Euhydrated Research Articles

Mild dehydration does not alter acute changes in sweat electrolyte concentrations during exercise.

The purpose of this study was to determine the effect of hydration status on the change in sweat sodium (Na+), chloride (Cl-), and potassium (K+) concentrations during exercise-heat stress. Fifteen subjects (Six female, nine male; 29 ± 9 y; 71 ± 14 kg) completed 90 min of cycling (81% HRmax) in the heat (~33°C, 42% rh) with fluid replacement to maintain euhydration (EUH) or without fluid to dehydrate to 2.4 ± 0.4% body mass loss (DEH). Sweat was collected from the forehead (FH), right scapula (SCAP), and left (LVFA) and right (RVFA) ventral forearms using the absorbent pad technique at the beginning (0-30 min) and end of exercise (60-90 min). Sweat was analyzed for Na+, Cl-, and K+ concentrations using ion chromatography. Data are reported as mean ± SD or median ± IQR. There were no differences (Paired t-tests or Wilcoxon signed-rank tests) between EUH and DEH in the change in sweat Na+ (FH: 24.3 ± 21.5 vs. 30.8 ± 22.4 mmol/L; SCAP: 9.7 ± 6.2 vs. 9.6 ± 8.2 mmol/L; LVFA: 7.5 ± 6.0 vs. 5.6 ± 5.9 mmol/L; RVFA: 8.2 ± 8.6 vs. 7.8 ± 5.2 mmol/L), sweat Cl-, or sweat K+ at any site (p = 0.07-0.99). The change in sweat electrolyte concentrations during 90 min of exercise in the heat was not significantly influenced by mild dehydration in recreational to moderately-trained male and female athletes.

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

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. 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 severelyHYP (S-HYP) groups experienced reductions of 2.0% and 4.0% of their initial body weight, respectively. 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. 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.

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% 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.

Change in Exercise Performance and Markers of Acute Kidney Injury Following Heat Acclimation with Permissive Dehydration.

Implementing permissive dehydration (DEH) during short-term heat acclimation (HA) may accelerate adaptations to the heat. However, HA with DEH may augment risk for acute kidney injury (AKI). This study investigated the effect of HA with permissive DEH on time-trial performance and markers of AKI. Fourteen moderately trained men (age and VO2max = 25 ± 0.5 yr and 51.6 ± 1.8 mL·kg−1·min−1) were randomly assigned to DEH or euhydration (EUH). Time-trial performance and VO2max were assessed in a temperate environment before and after 7 d of HA. Heat acclimation consisted of 90 min of cycling in an environmental chamber (40 °C, 35% RH). Neutrophil gelatinase-associated lipocalin (NGAL) and kidney injury molecule-1 (KIM-1) were assessed pre- and post-exercise on day 1 and day 7 of HA. Following HA, VO2max did not change in either group (p = 0.099); however, time-trial performance significantly improved (3%, p < 0.01) with no difference between groups (p = 0.485). Compared to pre-exercise, NGAL was not significantly different following day 1 and 7 of HA (p = 0.113) with no difference between groups (p = 0.667). There was a significant increase in KIM-1 following day 1 and 7 of HA (p = 0.002) with no difference between groups (p = 0.307). Heat acclimation paired with permissive DEH does not amplify improvements in VO2max or time-trial performance in a temperate environment versus EUH and does not increase markers of AKI.

High Salt Intake Recruits Tonic Activation of NR2D Subunit-Containing Extrasynaptic NMDARs in Vasopressin Neurons.

In addition to producing a classical excitatory postsynaptic current via activation of synaptic NMDA receptors (NMDARs), glutamate in the brain also induces a tonic NMDAR current (INMDA) via activation of extrasynaptic NMDARs (eNMDARs). However, since Mg2+ blocks NMDARs in nondepolarized neurons, the potential contribution of eNMDARs to the overall neuronal excitatory/inhibitory (E/I) balance remains unknown. Here, we demonstrate that chronic (7 d) salt loading (SL) recruited NR2D subunit-containing NMDARs to generate an Mg2+-resistant tonic INMDA in nondepolarized [Vh (holding potential) -70 mV] vasopressin (VP; but not oxytocin) supraoptic nucleus (SON) neurons in male rodents. Conversely, in euhydrated (EU) and 3 d SL mice, Mg2+-resistant tonic INMDA was not observed. Pharmacological and genetic intervention of NR2D subunits blocked the Mg2+-resistant tonic INMDA in VP neurons under SL conditions, while an NR2B antagonist unveiled Mg2+-sensitive tonic INMDA but not Mg2+-resistant tonic INMDA In the EU group VP neurons, an Mg2+-resistant tonic INMDA was not generated by increased ambient glutamate or treatment with coagonists (e.g., d-serine and glycine). Chronic SL significantly increased NR2D expression but not NR2B expression in the SON relative to the EU group or after 3 d under SL conditions. Finally, Mg2+-resistant tonic INMDA selectively upregulated neuronal excitability in VP neurons under SL conditions, independent of ionotropic GABAergic input. Our results indicate that the activation of NR2D-containing NMDARs constitutes a novel mechanism that generates an Mg2+-resistant tonic INMDA in nondepolarized VP neurons, thus causing an E/I balance shift in VP neurons to compensate for the hormonal demands imposed by a chronic osmotic challenge.SIGNIFICANCE STATEMENT The hypothalamic supraoptic nucleus (SON) consists of two different types of magnocellular neurosecretory cells (MNCs) that synthesize and release the following two peptide hormones: vasopressin (VP), which is necessary for regulation of fluid homeostasis; and oxytocin (OT), which plays a major role in lactation and parturition. NMDA receptors (NMDARs) play important roles in shaping neuronal firing patterns and hormone release from the SON MNCs in response to various physiological challenges. Our results show that prolonged (7 d) salt loading generated a Mg2+-resistant tonic NMDA current mediated by NR2D subunit-containing receptors, which efficiently activated nondepolarized VP (but not OT) neurons. Our findings support the hypothesis that NR2D subunit-containing NMDARs play an important adaptive role in adult brain in response to a sustained osmotic challenge.

Effects of Dehydration on Archery Performance, Subjective Feelings and Heart Rate during a Competition Simulation.

This study aimed to investigate the effect of dehydration on archery performance, subjective feelings and heart rate response. Ten national level archers performed two archery competition simulations, once under euhydration (EUH) and once in a dehydrated state (DEH), induced by 24-h reduced fluid intake. Hydration status was verified prior to each trial by urine specific gravity (USG ≥ 1.025). Archery score was measured according to official archery regulations. Subjective feelings of thirst, fatigue and concentration were recorded on a visual analogue scale. Heart rate was continuously monitored during the trials. Archery performance was similar between trials (p = 0.155). During DEH trial (USG 1.032 ± 0.005), the athletes felt thirstier (p < 0.001), more fatigued (p = 0.041) and less able to concentrate (p = 0.016) compared with the EUH trial (USG 1.015 ± 0.004). Heart rate during DEH at baseline (85 ± 5 b∙min−1) was higher (p = 0.021) compared with EUH (78 ± 6 b∙min−1) and remained significantly higher during the latter stages of the DEH compared to EUH trial. In conclusion, archery performance over 72 arrows was not affected by dehydration, despite the induced psychological and physiological strain, revealed from decreased feeling of concentration, increased sensation of fatigue and increased heart rate during the DEH trial.

The Relationship Between Whole-body Heat Exchange And Thermoregulatory Responses During Exercise In The Heat In A Dehydrated State

Whole-body heat loss has been extensively examined during exercise in hot environments. Interestingly, the relationship between predicted heat balance parameters and thermoregulatory strain have been limited to individuals in an euhydrated state. As dehydration has been shown to exacerbate thermal and cardiovascular strain, it is imperative to examine whether dehydration modulates heat exchange during exercise in the heat and its relationship to physiological responses to exercise in the heat. PURPOSE: to examine whether predicted heat balance parameters explain variance in core temperature (Tcore) and heart rate (HR) responses to exercise in the heat following 24 h of fluid restriction. METHODS: 8 participants (4 males and 4 females; age:19±2yrs; VO2max:47.4±6.5ml/kg/min; body mass:61.5±9.4kg; height:166.7±7.5cm) performed a 30-min bout of treadmill running and walking in the heat (32°C, 55% relative humidity) under two conditions: 1) 24 h of fluid restriction (DEH) and 2) euhydration (EUH). Participants exercised at 11W/kg for 15 min followed by 7W/kg for 15 min, which were derived via indirect calorimetry. Tcore was continuously assessed through rectal thermometry and HR was measured at the end of each intensity. Metabolic heat production (M-W), dry heat loss (DHL), and evaporative requirement (Ereq) were calculated for both exercise intensities. Pearson correlation coefficients were utilized to examine the relationship between M-W, DHL, Ereq and Tcore, change in Tcore (Tcore), HR, and change in HR (HR) under DEH and EUH. Linear regressions were performed for all significant correlations. Statistical significance was set at p ≤ 0.05. RESULTS: M-W and DHL were not correlated with Tcore, Tcore, HR, or HR in DEH or EUH at 11W/kg. At 7W/kg under DEH, DHL was negatively correlated with Tcore (R2=0.54, p=0.05) and HR (R2=0.67, p=0.024). All other heat balance parameters were not correlated with physiological responses at 7W/kg in DEH or EUH. CONCLUSION: In this preliminary dataset, Ereq and M-W did not explain variance in physiological responses during DEH. DHL under DEH explained 67% of the variance in post HR and 54% of the variance in Tcore at 7W/kg. Therefore, DHL may contribute to the variation in physiological strain during low intensity exercise in the heat under DEH.

Mild Hypohydration Following 24-hour Water Intake Reduction Does Not Affect Anaerobic Power Performance

Hypohydration is common among athletes and can be the result of a failure to maintain hydration between exercise bouts. The negative impact of hypohydration on aerobic performance is well characterized. However, little is known about the effect of hypohydration on anaerobic performance particularly when the hypohydration is the result of insufficient water intake prior to the onset of exercise, not water loss due to body temperature regulation. PURPOSE: The purpose of this study was to examine the effect of hypohydration on anaerobic performance following voluntary water intake reduction. METHODS: Fifteen healthy adults (8 women, 7 men) completed two exercise sessions, euhydrated (EUD) and hypohydrated (HYP). Subjects were asked to voluntarily limit water intake during the 24-hours prior to the hypohydrated trial. Sessions consisted of baseline anthropometric and blood lactate measurement followed by a 30-second Wingate test and 3 maximum vertical jump trials. The vertical jump trials were completed approximately 1 minute after finishing the 30-second Wingate test and used to measure anaerobic performance in an anaerobically challenged state. Additional blood lactate measurements were taken immediately and at 5, 10, and 15-min post Wingate test. RESULTS: The hypohydration protocol resulted in a significant 1.5% reduction in body mass (EUD 69.1 ± 17.2kg, HYP 68.1 ± 16.6kg, p = 0.039). The 30-sec Wingate peak power (EUD 971 ± 302W, HYP 960 ± 316W, p = 0.578) was not different between conditions, nor was maximum vertical jump height (EUH 26.4 ± 4.5cm, HYP 26.6 ± 3.6cm, p = 0.778). Blood lactate (p ≤ 0.001) was elevated immediately following the 30-sec Wingate test and remained elevated throughout the remainder of the trial. There were no differences in blood lactate between conditions. CONCLUSIONS: Acute anaerobic power and exercise performance are not negatively affected by mild voluntary hypohydration during and following a single 30-second Wingate test.

Potential for dehydration to impact the athlete biological passport.

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

Mild dehydration following voluntary water intake reduction does not affect anaerobic power performance.

Dehydration is common among athletes. The negative impact of dehydration on aerobic performance is well characterized. However, little is known about the effect of dehydration on anaerobic performance particularly when dehydration results from insufficient water intake, not water loss due to body temperature regulation. The purpose of this study was to examine the effect of dehydration on anaerobic performance following voluntary water intake reduction. Fifteen healthy adults completed two exercise sessions, euhydrated (EUD) and dehydrated (DEH). Sessions consisted of baseline anthropometric and blood lactate measurement followed by a 30-second Wingate test and three vertical jump trials to measure anaerobic performance. Additional blood lactate measurements were taken immediately and at 5, 10, and 15 minutes after taking the Wingate test. The dehydration protocol resulted in a reduction in body mass (EUD 69.1±17.2 kg, DEH 68.1±16.6 kg, P=0.039). The 30-s Wingate peak power (EUD 971±302 W, DEH 960±316 W, P=0.578) was not different between conditions, nor was the vertical jump height (EUH 26.4±4.5 cm, DEH 26.6±3.6 cm, P=0.778). Blood lactate (P<0.001) was elevated immediately following the 30-s Wingate test which remained throughout the trial. There were no differences in blood lactate between conditions. Acute anaerobic power and exercise performance is not negatively affected by voluntary dehydration.

The Utility of Thirst as a Measure of Hydration Status Following Exercise-Induced Dehydration.

The purpose of this study was to examine the perception of thirst as a marker of hydration status following prolonged exercise in the heat. Twelve men (mean ± SD; age, 23 ± 4 y; body mass, 81.4 ± 9.9 kg; height, 182 ± 9 cm; body fat, 14.3% ± 4.7%) completed two 180 min bouts of exercise on a motorized treadmill in a hot environment (35.2 ± 0.6 °C; RH, 30.0 ± 5.4%), followed by a 60 min recovery period. Participants completed a euhydrated (EUH) and hypohydrated (HYPO) trial. During recovery, participants were randomly assigned to either fluid replacement (EUHFL and HYPOFL; 10 min ad libitum consumption) or no fluid replacement (EUHNF and HYPONF). Thirst was measured using both a nine-point scale and separate visual analog scales. The percent of body mass loss (%BML) was significantly greater immediately post exercise in HYPO (HYPOFL, 3.0% ± 1.2%; HYPONF, 2.6% ± 0.6%) compared to EUH (EUHFL, 0.2% ± 0.7%; EUHNF, 0.6% ± 0.5%) trials (p < 0.001). Following recovery, there were no differences in %BML between HYPOFL and HYPONF (p > 0.05) or between EUHFL and EUHNF (p > 0.05). Beginning at minute 5 during the recovery period, thirst perception was significantly greater in HYPONF than EUHFL, EUHNF, and HYPOFL (p < 0.05). A 10 min, ad libitum consumption of fluid post exercise when hypohydrated (%BML > 2%), negated differences in perception of thirst between euhydrated and hypohydrated trials. These results represent a limitation in the utility of thirst in guiding hydration practices.

Hydration status affects thirst and salt preference but not energy intake or postprandial ghrelin in healthy adults: A randomised crossover trial

BackgroundFew studies have investigated the effect of hydration status on appetite for food in healthy adults. Prior work suggests hydration status does not alter appetite or energy intake, with mixed findings regarding appetite hormone secretion. However, an extensive investigation into both the psychological and physiological appetitive responses to hydration status has never been conducted. ObjectiveTo investigate the effect of hydration status on multiple facets of appetite. DesignAfter 3 days pre-trial standardization, a range of appetite tasks were conducted when hypohydrated (HYPO) and euhydrated (EUHY) in 16 healthy participants (8 men). Hydration status was manipulated via dehydration in a heat tent for 60 min and subsequent fluid restriction (HYPO) or replacement (EUHY). The next day, a food reward computer task was completed followed by an ad libitum pasta meal. Pre- and post-prandial visual analogue scales assessing hunger, fullness, and flavour desires (sweet, salty, savoury and fatty) were additionally completed. Blood samples were taken the previous day before the hydration interventions in a euhydrated state, and in the fasted and post-prandial state during HYPO and EUHY. ResultsHYPO induced -1.9 ± 1.2% body mass change, compared to -0.2 ± 0.6% , with accompanying changes in markers of hypohydration which were not seen during EUHY. A higher desire for foods was associated with a higher water content but the association was weaker in EUHY compared to HYPO, (β= -0.33 mm/g of food water content, p < 0.001) in the food reward task. Visual analogue scales showed similar hunger and fullness between interventions, but during HYPO there was consistently higher thirst (average range in difference 27–32 mm across all time points) and lower fasted desire for salt (−23, 95% CI −10, −35 mm). Ad libitum energy intake (HYPO 1953 ± 742 kJ, EUHY 2027 ± 926 kJ; p = 0.542) and post-prandial ghrelin concentrations (HYPO 180 ± 65 pg mL−1, EUHY 188 ± 71 pg mL−1; p = 0.736) were similar by hydration status. ConclusionsAn acute manipulation to hydration status altered desire for salt and foods of differing water contents, but did not influence energy intake at an ad libitum pasta meal. Further research should investigate whether these appetites would alter food choice.

Altered brain structure with preserved cortical motor activity after exertional hypohydration: a MRI study.

Hypohydration exceeding 2% body mass can impair endurance capacity. It is postulated that the brain could be perturbed by hypohydration, leading to impaired motor performance. We investigated the neural effects of hypohydration with magnetic resonance imaging (MRI). Ten men were dehydrated to approximately -3% body mass by running on a treadmill at 65% maximal oxygen consumption (V̇o2max) before drinking to replace either 100% [euhydration (EU)] or 0% [hypohydration (HH)] of fluid losses. MRI was performed before start of trial (baseline) and after rehydration phase (post) to evaluate brain structure, cerebral perfusion, and functional activity. Endurance capacity assessed with a time-to-exhaustion run at 75% V̇o2max was reduced with hypohydration (EU: 45.2 ± 9.3 min, HH: 38.4 ± 10.7 min; P = 0.033). Mean heart rates were comparable between trials (EU: 162 ± 5 beats/min, HH: 162 ± 4 beats/min; P = 0.605), but the rate of rise in rectal temperature was higher in HH trials (EU: 0.06 ± 0.01°C/min, HH: 0.07 ± 0.02°C/min; P < 0.01). In HH trials, a reduction in total brain volume (EU: +0.7 ± 0.6%, HH: -0.7 ± 0.9%) with expansion of ventricles (EU: -2.7 ± 1.6%, HH: +3.7 ± 3.3%) was observed, and vice versa in EU trials. Global and regional cerebral perfusion remained unchanged between conditions. Functional activation in the primary motor cortex in left hemisphere during a plantar-flexion task was similar between conditions (EU: +0.10 ± 1.30%, HH: -0.11 ± 0.31%; P = 0.637). Our findings demonstrate that with exertional hypohydration, brain volumes were altered but the motor-related functional activity was unperturbed. NEW & NOTEWORTHY Dehydration occurs rapidly during prolonged or intensive physical activity, leading to hypohydration if fluid replenishment is insufficient to replace sweat losses. Altered hydration status poses an osmotic challenge for the brain, leading to transient fluctuations in brain tissue and ventricle volumes. Therefore, the amount of fluid ingestion during exercise plays a critical role in preserving the integrity of brain architecture. These structural changes, however, did not translate directly to motor functional deficits in a simple motor task.

Impact of exercise-induced hypohydration on gastrointestinal integrity, function, symptoms, and systemic endotoxin and inflammatory profile.

It is commonly believed that gastrointestinal issues during exercise are exacerbated by hypohydration. This study aimed to determine the effect of exercise-induced hypohydration on gastrointestinal integrity, function, symptoms, and systemic endotoxin and inflammatory profiles. In a randomized crossover design, male endurance runners (n = 11) performed 2 h of running at 70% of maximum oxygen uptake in 25°C ambient temperature with water provision [euhydration (EuH)] and total water restriction [hypohydration (HypoH)] during running, which accounted for 0.6 ± 0.6% and 3.1 ± 0.7% body mass loss, respectively. Blood and fecal samples were collected before and after exercise. Breath samples (H2 determination) were collected and gastrointestinal symptoms (GIS) recorded before, during, and after exercise. HypoH resulted in a higher, yet insignificant, ∆ preexercise to postexercise plasma cortisol concentration (+286 nmol/l vs. +176 nmol/l; P = 0.098) but significantly higher intestinal fatty acid-binding protein (I-FABP) (+539 pg/ml vs. +371 pg/ml; P = 0.047) concentration compared with EuH. A greater breath H2 response (P = 0.026) was observed on HypoH (1,188 ppm/3 h, peak +12 ppm) vs. EuH (579 ppm/3 h, peak +6 ppm). Despite greater GIS incidence on HypoH (82%) vs. EuH (64%), GIS severity scores were not significant between trials. Exercise-induced leukocytosis (overall pre- to postexercise: 5.9 × 109/l to 12.1 × 109/l) was similar on both trials. Depressed in vitro neutrophil function was observed during recovery on HypoH (-36%) but not on EUH (+6%). A pre- to postexercise increase (P < 0.05) was observed for circulating cytokine concentrations but not endotoxin values. Hypohydration during 2 h of running modestly perturbs gastrointestinal integrity and function and increases GIS incidence but does not affect systemic endotoxemia and cytokinemia. NEW & NOTEWORTHY Despite anecdotal beliefs that exercise-induced hypohydration exacerbates perturbations to gastrointestinal status, the present study reports only modest perturbations in gastrointestinal integrity, function, and symptoms compared with euhydration maintenance. Exercise-induced hypohydration does not exacerbate systemic endotoxemia and cytokinemia compared with euhydration maintenance. Programmed water intake to maintain euhydration results in gastrointestinal symptom severity similar to exercise-induced hypohydration. Maintaining euhydration during exertional stress prevents the exercise-associated depression in bacterially stimulated neutrophil function.

Mild hypohydration impairs cycle ergometry performance in the heat: A blinded study.

The aim of the present study was to observe the effect of mild hypohydration on exercise performance with subjects blinded to their hydration status. Eleven male cyclists (weight 75.8±6.4kg, VO2peak : 64.9±5.6mL/kg/min, body fat: 12.0±5.8%, Powermax : 409±40W) performed three sets of criterium-like cycling, consisting of 20-minute steady-state cycling (50% peak power output), each followed by a 5-km time trial at 3% grade. Following a familiarization trial, subjects completed the experimental trials, in counter-balanced fashion, on two separate occasions in dry heat (30°C, 30% rh) either hypohydrated (HYP) or euhydrated (EUH). In both trials, subjects ingested 25mL of water every 5minutes during the steady-state and every 1km of the 5-km time trials. In the EUH trial, sweat losses were fully replaced via intravenous infusion of isotonic saline, while in the HYP trial, a sham IV was instrumented. Following the exercise protocol, the subjects' bodyweight was changed by -0.1±0.1% and -1.8±0.2% for the EUH and HYP trial, respectively (P<0.05). During the second and third time trials, subjects averaged higher power output (309±5 and 306±5W) and faster cycling speed (27.5±3.0 and 27.2±3.1km/h) in the EUH trial compared to the HYP trial (Power: 287±4 and 276±5W, Speed: 26.2±2.9 and 25.5±3.3km/h, all P<0.05). Core temperature (Tre ) was higher in the HYP trial throughout the third steady-state and 5-km time trial (P<0.05). These data suggest that mild hypohydration, even when subjects were unaware of their hydration state, impaired cycle ergometry performance in the heat probably due to greater thermoregulatory strain.

Maintaining Euhydration Preserves Cognitive Performance, But Is Not Superior to Hypohydration

Maintaining optimal physical and cognitive performance are keys to success for most exercise contexts. However, consensus on the effects of dehydration for cognitive function is equivocal, particularly given the addition of confounding variables when hypohydration (HYPO) results. Therefore, this study aimed to examine whether maintaining euhydration (EUH) would preserve cognitive function, and whether this physiological state would be superior than if HYPO were evoked in an identical exercise task. In a crossover design, 15 participants (12 males, age 27.93 ± 6.81 years, height 177.20 ± 6.95 cm, mass 84.40 ± 12.35 kg) completed a 90 min self-paced simulated military march in the heat, whilst either maintaining EUH by consuming fluid ad libitum or becoming hypohydrated via fluid restriction. A cognitive testing battery was administered pre-exercise and following a rest period (55 ± 8 min), and evaluated information processing, memory, impulsivity, attention and concentration, and response time domains, whilst subjective estimates of performance were also quantified. Aspects of memory and impulsivity were not comparable to pre-exercise data (both P ≤ 0.05), whilst a shift in the speed-accuracy trade-off was apparent in the switching attention task, with accuracy decreasing (P = 0.003), and reaction time being supplemented (P = 0.028). Despite body mass losses of 2.28%, hydration status did not influence performance for any of the measured cognitive domains (all P > 0.05). When hypohydrated, subjective estimates of thirst were significantly greater post-exercise (P = 0.004), whilst medium effect sizes were found for lethargy (d = 0.532) and task difficulty (d = 0.553) post-exercise. Although maintaining EUH by en-large preserves cognitive function, this does not produce superior cognitive performance compared with fluid restriction following an identical exercise task. Therefore, despite losses in body mass exceeding 2%, cognitive performance remains largely stable.

Effect of Dehydration on Passing Decision Making in Soccer Athletes

ABSTRACTIt seems that dehydration may impair decision-making performance in athletes. Purpose: This study aimed to investigate the influence of dehydration on passing decision-making performance in soccer players. Method: Participants were 40 male soccer players (Mage = 22.3 ± 2.3 years) who agreed to participate in the study and were randomly assigned to the following conditions: control (CON), dehydration (DEH), and euhydration (EUH). The players played in 2 games of 90 min in duration (2 45-min halves) followed by 2 15-min halves (overtime) with and without proper hydration. The Game Performance Assessment Instrument (GPAI) was considered for the analysis of passing decision making. Results: The GPAI analysis indicated effective reduction in the decision-making index in the DEH condition compared with the EUH and CON conditions, F(2, 38) = 31.4, p < .05, ES = 0.8. Conclusions: In conclusion, dehydration may be considered a mediating factor in the passing decision-making performance of male soccer athletes.

Effect of Short‐term Water Restriction on Blood Pressure Variability in Young Adults

Water restriction causes an acute decline in plasma volume and subsequently elevates serum sodium and plasma osmolality. Rodent models demonstrate that elevated serum sodium and plasma osmolality increases blood pressure (BP) variability. This is important because elevated BP variability is an independent risk factor for adverse cardiovascular events. However, the effects of water restriction on BP variability in humans remains to be determined.PURPOSETo test the hypothesis that short‐term water restriction increases serum sodium and plasma osmolality and leads to greater BP variability in humans.METHODSYoung healthy adults (13M/11F, age: 25±1 yrs; BMI: 24±1 kg/m2; BP 107±2/60±1 mmHg) completed two three‐day‐long hydration protocols in randomized order, separated by at least one week. Women were tested in the early follicular phase of their menstrual cycle. Daily water intake for euhydration (EU) was 23 mL H2O/kg/day. Water intake for hypohydration (HYPO) consisted of a stepwise daily reduction in water intake, followed by a 16‐hour water abstention period prior to testing. Laboratory testing was conducted on day four of the protocols. Participants wore an ambulatory BP monitor and collected urine for urinalysis for 24 hours preceding each study visit. The ambulatory BP monitoring provides BP variability under free‐living conditions. Upon arrival to the laboratory, participants rested quietly in a dimly lit room in the supine position for ten minutes for the assessment of beat‐to‐beat BP variability via finger photoplethysmography under controlled conditions. The average real variability (ARV) index, the average of the absolute differences between all consecutive BP measurements, was determined. Standard deviation (SD) of BP was also determined.RESULTSHYPO led to higher plasma osmolality (290.6±1.0 vs. 287.7±1.0 mOsm/kg H2O, p&lt;0.05), urine osmolality (707±42 vs. 470±32 mOsm/kg H2O, p&lt;0.05), urine specific gravity (1.023±0.001 vs. 1.016±0.006, p&lt;0.05) and thirst rating (7.0±0.4 vs. 2.7±0.6 on a 0–10 scale, p&lt;0.05) compared to EU. Plasma volume declined (−5.4±1.3%) during HYPO compared to EU. Daytime ambulatory systolic BP variability was not different between HYPO and EU (ARV BP 9.1±0.4 vs. 10.0±0.6; SD BP 10.3±0.8 vs. 12.4±1.1, p&gt;0.05 for both). Ambulatory mean and diastolic BP variability were not different between conditions (p&gt;0.05). Beat‐to‐beat systolic BP variability was not different between HYPO and EU (ARV BP 2.0±0.1 vs. 1.9±0.1; SD BP 5.4±0.4 vs. 5.0±0.3, p&gt;0.05 for both). Beat‐to‐beat mean and diastolic BP variability were also not different between conditions (p&gt;0.05).CONCLUSIONThese preliminary data suggest that short‐term water restriction in young healthy adults does not increase ambulatory or beat‐to‐beat BP variability.Support or Funding InformationSupported by NIH Grant 1R01HL128388This abstract is from the Experimental Biology 2018 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Water intake reverses dehydration associated impaired executive function in healthy young women

IntroductionHealthy women do not always consume Recommended Daily Levels of fluid intake ad libitum. We hypothesized that 1) women lose≥1.0% BW during daily activities, 2) that mild body water loss impairs memory and executive function, 3) water intake to recommended daily levels will improve cognitive function. MethodsWe tested 12 women (26±5yr, 22.5±2.6kg/m2 BMI). Session 1 was a control (CON) session, during which subjects monitored their food and fluid intake (diary) and activity (Fitbit®). The next two sessions were applied in balanced order: dehydration (DEH) session, where subjects minimized drinking, and a euhydration (EUH) session, where subjects drank Recommended Daily Levels of fluid for their age and sex, or 2500ml/24h. We compared emotion, sensory perception and cognition with computer based visual analog tests and computer based cognitive tasks (Cogstate) at 5PM, i.e. baseline (BL) on the evening prior to the session, and at 7AM, 12PM, and 5PM during the session. ResultsUrine specific gravity (USG) was similar at BL across conditions (CON 1.013±0.002, DEH 1.015±0.002, EUH 1.014±0.002) and increased with dehydration (CON 1.011±0.003, DEH 1.021±0.002, EUH 1.010±0.002, P<0.05) by 5PM of the session. Uncontrolled fluid intake and physical activity were similar across sessions. The water challenges did not impact Detection, Identification, One-Card Learning, but EUH improved visual and working memory (Groton Maze Learning Test) errors: CON 40.1±11.1, DEH 40.5±10.1, EUH 33.9±10.9, P<0.05. Executive function [Set Shifting (SETS)] also improved under EUH, errors: BL 22.5±12.7 vs. 5PM 17.8±6.2, P<0.05. ConclusionsMild dehydration caused deficits in visual and working memory and executive function in healthy young women. These deficits were reversed by drinking water to the European Food Safety Authority and Institute of Medicine requirements of 2.5l/day for adult women.