Hypohydration Level Research Articles

Hydration status assessment and impinging factors among university students in the UAE.

Insufficient water intake has been a global health concern as it is linked to numerous adverse health consequences. Risk factors for dehydration include low fluid intake, sun and heat exposure which is a key element especially in the Gulf region. The aim of this study was to identify the prevalence and the impinging factors of hypohydration among college students in UAE. Bioelectrical Analysis Impedance (BIA), attained using BodyStat 1,500 MDD, was used to assess participants' body water levels. Adequate hydration level was defined as body water level of 50-60% for females and 55-65% for males. Alongside this, a scale and a stadiometer were used to measure the participants' weight and height in order to calculate their BMI. A self-administered questionnaire was also used to assess and correlate the test findings with the risk factors, signs and symptoms, and the level of knowledge awareness of the participants. Of the 201 university students that participated in the study, 41.3% were hypohydrated, 55.7% were well hydrated and 3% were hyper-hydrated. Among hypohydrated participants, 56.6% were females and 43.4% were males, highlighting that females were at higher risk of becoming dehydrated than males. A major factor that negatively affected hydration status was BMI; as BMI increased, water percentage and therefore hydration status decreased. We checked for numerous signs and symptoms that could indicate hypohydration levels, and the following were the top five most prevalent among our participants: dry lips (51.90%), thirst (46.90%), tiredness (46.80%), dry skin (39.70%) and headache (36.90%). According to The Urine Color Chart (Human Kinetics, Champaign, IL, USA), 3.5% were classified as dehydrated, 46% were in danger of getting hypohydration levels while 19.5% were classified as having good hydration levels. There was no significant correlation between water intake and urine colour chart (p = 0.334). Among the study participants, 64.2% acquired their knowledge from internet, 30.80% from TV and radio and 26.90% from books and courses. The behavior aspect of the participants when feeling thirsty, was that 79% of them would resort to water, while 11% resorted to soft drinks and 10% to juices. The prevalence of hypohydration levels was 41.3% among the study participants of young university students. The main risk factors affecting hydration levels were BMI and gender. This signifies the importance of good hydration habits which were not commonly practiced among students even though they had adequate knowledge regarding the topic. Regular check-ups held intermittently can aid in recognizing those at risk of dehydration and help in educating about the importance of such topic especially regionally.

Habit or lack of education? Hypohydration is present in elite senior judo athletes even during a weight-stable training camp

It has been well-documented that high-level judo athletes presented a high level of hypohydration during weight-cutting and competition periods. However, there is a lack of studies investigating the hydration status of high-level judo athletes during a weight-stable training period. Therefore, this study aimed to investigate elite judo athletes’ hydration status, body mass change, and fluid intake during a weight-stable training camp. Twenty-seven judo athletes (women n = 8, men n = 19, body weight = 79.6 ± 20.9 kg) from the senior national judo team voluntarily participated in this study. Data were collected in the morning after waking up and before and after the morning and evening training sessions. On the second day, the measurements were taken again in the morning after waking up. Urine-specific gravity (USG) was classified as hydrated (USG < 1.020) and hypohydrated (USG ≥ 1.020). The athletes’ USG values measured on two consecutive mornings increased (1.025 ± 0.007 to 1.029 ± 0.006) during 24 h, in which athletes performed judo training in the morning and evening. Moreover, sex and weight category did not affect the changes in USG values ( p > .05). Most of the elite judo athletes presented hypohydration (92.6%). The relationship between the fluid intake of the athletes and the changes in USG and body weight values during 24 h was not significant ( p > .05). The current study’s findings revealed that high-level judo athletes present a high level of hypohydration even during a weight-stable training camp. Furthermore, the training sessions during the experiment period (24 h) worsened the hydration status of the senior athletes in all weight categories for both women and men.

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.

Impact of Repeated Acute Exposures to Low and Moderate Exercise-Induced Hypohydration on Physiological and Subjective Responses and Endurance Performance.

This study aimed to examine whether repeated exposures to low (2%) and moderate (4%) exercise-induced hypohydration may reverse the potentially deleterious effect of hypohydration on endurance performance. Using a randomized crossover protocol, ten volunteers (23 years, O2max: 54 mL∙kg−1∙min−1) completed two 4-week training blocks interspersed by a 5-week washout period. During one block, participants replaced all fluid losses (EUH) while in the other they were fluid restricted (DEH). Participants completed three exercise sessions per week (walking/running, 55% O2max, 40 °C): (1) 1 h while fluid restricted or drinking ad libitum, (2) until 2 and (3) 4% of body mass has been lost or replaced. During the first and the fourth week of each training block, participants completed a 12 min time-trial immediately after 2% and 4% body mass loss has been reached. Exercise duration and distance completed (14.1 ± 2.7 vs. 6.9 ± 1.5 km) during the fixed-intensity exercise bouts were greater in the 4 compared to the 2% condition (p < 0.01) with no difference between DEH and EUH. During the first week, heart rate, rectal temperature and perceived exertion were higher (p < 0.05) with DEH than EUH, and training did not change these outcomes. Exercise-induced hypohydration of 2% and 4% body mass impaired time-trial performance in a practical manner both at the start and end of the training block. In conclusion, exercise-induced hypohydration of 2% and 4% body mass impairs 12 min walking/running time-trial, and repeated exposures to these hypohydration levels cannot reverse the impairment in performance.

Predicting the Magnitudes of Hyperthermia and Hypohydration during Prolonged Exposures to Warm and Very Humid Environments

In the event of a disabled submarine a pressurized rescue module (PRM) may be deployed. Safe deployment of the PRM depends on understanding the challenges should failures occur. If a PRM were to become disabled, temperature and humidity are predicted to rise quickly, and submariners may need to endure environments approaching 35°C, 95% relative humidity (RH) until rescued. Models predicting increases in core temperature (i.e., hyperthermia) and the magnitude of hypohydration incurred over 24 h in 95% RH environments yield physiologically impossible outcomes at ambient temperatures ≥32°C. Thus, it is not possible to accurately predict the magnitudes of hyperthermia and hypohydration during prolonged exposures to warm and very humid environments. By extension, the fluid prescription required to prevent unsafe levels of hypohydration, defined as a loss of body weight &gt;4%, in a disabled PRM is also unknown.PurposeTest the hypothesis that the predicted magnitudes of hyperthermia and hypohydration during a 24 h exposure to a 95% RH environment are dependent on ambient temperature.Methods10 healthy males (23 ± 3 y) sat in a 95 ± 2% RH normobaric environment for 8 h on three occasions separated by ≥7 days. Trials differed by temperature (32 ± 0°C, 33 ± 0°C, 35 ± 0°C). The order of the trials was randomly assigned. Subjects were not allowed to eat or drink throughout. Core temperature (telemetry pill) and percent changes in body weight (%ΔBW), an index of changes in total body water, were measured every hour. Sweat rate was calculated from %ΔBW. Linear regression models were fit to core temperature (over the final 3 h of exposure), and %ΔBW and sweat rate (over the entire 8 h exposure) over time for each subject. The resulting equations were used to predict the magnitudes of hyperthermia, %ΔBW, and sweat losses for up to 24 h. The volume of fluid required to prevent &gt;4% loss of body weight was calculated accordingly. Data are presented as mean ± SD.ResultsAt the end of the 8 h exposure, core temperature was higher in 35°C (38.0 ± 0.3°C, P&lt;0.01) compared to 32°C (37.6 ± 0.2°C) and 33°C (37.5 ± 0.2°C). At this time, %ΔBW was greater in 35°C (−2.0 ± 0.5%, P&lt;0.01) compared to 32°C (−1.5 ± 0.5%) and 33°C (−1.7 ± 0.4%). At 24 h, predicted core temperature was higher in 35°C (39.0 ± 1.1°C, P&lt;0.01) compared to 32°C (37.7 ± 1.0°C) and 33°C (37.8 ± 0.9°C), and the predicted %ΔBW was greater in 35°C (−6.1 ± 1.2%, P&lt;0.01) compared to 32°C (−4.5 ± 1.2%) and 33°C (−5.3 ± 1.3%). Predicted sweat loss at 24 h was greater in 35°C (−5.2 ± 1.4 L, P&lt;0.01) compared to 32°C (−3.8 ± 1.6 L) and 33°C (−4.4 ± 1.1 L). The predicted fluid prescription required to prevent &gt;4% loss of body weight was greater in 35°C (1.8 ± 0.9 L) compared to 32°C (0.7 ± 0.8 L, P&lt;0.02), and 33°C (1.0 ± 0.8 L, P=0.06).ConclusionIn a 95% RH environment, the magnitudes of hyperthermia and hypohydration predicted to occur during a 24 h exposure are dependent on ambient temperature. Moreover, the volume of fluid required to prevent &gt;4% loss in body weight during a 24 h exposure in ambient temperatures ≤35°C is ~1.8 L.Support or Funding InformationNaval Sea Systems Command Award N00024‐18‐C‐4316.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Longitudinal Hydration Assessment in Collegiate Basketball Players Over Various Training Phases

Heishman, AD, Daub, BD, Miller, RM, Freitas, EDS, and Bemben, MG. Longitudinal hydration assessment in collegiate basketball players over various training phases. J Strength Cond Res 35(4): 1089-1094, 2021-To the best of our knowledge, previous literature has not longitudinally examined hydration status in collegiate basketball players. Therefore, the purpose of this investigation was to examine the prepractice hydration status of collegiate basketball players across various training phases for 2 consecutive years. Retrospective analyses examined prepractice urine-specific gravity (USG) assessments obtained from National Collegiate Athletic Association (NCAA) Division I male basketball players during the preseason and competitive season, for 2 consecutive years. The first year (year 1 = Y1) of analysis consisted of 15 athletes and the second year (year 2 = Y2) consisted of 16 athletes, with 8 athletes in both seasons. Hydration status was classified based on the National Athletic Trainers' criteria: (a) euhydrated, USG < 1.020; (b) hypohydrated, USG = 1.020-1.030; and (c) significantly hypohydrated, USG > 1.030. Additional comparisons examined the association of minutes played with hydration status and changes in hydration status for athletes returning from Y1 to Y2. The results indicated 55-65.7% of cases showed levels of significant hypohydration during the preseason and competitive seasons for both years. Preseason hydration status was significantly better than the competitive season (Y1, p = 0.008; Y2, p = 0.005). Despite significant differences in minutes played (p < 0.001), no differences in hydration status were observed. Returning athletes displayed no differences in hydration status between Y1 and Y2. Collegiate basketball players show levels of hypohydration when longitudinally examined across various training phases. Although hydration may be improved in the preseason, alternative factors such as average game minutes played and length in program may not influence hydration status.

Impact of acute versus prolonged exercise and dehydration on kidney function and injury.

Exercise and dehydration may be associated with a compromised kidney function and potential signs of kidney injury. However, the kidney responses to exercise of different durations and hypohydration levels are not yet known. Therefore, we aimed to compare the effects of acute versus prolonged exercise and dehydration on estimated glomerular filtration rate (eGFR) and kidney injury biomarkers in healthy male adults. A total of 35 subjects (23 ± 3 years) were included and invited for two study visits. Visit 1 consisted of a maximal cycling test. On Visit 2, subjects performed a submaximal exercise test at 80% of maximal heart rate until 3% hypohydration. Blood and urine samples were taken at baseline, after 30 min of exercise (acute effects; low level of hypohydration) and after 150 min of exercise or when 3% hypohydration was achieved (prolonged effects, high level of hypohydration). Urinary outcome parameters were corrected for urinary cystatin C, creatinine, and osmolality. Subjects dehydrated on average 0.6 ± 0.3% and 2.9 ± 0.7% after acute and prolonged exercise, respectively (P < 0.001). The eGFR cystatin C did not differ between baseline and acute exercise (118 ± 11 vs. 116 ± 12 mL/min/1.73 m2, P = 0.12), whereas eGFR cystatin C was significantly lower after prolonged exercise (103 ± 16 mL/min/1.73 m2, P < 0.001). We found no difference in osmolality corrected uKIM1 concentrations after acute and prolonged exercise (P > 0.05), and elevated osmolality corrected uNGAL concentrations after acute and prolonged exercise (all P‐values < 0.05). In conclusion, acute exercise did barely impact on eGFR cystatin C and kidney injury biomarkers, whereas prolonged exercise is associated with a decline in eGFR cystatin C and increased biomarkers for kidney injury.

Temperate-Water Immersion as a Treatment for Hyperthermic Humans Wearing American Football Uniforms.

Cold-water immersion (CWI; 10°C) can effectively reduce body core temperature even if a hyperthermic human is wearing a full American football uniform (PADS) during treatment. Temperate-water immersion (TWI; 21°C) may be an effective alternative to CWI if resources for the latter (eg, ice) are unavailable. To measure rectal temperature (Trec) cooling rates, thermal sensation, and Environmental Symptoms Questionnaire (ESQ) scores of participants wearing PADS or shorts, undergarments, and socks (NOpads) before, during, and after TWI. Crossover study. Laboratory. Thirteen physically active, unacclimatized men (age = 22 ± 2 years, height = 182.3 ± 5.2 cm, mass = 82.5 ± 13.4 kg, body fat = 10% ± 4%, body surface area = 2.04 ± 0.16 m2). Participants exercised in the heat (40°C, 50% relative humidity) on 2 days while wearing PADS until Trec reached 39.5°C. Participants then underwent TWI while wearing either NOpads or PADS until Trec reached 38°C. Thermal sensation and ESQ responses were collected at various times before and after exercise. Temperate-water immersion duration (minutes), Trec cooling rates (°C/min), thermal sensation, and ESQ scores. Participants had similar exercise times (NOpads = 38.1 ± 8.1 minutes, PADS = 38.1 ± 8.5 minutes), hypohydration levels (NOpads = 1.1% ± 0.2%, PADS = 1.2% ± 0.2%), and thermal sensation ratings (NOpads = 7.1 ± 0.4, PADS = 7.3 ± 0.4) before TWI. Rectal temperature cooling rates were similar between conditions (NOpads = 0.12°C/min ± 0.05°C/min, PADS = 0.13°C/min ± 0.05°C/min; t12 = 0.82, P = .79). Thermal sensation and ESQ scores were unremarkable between conditions over time. Temperate-water immersion produced acceptable (ie, >0.08°C/min), though not ideal, cooling rates regardless of whether PADS or NOpads were worn. If a football uniform is difficult to remove or the patient is noncompliant, clinicians should begin water-immersion treatment with the athlete fully equipped. Clinicians should strive to use CWI to treat severe hyperthermia, but when CWI is not feasible, TWI should be the next treatment option because its cooling rate was higher than the rates of other common modalities (eg, ice packs, fanning).

Necessity of Removing American Football Uniforms From Humans With Hyperthermia Before Cold-Water Immersion.

The National Athletic Trainers' Association and the American College of Sports Medicine have recommended removing American football uniforms from athletes with exertional heat stroke before cold-water immersion (CWI) based on the assumption that the uniform impedes rectal temperature (T(rec)) cooling. Few experimental data exist to verify or disprove this assumption and the recommendations. To compare CWI durations, T(rec) cooling rates, thermal sensation, intensity of environmental symptoms, and onset of shivering when hyperthermic participants wore football uniforms during CWI or removed the uniforms immediately before CWI. Crossover study. Laboratory. Eighteen hydrated, physically active men (age = 22 ± 2 years, height = 182.5 ± 6.1 cm, mass = 85.4 ± 13.4 kg, body fat = 11% ± 5%, body surface area = 2.1 ± 0.2 m(2)) volunteered. On 2 days, participants exercised in the heat (approximately 40°C, approximately 40% relative humidity) while wearing a full American football uniform (shoes; crew socks; undergarments; shorts; game pants; undershirt; shoulder pads; jersey; helmet; and padding over the thighs, knees, hips, and tailbone [PADS]) until T(rec) reached 39.5°C. Next, participants immersed themselves in water that was approximately 10°C while wearing either undergarments, shorts, and crew socks (NOpads) or PADS without shoes until Trec reached 38°C. The CWI duration (minutes) and T(rec) cooling rates (°C/min). Participants had similar exercise times (NOpads = 40.8 ± 4.9 minutes, PADS = 43.2 ± 4.1 minutes; t(17) = 2.0, P = .10), hypohydration levels (NOpads = 1.5% ± 0.3%, PADS = 1.6% ± 0.4%; t(17) = 1.3, P = .22), and thermal-sensation ratings (NOpads = 7.2 ± 0.3, PADS = 7.1 ± 0.5; P > .05) before CWI. The CWI duration (median [interquartile range]; NOpads = 6.0 [5.4] minutes, PADS = 7.3 [9.8] minutes; z = 2.3, P = .01) and T(rec) cooling rates (NOpads = 0.28°C/min ± 0.14°C/min, PADS = 0.21°C/min ± 0.11°C/min; t(17) = 2.2, P = .02) differed between uniform conditions. Whereas participants cooled faster in NOpads, we still considered the PADS cooling rate to be acceptable (ie, >0.16°C/min). Therefore, if clinicians experience difficulty removing PADS or CWI treatment is delayed, they may immerse fully equipped hyperthermic football players in CWI and maintain acceptable T(rec) cooling rates. Otherwise, PADS should be removed preimmersion to ensure faster body core temperature cooling.

Effect of Hypohydration on Muscle Endurance, Strength, Anaerobic Power and Capacity and Vertical Jumping Ability: A Meta-Analysis.

How hypohydration impacts non-bodyweight (BW)-dependent muscle performance and vertical jumping ability remains to be determined using meta-analytic procedures. Our objective was to determine the impact of hypohydration on muscle endurance, strength, anaerobic power and capacity and vertical jumping ability using a meta-analytic approach. Studies were located using database searches and cross-referencing. Effect summaries were obtained using random-effects models; method of moments mixed-effects analysis-of-variance-like procedures were used to determine differences between groups; and restricted maximum likelihood random-effects meta-regressions were performed to determine relationships between variables, impact of confounders, and interaction effects. A total of 28 manuscripts met the inclusion criteria, producing six (upper body muscle endurance), ten (lower body muscle endurance), 14 (upper body muscle strength), 25 (lower body muscle strength), nine (muscle anaerobic power), nine (muscle anaerobic capacity), and 12 (vertical jumping ability) effect estimates. Hypohydration impaired overall muscle endurance by 8.3 ± 2.3% (P < 0.05), with no significant difference between upper body (-8.4 ± 3.3%) and lower body (-8.2 ± 3.2%). As a whole, muscle strength fell by 5.5 ± 1.0% (P < 0.05) with hypohydration; the difference between lower (-3.7 ± 1.8%) and upper (-6.2 ± 1.1%) body was non-significant. Anaerobic power (-5.8 ± 2.3%) was significantly altered with hypohydration, but anaerobic capacity (-3.5 ± 2.3%) and vertical jumping ability (0.9 ± 0.7%) were not. No significant correlations were observed between the changes in any of the muscle performance variables or vertical jumping ability and the changes in hypohydration level. Using an active procedure to dehydrate participants decreased muscle performance by an additional 5.4 ± 1.9% (2.76-fold) (P = 0.02) compared with using a passive dehydration procedure. Trained individuals demonstrated a 3.3 ± 1.7% (1.76-fold) (P = 0.06) lesser decrease in muscle performance with hypohydration than did untrained individuals. Hypohydration, or factors associated with dehydration, are likely to be associated with practically important decrements in muscle endurance, strength, and anaerobic power and capacity. However, their impact on non-BW-dependent muscle performance is substantially mitigated in trained individuals or when hypohydration is induced passively. Conversely, it is possible that body water loss (~3% BW) may improve performance in BW-dependent tasks such as vertical jumping ability.

Intestinal temperature does not reflect rectal temperature during prolonged, intense running with cold fluid ingestion

It is generally assumed that intestinal temperature (Tint), as measured with a telemetric pill, agrees relatively well with rectal temperature (Trec) during exercise. However, whether Tint reflects Trec during prolonged, intense and continuous exercise when cold fluids are consumed is unknown. Therefore, we compared Trec and Tint during a half-marathon during which cold water was ingested to prevent bodyweight (BW) losses >2%. Nine endurance athletes (age 30 ± 5 years) underwent a 21.1 km running time-trial (TT) in the heat (~30 °C and 44% RH) while BW losses were maintained to ~1% with continuous cold (4 °C) water provision. Tint and Trec were monitored throughout the TT. Hypohydration level, TT time and fluid intake were 1.2 ± 0.4% BW, 93.2 ± 9.9 min and 2143 ± 264 ml, respectively. Trec was systematically higher than Tint by 0.25 °C (95% CI: 0.14–0.37 °C). Tint and Trec showed an excellent relative (r = 0.90, p < 0.01), but poor absolute agreement as reflected by a 95% limit of agreement of ±1.07 °C and a standard error of measurement of ±0.39 °C. In conclusion, Tint does not mirror Trec during prolonged, intense running with cold fluid ingestion and, therefore, these measures should not be used interchangeably under this scenario.

Two percent hypohydration does not impair self-selected high-intensity intermittent exercise performance.

The level of hypohydration at which power output during intermittent exercise performance starts to decrease is not fully understood. The purpose of this study was to investigate the effects of 2% hypohydration without hyperthermia on intermittent exercise performance. Eight collegiate amateur boxers completed 2 exercise tests. On day 1, subjects hypohydrated by 2% of body mass by exercising in a hot environment, and on day 2, subjects performed intermittent exercise (4 × 2 minute per round [R] separated by 1-minute recovery) under a randomly assigned condition of with (HYP) or without (EUH) hypohydration. Each bout consisted of 8 × 5 seconds of maximal cycling exercise (0.05 kp × body mass) separated by 10 seconds of passive recovery. Mean power output per kilogram (MPO), total power output per kilogram (TPO), energy system relative contribution, and core rectal temperature (Tre) were measured. Changes in body mass before the exercise tests were -2.25 ± 0.18% (HYP) and -0.17 ± 0.19% (EUH) (p < 0.001). Mean power output, TPO, and each energy contribution ratio were not significantly different between the trials, and pre- and postexercise test Tre did not differ significantly between trials. Results demonstrated that approximately 2% hypohydration lies below the point at which power output during intermittent exercise starts to decline.

Mild to moderate hypohydration reduces boys’ high-intensity cycling performance in the heat

To evaluate the effect of 1 and 2 % hypohydration on high-intensity cycling performance of 10- to 12-year-old boys in the heat. In a counterbalanced order, nine boys attended three sessions in which they cycled intermittently (6 × 10-min bouts at 40-45 % [Formula: see text]) in a climate chamber. During each session, environmental conditions and water intake were individually adjusted to achieve a target hypohydration level of 0, 1 or 2 %, based on change in body weight (BW). Following 45 min of rest in thermoneutral conditions when the target hypohydration was maintained, each boy re-entered the climate chamber (35 °C and 50-55 % RH) to perform the cycling performance test at 90 % [Formula: see text] until exhaustion. Heart rate (HR) and rectal temperature (T re) were recorded continuously throughout each session. Total mechanical work (TMW) was taken as a measure of cycling performance. Actual hypohydration level at the start of the cycling performance test in each session was: 0.1 ± 0.0 %, 1.1 ± 0.1 % and 2.0 ± 0.1 %. With 2 % hypohydration, TMW (35.5 ± 6.8 kJ) was significantly (p < 0.05) lower than with 0 % hypohydration (49.3 ± 9.8 kJ). When expressed as a percentage of TMW with 0 % hypohydration, TMW was reduced by 15.5 and 23.3 % with 1 and 2 % hypohydration, respectively (p < 0.05 for both). At the start of the cycling performance test, HR was 13 and 15 bpm higher, and T re was 0.3 °C higher (p < 0.05 for all) with 1 and 2 % hypohydration, respectively, compared with 0 % hypohydration. Mild (~1 %) to moderate (~2 %) hypohydration reduces high-intensity cycling performance of healthy young boys in the heat.

Meta-Analysis Of The Effects Of Pre-Exercise Hypohydration On Endurance Performance, Lactate Threshold And Vo2max

Meta-Analysis Of The Effects Of Pre-Exercise Hypohydration On Endurance Performance, Lactate Threshold And Vo2max

Pre-Exercise Hypohydration Effects On Jumping Ability And Muscle Strength, Endurance And Anaerobic Capacity: A Meta-Analysis

A recent systematic review reported that pre-exercise hypohydration (PEH) impairs skeletal muscle performance. The extent to which PEH influences muscular performance-related outcomes remains to be quantified using standard meta-analytic procedures. PURPOSE: To determine the magnitude of the effects of PEH on leg and arm muscle strength, leg muscle endurance and anaerobic capacity, and jumping ability using a meta-analytic approach. METHODS: Studies were located via database searches and cross-referencing. Inclusion criteria: standard measures of muscular performance; hydration level in the euhydrated control group < 0.5% ≥ -1% bodyweight (BW); hypohydration level in the experimental group > 1% BW and > 0.5% than control BW. Exclusion criteria: diuretics- and caloric restriction-induced BW loss. Results were analyzed using a random-effect model for mean weighted summary effects and a random-effect analog to the ANOVA for subgroup analyses. RESULTS: Thirty-five research articles were retrieved, among which 11, 4, 7 and 4 met the inclusion criteria for muscle strength, muscle endurance, anaerobic capacity and jumping ability, respectively, providing 27, 7, 11 and 11 effect estimates. Mean BW decrease in experimental groups was 3.0 ± 1.4%, 3.2 ± 0.5%, 3.2 ± 1.2% and 2.5 ± 1.3% for muscle strength, muscle endurance, anaerobic capacity and jumping ability, respectively (range: 1.3 to 5.7%). Mean muscle strength fell by 4.6% (95% CI: 2.9 to 6.3%) with PEH relative to control, with leg (3.8%, 95% CI: 0.4 to 7.2%) and arm (4.8%, 95% CI: 2.9 to 6.8%) strength declining similarly. PEH resulted in a mean decrease in muscle endurance of 11.7% (95% CI: 0.002 to 23.4%) and a decline in anaerobic capacity by 5.7% (95% CI: 1.5 to 9.9%). When pooled together, results of studies indicated that the decline in muscular performance is not significantly different between studies with BW losses ≤ or > 3%. PEH did not alter jumping ability compared with control. CONCLUSIONS: PEH of 1.5 to 5.5% BW does not affect jumping ability, but decreases leg (-4%) and arm (-5%) muscle strength, as well as leg muscle endurance (-12%) and anaerobic capacity (-6%) in a significant and practical manner. The opinions or assertions contained herein should not to be construed as official or reflecting the views of the Army or the DoD.

Pregame Urine Specific Gravity and Fluid Intake by National Basketball Association Players During Competition

Urine specific gravity (USG) has been used to estimate hydration status in athletes on the field, with increasing levels of hypohydration indicated by higher USG measurements (eg, greater than 1.020). Whether initial hydration status based on a urine measure is related to subsequent drinking response during exercise or athletic competition is unclear. To determine the relationship between pregame USG and the volume of fluid consumed by players in a professional basketball game. Cross-sectional study. Basketball players were monitored during Summer League competition. Players (n = 29) from 5 teams of the National Basketball Association agreed to participate. Pregame USG was measured for each player on 2 occasions. Athletes were given ad libitum access to fluid during each game and were unaware of the purpose of the study. Volume of fluid intake was measured for each player. To assess sweat loss, athletes were weighed in shorts before and after each game. Sweat loss ranged from 1.0 to 4.6 L, with a mean sweat loss of 2.2 +/- 0.8 L. Fluid intake ranged from 0.1 to 2.9 L, with a mean fluid intake of 1.0 +/- 0.6 L. Pregame USG was greater than 1.020 in 52% of the urine samples collected and was not correlated with fluid volume consumed during either of the games (r = 0.15, P = .48, and r = 0.15, P = .52, respectively). Approximately half of the players began the games in a hypohydrated state, as indicated by USG. Fluid intake during the game did not compensate for poor hydration status before competition. Furthermore, sweat losses in these players during games were substantial (greater than 2 L in approximately 20 minutes of playing time). Therefore, both pregame and during-game hydration strategies, such as beverage availability and player education, should be emphasized.

Low levels of hypohydration and endurance capacity during heavy exercise in untrained individuals

Untrained subjects ( n = 6 ) performed three cycle exercise trials at 80% maximal O 2 uptake until exhaustion in a climatic chamber (32 °C, 60% relative humidity) under the following three conditions: (1) 2% hypohydration, (2) 1% hypohydration, and (3) euhydration. Exercise tolerance time averaged 7.7±1.5, 14.0±2.4, and 20.9±3.7 min, respectively, under these three conditions. Endurance capacity in untrained individuals is substantially impaired even at low levels of hypohydration during heavy exercise in a compensable hot environment, and this impairment is associated with hypohydration-induced higher initial body temperatures that leads to earlier attainment of a critical core temperature.

Hydration status measurement by radio frequency absorptiometry in young athletes—a new method and preliminary results**US and International Patents pending.

A new method for non-invasive measurement of the human state of hydration is presented. This method is based on frequency-dependent absorptiometry of radio-waves passing through tissues. A device utilizing this method was constructed and applied to 12 young (24 ± 1) male volunteers, who were dehydrated for 1–2.5% of their weight by performance of a physical effort (two 30 min bouts of treadmill walking/running at 2, 3, 4, 5, 6 and 7 mph, 5 min at each speed, separated by 10 min rest), under moderate heat stress (40 °C, 40% RH). Hypohydration level was determined by body weight measurements taken before each session, after 30 min and at the end of each session. Concomitantly, measurements of radio frequency (RF) absorption were taken. Each volunteer underwent the heat stress exercise twice: one in which no drinking was permitted, and another with free drinking. A correlation (R2 = 0.734) between weight loss and a change in the radio-waves absorption pattern was observed in most of the volunteers, in both hypo and euhydration sessions. Further work to establish the reproducibility and validity of the RF methodology in larger and different populations, i.e., females, other age groups and different health conditions, is already being researched.

Impact of mild dehydration on wellness and on exercise performance.

Chronic mild dehydration is a common condition in some population groups, including especially the elderly and those who participate in physical activity in warm environments. Hypohydration is recognised as a precipitating factor in a number of acute medical conditions in the elderly, and there may be an association, although not necessarily a causal one, between a low habitual fluid intake and some cancers, cardiovascular disease and diabetes. There is some evidence of impairments of cognitive function at moderate levels of hypohydration, but even short periods of fluid restriction, leading to a loss of body mass of 1-2%, lead to reductions in the subjective perception of alertness and ability to concentrate and to increases in self-reported tiredness and headache. In exercise lasting more than a few minutes, hypohydration clearly impairs performance capacity, but muscle strength appears to be relatively unaffected.

EFFECT OF DRINK COMPOSITION ON VOLUNTARY REHYDRATION IN BOYS FOLLOWING EXERCISE IN THE HEAT DEHYDRATION

PURPOSE To assess the effect of beverage composition on voluntary rehydration, thermoregulation and physiologic responses of hypohydrated boys during intermittent exercise in the heat. METHODS Six 10- to 12-year-old boys attended two identical (counterbalanced) sessions in which they first were dehydrated (2.1 % of initial body weight) through exercise (6x10-min bouts at 40–45% VO2max) in a climatic chamber at 35°C, 55% relative humidity (RH). After resting for 45 min in a thermoneutral room, they performed intermittent exercise (3x15-min bouts at 50% VO2max interspersed by 10 min rest) in 35°C, 50% RH, while drinking ad libitum either flavored water (FW) or FW with carbohydrate (6%) and NaCl 18 mmol·L−1 (CNa). Body weight (BW), heart rate (HR), body temperatures and perceptual variables were measured periodically. RESULTS Hypohydration level just prior of rehydration was identical in both FW and CNa. Total cumulative voluntary drink intake was similar (3.2–3.3 %BW) in both sessions. Almost half of it occurred in the first 15 minutes. Full rehydration was reached at 50 min. In both sessions the intensity of thirst perception dropped from initial 82–86 % to 50–53 % within first 15 min and to 30–40 % by the end of rehydration. Although rectal temperature increased significantly (p < 0.05) in CNa (from 37.6°C to 38.0°C) but not in FW (from 37.6°C to 37.8°C), differences between FW and CNa were insignificant. Heart rate at rest (90–97 bpm) and during exercise (145–150 bpm) was similar in both sessions. CONCLUSION Voluntary drinking of both flavored water and a flavored carbohydrate-electrolyte beverage is similarly effective in rehydrating boys who began exercise in the heat while hypohydrated. Supported by Gatorade Sports Science Institute