i.e., sweating and skin blood flow) and lowers cardiovascular strain (i.e., heart rate) during heat stress. However, the mechanisms mediating these adaptations remain understudied. Furthermore, several possible benefits of heat acclimation for other systems and functions involved in maintaining health and performance during heat stress remain to be elucidated. This review summarizes recent advances in human heat acclimation, with emphasis on recent studies that (1) advanced our understanding of the mechanisms mediating improved thermoeffector output and (2) investigated adaptations that go beyond those classically associated with heat acclimation. We highlight that these studies have contributed to a better understanding of the integrated physiological responses underlying human heat acclimation while leaving key unanswered questions that will need to be addressed in the future.

Water Intake and Hydration Status among Pregnant Women in the Second Trimester in China: A Three-Day Metabolic Trial

Adequate water intake and optimal hydration status during pregnancy are crucial for maternal and infant health. However, research on water intake by pregnant women in China is very limited. This study mainly aimed to observe the daily total water intake (TWI) of pregnant women and its different sources and to investigate the relationship between their water intake and hydration biomarkers. From October to November 2020, a convenience sample of pregnant women in the second trimester (n = 21) was recruited. Under conditions close to daily life, they undertook a 3-day metabolic trial. Each participant was provided with sufficient bottled water, and the weight of what they drank each time was measured. The intake of other beverages and foods was measured using a combination of weighing and duplicate portion method. Fasting venous blood and 24 h urine samples were collected and analyzed for the hydration biomarkers, including the serum/urine osmolality, urine pH, urine specific gravity, and the concentrations of major electrolytes in urine and serum. The results showed that the mean daily TWI was 3151 mL, of which water from beverages and foods accounted for 60.1% and 39.9%, respectively. The mean total fluid intake (TFI) was 1970 mL, with plain water being the primary contributor (68.7%, r = 0.896). Among the participants, 66.7% (n = 14, Group 1) met the TWI recommendation set by the Chinese Nutrition Society. Further analysis revealed that the TFI, water from beverages and foods, plain water, and milk and milk derivatives (MMDs) were significantly higher in Group 1 than those who did not reach the adequate intake value (Group 2) (p < 0.05). The results of hydration biomarkers showed that the mean 24 h urine volume in Group 1 was significantly higher than that in Group 2 (p < 0.05), while the 24 h urine osmolality, sodium, magnesium, phosphorus, chloride, and creatinine concentrations in Group 1 were significantly lower than those in Group 2 (p < 0.05). However, no significant differences were observed in serum biomarkers. Partial correlation analysis showed that TWI was moderately positively correlated with 24 h urine volume (r = 0.675) and negatively correlated with urine osmolality, sodium, potassium, magnesium, calcium, phosphorus, and chloride concentrations (r = from-0.505 to -0.769), but it was not significantly correlated with serum biomarkers. Therefore, under free-living conditions, increasing the daily intake of plain water and MMDs is beneficial for pregnant women to maintain optimal hydration. The hydration biomarkers in urine are more accurate indicators of water intake and exhibit greater sensitivity compared to serum biomarkers. These findings provide a scientific basis for establishing appropriate water intake and hydration status for pregnant women in China.

Cognitive Function among Young Women's Football Players in the Summer Heat

Recently, there has been a growing focus on studies related to women's football. However, the cognitive function of female football players has not been extensively characterized. Thus, we explored how the cognitive function of female football players was altered during a series of matches in summer and examined day-to-day variations in cognitive function with regard to dehydration status. Resting cognitive function was assessed from 17 young women football players during the Japan Club Youth Women's football tournament, which spanned eight consecutive days. Cognitive function initially improved, with this improvement sustained throughout the tournament. It is worth noting that ten participants experienced symptoms of dehydration at least once during the tournament; however, these symptoms were not found to be linked to impaired cognitive function, suggesting that resting cognitive function remains unaffected during summer matches, even in the presence of dehydration symptoms.

Popular education to improve water quality and hygiene in a Mexican indigenous community

Long-term research has identified significant water contamination and associated poor health outcomes in the indigenous community of Alpuyeca, located in south-central Mexico. We set out to develop a popular education initiative in this community to improve water, sanitation and hygiene (WaSH) knowledge and practices. In order to avoid recreating hierarchical power dynamics in this vulnerable community, a participatory action research (PAR) design was used, wherein the community took leadership and facilitation roles in each stage of the research process. In qualitative interviews and design sessions, community members identified unsatisfied WaSH needs in households and community institutions and articulated a clear worldview of the spiritual role of water, which guided the development of a series of popular education-based workshops and discussions. The popular education initiative process was documented with a mixed methods framework, using before-and-after surveys, semi-structured interviews and participatory observation. Increases in knowledge and practices related to water purification, water consumption and hand hygiene were noted in the community. The community identified locally installed and managed ecotechnologies as a key opportunity for sustainable development, community participation and the adoption of water and sanitation systems, compatible with public imaginaries of the role of water.

Educational Needs for Coaching Judo in Older Adults: The EdJCO Focus Groups

Judo coaches are urged to develop specific competencies and skills for addressing the special needs of older practitioners. Thus, the purpose of this study was to investigate the experts' opinions on judo training in late adulthood to develop sound educational programs for coaches of older judo practitioners. Overall, eighty-eight experts from an international consortium of judo and educational partners participated in national focus groups. During the focus groups, experts discussed five themes and generated statements pertinent to educate coaches to support older judo practitioners (e.g., benefits; necessary knowledge; risks; training groups definition; tools; and tests for monitoring training plans). The initial list of 262 statements was synthesized, validated, analyzed, and organized into a final list of 55 statements and six macro-areas: aging process (n = 10); safety and first aid (n = 6); physiology and fitness (n = 12); psychology and mental health (n = 11); organization and environment (n = 5); adapted judo teaching and training (n = 11). The present international eminence-based study, harmonizing diverse intercultural perspectives, highlighted the specific needs of older judo practitioners. The results of this study will contribute to the structure of a sound educational program for coaches of older judo practitioners to enhance the quality of older adults' sports experiences by linking safety, enjoyment, social interactions, and learning principles.

Young Artistic Gymnasts Drink Ad Libitum Only Half of Their Fluid Lost during Training, but More Fluid Intake Does Not Influence Performance

To examine the effect of the fluid balance on and performance in young artistic gymnasts during training under ad libitum and prescribed fluid intake conditions, eleven males (12.3 ± 2.6 years, mean ± SD) performed two 3 h identical training sessions. Participants ingested, in a random order, water equivalent to either 50% (LV) or 150% (HV) of their fluid loss. After the 3 h training, the gymnasts performed program routines on three apparatuses. The pre-exercise urine specific gravity (USG) was similar between conditions (LV: 1.018 ± 0.007 vs. HV: 1.015 ± 0.007; p = 0.09), while the post-exercise USG was lower in the HV condition (LV: 1.017 ± 0.006 vs. HV: 1.002 ± 0.003; p < 0.001). Fluid loss corresponding to percentage of body mass was higher in the LV condition (1.2 ± 0.5%) compared to the HV condition (0.4 ± 0.8%) (p = 0.02); however, the sums of the score performances were not different (LV: 26.17 ± 2.04 vs. HV: 26.05 ± 2.00; p = 0.57). Ingesting fluid equivalent to about 50% of the fluid lost, which was the amount that was drunk ad libitum during training, maintained short-term hydration levels and avoided excessive dehydration in artistic preadolescent and adolescent gymnasts. A higher amount of fluid, equivalent to about 1.5 times the fluid loss, did not provide an additional performance benefit.

Neuropsychological considerations for long-duration deep spaceflight

The deep space environment far beyond low-Earth orbit (LEO) introduces multiple and simultaneous risks for the functioning and health of the central nervous system (CNS), which may impair astronauts' performance and wellbeing. As future deep space missions to Mars, moons, or asteroids will also exceed current LEO stay durations and are estimated to require up to 3 years, we review recent evidence with contemporary and historic spaceflight case studies addressing implications for long-duration missions. To highlight the need for specific further investigations, we provide neuropsychological considerations integrating cognitive and motor functions, neuroimaging, neurological biomarkers, behavior changes, and mood and affect to construct a multifactorial profile to explain performance variability, subjective experience, and potential risks. We discuss the importance of adopting a neuropsychological approach to long-duration deep spaceflight (LDDS) missions and draw specific recommendations for future research in space neuropsychology.

Fluid Balance, Sodium Losses and Hydration Practices of Elite Squash Players during Training

Elite squash players are reported to train indoors at high volumes and intensities throughout a microcycle. This may increase hydration demands, with hypohydration potentially impairing many key performance indicators which characterise elite squash performance. Consequently, the main aim of this study was to quantify the sweat rates and sweat [Na+] of elite squash players throughout a training session, alongside their hydration practices. Fourteen (males = seven; females = seven) elite or world class squash player’s fluid balance, sweat [Na+] and hydration practices were calculated throughout a training session in moderate environmental conditions (20 ± 0.4 °C; 40.6 ± 1% RH). Rehydration practices were also quantified post-session until the players’ next training session, with some training the same day and some training the following day. Players had a mean fluid balance of −1.22 ± 1.22% throughout the session. Players had a mean sweat rate of 1.11 ± 0.56 L·h−1, with there being a significant difference between male and female players (p < 0.05), and a mean sweat (Na+) of 46 ± 12 mmol·L−1. Players training the following day were able to replace fluid and sodium losses, whereas players training again on the same day were not. These data suggest the variability in players hydration demands and highlight the need to individualise hydration strategies, as well as training prescription, to ensure players with high hydration demands have ample time to optimally rehydrate.

Ergonomic impact of prehospital clinicians using body armour: A qualitative study

Armed crime constitutes a significant number of offences in England. The associated healthcare burden forms 32% of the workload of London HEMS, requiring these clinicians to use body armour. Much research has explored the ergonomic impact of body armour in police and military populations however the impact on prehospital clinicians is not known. The aim of this study is to explore the perceptions of prehospital clinicians of wearing body armour.Focus groups were conducted until theoretical saturation was reached, utilising hermeneutic phenomenology.Problems with the comfort, safety, time, hygiene, coverage, and female fit of armour were identified. Clinicians feel hot in summer, time to respond to scenes is increased and the fit for females is poor.Consideration should be given to sourcing specific female-fit armour and to the interoperability with the rest of the protective clothing. A redesign of uniform could provide greater flexibility to mitigate some of the issues.

Water intake, hydration status and 2-year changes in cognitive performance: a prospective cohort study

BACKGROUND

Water intake and hydration status have been suggested to impact cognition; however, longitudinal evidence is limited and often inconsistent. This study aimed to longitudinally assess the association between hydration status and water intake based on current recommendations, with changes in cognition in an older Spanish population at high cardiovascular disease risk.

METHODS

A prospective analysis was conducted of a cohort of 1957 adults (aged 55-75) with overweight/obesity (BMI between ≥ 27 and < 40 kg/m²) and metabolic syndrome from the PREDIMED-Plus study. Participants had completed bloodwork and validated, semiquantitative beverage and food frequency questionnaires at baseline, as well as an extensive neuropsychological battery of 8 validated tests at baseline and 2 years of follow-up. Hydration status was determined by serum osmolarity calculation and categorized as < 295 mmol/L (hydrated), 295-299.9 mmol/L (impending dehydration), and ≥ 300 mmol/L (dehydrated). Water intake was assessed as total drinking water intake and total water intake from food and beverages and according to EFSA recommendations. Global cognitive function was determined as a composite z-score summarizing individual participant results from all neuropsychological tests. Multivariable linear regression models were fitted to assess the associations between baseline hydration status and fluid intake, continuously and categorically, with 2-year changes in cognitive performance.

RESULTS

The mean baseline daily total water intake was 2871 ± 676 mL/day (2889 ± 677 mL/day in men; 2854 ± 674 mL/day in women), and 80.2% of participants met the ESFA reference values for an adequate intake. Serum osmolarity (mean 298 ± 24 mmol/L, range 263 to 347 mmol/L) indicated that 56% of participants were physiologically dehydrated. Lower physiological hydration status (i.e., greater serum osmolarity) was associated with a greater decline in global cognitive function z-score over a 2-year period (β: - 0.010; 95% CI - 0.017 to - 0.004, p-value = 0.002). No significant associations were observed between water intake from beverages and/or foods with 2-year changes in global cognitive function.

CONCLUSIONS

Reduced physiological hydration status was associated with greater reductions in global cognitive function over a 2-year period in older adults with metabolic syndrome and overweight or obesity. Future research assessing the impact of hydration on cognitive performance over a longer duration is needed.

TRIAL REGISTRATION

International Standard Randomized Controlled Trial Registry, ISRCTN89898870. Retrospectively registered on 24 July 2014.

Association of in-competition injury risk and the degree of rapid weight cutting prior to competition in division I collegiate wrestlers

OBJECTIVES

Weight cutting is thought to offer a competitive advantage in wrestling. Dehydration has deleterious effects on physical and cognitive function, which may increase the risk of injury. The purpose of the study was to investigate whether the degree of weight cutting was associated with injury risk.

METHODS

Data were collected prospectively in a cohort of collegiate wrestlers over seven seasons. Changes in weight, body fat and lean mass were measured during the preseason, at midseason and before competition. Cox proportional-hazard ratios were calculated for risk of in-competition injury.

RESULTS

Among 67 unique division 1 collegiate wrestlers (163 athlete seasons), there were 53 unique injuries affecting 46 athletes. There was no difference in absolute weight change, per cent weight change, per cent body fat change or per cent lean mass change between injured and non-injured wrestlers from the preseason to midseason measurements. From midseason to competition weight, change in body weight was -7.0%±3.2% (-5.3 kg±2.6) in injured athletes compared with -5.7%±3.3% (-4.3 kg±2.5) in non-injured athletes. For every kilogram of body weight lost, wrestlers had a 14% increased hazard of injury (HR 1.14, 95% CI 1.04 to 1.25, p=0.004). For every 1% of body weight lost, wrestlers had an 11% increased hazard of injury (HR 1.11, 95% CI 1.03 to 1.19, p=0.005).

CONCLUSION

Rapid weight cutting was associated with a higher risk of in-competition injuries in division 1 collegiate wrestlers. For every per cent in body weight lost, wrestlers had an 11% increased hazard of injury during competition.

Comparative proteomic changes in rabbit vocal folds undergoing systemic dehydration and systemic rehydration

BACKGROUND

A considerable body of clinical evidence suggests that systemic dehydration can negatively affect voice production, leading to the common recommendation to rehydrate. Evidence for the corrective benefits of rehydration, however, is limited with mixed conclusions, and biological data on the underlying tissue changes with rehydration is lacking. In this study, we used a rabbit model (n = 24) of acute (5 days) water restriction-induced systemic dehydration with subsequent rehydration (3 days) to explore the protein-level changes underlying the molecular transition from euhydration to dehydration and following rehydration using LC-MS/MS protein quantification in the vocal folds. We show that 5-day water restriction led to an average 4.3% decrease in body weight with relative increases in anion gap, Cl-, creatinine, Na+, and relative decreases in BUN, iCa2+, K+, and tCO2 compared to control (euhydrated) animals. A total of 309 differentially regulated (p < 0.05) proteins were identified between the Control and Dehydration groups. We observed a noteworthy similarity between the Dehydration and Rehydration groups, both well differentiated from the Control group, highlighting the distinct timelines of resolution of the clinical symptoms of systemic dehydration and the underlying molecular changes.

SIGNIFICANCE

Voice disorders are a ubiquitous problem with considerable economic and psychological impact. Maintenance of proper hydration is commonly prescribed as a general vocal hygiene practice. There is evidence that dehydration negatively impacts phonation, but our understanding of the state of vocal folds in the context of systemic dehydration are limited, particular from a molecular perspective. Further, ours is a novel molecular study of the short-term impact of rehydration on the tissue. Given the relatively minimal difference in vocal fold proteomic profiles between the Dehydration and Rehydration groups, our data demonstrate a complex physiological response to acute systemic dehydration, and highlight the importance of considering persistent underlying molecular pathology despite the rapid resolution of clinical measures. This study sets a foundation for future research to confirm the nature of potential beneficial outcomes of clinical recommendations related to hydration.

Post-exercise rehydration: Comparing the efficacy of three commercial oral rehydration solutions

Introduction

This study compared the efficacy of three commercial oral rehydration solutions (ORS) for restoring fluid and electrolyte balance, after exercise-induced dehydration.

Method

Healthy, active participants (N = 20; ♀ = 3; age ∼27 y, V˙O₂peak ∼52 ml/kg/min) completed three randomised, counterbalanced trials whereby intermittent exercise in the heat (∼36°C, ∼50% humidity) induced ∼2.5% dehydration. Subsequently, participants rehydrated (125% fluid loss in four equal aliquots at 0, 1, 2, 3 h) with a glucose-based (G-ORS), sugar-free (Z-ORS) or amino acid-based sugar-free (AA-ORS) ORS of varying electrolyte composition. Urine output was measured hourly and capillary blood samples collected pre-exercise, 0, 2 and 5 h post-exercise. Sodium, potassium, and chloride concentrations in urine, sweat, and blood were determined.

Results

Net fluid balance peaked at 4 h and was greater in AA-ORS (141 ± 155 ml) and G-ORS (101 ± 195 ml) than Z-ORS (-47 ± 208 ml; P ≤ 0.010). Only AA-ORS achieved positive sodium and chloride balance post-exercise, which were greater for AA-ORS than G-ORS and Z-ORS (P ≤ 0.006), as well as for G-ORS than Z-ORS (P ≤ 0.007) from 1 to 5 h.

Conclusion

when provided in a volume equivalent to 125% of exercise-induced fluid loss, AA-ORS produced comparable/superior fluid balance and superior sodium/chloride balance responses to popular glucose-based and sugar-free ORS.

Time-restricted feeding and cognitive function in sedentary and physically active elderly individuals: Ramadan diurnal intermittent fasting as a model

Objectives

This study aimed to investigate the effects of Ramadan diurnal intermittent fasting (RDIF) on cognitive performance, sleep quality, daytime sleepiness, and insomnia in physically active and sedentary elderly individuals.

Methods

A total of 58 participants (62.93 ± 3.99 years) were assigned to one of the following two groups: a sedentary group (control group) who observed Ramadan (n = 32) and a physically active group (n = 26) who continued to train while observing Ramadan. Participants were assessed 2 weeks before Ramadan and during the fourth week of Ramadan. On each occasion, participants completed a digital assessment of their cognitive performance and responded to the Pittsburgh sleep quality index (PSQI), the insomnia severity index (ISI) and the Epworth sleepiness scale (ESS) questionnaires to assess sleep parameters.

Results

Compared to before Ramadan, performance in executive function (p = 0.035), attention (p = 0.005), inhibition (p = 0.02), associative memory (p = 0.041), and recognition memory (p = 0.025) increased significantly during Ramadan in the physically active group. For the sedentary group, associative learning performance decreased (p = 0.041), whilst performances in the remaining domains remained unchanged during Ramadan. Global PSQI, ISI, and ESS scores indicated both groups suffered from poor sleep quality and excessive daytime sleepiness, with significantly higher negative effects of RDIF observed in the sedentary group.

Conclusion

Older adults who continue to train at least three times per week during Ramadan may improve their cognitive performance, despite the impairment of sleep quality. Future studies in older adults during Ramadan including objective measures of sleep (e.g., polysomnography, actigraphy) and brain function (e.g., functional magnetic resonance imaging) are warranted.

Physical Exertion Partially Mitigates Task-Switching Deficits From Sleep Loss: Implications for Firefighters

OBJECTIVE

The aim of the study is to investigate effects of physical exertion on cognitive deficits from sleep loss under conditions that mimic a firefighting scenario.

METHODS

Twenty-four male participants completed a crossover study design with 3 conditions: total sleep deprivation, sleep disruption (three 60-minute awakenings), and rested control. Participants then completed 50 minutes of a physical exertion task involving treadmill exercise in a heated room while wearing firefighter protective clothing. Vigilant attention and task-switching performance were assessed pre- and post-sleep manipulation and pre- and post-physical exertion. Vigilant attention was also assessed mid-physical exertion.

RESULTS

Total sleep deprivation and sleep disruption increased attentional lapses and task-switching RT. Total sleep deprivation additionally reduced task-switching accuracy. Performance after physical exertion improved only for task-switching RT after total sleep deprivation.

CONCLUSIONS

Physical exertion selectively mitigated task-switching RT deficits from the most severe sleep loss condition, total sleep deprivation.

Exertional heat stroke: nutritional considerations

NEW FINDINGS

What is the topic of this review? The potential role of nutrition in exertional heat stroke. What advances does it highlight? Certain nutritional and dietary strategies used by athletes and workers may exert a protective effect the pathophysiological processes of exertional heat stroke, whereas others may be detrimental. While current evidence suggests that some of these practices may be leveraged as a potential countermeasure to exertional heat stroke, further research on injury-related outcomes in humans is required.

ABSTRACT

Exertional heat stroke (EHS) is a life-threatening illness and an enduring problem among athletes, military servicemen and -women, and occupational labourers who regularly perform strenuous activity, often under hot and humid conditions or when wearing personal protective equipment. Risk factors for EHS and mitigation strategies have generally focused on the environment, health status, clothing, heat acclimatization and aerobic conditioning, but the potential role of nutrition is largely underexplored. Various nutritional and dietary strategies have shown beneficial effects on exercise performance and health and are widely used by athletes and other physically active populations. There is also evidence that some of these practices may dampen the pathophysiological features of EHS, suggesting possible protection or abatement of injury severity. Promising candidates include carbohydrate ingestion, appropriate fluid intake and glutamine supplementation. Conversely, some nutritional factors and low energy availability may facilitate the development of EHS, and individuals should be cognizant of these. Therefore, the aims of this review are to present an overview of EHS along with its mechanisms and pathophysiology, discuss how selected nutritional considerations may influence EHS risk focusing on their impact on the key pathophysiological processes of EHS, and provide recommendations for future research. With climate change expected to increase EHS risk and incidence in the coming years, further investigation on how diet and nutrition may be optimized to protect against EHS would be highly beneficial.

Hypohydration alters pre-frontal cortex haemodynamics, but does not impair motor learning

It is unknown how hypohydration influences fine motor performance training and motor learning. Here, 30 participants (aged 19–46 years) were randomly assigned to a hypohydration (HYPO) or control (CON) group (both n = 15). Moderate hypohydration (~ 2.4% loss in body mass) was produced in HYPO via active dehydration before a 46 min fluid restricted rest period was undertaken. The conclusion of rest coincided with when CON attended the facilities. Both groups undertook a discrete sequence production task consisting of 6 training blocks, and returned ~ 300 min later to complete a delayed retention and transfer test while euhydrated. Bilateral pre-frontal cortex (PFC) haemodynamics were assessed using functional near-infrared spectroscopy throughout training and delayed learning assessments. Response time improved across training (P < 0.01) and was similar between the groups (both P = 0.22). Analysis of training PFC haemodynamics revealed a significant group by block interaction for oxygenated (O₂Hb; P < 0.01), but not deoxygenated haemoglobin (P = 0.77). In training block 1, bilateral O₂Hb was higher in HYPO (P = 0.02), while bilateral O₂Hb increased in CON between blocks 2–3 and 5–6 (both P ≤ 0.03). During the delayed retention and transfer test, no group differences or interactions were found in response time, response error, or PFC haemodynamics (all P ≥ 0.27). Moderate hypohydration does increase PFC activation during motor skill learning, however, this appears to be transient and of little consequence to training or delayed retention or transfer performance.

Effects of heat strain on cognitive function among a sample of miners

Heat stress is associated with workplace injuries, likely through a combination of fatigue, reduced cognitive function, and thermal discomfort. The purpose of this study was to evaluate four cognitive tasks for sensitivity to heat stress. Eight participants performed treadmill exercise followed by assessments of serial reaction time (RT), Stroop effect, verbal delayed memory, and continuous performance working memory in an environmental chamber. A control (21.1 °C) trial, and "Hot 1" and "Hot 2" (both 37.8 °C) trials were run sequentially on two separate days to evaluate the four cognitive tasks. Heat strain (comparing Hot 1 and Hot 2 with the control trial) resulted in impairments in the serial RT test response and Stroop accuracy. Delayed memory was impacted only in the Hot 2 trial compared with the control trial. Given the demonstrated impact of heat on cognitive processes relevant to workers' real-world functioning in the workplace, understanding how to assess and monitor vigilant attention in the workplace is essential.

Acute Water Supplementation Improved the Body Composition of Young Female Adults After Water Restriction of 12 h in Baoding, China: A Randomized Controlled Trial (RCT)

Insufficient intake of water may influence the balance of water in the human body. In this study, we explore the impacts of water supplementation on body composition indices among young adults after 12 h of water restriction, with the aim to determine the optimum volume of water for improving body water composition. A randomized controlled trial study was conducted among 64 young men and women in Baoding, China. After fasting overnight for 12 h, anthropometric measurements and urine and blood samples were collected as a baseline test at 8:00 a.m. of Day 2. Body composition was determined by measuring the ECW (extracellular water), ICW (intracellular water), and TBW (total body water) through bioelectrical impedance analysis (BIA). The participants were randomly divided into four groups, including water supplementation (WS) groups 1, 2, and 3, with 500, 200, and 100 mL of water, respectively, and a no water supplementation (NW) group. After 90 min, they were reassessed in a rehydration test (at 10:00 a.m. of Day 2). Repeated measurement ANOVA was used to assess the impact of water supplementation on body composition. Comparing the baseline and rehydration tests, interactions between time and volume were not significant among the men (all p > 0.05). Among women, a significant interaction was only found in ECW (p = 0.043), with TBW tending toward being significant (p = 0.055). Comparing the baseline and rehydration tests, the ECW in WS group 1, WS group 3, and the NW group all decreased (p = 0.028, p = 0.001, and p = 0.029), with reductions of 0.1, 0.3, and 0.2 kg, respectively; however, no significant decrease was observed in WS group 2 (p = 0.329). Furthermore, comparing the WS groups with the NW group in the rehydration test, the differences were not significant (p = 1.000, p = 1.000, and p = 0.288, respectively). Between men and women within groups, all of the body composition indices differed significantly, both at baseline and rehydration tests (all p < 0.05). Water supplementation led to changes in the distribution of the water content in young female adults in this study-but not men-after 12 h of water restriction, with no decrease in ECW. Finally, we found that 200 mL was the minimum volume capable of improving the water content distribution in participants in this study.

Trial Registration

[www.chictr.org.cn], identifier [ChiCTR-IOR-17011568].

Habitual Total Drinking Fluid Intake Did Not Affect Plasma Hydration Biomarkers among Young Male Athletes in Beijing, China: A Cross-Sectional Study

The purposes of this study were to explore the drinking patterns, and urinary and plasma hydration biomarkers of young adults with different levels of habitual total drinking fluid intake. A cross-sectional study was conducted among 111 young male athletes in Beijing, China. Total drinking fluids and water from food were assessed by a 7-day, 24-h fluid intake questionnaire and the duplicate portion method, respectively. The osmolality and electrolyte concentrations of the 24-h urine and fasting blood samples were tested. Differences in groups LD1 (low drinker), LD2, HD1, and HD2 (high drinker), divided according to the quartiles of total drinking fluids, were compared using one-way ANOVA, Kruskal−Wallis H-tests, and chi-squared tests. A total of 109 subjects completed the study. The HD2 group had greater amounts of TWI (total water intake) and higher and lower contributions of total drinking fluids and water from food to TWI, respectively, than the LD1, LD2, and HD1 groups (p < 0.05), but the amounts of water from food did not differ significantly among the four groups (all p > 0.05). Participants in the HD2 group had higher amounts of water than participants in the LD1, LD2, and HD1 groups (p < 0.05); SSBs were the second top contributor of total drinking fluids, ranging from 24.0% to 31.8%. The percentage of subjects in optimal hydration status increased from 11.8% in the LD1 group to 58.8% in the HD2 group (p < 0.05). The HD2 and HD1 groups had 212−227 higher volumes of urine than the LD1 and LD2 groups (p < 0.05). No significant differences were found in the plasma biomarkers (p > 0.05), with the exception of higher concentrations of K in the HD1 group than in the LD1 group (p < 0.05). Subjects with higher amounts of total drinking fluids had better hydration status than those with lower total drinking fluids, but not better drinking patterns. Habitual total drinking fluids did not affect the plasma biomarkers.

Prevalence of Dehydration and the Relationship with Fluid Intake and Self‐Assessment of Hydration Status in Czech First League Soccer Players

The objective of this cross-sectional study was to evaluate the hydration status of Czech First League soccer players, and to compare the reported fluid intake, perceived fluid intake and thirst sensation of euhydrated (EU) and dehydrated (DE) players. The study involved 124 Czech male professional soccer players (age 25.2±5.0 years) participating in annual winter, pre-season laboratory testing. Hydration status was assessed based on urine specific gravity (USG), euhydration was set at USG≤1.020. Fluid intake and thirst perception were evaluated by a questionnaire. The sample mean for USG was 1.021±0.008, 56% of players were dehydrated. Reported daily fluid intake was significantly (p<0.001, d=0.95, large effect) higher in EU compared to DE players. Daily fluid intake negatively correlated with USG (rS=-0.46, p<0.001, medium effect). The fluid intake perception score was significantly (p=0.005, d=0.54, medium effect) better in EU compared to DE players. Reported intake perception scores negatively correlated with USG (rS=-0.32, p<0.001, medium effect). However, there was no correlation (rS=-0.09, p=0.34, trivial effect) between thirst perception scores and USG. Thirst perception scores were not significantly different between EU and DE players (p=0.35, d=0.18, trivial effect). Our results indicated that self-assessment of both daily fluid intake and perceived fluid intake matched with objective hydration status, while self-assessment of thirst perception was not an appropriate indicator of hydration status in elite soccer players.

Cognitive Performance Before and Following Habituation to Exercise-Induced Hypohydration of 2 and 4% Body Mass in Physically Active Individuals

We investigated the effect of repeated exposures to hypohydration upon cognitive performance. In a randomized crossover design, ten physically active adults completed two 4-week training blocks, one where they maintained euhydration (EUH) and the other where they were water-restricted (DEH) during walking/running at 55% V.O2max, 40 °C. Three sessions per week were performed: (1) 1 h of exercise, (2) exercise until 2% or (3) 4% of body mass has been lost or replaced. Limited to the first and fourth training week, a 12 min walking/running time-trial was completed following the 2 and 4% exercise bouts. Trail making, the Wisconsin card sort, the Stop signal task, Simple visual reaction time and Corsi block-tapping tests were performed immediately following the time-trials. Body mass loss was maintained < 1% with EUH and reached 2.7 and 4.7% with DEH following the time-trials. Except for a lower percentage of correct responses (% accuracy) during the Wisconsin card sort test (p < 0.05) with DEH compared to EUH, no statistically significant decline in cognitive performance was induced by low and moderate levels of hypohydration. Compared to week 1, no statistical differences in cognitive responses were observed after repeated exposures to hypohydration (all p > 0.05). From a practical perspective, the gains in cognitive performance following training to DEH were mostly unclear, but under certain circumstances, were greater than when EUH was maintained. Based on the battery of cognitive tests used in the current study, we conclude that whether physically active individuals are habituated or not to its effect, exercise-induced hypohydration of 2 and 4% has, in general, no or unclear impact on cognitive performance immediately following exercise. These results encourage further research in this area.

Extracellular to Intracellular Body Water and Cognitive Function among Healthy Older and Younger Adults

Compromised cognitive function is associated with increased mortality and increased healthcare costs. Physical characteristics including height, weight, body mass index, sex, and fat mass are often associated with cognitive function. Extracellular to intracellular body water ratio offers an additional anthropometric measurement that has received recent attention because of its association with systemic inflammation, hypertension, and blood−brain barrier permeability. The purposes of this study were to determine whether extracellular to intracellular body water ratios are different between younger and older people and whether they are associated with cognitive function, including executive function and attention, working memory, and information processing speed. A total of 118 healthy people (39 older; 79 younger) participated in this study. We discovered that extracellular to intracellular body water ratio increased with age, was predictive of an older person’s ability to inhibit information and stay attentive to a desired task (Flanker test; R2 = 0.24; p < 0.001), and had strong sensitivity (83%) and specificity (91%) to detect a lower executive function score. These findings support that extracellular to intracellular body water ratio offers predictive capabilities of cognitive function, even in a healthy group of elderly people.

Can Nutrients and Dietary Supplements Potentially Improve Cognitive Performance Also in Esports?

Factors influencing brain function and cognitive performance can be critical to athletic performance of esports athletes. This review aims to discuss the potential beneficial effects of micronutrients, i.e., vitamins, minerals and biologically active substances on cognitive functions of e-athletes. Minerals (iodine, zinc, iron, magnesium) and vitamins (B vitamins, vitamins E, D, and C) are significant factors that positively influence cognitive functions. Prevention of deficiencies of the listed ingredients and regular examinations can support cognitive processes. The beneficial effects of caffeine, creatine, and probiotics have been documented so far. There are many plant products, herbal extracts, or phytonutrients that have been shown to affect precognitive activity, but more research is needed. Beetroot juice and nootropics can also be essential nutrients for cognitive performance. For the sake of players’ eyesight, it would be useful to use lutein, which, in addition to improving vision and protecting against eye diseases, can also affect cognitive functions. In supporting the physical and mental abilities of e-athletes the base is a well-balanced diet with adequate hydration. There is a lack of sufficient evidence that has investigated the relationship between dietary effects and improved performance in esports. Therefore, there is a need for randomized controlled trials involving esports players.

Dehydration Status Aggravates Early Renal Impairment in Children: A Longitudinal Study

Dehydration is common in children for physiological and behavioral reasons. The objective of this study was to assess changes in hydration status and renal impairment across school weekdays. We conducted a longitudinal study of three repeated measures of urinalysis within one week in November 2019 in a child cohort in Beijing, China. We measured urine specific gravity (USG) to determine the dehydration status, and the concentration of β₂-microglobulin (β₂-MG) and microalbumin (MA) to assess renal function impairment among 1885 children with a mean age of 7.7 years old. The prevalence of dehydration was 61.9%, which was significantly higher in boys (64.3%). Using chi-square tests and linear mixed-effects regression models, we documented the trends of the renal indicators’ change over time among different hydration statuses. Compared to Mondays, there were apparent increases of β₂-MG concentrations on Wednesdays (β = 0.029, p < 0.001) and Fridays (β = 0.035, p < 0.001) in the dehydrated group, but not in the euhydrated group. As for the MA concentrations, only the decrease on Fridays (β = −1.822, p = 0.01) was significant in the euhydrated group. An increased trend of elevated β₂-MG concentration was shown in both the euhydrated group (Z = −3.33, p < 0.001) and the dehydrated group (Z = −8.82, p < 0.001). By contrast, there was a decreased trend of elevated MA concentrations in the euhydrated group (Z = 3.59, p < 0.001) but not in the dehydrated group. A new indicator ratio, β₂-MG/MA, validated the consistent trends of renal function impairment in children with dehydration. Renal impairment trends worsened as a function of school days during the week and the dehydration status aggravated renal impairment during childhood across school weekdays, especially tubular abnormalities in children.

Young Adults with Higher Salt Intake Have Inferior Hydration Status: A Cross-Sectional Study

The body’s water and sodium balances are tightly regulated and monitored by the brain. Few studies have explored the relationship between water and salt intake, and whether sodium intake with different levels of fluid intake leads to changes in hydration status remains unknown. The aim of the present study was to determine the patterns of water intake and hydration status among young adults with different levels of daily salt intakes. Participants’ total drinking fluids and water from food were determined by a 7-day 24-h fluid intake questionnaire for 7 days (from Day 1 to Day 7) and duplicate portion method (Day 5, Day 6 and Day 7). Urine of 24 h for 3 days (Day 5, Day 6 and Day 7) was collected and tested for the osmolality, the urine-specific gravity (USG), the concentrations of electrolytes, pH, creatinine, uric acid and the urea. The fasting blood samples for 1 day (Day 6) were collected and measured for the osmolality and the concentrations of electrolytes. The salt intakes of the participants were evaluated from the concentrations of Na of 24 h urine of 3 days (Day 5, Day 6 and Day 7). Participants were divided into four groups according to the quartile of salt intake, including the low salt intake (LS₁), LS₂, high salt intake (HS₁) and HS₂ groups. In total, 156 participants (including 80 male and 76 female young adults) completed the study. The salt intakes were 7.6, 10.9, 14.7 and 22.4 g among participants in the four groups (LS₁, LS₂, HS₁ and HS₂ groups, respectively), which differed significantly in all groups (F = 252.020; all p < 0.05). Compared to the LS₁ and LS₂ groups, the HS₂ group had 310–381, 250–358 and 382–655 mL more amounts of water from the total water intake (TWI), total drinking fluids and water from food (all p < 0.05), respectively. Participants in the HS₂ group had 384–403, 129–228 and 81–114 mL more in the water, water from dishes and staple foods, respectively, than those in the groups of LS₁ and LS₂ (p < 0.05). The HS₂ group excreted 386–793 mL more urine than those in the groups of LS₁ and LS₂ (p < 0.05). However, regarding urine osmolality, the percentage of participants with optimal hydration status decreased from 41.0% in LS₁ and LS₂ to 25.6% in the HS₂ group (p < 0.05). Participants with higher salt intake had higher TWI, total drinking fluids and water from food. Nevertheless, they had inferior hydration status. A reduction in salt intake should be encouraged among young adults to maintain optimal hydration status.

Fluid Restriction Negatively Influences Perceived Morning Alertness and Visuomotor Ability

The purpose of this study was to assess the effect of two fluid intake protocols on alertness and reaction time before and after fluid intake. Healthy college-age males (n = 12) followed two fluid intake protocols on separate occasions: (1) prescribed fluid (PF) and fluid restricted (FR). In PF, participants were instructed to consume 500 mL of fluid the night prior to and the morning of data collection. In FR, participants were instructed to refrain from the consumption of fluid for 12 h. To assess hydration status, urine specific gravity and urine color were measured. Participants perceived level of thirst and alertness were also recorded. Participants then completed visuomotor reaction time tests using the Dynavision LED board, using both a central visuomotor test and a peripheral visuomotor test (PVRT) prior to (1) and following (2) the ingestion of 100 mL of water. Participants displayed significantly improved PVRT in PF state as compared to FR (PF1 = 1.13 ± 0.16, PF2 = 1.04 ± 0.14; FR1 = 1.27 ± 0.27, FR2 = 1.18 ± 0.20; p = 0.038, η_p² = 0.363). Both CVRT and PVRT improved over time, following the ingestion of 100 mL of fluid. Participants in the PF state were also significantly more alert than participants in the FR state (PF = 4 ± 2, FR = 5 ± 2; p = 0.019, ES = 0.839). Collectively, perceived alertness and PVRT were negatively impacted by FR.

Modified Stroop Task Performance When Wearing Protective Clothing in the Heat: An Evaluation of the Maximum Adaptability Model

INTRODUCTION

This exploratory study investigated whether performance in a behavioural inhibition task followed the shape proposed by the Maximum Adaptability Model during progressive exertional heat stress-that is, an initial improvement in cognitive performance is followed by a plateau, and subsequent decline once body temperature continues to rise unabated.

METHODS

Seventeen adult males walked on a treadmill at 4 km•h^-1 (1% grade) for up to 120 min, in three protective clothing ensembles, across three simulated environments. The simulated environments were equivalent to wet bulb globe temperatures 21, 30 and 37°C. Cognitive function was assessed using a modified colour-word Stroop Task, with performance expressed as inverse efficiency scores in the simple (congruent) and more complex (incongruent) task conditions. The Stroop Task was completed before a trial, at termination, and every 30 min during walking, and core body temperature was continuously measured. Data were modelled using Bayesian penalised regression, with core body temperature included as a non-linear term (i.e., second degree polynomial).

RESULTS

We did not find any evidence that core body temperature had an effect on congruent or incongruent inverse efficiency scores, and no evidence that the relationship between these variables followed the shaped described by the Maximum Adaptability Model. There was, however, evidence that higher pre-exercise serum osmolality values were associated with slower congruent (β = 9.19) and incongruent (β = 8.67) inverse efficiency scores. The posterior probability that these effects were greater than zero was 0.971 and 0.952, respectively.

CONCLUSIONS

In young, fit men, performance in the behavioural inhibition task was unaffected by increases in body temperature up to 39°C and did not follow the shape proposed by the Maximum Adaptability Model. A secondary finding of the study was that pre-exercise hydration status affected performance in the inhibition task. Future studies are needed to confirm this result.

Estrogen to Progesterone Ratio and Fluid Regulatory Responses to Varying Degrees and Methods of Dehydration

The purpose of this study was to investigate the relationship between volume regulatory biomarkers and the estrogen to progesterone ratio (E:P) prior to and following varying methods and degrees of dehydration. Ten women (20 ± 1 year, 56.98 ± 7.25 kg, 164 ± 6 cm, 39.59 ± 2.96 mL•kg•min⁻¹) completed four intermittent exercise trials (1.5 h, 33.8 ± 1.3°C, 49.5 ± 4.3% relative humidity). Testing took place in two hydration conditions, dehydrated via 24-h fluid restriction (Dehy, USG > 1.020) and euhydrated (Euhy, USG ≤ 1.020), and in two phases of the menstrual cycle, the late follicular phase (days 10–13) and midluteal phase (days 18–22). Change in body mass (%BMΔ), serum copeptin concentration, and plasma osmolality (P_osm) were assessed before and after both dehydration stimuli (24-h fluid restriction and exercise heat stress). Serum estrogen and progesterone were analyzed pre-exercise only. Estrogen concentration did not differ between phases or hydration conditions. Progesterone was significantly elevated in luteal compared to follicular in both hydration conditions (Dehy—follicular: 1.156 ± 0.31, luteal: 5.190 ± 1.56 ng•mL⁻¹, P < 0.05; Euhy—follicular: 0.915 ± 0.18, luteal: 4.498 ± 1.38 ng·mL⁻¹, P < 0.05). As expected, E:P was significantly greater in the follicular phase compared to luteal in both hydration conditions (Dehy—F:138.94 ± 89.59, L: 64.22 ± 84.55, P < 0.01; Euhy—F:158.13 ± 70.15, L: 50.98 ± 39.69, P < 0.01, [all •10³]). Copeptin concentration was increased following 24-h fluid restriction and exercise heat stress (mean change: 18 ± 9.4, P < 0.01). We observed a possible relationship of lower E:P and higher copeptin concentration following 24-h fluid restriction (r = −0.35, P = 0.054). While these results did not reach the level of statistical significance, these data suggest that the differing E:P ratio may alter fluid volume regulation during low levels of dehydration but have no apparent impact after dehydrating exercise in the heat.

Effects of Water Restriction and Supplementation on Cognitive Performances and Mood among Young Adults in Baoding, China: A Randomized Controlled Trial (RCT)

The brain is approximately 75% water. Therefore, insufficient water intake may affect the cognitive performance of humans. The present study aimed to investigate the effects of water restriction and supplementation on cognitive performances and mood, and the optimum amount of water to alleviate the detrimental effects of dehydration, among young adults. A randomized controlled trial was conducted with 76 young, healthy adults aged 18–23 years old from Baoding, China. After fasting overnight for 12 h, at 8:00 a.m. of day 2, the osmolality of the first morning urine and blood, cognitive performance, and mood were measured as a baseline test. After water restriction for 24 h, at 8:00 a.m. of day 3, the same indexes were measured as a dehydration test. Participants were randomly assigned into four groups: water supplementation group (WS group) 1, 2, or 3 (given 1000, 500, or 200 mL purified water), and the no water supplementation group (NW group). Furthermore, participants were instructed to drink all the water within 10 min. Ninety minutes later, the same measurements were performed as a rehydration test. Compared with the baseline test, participants were all in dehydration and their scores on the portrait memory test, vigor, and self-esteem decreased (34 vs. 27, p < 0.001; 11.8 vs. 9.2, p < 0.001; 7.8 vs. 6.4, p < 0.001). Fatigue and TMD (total mood disturbance) increased (3.6 vs. 4.8, p = 0.004; 95.7 vs. 101.8, p < 0.001) in the dehydration test. Significant interactions between time and volume were found in hydration status, fatigue, vigor, TMD, symbol search test, and operation span test (F = 6.302, p = 0.001; F = 3.118, p = 0.029; F = 2.849, p = 0.043; F = 2.859, p = 0.043; F = 3.463, p = 0.021) when comparing the rehydration and dehydration test. Furthermore, the hydration status was better in WS group 1 compared to WS group 2; the fatigue and TMD scores decreased, and the symbol search test and operation span test scores increased, only in WS group 1 and WS group 2 (p < 0.05). There was no significant difference between them (p > 0.05). Dehydration impaired episodic memory and mood. Water supplementation improved processing speed, working memory, and mood, and 1000 mL was the optimum volume.

A quasi-experimental examination of weight-reducing dehydration practices in collegiate male rowers

Background

Lightweight rowers commonly utilize weight loss techniques over 24-h before competition to achieve the qualifying weight for racing. The objective was to investigate, using a quasi-experimental design, whether changes in weight resulting from dehydration practices are related to changes in proxies of bodily systems involved in rowing and whether these relationships depend on the dehydration technique used.

Methods

Twelve elite male rowers performed a power test, an incremental VO₂max test, and a visuomotor battery following: weight loss via thermal exposure, weight loss via fluid abstinence and then thermal exposure, and no weight loss. The total percent body mass change (%BMC), %BMC attributable to thermal exposure, and %BMC attributable to fluid abstinence were used to predict performance variables.

Results

Fluid abstinence but not thermal exposure was related to a lower total wattage produced on a incremental VO₂max test (b = 4261.51 W/1%BMC, 95%CI = 1502.68–7020.34), lower wattages required to elicit 2 mmol/L (b = 27.84 W/1%BMC, 95%CI = 14.69–40.99) and 4 mmol/L blood lactate (b = 20.45 W/1%BMC, 95%CI = 8.91–31.99), and slower movement time on a visuomotor task (b = -38.06 ms/1%BMC, 95%CI = -62.09–-14.03).

Conclusions

Dehydration related weight changes are associated with reductions in some proxies of bodily systems involved in rowing but depend on the dehydration technique used.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13102-021-00344-7.

Proposed framework for forecasting heat-effects on motor-cognitive performance in the Summer Olympics

Heat strain impairs performance across a broad spectrum of sport disciplines. The impeding effects of hyperthermia and dehydration are often ascribed to compromised cardiovascular and muscular functioning, but expert performance also depends on appropriately tuned sensory, motor and cognitive processes. Considering that hyperthermia has implications for central nervous system (CNS) function and fatigue, it is highly relevant to analyze how heat stress forecasted for the upcoming Olympics may influence athletes. This paper proposes and demonstrates the use of a framework combining expected weather conditions with a heat strain and motor-cognitive model to analyze the impact of heat and associated factors on discipline- and scenario-specific performances during the Tokyo 2021 games. We pinpoint that hyperthermia-induced central fatigue may affect prolonged performances and analyze how hyperthermia may impair complex motor-cognitive performance, especially when accompanied by either moderate dehydration or exposure to severe solar radiation. Interestingly, several short explosive performances may benefit from faster cross-bridge contraction velocities at higher muscle temperatures in sport disciplines with little or no negative heat-effect on CNS fatigue or motor-cognitive performance. In the analyses of scenarios and Olympic sport disciplines, we consider thermal impacts on “motor-cognitive factors” such as decision-making, maximal and fine motor-activation as well as the influence on central fatigue and pacing. From this platform, we also provide perspectives on how athletes and coaches can identify risks for their event and potentially mitigate negative motor-cognitive effects for and optimize performance in the environmental settings projected.

The Impact of Context on EEG Motor Imagery Neurofeedback and Related Motor Domains

Neurofeedback (NF) is a versatile non-invasive neuromodulation technique. In combination with motor imagery (MI), NF has considerable potential for enhancing motor performance or supplementing motor rehabilitation. However, not all users achieve reliable NF control. While research has focused on various brain signal properties and the optimisation of signal processing to solve this issue, the impact of context, i.e. the conditions in which NF motor tasks occur, is comparatively unknown. We review current research on the impact of context on MI NF and related motor domains. We identify long-term factors that act at the level of the individual or of the intervention, and short-term factors, with levels before/after and during a session. The reviewed literature indicates that context plays a significant role. We propose considering context factors as well as within-level and across-level interactions when studying MI NF.

Physiological Characteristics of Female Soccer Players and Health and Performance Considerations: A Narrative Review

Female soccer has seen a substantial rise in participation, as well as increased financial support from governing bodies over the last decade. Thus, there is an onus on researchers and medical departments to develop a better understanding of the physical characteristics and demands, and the health and performance needs of female soccer players. In this review, we discuss the current research, as well as the knowledge gaps, of six major topics: physical demands, talent identification, body composition, injury risk and prevention, health and nutrition. Data on female talent identification are scarce, and future studies need to elucidate the influence of relative age and maturation selection across age groups. Regarding the physical demands, more research is needed on the pattern of high-intensity sprinting during matches and the contribution of soccer-specific movements. Injuries are not uncommon in female soccer players, but targeting intrinsically modifiable factors with injury prevention programmes can reduce injury rates. The anthropometric and physical characteristics of female players are heterogeneous and setting specific targets should be discouraged in youth and sub-elite players. Menstrual cycle phase may influence performance and injury risk; however, there are few studies in soccer players. Nutrition plays a critical role in health and performance and ensuring adequate energy intake remains a priority. Despite recent progress, there is considerably less research in female than male soccer players. Many gaps in our understanding of how best to develop and manage the health and performance of female soccer players remain.

Cellular dehydration acutely degrades mood mainly in women: a counterbalanced, crossover trial

It is unclear if mild-to-moderate dehydration independently affects mood without confounders like heat exposure or exercise. This study examined the acute effect of cellular dehydration on mood. Forty-nine adults (55 % female, age 39 (sd 8) years) were assigned to counterbalanced, crossover trials. Intracellular dehydration was induced with 2-h (0·1 ml/kg per min) 3 % hypertonic saline (HYPER) infusion or 0·9 % isotonic saline (ISO) as a control. Plasma osmolality increased in HYPER (pre 285 (sd 3), post 305 (sd 4) mmol/kg; P < 0·05) but remained unchanged in ISO (pre 285 (sd 3), post 288 (sd 3) mmol/kg; P > 0·05). Mood was assessed with the short version of the Profile of Mood States Questionnaire (POMS). The POMS sub-scale (confusion-bewilderment, depression-dejection, fatigue-inertia) increased in HYPER compared with ISO (P < 0·05). Total mood disturbance score (TMD) assessed by POMS increased from 10·3 (sd 0·9) to 16·6 (sd 1·7) in HYPER (P < 0·01), but not in ISO (P > 0·05). When TMD was stratified by sex, the increase in the HYPER trial was significant in females (P < 0·01) but not in males (P > 0·05). Following infusion, thirst and copeptin (surrogate for vasopressin) were also higher in females than in males (21·3 (sd 2·0), 14·1 (sd 1·4) pmol/l; P < 0·01) during HYPER. In conclusion, cellular dehydration acutely degraded specific aspects of mood mainly in women. The mechanisms underlying sex differences may be related to elevated thirst and vasopressin.

Hydration and water intake practices of commercial long-distance drivers in Ghana: what do they know and why does it matter?

BACKGROUND

The World Health Organization indicates that hydration is indispensable to human life. A long-period of dehydration can result in fatigue, drowsiness and mental confusion which can result in committing serious blunders. For commercial drivers, however, these blunders can be life-threatening and their hydration cannot be overemphasized.

AIM

This study was therefore undertaken to assess the water intake practices of Commercial Long-Distance drivers (CLDDs). The study was also aimed at assessing their knowledge levels on the role of water in promoting a healthy body and the consequences of dehydration.

SETTING

CLDDs in Ghana who ply between Accra - Cape Coast - Takoradi or Accra - Kumasi.

METHODS

A cross-sectional study which involved 256 CLDDs was conducted at six (6) commercial bus stations in Accra and Cape Coast from December 2019 to January 2020. Structured questionnaires were administered to obtain socio-demographic and water intake practices of CLDDs. SPSS was used to generate descriptive statistics based on the data collected.

RESULTS

A high proportion (57.8%) of the CLDDs reported that they drunk about 2500ml-3000ml of water on a daily basis. Most (53.1%) relied on their thirst feeling to prompt them to drink water. A little over half (51.1%) consumed energy drinks believed to hydrate the body. A major barrier to drinking water regularly was to avoid frequent stop-overs to use the washroom while travelling.

CONCLUSION

The findings reveal concerns about knowledge gaps with regard to the importance of water consumption and barriers to adequate drinking of water among CLDDs. Findings also suggest that many CLDDs relied on their thirst perceptions to prompt them to drink water. Health Education programmes targeting CLDDs should include conveying the importance of water intake and healthy hydration practices for optimal physical and cognitive performance.

Dehydration in older people: A systematic review of the effects of dehydration on health outcomes, healthcare costs and cognitive performance

OBJECTIVE

To systematically examine the effect of dehydration on health outcomes, identify associated financial costs and consider impacts on cognitive performance in older adults.

DESIGN

A systematic review of English-language articles via OVID using MEDLINE, PsychINFO, EMBASE, and others, to March 2018. Included studies examined the relationship between hydration status and health, care costs or cognitive outcome.

SETTING

Cross sectional and cohort data from studies reporting on dehydration in older adults.

PARTICIPANTS

Adults aged 60 years and older.

MEASUREMENTS

Independent quality ratings were assessed for all extracted articles.

RESULTS

Of 1684 articles screened, 18 papers (N = 33,707) met inclusion criteria. Participants were recruited from hospital settings, medical long-term care centres and the community dwelling population. Data were synthesised using a narrative summary. Mortality rates were higher in dehydrated patients. Furthermore, health outcomes, including frailty, bradyarrhythmia, transient ischemic attacks, oral health and surgery recovery are linked to and worsened by dehydration. Length of hospital stay, either as a principal or secondary diagnosis, is greater in those with dehydration, compared to those who are euhydrated. Finally, neurocognitive functioning may be impacted by dehydration. There are issues with study design, inconsistency in hydration status measurement and different measures used for outcome assessment.

CONCLUSION

Dehydration in older people is associated with increased mortality, poorer course of illness and increased costs for health services. In addition, there is some, but sparse evidence that dehydration in older people is linked to poorer cognitive performance. Intervention studies should test strategies for reducing dehydration in older adults.

Does Hydration Status Influence Executive Function? A Systematic Review

BACKGROUND

Cognitive function, including executive function (EF)-related capacities (eg, working memory, inhibitory and attentional control), has been linked to adherence to healthy lifestyle behaviors. Dehydration is associated with impaired cognitive function, whereas improvements in hydration status may improve inhibitory and attentional performance. No systematic reviews have examined the effects of both dehydration and euhydration on EF.

OBJECTIVE

The objectives of this systematic review are to examine studies that have investigated the spectrum of hydration status and EF in adults, and to identify future research needs.

DESIGN

The review was conducted according to the 2015 Preferred Reporting Items for Systematic Reviews and Meta-Analyses Protocols (PRISMA-P) guidelines. The database search was initially conducted on May 12, 2019 and then updated on April 26, 2020. Databases searched included PubMed, Medline, Psyc Info, SCOPUS, Proquest, and ISI Web of Science. Data extraction included the following: method used to assess de/hydration status, study design, participant characteristics, EF tasks and domain, and results. Article quality ratings were performed on included studies using the Academy of Nutrition and Dietetics Quality Rating Checklist.

PARTICIPANTS/SETTING

Studies done with healthy or diseased adults, aged older than 18 years, in any setting, were included. Studies of individuals with disease states that impact fluid balance or require fluid restrictions as treatments were excluded.

MAIN OUTCOME MEASURE

All EF-related outcomes were included, such as working memory, inhibitory control, task switching, and attention.

RESULTS

Four thousand eight hundred thirty-three articles were screened using title/abstracts. Seventy-one full-text articles were assessed for eligibility; 33 were included (26 included investigations of dehydration; 27 included investigations of rehydration/euhydration) with 3,636 participants across all studies. Little consistency was found across outcomes. Roughly half of the available studies suggested unclear or neutral EF effects, and half suggested effects on EF domains, particularly working memory, inhibitory control, and attention. Studies including a euhydration condition were slightly more likely to demonstrate improvements to EF capacities.

CONCLUSIONS

Overall, there is a strong need for consistent methodological approaches and a greater number of long-term (ie, >3 days) studies of dehydration and euhydration and EF.

The comparison of water intake patterns and hydration biomarkers among young adults with different hydration statuses in Hebei, China

Background

Water is essential for maintaining the functions of human body properly. Studies have shown that the amounts and contributions of fluids were associated with health and hydration status. The objectives of the study was that to explore the differences of water intake pattern and hydration biomarkers among young males and females in different hydration statuses.

Methods

A cross-sectional study was implemented among 159 young adults aged 18–23 years in Hebei, China. The total drinking fluids and water from food were obtained by 7-day 24-h fluid intake questionnaire and duplicate portion method, respectively. The osmolality and electrolyte concentrations of the 24 h urine and plasma were tested. Differences in optimal hydration (OH), middle hydration (MH) and hypohydration (HH) groups, divided by the osmolality of 24 h urine, were compared.

Results

Totally, 156 participants (80 males and 76 females) completed the study. OH group had highest proportions of participants met the recommendations of total water intake (TWI) and total drinking fluids of China (34.5%, 36.2%), while HH group had lowest (7.7%, 0.0%). OH group had higher amounts of TWI, total drinking fluids, water and lower amounts of sugar-sweetened-beverages (SSBs) (P < 0.05). The percentage of total drinking fluids in TWI decreased from 54.1% in OH group to 42.6% in HH group (P < 0.05). OH group had higher and lower contributions of water and SSBs to total drinking fluids (P < 0.05); produced 551–950 mL more, excreted significantly less quantity of solutes of urine (P < 0.05). No significant differences were found in plasma osmolality among the three groups (P > 0.05). Among both males and females, the amounts of TWI and water were higher in OH group than others (P < 0.05). Males had 4.3% lower, 5.4% and 1.1% higher contributions of milk and milk products, SSBs and alcohol to total drinking fluids than females (P < 0.05); males had higher volume of urine than females only in MH group (P < 0.05). There were no significant differences of plasma osmolality between males and females in the same group (P > 0.05).

Conclusions

Young adults with optimal hydration status had better water intake pattern and less concentrated urine. Females maybe have better water intake pattern than males.

Trial registration Chinese clinical trial registry. Name of the registry: Relationship of drinking water and urination. Trial registration number: ChiCTR-ROC-17010320. Date of registration: 01/04/2017. URL of trial registry record: http://www.chictr.org.cn/edit.aspx?pid=17601&htm=4.

Health vs. wealth: Employer, employee and policy-maker perspectives on occupational heat stress across multiple European industries

Successful implementation of cooling strategies obviously depends on identifying effective interventions, but in industrial settings, it is equally important to consider feasibility and economic viability. Many cooling interventions are available, but the decision processes affecting adoption by end-users are not well elucidated. We therefore arranged two series of meetings with stakeholders to identify knowledge gaps, receive feedback on proposed cooling interventions, and discuss factors affecting implementation of heat-health interventions. This included four meetings attended by employers, employees, and health and safety officers (n = 41), and three meetings attended primarily by policy makers (n = 74), with feedback obtained via qualitative and quantitative questionnaires and focus group discussions. On a 10-point scale, both employers and employees valued worker safety (9.1 ± 1.8; mean±SD) and health (8.5 ± 1.9) as more important than protecting company profits (6.3 ± 2.3). Of the respondents, 41% were unaware of any cooling strategies at their company and of those who were aware, only 30% thought the interventions were effective. Following presentation of proposed interventions, the respondents rated "facilitated hydration", "optimization of clothing/protective equipment", and "rescheduling of work tasks" as the top-three preferred solutions. The main barriers for adopting cooling interventions were cost, feasibility, employer perceptions, and legislation. In conclusion, preventing negative health and safety effects was deemed to be more important than preventing productivity loss. Regardless of work sector or occupation, both health and wealth were emphasized as important parameters and considered as somewhat interrelated. However, a large fraction of the European worker force lacks information on effective measures to mitigate occupational heat stress. List of abbreviations: OH-Stress: Occupational heat stress; WBGT: Wet Bulb Globe Temperature.