Hypohydrated Trials Research Articles

The effects of hydration status and ice-water dousing on physiological and performance indices during a simulated soccer match in the heat

ObjectivesTo assess the effects of hydration status and ice-water dousing on physiological and performance parameters. DesignRandomized, crossover. MethodsTwelve athletes (mean[M] ± standard deviation[SD]; age, 20 ± 1 years; height, 174 ± 8 cm; body mass, 72.1 ± 11.0 kg; VO2max 53.9 ± 7.3 mL⋅kg−1⋅min−1) completed four trials (euhydrated without dousing, hypohydrated without dousing, euhydrated with dousing, and hypohydrated with dousing), which involved intermittent treadmill running (five 15-minute bouts) in the heat (M ± SD; ambient temperature, 34.7 ± 2.1 °C; relative humidity, 46 ± 3%; wet-bulb globe temperature, 28.0 ± 0.4 °C). Participants also completed four cognitive, power, agility, reaction time, and repeated sprint performance tests throughout each trial. Heart rate (HR) and rectal temperature (Trec) were measured continuously. Repeated measures ANOVAs were performed to assess differences between physiological and performance variables. Alpha was set at ≤0.05, a priori. Data are reported as mean difference ± standard error (MD ± SE). ResultsHR was significantly lower in euhydrated trials compared to hypohydrated trials, irrespective of dousing (8 ± 2 bpm; p = 0.001). Dousing did not significantly impact HR (p = 0.455) and there was no interaction between hydration and dousing (p = 0.893). Trec was significantly lower in euhydrated trials compared to hypohydrated trials (0.39 ± 0.05 °C, p < 0.001), with no effect from dousing alone (p = 0.113) or the interaction of hydration and dousing (p = 0.848). Dousing resulted in improved sprint performance (11 ± 3 belt rotations, p = 0.007), while hydration status did not (p = 0.235). ConclusionsAthletes should aim to maintain euhydration during exercise in the heat for improved physiological function and cooling with ice-water dousing elicits additional performance benefits.

The effect of hydration status on plasma FGF21 concentrations in humans:A subanalysis of a randomised crossover trial.

Fibroblast growth factor 21 (FGF21) has recently been implicated in thirst in rodent models. The mechanisms for this are currently uncertain, and it is unclear whether hydration status can alter FGF21 concentrations, potentially providing an additional mechanism by which hypohydration induces thirst. The aim of this study is therefore to understand whether hydration status can alter circulating FGF21 in humans. Using a heat tent and fluid restriction, we induced hypohydration (1.9% body mass loss) in 16 healthy participants (n = 8 men), and compared their glycaemic regulation to a rehydration protocol (heat tent and fluid replacement) in a randomised crossover design. After the hypohydration procedure, urine specific gravity, urine and serum osmolality, and plasma copeptin (as a marker for arginine vasopressin) increased as expected, with no change after the rehydration protocol. In the fasted state, the median paired difference in plasma FGF21 concentrations from the rehydrated to hypohydrated trial arm was -37 (interquartile range -125, 10) pg∙mL-1(P = 0.278), with average concentrations being 458 ± 462 pg∙mL-1 after hypohydration and 467 ± 438 pg∙mL-1 after rehydration; mean difference -9 ± 173 pg∙mL-1. To our knowledge, these are the first causal data in humans investigating hydration and FGF21, demonstrating that an acute bout of hypohydration does not impact fasted plasma FGF21 concentrations. These data may suggest that whilst previous research has found FGF21 administration can induce thirst and drinking behaviours, a physiological state implicated in increased thirst (hypohydration) does not appear to impact plasma FGF21 concentrations in humans.

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.

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.

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.

Comparison of Esophageal, Rectal, and Gastrointestinal Temperatures During Passive Rest After Exercise in The Heat: The Influence of Hydration.

Context: It is unknown how valid esophageal, rectal, and gastrointestinal temperatures (TES, TRE, and TGI) compare after exercise-induced hyperthermia under different hydration states. Objective: To examine the differences between TES, TRE, and TGI during passive rest following exercise-induced hyperthermia under 2 different hydration states: euhydrated (EU) and hypohydrated (HY). Design: Randomized crossover design. Setting: Controlled laboratory setting. Participants: 9 recreationally active male participants (mean ± SD age 24 ± 4 y, height 177.3 ± 9.9 cm, body mass 76.7 ± 11.6 kg, body fat 14.7% ± 5.8%). Intervention: Participants completed 2 trials (EU and HY) consisting of a bout of treadmill exercise (a 10-min walk at 4.8-7.2 km/h at a 5% grade followed by a 20-min jog at 8.0-12.1 km/h at a 1% grade) in a hot environment (ambient temperature 39.3 ± 1.0°C, relative humidity 37.6% ± 6.0%, wet bulb globe temperature 31.3 ± 1.5°C) followed by passive rest. Main Outcome Measures: Root-mean-squared difference (RMSD) was used to compare the variance of temperature readings at corresponding time points for TRE vs TGI, TRE vs TES, and TGI vs TES in EU and HY. RMSD values were compared using 3-way repeated-measures ANOVA. Post hoc analysis of significant main effects was done using Tukey honestly significant difference with significance set at P < .05. Results: RMSD values (°C) for all device comparisons were significantly different in EU (TRE-TGI, 0.11 ± 0.12; TRE-TES, 1.58 ± 1.01; TGI-TES, 2.04 ± 1.19) than HY (TRE-TGI, 0.22 ± 0.28; TRE-TES, 1.27 ± 0.61; TGI-TES, 1.16 ± 0.76) (P < .01). Across the 45-min bout of passive rest, there were no differences in TRE, TGI, and TES between EU and HY trials (P = .468). Conclusions: During passive rest after exercise in the heat, TRE and TGI were in good agreement when tracking body temperature, with a better agreement appearing in those maintaining a state of euhydration versus those who became hypohydrated during exercise; however, this small difference does not appear to be of clinical significance. The large differences were observed when comparing TGI and TRE with TES.

Thirst As A Marker Of Hydration Status During And After Exercise In The Heat

PURPOSE: The purpose of this study was two-fold: 1) examine the perception of thirst as a potential marker of hydration status during and after exercise in the heat 2) investigate changes in thirst perception following consumption of a bolus of fluid post exercise. METHODS: 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-minute bouts of exercise on a motorized treadmill in a warm environment (ambient temperature, 35.2±0.6°C; RH, 30.0±5.4%; WBGT, 26.6±1.1°C) followed by a 60-minute recovery period. Participants completed a euhydrated (EUH) and hypohydrated (HYPO) trial, where fluid losses were minimized or fluid consumption was restricted, respectively. During recovery, participants were randomly assigned to a fluid replacement (FL) or no fluid replacement (NFL) group where they were given 10-minutes to consume water ad libitum at a volume matching fluid losses. Perception of thirst was measured using a 9-point scale and was measured periodically during and after exercise. A three-factor (trial x condition x time) repeated-measures ANOVA was used to measure differences in thirst perception post exercise between EUH-FL, EUH-NFL, HYPO-FL and HYPO-NFL. RESULTS: %BML was significantly greater in HYPO (2.7±0.7%) than EUH (0.4±0.6%) trials (p<0.001). Fluid replacement after exercise did not influence %BML between HYPO (HYPO-FL, 2.8±0.9%; HYPO-NFL, 2.6±0.6%) and EUH (EUH-FL, 0.2±0.7%; EUH-NFL, 0.6±0.5%) trials (p=0.330). During exercise, thirst perception was significantly greater in HYPO trials than EUH trials beginning at minute 90 of exercise (p<0.05). Beginning at minute 5 during the recovery period, thirst perception was significantly greater in HYPO-NFL than EUH-FL, EUH-NFL and HYPO-FL (p<0.05). CONCLUSIONS: During exercise, changes in perception of thirst were reflective of increased fluid losses, especially when %BML >2%. However, receiving a bolus of fluid post exercise when hypohydrated (%BML >2%) negated differences in perception of thirst between those euhydrated and hypohydrated. Thirst could have limited utility in guiding hydrated practices when attempting to quickly reestablish euhydration following prolonged exercise in the heat.

Effects of mild hypohydration on cooling during cold-water immersion following exertional hyperthermia.

We investigated the effects of mild hypohydration compared to euhydration on the cooling efficacy of cold-water immersion (CWI). Fourteen participants (eight male, six female; age 26 ± 5 years; ht 1.77 ± 0.08 m; wt 72.2 ± 8.8 kg; 20.6 ± 7.4 % body fat) completed one euhydrated (EU) trial followed by one hypohydrated trial (HY; via 24 h fluid restriction) in an environmental chamber (33.6 ± 0.9 °C, 55.8 ± 1.7 % RH). Volitional exercise was performed in a manner that matched end-exercise rectal temperature (T re) through repeating exercise mode and intensity. Participants were then immersed in ice water (2.0 ± 0.8 °C) until T re reached 38.1 °C or for a maximum of 15 min. T re, heart rate (HR), skin blood flux (SBF) and mean skin temperature (T sk) were monitored continuously during cooling. Pre-cooling body mass was decreased in the HY trial (-2.66 ± 1.23 % body mass) and maintained in the EU trial (-0.66 ± 0.44 %) compared to baseline mass (P < 0.001). Cooling rates were faster when EU (0.14 ± 0.05 °C/min) compared to HY (0.11 ± 0.05 °C/min, P = 0.046). HR, SBF, and T sk were not different between EU and HY trials (P > 0.05), however, all variables significantly decreased with immersion independent of hydration status (P < 0.001). The primary finding was that hypohydration modestly attenuates the rate of cooling in exertionally hyperthermic individuals. Regardless of hydration status, the cooling efficacy of CWI was preserved and should continue to be utilized in the treatment of exertional hyperthermia.

Blood Glucose Kinetics are Related to Hydration Status in Men with Type II Diabetes Mellitus

Daily total water intake (TWI) has been linked to a number of chronic diseases, such as urolithiasis and chronic kidney disease. Additionally, epidemiological and animal model data have tied low TWI to impaired blood glucose regulation. However, the effect of a fluid intake intervention on blood glucose regulation has not yet been observed in humans. PURPOSE: Thus, the purpose of the current investigation was to determine if the response to an oral glucose tolerance test (OGTT) was altered by manipulation of hydration status in people with diabetes. METHODS: Nine men (53±9 y, 94.9± 23.8 kg, 1.75± 0.11 m, 30.0± 4.3 mkg-2, 31.5± 6.5 %BF) who had previously been diagnosed with type II diabetes mellitus (T2DM) (hemoglobin A1C; 6.8±0.9 %) were recruited to take part. Participants completed two OGTTs in a euhydrated and hypohydrated state one week apart in a counterbalanced order. Euhydration was achieved by standard water prescription in line with the dietary reference intakes for water, and hypohydration was achieved through progressive water restriction over three days leading up to the OGTT. Blood samples were taken at time points 0, 15, 30, 45, 60, 90, 120 min of the OGTT. RESULTS: The changes in TWI in the three days before each trial resulted in significantly lower body mass (-1.5±1.5 kg; p = 0.017) and increased urine specific gravity (0.017±0.009; p = 0.001), and plasma osmolality (10±8 mmolkg-1). Repeated measures analysis of variance identified a main effect of condition for blood glucose concentration F[1,48] = 10.772, p = 0.011, but not for insulin concentration F[1,48] = .657, p = 0.441. Insulin sensitivity calculated with the Matsuda index revealed attenuated insulin sensitivity during the hypohydrated trial (3.59±3.28) versus the euhydrated trial (4.10±3.78; t[8] = 2.834, p = 0.022) CONCLUSION: Hypohydration elicits an acute, negative effect on the blood glucose response to OGTT in men with T2DM. Although, blood insulin did not change, blood glucose and insulin sensitivity were reduced during the euhydrated trial. This suggests that inadequate TWI can negatively impact blood glucose regulation via decreased insulin sensitivity.

Ad-libitum drinking and performance during a 40-km cycling time trial in the heat

The aim of this study was to investigate if drinking ad-libitum can counteract potential negative effects of a hypohydrated start caused by fluid restriction during a 40-km time trial (TT) in the heat. Twelve trained males performed one 40-km cycling TT euhydrated (EU: no water during the TT) and two 40-km cycling TTs hypohydrated. During one hypohydrated trial no fluid was ingested (HYPO), during the other trial ad-libitum water ingestion was allowed (FLUID). Ambient temperature was 35.2 ± 0.2°C, relative humidity 51 ± 3% and airflow 7 m·s−1. Body mass (BM) was determined at the start of the test, and before and after the TT. During the TT, power output, heart rate (HR), gastrointestinal temperature, mean skin temperature, rating of perceived exertion (RPE), thermal sensation, thermal comfort and thirst sensation were measured. Prior to the start of the TT, BM was 1.2% lower in HYPO and FLUID compared to EU. During the TT, BM loss in FLUID was lower compared to EU and HYPO (1.0 ± 0.8%, 2.7 ± 0.2% and 2.6 ± 0.3%, respectively). Hydration status had no effect on power output (EU: 223 ± 32 W, HYPO: 217 ± 39 W, FLUID: 224 ± 35 W), HR, gastrointestinal temperature, mean skin temperature, RPE, thermal sensation and thermal comfort. Thirst sensation was higher in HYPO than in EU and FLUID. It was concluded that hypohydration did not adversely affect performance during a 40-km cycling TT in the heat. Therefore, whether or not participants consumed fluid during exercise did not influence their TT performance.

Response

Dear Editor-in-Chief We are pleased that our data have provided stimulus for further inquiry. Indeed, as Goulet et al. point out, although the majority of the scientific data clearly state that hypohydration decreases endurance exercise performance—especiallyin the heat (5)—some scientists are arguing that the greatest side effect of hypohydration is thirst (4). Laboratory findings Of course our data do not apply to all cycling events but could have application to intermittent events like criterium race, endurance track cycling, or breakaways. During the performance test in the laboratory, we used a simulated video while cyclists exercised on their own bikes to help them feel close to outdoor conditions. Moreover, a recent outdoor cycling study linked mild hypohydration to decreased performance (1). Cardiovascular strain Goulet et al. argue the absence of cardiovascular strain because heart rate during the cycling performance test was similar between trials. In our case, the same near-maximal heart rate was observed in both trials, although subjects were cycling faster (+4.6%) on greater power output. Although we did not measure cardiac output, we hypothesized that higher stroke volume with similar heart rate could be a potential cardiovascular explanation of our findings. Familiarization We do agree that familiarization is an important part of a performance-related study. However, the exercise protocol was already familiar to cyclist because they were regularly participating in similar criterium cycling races. Likewise, subjects regularly exercise on cycling ergometers similar tothe ones used in the experiment. In addition, statistical analysis for order effect ensured that protocol familiarity did not influence performance. Counterbalanced design The administration of experimental conditions in counterbalanced fashion is considered the best practice for controlling order effects in a repeated-measures design. This way, we made sure that half of the subjects performed first the euhydrated trial, while the other half performed first the hypohydrated trial. Fan cooling As stated in the manuscript, subjects were fan-cooled with an airflow of 3.2 m·s−1. Actually, convecting heat loss was insignificant because of the fact that air and skin temperatures were almost identical. In addition, because the walls and all the objects had reached ambient temperature, heat loss via radiation was minimal, making evaporation the only mechanism for heat dissipation. Hypohydration and endurance It seems that the supporting studies for the closing remark “hypohydration does not impair cycling or running endurance performance...” is based on two studies that have been misinterpreted. The study by Dugas et al. (2) nicely demonstrated that low versus high fluid intake induced hypohydration of −3.75% and −1.5%, respectively. The greater hypohydration was linked to lower power output, slower exercise performance, but similar core temperature. The study by Gigou et al. (3) investigated the effect of preexercise hyperhydration on running performance. Hypohydration by −3.1% versus −1.4% resulted in greater cardiovascular and thermoregulatory strain as indicated by elevated heart rate and core temperature. We thank Dr. Goulet and colleagues for helping us to clarify some issues in this very important field of hydration and performance. Stavros A. Kavouras, PhD Costas N. Bardis, PhD Human Performance Laboratory Department of Health, Human Performance, and Recreation University of Arkansas, Fayetteville, AR

Mild Hypohydration Decreases Cycling Performance in the Heat

Hypohydration exceeding 2% of body mass decreases exercise performance. However, the effects of mild hypohydration (<2%) are not clear. The aim of this study was to determine the effects of mild hypohydration on cycling performance during a simulated-hill circuit course in a warm environment (32.5°C ± 0.5°C). Ten trained male cyclists (age, 30 ± 7 yr; mass, 78.4 ± 9.5 kg; height, 1.80 ± 0.01 m; V˙O2max, 52.4 ± 3.3 mL·min·kg; and Powermax, 355 ± 29 W) performed a cycling circuit three times on a laboratory ergometer consisting of 5 km at 50% of maximum power output and 5 km at an all-out pace, followed by a 5-min rest every 5 km. Subjects started the performance test either euhydrated (EUH) or hypohydrated (HYP), by 0% ± 0% and -1.0% ± 0.1% of body mass, respectively. Mean speed at the first, second, and third 5-km simulated-hill cycling was higher in the EUH (28.1 ± 3.1, 27.7 ± 3, and 27.0 ± 3.6 km·h) than that in the HYP trial (27.0 ± 2.9, 26.1 ± 3.7, and 25.9 ± 3.6 km·h) (P < 0.05). Mean power output at the first, second, and third 5-km simulated-hill cycling was greater in the EUH (284 ± 55, 266 ± 53, and 254 ± 58 W) than that in the HYP trial (272 ± 56, 250 ± 61, and 240 ± 57 W) (P < 0.05). Gastrointestinal temperature at the end of the first, second, and third 5-km simulated-hill cycling was greater in the HYP (38.3°C ± 0.4°C, 38.4°C ± 0.2°C, and 38.6°C ± 0.2°C) than that in the EUH trial (38.1°C ± 0.3°C, 38.1°C ± 0.3, and 38.3°C ± 0.3°C) (P < 0.05). Overall, sweat sensitivity during the circuit course was greater in the EUH (115 ± 58 g·°C·min) versus HYP trial (67 ± 19 g·°C·min) (P < 0.05). Furthermore, RPE and heart rate were similar and near maximal between trials (P > 0.05). The data showed that mild hypohydration decreased cycling performance, possible by inducing greater thermal and cardiovascular strain.

The Acute Effects of Fluid Intake on Urine Specific Gravity and Fluid Retention in a Mildly Dehydrated State

Many athletes arrive at training sessions and competitions in a mildly hypohydrated (HYPO) state and are instructed to drink fluids before exercise to reach a euhydrated (HYD) state. Ten recreational athletes (6 women, 4 men; 71.9 ± 4.6 kg, 25.2 ± 0.9 years) participated in the studies to examine (a) the day-to-day variability of morning urine specific gravity (USG), (b) the effects of consuming 600 ml of water on the hydration status of HYD and HYPO (USG > 1.020) subjects, and (c) the effects of consuming water (W), salt-water (SW, 40 mM Na), a carbohydrate-electrolyte solution with 3% or light carbohydrate (CES-L, 20 mM Na) or a CES with 6% carbohydrate (CES, 20 mM Na) on the hydration status of HYPO subjects. The hydration status was assessed with USG and body mass measures and urine volume collections. The day-to-day variability in morning USG (coefficient of variation = 0.2 ± 0.1%) was low and the responses to 600 ml of W ingestion were repeatable. Pretrial USG was 1.022 ± 0.001 in the HYPO trial and decreased <1.020 by 45 minutes (1.013 ± 0.003). In the CES study, HYPO subjects reached HYD status at 45 minutes in all conditions (W 1.013 ± 0.003, SW 1.013 ± 0.003, CES-L 1.011 ± 0.003, CES 1.017 ± 0.004) because salt or CES ingestion did not affect fluid retention (W 68%, SW 72%, CES-L 68%, CES 76%). This study demonstrated that mildly HYPO subjects could reach euhydration within 45 minutes of the ingestion of 600 ml of W or a combination of salt and CES solutions. Following this practice will minimize the incidence of starting a practice or competition hypohydrated.

Hydration Status and the Diuretic Action of a Small Dose of Alcohol

This study was conducted to examine the effect of consuming a dilute alcohol solution (weak beer) on urine production in euhydrated and hypohydrated individuals. Twelve males completed an intermittent cycle protocol in hot (35.1 +/- 0.3 degrees C), humid (68 +/- 2%) conditions to dehydrate by 1.9 +/- 0.3% body mass in the evening. Twice they were then fed and rehydrated, while on two other occasions they were fed the same meal but remained hypohydrated. The following morning they were given 1 l of beer to drink. On two occasions the beer was alcohol-free, while on the other two occasions the same beer contained 4% ethanol. Participants remained in the laboratory for monitoring over the subsequent 4 h. Blood and urine samples were taken prior to dehydration, prior to drink administration and once every hour of the monitoring period. No difference existed in the volume of urine produced between the alcohol (261 +/- 138 ml; mean +/- SD) and non-alcohol (174 +/- 61 ml) beer when hypohydrated (P = 0.057), but there was a difference when euhydrated (1279 +/- 256 vs 1121 +/- 148 ml alcohol and non-alcohol, respectively; P < 0.001). Unsurprisingly, more urine was produced on both euhydrated trials than either of the hypohydrated trials (P < 0.001). Blood alcohol concentration was elevated (P < 0.001) 1 h after drinking to 7.1 +/- 1.8 and 6.0 +/- 2.7 mmol/l (hypohydrated and euhydrated, respectively) on the alcohol trials. Serum osmolality was higher 1 h after drinking on both the alcohol trials (303 +/- 5 and 298 +/- 5 mosmol/l) than on their non-alcohol, equivalent hydration trials (290 +/- 8 and 284 +/- 5 mosmol/l hypohydrated and euhydrated, respectively; P < 0.001). These results suggest that the diuretic action of alcohol is blunted when the body is hypohydrated.

The Role of Dehydration and Electrolyte Loss on Exercise-Associated Muscle Cramps

1241 Dehydration, electrolyte imbalance, environmental stress, and neuromuscular fatigue have all been implicated as potential causes of exercise-associated muscle cramps (EAMC). Additionally, maintenance of fluid and electrolyte balance is often prescribed in the prevention of EAMC. However, there is little scientific data to support these assertions. PURPOSE: To determine the role of hydration and electrolyte balance in the prevention of EAMC. METHODS: Thirteen, college-aged males each completed two counter-balanced trials in a repeated-measures design. In each trial, participants performed a calf-fatiguing protocol known to induce EAMC in the calf muscle group. Each trial was performed in the same hot environment (dry bulb = 37 C, relative humidity = 60%). Participants consumed a carbohydrate-electrolyte beverage two hours and 30 minutes prior to each trial in order to optimize hydration and electrolyte levels. In one trial (euhydrated), participants consumed a carbohydrate-electrolyte beverage (with 3.0g NaCl added per liter of fluid) at a rate similar to sweat loss. In a second trial (hypohydrated), subjects were not allowed to consume any fluids. RESULTS: Cramps were induced in nine of the participants, while seven participants cramped in both trials. For those who cramped in both trials exercise duration prior to the onset of EAMC was significantly longer in the euhydrated trial (36.8 ± 17.3 minutes) compared to the hypohydrated trial (14.6 ± 5.0 minutes; p < .01). Mean weight loss for the hypohydrated trial was 1.0% ± 0.4% of body mass. No weight loss occurred during the euhydrated trial. CONCLUSIONS: The results suggest that dehydration and electrolyte loss are not the singular cause(s) of EAMC, since subjects cramped when they were euhydrated and in electrolyte balance. However, it appears that consumption of a carbohydrate-electrolyte beverage prior to and during exercise in a hot environment may delay the onset of EAMC.