Hydration and physical performance

A Real-Time Wireless Sweat Rate Measurement System for Physical Activity Monitoring

There has been significant research on the physiology of sweat in the past decade, with one of the main interests being the development of a real-time hydration monitor that utilizes sweat. The contents of sweat have been known for decades; sweat provides significant information on the physiological condition of the human body. However, it is important to know the sweat rate as well, as sweat rate alters the concentration of the sweat constituents, and ultimately affects the accuracy of hydration detection. Towards this goal, a calorimetric based flow-rate detection system was built and tested to determine sweat rate in real time. The proposed sweat rate monitoring system has been validated through both controlled lab experiments (syringe pump) and human trials. An Internet of Things (IoT) platform was embedded, with the sensor using a Simblee board and Raspberry Pi. The overall prototype is capable of sending sweat rate information in real time to either a smartphone or directly to the cloud. Based on a proven theoretical concept, our overall system implementation features a pioneer device that can truly measure the rate of sweat in real time, which was tested and validated on human subjects. Our realization of the real-time sweat rate watch is capable of detecting sweat rates as low as 0.15 µL/min/cm², with an average error in accuracy of 18% compared to manual sweat rate readings.

Effects of 2% Dehydration on Lactate Concentration During Constant-Load Cycling

Green, JM, Miller, B, Simpson, J, Dubroc, D, Keyes, A, Neal, K, Gann, J, and Andre, T. Effects of 2% dehydration on lactate concentration during constant-load cycling. J Strength Cond Res 32(7): 2066-2071, 2018-The lactate [La] threshold (LT) can predict endurance performance potential. Dehydration may alter LT. This study examined effects of dehydration on [La] response during constant-load cycling. Recreationally fit (V[Combining Dot Above]O2peak = 48.7 ± 5.2 ml·kg·min) male participants (n = 9) completed 2 × 40-minute constant-load cycling trials; euhydrated (HYD) and after previous evening passive (water bath) dehydration (2% body weight, DEH) (HYD and DEH counterbalanced). Lactate, heart rate (HR), 10-point Omni ratings of perceived exertion (RPE), and rectal temperature (Trec) were measured after warm-up (WU) and at 10, 20, 30, and 40 minutes. Before cycling, urine specific gravity (USG) was measured and participants estimated perceived recovery status (PRS). Urine specific gravity DEH (1.027 ± 0.004) was significantly greater than HYD (1.013 ± 0.007). After WU, [La] was significantly greater (all time points) for DEH (∼4.1 mmol·L) vs. HYD (∼3.5 mmol·L) with similar results for HR (DEH: ∼167, HYD: ∼158 b·min). For DEH, RPE was significantly greater (∼1 unit) at 20, 30, and 40 minutes, and Trec was significantly greater at 30 and 40 minutes (∼0.4° C). DEH (vs. HYD) also resulted in significantly different resting HR (93 ± 6, vs. 85 ± 7 b·min), significantly greater session RPE (7.7 ± 1.1 vs. 5.3 ± 1.1), and significantly lower subjective feelings of recovery (PRS = 6.4 ± 2.9, vs. 9.0 ± 1.5). Current results indicate systematic changes in [La] and associated physiological responses result from previous day dehydration. Hydration status should be a concern in paradigms where [La] assessment is used.

Fluid replacement advice during work in fully encapsulated impermeable chemical protective suits

A major concern for responders to hazardous materials (HazMat) incidents is the heat strain that is caused by fully encapsulated impermeable chemical protective suits. In a research project, funded by the US Department of Defense, the thermal strain experienced when wearing these suits was studied. One particular area of interest was the fluid loss of responders during work in these suits as dehydration may be an additional health concern to the heat strain. 17 City of Raleigh firemen and 24 students were tested at two different labs. Subjects between the ages of 25 and 51 were used for human subject trials in a protocol approved by the local ethical committee. Six different Level A HazMat suits were evaluated in three climates: moderate (24°C, 50% RH, 20°C WBGT), warm-wet (32°C, 60% RH, 30°C WBGT), and hot-dry (45°C, 20% RH, 37°C WBGT, 200 W/m² radiant load) and at three walking speeds: 2.5 km/hr, 4 km/hr, and 5.5 km/hr. 4 km/hr was tested in all three climates and the other two walking speeds were tested in the moderate climate. Weight loss data was collected to determine fluid loss during these experiments. Working time ranged from as low as 20 min in the hot-dry condition to 60 min (the maximum) in the moderate climate, especially common at the lowest walking speed. The overall results from all experiments showed that fluid loss ranged from 0.2-2.2 L during these exposures, with the average fluid loss being 0.8 L, with 56% of the data between 0.5 L and 1 L of fluid loss. Further analysis showed that a suggestion of drinking 0.7 Liter per hour would safely hydrate over 50% of responders after one work-rest cycle. Applying this fluid volume over three work-rest cycles only put 11% of responders at risk of hypohydration vs. the 57% at risk with no fluid intake.

Beverage Consumption Habits among the European Population: Association with Total Water and Energy Intakes

BACKGROUND

Fluid and water intake have received limited attention in epidemiological studies. The aim of this study was to compare the average daily consumption of foods and beverages in adults of selective samples of the European Union (EU) population in order to understand the contribution of these to the total water intake (TWI), evaluate if the EU adult population consumes adequate amounts of total water (TW) according to the current guidelines, and to illustrate the real water intake in Europe.

METHODS

Three national European dietary surveys have been selected: Spain used the Anthropometry, Intake, and Energy Balance Study (ANIBES) population database, Italy analyzed data from the Italian National Food Consumption Survey (INRAN-SCAI 2005-06), and French data came from the NutriNet-Santé database. Mean daily consumption was used to compare between individuals. TWI was compared with European Food Safety Authority (EFSA) reference values for adult men and women.

RESULTS

On average, in Spain, TWI was 1.7 L (SE 22.9) for men and 1.6 L (SE 19.4) for women; Italy recorded 1.7 L (SE 16.9) for men and 1.7 L (SE 14.1) for women; and France recorded 2.3 L (SE 4.7) for men and 2.1 L (SE 2.4) for women. With the exception of women in France, neither men nor women consumed sufficient amounts of water according to EFSA reference values.

CONCLUSIONS

This study highlights the need to formulate appropriate health and nutrition policies to increase TWI in the EU population. The future of beverage intake assessment requires the use of new instruments, techniques, and the application of the new available technologies.

The role of obesity in the relation between total water intake and urine osmolality in US adults, 2009-2012

BACKGROUND

Adequate water intake is critical to physiologic and cognitive functioning. Although water requirements increase with body size, it remains unclear whether weight status modifies the relation between water intake and hydration status.

OBJECTIVE

We examined how the association between water intake and urine osmolality, which is a hydration biomarker, varied by weight status.

DESIGN

NHANES cross-sectional data (2009-2012) were analyzed in 9601 nonpregnant adults aged ≥20 y who did not have kidney failure. Weight status was categorized with the use of body mass index on the basis of measured height and weight (underweight or normal weight, overweight, and obesity). Urine osmolality was determined with the use of freezing-point depression osmometry. Hypohydration was classified according to the following age-dependent formula: ≥831 mOsm/kg - [3.4 × (age - 20 y)]. Total water intake was determined with the use of a 24-h dietary recall and was dichotomized as adequate or low on the basis of the Institute of Medicine's adequate intake recommendations for men and women (men: ≥3.7 or <3.7 L; nonlactating women: ≥2.7 or <2.7 L; lactating women: ≥3.8 or <3.8 L for adequate or low intakes, respectively). We tested interactions and conducted linear and log-binomial regressions.

RESULTS

Total water intake (P = 0.002), urine osmolality (P < 0.001), and hypohydration prevalence (P < 0.001) all increased with higher weight status. Interactions between weight status and water intake status were significant in linear (P = 0.005) and log-binomial (P = 0.015) models, which were then stratified. The prevalence ratio of hypohydration between subjects with adequate water intake and those with low water intake was 0.56 (95% CI: 0.43, 0.73) in adults who were underweight or normal weight, 0.67 (95% CI: 0.57, 0.79) in adults who were overweight, and 0.78 (95% CI: 0.70, 0.88) in adults who were obese.

CONCLUSION

On a population level, obesity modifies the association between water intake and hydration status.

Monitoring hydration status pre- and post-training among university athletes using urine color and weight loss indicators

OBJECTIVE

To investigate the hydration status pre- and post-training among university athletes using urine color and weight loss as indicators.

PARTICIPANTS

Participants were 52 university athletes training for campus games in a developing country.

METHODS

Pre- and post-training urine specimens were compared with a standard urine color scale. Paired t tests were used to compare urine color and difference in body mass pre- and post-training.

RESULTS

The mean age of the athletes was 22.87 ± 3.21. A statistically significance difference (p < .01) was observed between pre- (4.31 ± 1.75) and post- (5.67 ± 1.45) training urine color values for males. Hydration status and weight post-training were statistically significantly different both at the level of p < .01.

CONCLUSIONS

The results suggest that there is a link between urine color and body mass difference among the student athletes tested. Exercise increases hypohydration due to fluid losses, and therefore attention should be given to fluid supplementation and individualization of fluid intake for each athlete.

Evaluation of tympanic temperature and thermal sensation responses during exercise to verify the positive effects of wearing germanium-coated functional clothing

[Purpose] The present study investigated the effects of wearing germanium-coated functional clothing on tympanic temperature, thermal sensation, heat shock protein 70 (Hsp70), and lactate during endurance exercise. [Subjects and Methods] Nine healthy and untrained male subjects were enrolled. Subjects ran for 60 min on a treadmill (75% heart rate reserve) in the following 2 tests: 1) control test (wearing conventional clothing) and 2) experimental test (wearing germanium-coated functional clothing). During each test, the tympanic temperature and thermal sensation were measured, and blood samples were collected immediately before exercise and immediately after exercise. Thermal sensation was measured using a DISC score. [Results] The tympanic temperature immediately after exercise was significantly increased compared to the temperature immediately before exercise in the control test, while no significant change was observed in the experimental test. In both tests, the DISC score and Hsp70 and lactate levels immediately after exercise were significantly increased compared to those immediately before exercise. In addition, the DISC score immediately after exercise was significantly higher in the control test than in the experimental test. [Conclusion] Wearing germanium-coated functional clothing during endurance exercise may have the positive effect of alleviating thermal stress that accumulates in the body during exercise.

Physical Activity and Beverage Consumption among Adolescents

This study assessed the relationship between physical activity and beverage consumption among adolescents with a population based cross-sectional survey was carried out in the Balearic Islands, Spain (n = 1988; 12-17 years old). Body composition, educational and income level, physical activity (PA), and beverage consumption and energy intake were assessed. Sixty-two percent of adolescents engaged in >300 min/week of PA. Boys were more active than girls, younger adolescents were more active than older counterparts, low parental income was associated with physical inactivity, and time spent watching TV (including, TV, Internet or handheld cellular devices) was inversely associated with PA practice. The average beverage intake of the studied adolescents was 0.9 L/day, higher in boys than in girls. Beverage intake was positively associated with PA practice, and the highest amount of energy intake from beverages was observed in active boys and girls. Most of the studied adolescent population met the PA recommendations. Gender, age, parental income, and time spent watching TV were significant determinants of PA. Type and amount of beverages drunk varied according to gender and PA, and general daily total beverage intake was lower than recommended adequate fluid intake. PA behavior should be considered when analyzing beverage consumption in adolescents.

A Pilot Study of Self-Reported Physical Activity and Eating Habits in Turkish Cancer Patients Under Chemotherapy

As in all individuals, improving the quality of life, balanced nutrition and physical activity habits must be acquired in cancer patients. The purpose of this study was to determine eating habits and physical activity of cancer patients receiving chemotherapy. Sixty-six patients were completed the questionnaire included sociodemographic data, type of cancer, anthropometric measurements (size and body weight), dietary and physical activity habits. Body mass index for each patient was calculated. Data were analyzed using Statistical Package for Social Science software. Patients were ranged from underweight to obese according to their body mass index: 6.1% of patients were classified as underweight. Almost half (48.5%, n = 32) reported to be regularly physical active, and 46.9% (n = 15) thereof reported 30 min brisk walking. More vegetables consumption was the most popular answer with 62.1% (n = 41), whereas vegetables/fruit or vegetables/legume consumption was 22.7% (n = 15). Gender differences in food choice and preferring the taste of food were not seen as statistically significant. In this article, patients with different types of cancer reported their eating habits and physical activity. Disease-related and worse prognostic factors were found. An institutional program should be offered to cancer patients for consulting about nutrition and physical activity.

Drinking water in California child care sites before and after 2011-2012 beverage policy

Introduction

Drinking water is promoted to improve beverage nutrition and reduce the prevalence of obesity. The aims of this study were to identify how water was provided to young children in child care and to determine the extent to which water access changed after a federal and state child care beverage policy was instituted in 2011 and 2012 in California.

Methods

Two independent cross-sectional samples of licensed child care providers completed a self-administered survey in 2008 (n = 429) and 2012 (n = 435). Logistic regression was used to analyze data for differences between 2008 and 2012 survey responses, after adjustment for correlations among the measurements in each of 6 child care categories sampled.

Results

A significantly larger percentage of sites in 2012 than in 2008 always served water at the table with meals or snacks (47.0% vs 28.0%, P = .001). A significantly larger percentage of child care sites in 2012 than in 2008 made water easily and visibly available for children to self-serve both indoors (77.9% vs 69.0%, P = .02) and outside (78.0% vs 69.0%, P = .03). Sites that participated in the federal Child and Adult Care Food Program had greater access to water indoors and outside than sites not in the program. In 2012 most (76.1%) child care providers reported no barriers to serving water to children. Factors most frequently cited to facilitate serving water were information for families (39.0% of sites), beverage policy (37.0%), and lessons for children (37.9%).

Conclusion

Water provision in California child care improved significantly between samples of sites studied in 2008 and 2012, but room for improvement remains after policy implementation. Additional training for child care providers and parents should be considered.

Influence of body mass loss on changes in heart rate during exercise in the heat: a systematic review

The purpose of this review was to compare the changes in heart rate (HR) for every 1% change in body mass loss (ΔBML) in individuals while exercising in the heat. PubMed, SPORTDiscus, ERIC, CINAHL, and Scopus were searched from the earliest entry to February 2013 using the search terms dehydration, heart rate, and exercise in various combinations. Original research articles that met the following criteria were included: (a) valid measure of HR, (b) exercise in the heat (>26.5° C [79.7 °F]), (c) the level of dehydration reached at least 2%, (d) a between-group comparison (a euhydrated group or a graded dehydration protocol) was evident, and (e) for rehydration protocols, only oral rehydration was considered for inclusion. Twenty articles were included in the final analysis. Mean values and SDs for HR and percentage of body mass loss immediately after exercise were used for this review. The mean change in HR for every 1% ΔBML was 3 b·min-1. In trials where subjects arrived euhydrated and hypohydrated, the mean change in HR for every 1% ΔBML was 3 and 3 b·min-1, respectively. Fixed intensity and variable intensity trials exhibited a mean HR change of 4 and 1 b·min-1, respectively. Exercising in the heat while hypohydrated (≥2%) resulted in an increased HR after exercise. This increase in HR for every 1% ΔBML exacerbates cardiovascular strain in exercising individuals, thus causing decrements in performance. It should be encouraged that individuals should maintain an adequate level of hydration to maximize performance, especially in the heat.

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.

Saturation diving; physiology and pathophysiology

In saturation diving, divers stay under pressure until most of their tissues are saturated with breathing gas. Divers spend a long time in isolation exposed to increased partial pressure of oxygen, potentially toxic gases, bacteria, and bubble formation during decompression combined with shift work and long periods of relative inactivity. Hyperoxia may lead to the production of reactive oxygen species (ROS) that interact with cell structures, causing damage to proteins, lipids, and nucleic acid. Vascular gas-bubble formation and hyperoxia may lead to dysfunction of the endothelium. The antioxidant status of the diver is an important mechanism in the protection against injury and is influenced both by diet and genetic factors. The factors mentioned above may lead to production of heat shock proteins (HSP) that also may have a negative effect on endothelial function. On the other hand, there is a great deal of evidence that HSPs may also have a "conditioning" effect, thus protecting against injury. As people age, their ability to produce antioxidants decreases. We do not currently know the capacity for antioxidant defense, but it is reasonable to assume that it has a limit. Many studies have linked ROS to disease states such as cancer, insulin resistance, diabetes mellitus, cardiovascular diseases, and atherosclerosis as well as to old age. However, ROS are also involved in a number of protective mechanisms, for instance immune defense, antibacterial action, vascular tone, and signal transduction. Low-grade oxidative stress can increase antioxidant production. While under pressure, divers change depth frequently. After such changes and at the end of the dive, divers must follow procedures to decompress safely. Decompression sickness (DCS) used to be one of the major causes of injury in saturation diving. Improved decompression procedures have significantly reduced the number of reported incidents; however, data indicate considerable underreporting of injuries. Furthermore, divers who are required to return to the surface quickly are under higher risk of serious injury as no adequate decompression procedures for such situations are available. Decompression also leads to the production of endothelial microparticles that may reduce endothelial function. As good endothelial function is a documented indicator of health that can be influenced by regular exercise, regular physical exercise is recommended for saturation divers. Nowadays, saturation diving is a reasonably safe and well controlled method for working under water. Until now, no long-term impact on health due to diving has been documented. However, we still have limited knowledge about the pathophysiologic mechanisms involved. In particular we know little about the effect of long exposure to hyperoxia and microparticles on the endothelium.

Assessment of hydration status in a large population

Both acute and chronic dehydration can have important implications for human behaviour and health. Young children, non-autonomous individuals and the elderly are at a greater risk of dehydration. Mild hypertonic dehydration could be related to less efficient cognitive and physical performance and has been reported to be associated with frequently occurring pathological conditions, especially nephrolithiasis. The assessment of hydration status in a large sample appears to be of interest for conducting epidemiological and large clinical studies aimed at improving preventive and curative care. Especially in large-population studies, methods that are used have to be accurate, cheap, quick and require no technical expertise. Body weight change is widely used to determine acute hydration changes, but seems to be insufficiently accurate in longitudinal studies. Bioimpedance analysis methods enable the assessment of total body water content, but their use is still under debate. Because plasma osmolality directly reflects intracellular osmolality, it constitutes a good marker to assess acute hydration changes, but not chronic hydration status because it changes constantly. Moreover, venepuncture is considered to be invasive and is not suitable for a large-sample study, especially in children. Urinary markers appear to be good alternatives for assessing hydration status in large populations. Collection of urine samples is non-invasive and cheap. High technical expertise is not required to perform urinary marker measurements and these measurements can be carried out quickly. Thus, methods based on urinary markers are very well suited for field studies. Urine colour is probably the least sensitive marker despite its high specificity. Urine osmolality and especially urine specific gravity could be easily used for determining hydration status in large-sample studies.

Water from fruit or the river? Examining hydration strategies and gastrointestinal illness among Tsimane’ adults in the Bolivian Amazon

Objective

Water is an essential nutrient overlooked in many cross-cultural studies of human nutrition. The present article describes dietary water intake patterns among forager-horticulturalist adults in lowland Bolivia, compares daily intake with international references and examines if variation in how people acquire water relates to gastrointestinal illness.

Design

Cross-sectional observational study used survey, anthropometric and qualitative methods with Tsimane’ adults selected by age and sex stratification sampling in one community.

Setting

Research occurred in one Tsimane’ village in the Beni department, Bolivia with limited access to clean water. The 24 h diet and health recalls were conducted in July–August 2012 and qualitative interviews/ethnographic observation in September–October 2013.

Subjects

Forty-five Tsimane’ household heads (49 % men) took part in the first data collection and twenty-two Tsimane’ (55 % men) were included in the follow-up interviews.

Results

Men and women reported consuming 4·9 litres and 4·4 litres of water daily from all dietary sources, respectively. On average, water from foods represented 50 % of total water intake. Thirteen per cent of participants reported symptoms of gastrointestinal illness. In a logistic regression model adjusted for age, BMI, sex and raw water consumed, each percentage increase in water obtained from foods was associated with a reduced risk of gastrointestinal illness (OR=0·92; 95 % CI 0·85, 0·99).

Conclusions

Both total water intake and percentage of water from foods were higher than averages in industrialized countries. These findings suggest that people without access to clean water may rely on water-rich foods as a dietary adaptation to reduce pathogen exposures.

Improved noncontact optical sensor for detection of glucose concentration and indication of dehydration level

The ability to extract different bio-medical parameters from one single wristwatch device can be very applicable. The wearable device that is presented in this paper is based on two optical approaches. The first is the extraction and separation of remote vibration sources and the second is the rotation of linearly polarized light by certain materials exposed to magnetic fields. The technique is based on tracking of temporal changes of reflected secondary speckles produced in the wrist when being illuminated by a laser beam. Change in skin's temporal vibration profile together with change in the magnetic medium that is generated by time varied glucose concentration caused these temporal changes. In this paper we present experimental tests which are the first step towards an in vivo noncontact device for detection of glucose concentration in blood. The paper also shows very preliminary results for qualitative capability for indication of dehydration.

Water deprivation induces neurovascular and cognitive dysfunction through vasopressin-induced oxidative stress

Adequate hydration is essential for normal brain function and dehydration induces cognitive deterioration. In addition, dehydration has emerged as a stroke risk factor. However, it is unknown whether alterations in cerebrovascular regulation are responsible for these effects. To address this issue, C57Bl/6 mice were water deprived for 24 or 48 hours and somatosensory cortex blood flow was assessed by laser-Doppler flowmetry in a cranial window. Dehydration increased plasma osmolality and vasopressin levels, and suppressed the increase in blood flow induced by neural activity, by the endothelium-dependent vasodilator acetylcholine and the smooth muscle relaxant adenosine. The cerebrovascular dysfunction was associated with oxidative stress and cognitive deficits, assessed using the Y maze. The vasopressin 1a receptor antagonist SR49059 improved the dehydration-induced oxidative stress and vasomotor dysfunction. Dehydration upregulated endothelin-1 in cerebral blood vessels, an effect blocked by SR49059. Furthermore, the endothelin A receptor antagonist BQ123 ameliorated cerebrovascular function. These findings show for the first time that dehydration alters critical mechanisms regulating the cerebral circulation through vasopressin and oxidative stress. The ensuing cerebrovascular dysregulation may alter cognitive function and increase the brain's susceptibility to cerebral ischemia.

Validity of hydration non-invasive indices during the weightcutting and official weigh-in for Olympic combat sports

Background

In Olympic combat sports, weight cutting is a common practice aimed to take advantage of competing in weight divisions below the athlete's normal weight. Fluid and food restriction in combination with dehydration (sauna and/or exercise induced profuse sweating) are common weight cut methods. However, the resultant hypohydration could adversely affect health and performance outcomes.

Purpose

The aim of this study is to determine which of the routinely used non-invasive measures of dehydration best track urine osmolality, the gold standard non-invasive test.

Method

Immediately prior to the official weigh-in of three National Championships, the hydration status of 345 athletes of Olympic combat sports (i.e., taekwondo, boxing and wrestling) was determined using five separate techniques: i) urine osmolality (U_OSM), ii) urine specific gravity (U_SG), iii) urine color (U_COL), iv) bioelectrical impedance analysis (BIA), and v) thirst perception scale (TPS). All techniques were correlated with U_OSM divided into three groups: euhydrated (G₁; U_OSM 250–700 mOsm·kg H₂O⁻¹), dehydrated (G₂; U_OSM 701–1080 mOsm·kg H₂O⁻¹), and severely dehydrated (G₃; U_OSM 1081–1500 mOsm·kg H₂O⁻¹).

Results

We found a positive high correlation between the U_OSM and U_SG (r = 0.89: p = 0.000), although this relationship lost strength as dehydration increased (G₁ r = 0.92; G₂ r = 0.73; and G₃ r = 0.65; p = 0.000). U_COL showed a moderate although significant correlation when considering the whole sample (r = 0.743: p = 0.000) and G₁ (r = 0.702: p = 0.000) but low correlation for the two dehydrated groups (r = 0.498–0.398). TPS and BIA showed very low correlation sizes for all groups assessed.

Conclusion

In a wide range of pre-competitive hydration status (U_OSM 250–1500 mOsm·kg H₂O⁻¹), U_SG is highly associated with U_OSM while being a more affordable and easy to use technique. U_COL is a suitable tool when U_SG is not available. However, BIA or TPS are not sensitive enough to detect hypohydration at official weight-in before an Olympic combat championship.

Healthy snacking recommendations: one size does not fit all

An underlying factor contributing to a lack of consensus in the scientific literature regarding the health effects of snacking may be the diversity of study populations. In fact, the influence of snacking likely varies with different target populations. Accordingly, the purpose of this paper is to demonstrate that snacking may make important contributions to a healthy diet, especially among older adults (≥65 years). However, these dietary behaviors may have a different consequence among adults (18-60 years) experiencing psychosocial stress as measured by food insecurity. Food insecurity refers to the condition in which individuals do not have access at all times to enough food for an active, healthful life. Another reason for a lack of consensus regarding the effects of snacking is that reports describing the contribution of snacking to the diet of adults have generally focused on single nutrients. Because of the complexity of dietary intake and the possible interaction of nutrients, it is often difficult to attribute health outcomes to the effects of a single dietary component. Thus, the relationship between snacking frequency and overall dietary quality among adults (≥20 years) will be described. Developing recommendations regarding snacking and meal frequency is extremely problematic for numerous reasons. One universal dietary recommendation regarding snacking and meal frequency is not appropriate for every life-stage group. Also, research has demonstrated that individuals view snacking as an unhealthy behavior. Because individuals are more likely to acknowledge, integrate, and act on nutrition knowledge that corresponds with their existing knowledge, changing dietary behaviors with messages containing the term snacking may be ill-conceived. Descriptive alternatives to the term snacking are needed in developing messages for health promotion campaigns.

Beyond muscle hypertrophy: why dietary protein is important for endurance athletes

Recovery from the demands of daily training is an essential element of a scientifically based periodized program whose twin goals are to maximize training adaptation and enhance performance. Prolonged endurance training sessions induce substantial metabolic perturbations in skeletal muscle, including the depletion of endogenous fuels and damage/disruption to muscle and body proteins. Therefore, increasing nutrient availability (i.e., carbohydrate and protein) in the post-training recovery period is important to replenish substrate stores and facilitate repair and remodelling of skeletal muscle. It is well accepted that protein ingestion following resistance-based exercise increases rates of skeletal muscle protein synthesis and potentiates gains in muscle mass and strength. To date, however, little attention has focused on the ability of dietary protein to enhance skeletal muscle remodelling and stimulate adaptations that promote an endurance phenotype. The purpose of this review is to critically discuss the results of recent studies that have examined the role of dietary protein for the endurance athlete. Our primary aim is to consider the results from contemporary investigations that have advanced our knowledge of how the manipulation of dietary protein (i.e., amount, type, and timing of ingestion) can facilitate muscle remodelling by promoting muscle protein synthesis. We focus on the role of protein in facilitating optimal recovery from, and promoting adaptations to strenuous endurance-based training.

Perda hidrica e pratica de hidratacao em atletas de futebol

INTRODUÇÃO: Atletas de futebol sofrem grande estresse fisiológico durante os treinos. As características da atividade associadas às condições climáticas desfavoráveis podem provocar desidratação intensa resultando em redução de desempenho físico. OBJETIVO: Estimar o percentual de desidratação de atletas futebolistas durante sessões de treino na cidade de Cuiabá-MT, Brasil. MÉTODOS: Os dados foram coletados nas instalações do centro de treinamento da equipe. Participaram do estudo 17 atletas profissionais do sexo masculino (idade = 21,53 ± 1,19 anos; peso=71,99±7,66 kg; estatura=1,76±0,08m; IMC=23,31±1,69kg/m²). Foram analisadas as pesagens de pré e pós-treino em dois dias não consecutivos de treino (A e B) e pela perda de peso ocorrida, obteve-se a diferença de massa corporal (ΔMC); também se anotou toda a ingestão de líquidos. Os dados registrados foram aplicados às fórmulas específicas para análise. RESULTADOS: O ΔMC entre a medida inicial e a medida final do treino A foi de 1,08 ± 0,45 kg, já a do treino B foi de 0,85 ± 0,47kg, representando 1,5 ± 0,63% e 1,19 ± 0,59% de desidratação, respectivamente. O volume de líquido ingerido foi de 2.591 ± 440 ml no treino A e de 926 ± 356 ml no treino B. A prática do futebol reduziu a massa corporal dos atletas após o treino, indicando que houve desidratação. CONCLUSÃO: Apesar da oferta constante de água aos jogadores, observamos que a reposição hídrica ad libitum não foi suficiente para manter o estado eu-hidratado de todos os atletas.

The Hydration Equation: Update on Water Balance and Cognitive Performance

To become aware of the most practical measures of hydration status.To describe sources of water input and output and the basics of water balance.To understand how hydration status may impact daily cognitive performance.

CONDENSED VERSION AND BOTTOM LINE

Water is a crucial nutrient and euhydration is necessary for optimal daily functioning. Water balance is precisely regulated within the body and many methods exist for assessing hydration status. Cognitive performance measures an individual's attentiveness, critical thinking skills, and memory. Traditionally a 2% or more body water deficit was thought to produce cognitive performance decrements; however, recent literature suggests that even mild dehydration - a body water loss of 1-2% - can impair cognitive performance. Counseling clients about their health and wellbeing should include conveying the importance of water for normal body functioning, as well as its effects on physical and cognitive performance.

Smartphone based health accessory for colorimetric detection of biomarkers in sweat and saliva

The mobile health market is rapidly expanding and portable diagnostics tools offer an opportunity to decrease costs and increase the availability of healthcare. Here we present a smartphone based accessory and method for the rapid colorimetric detection of pH in sweat and saliva. Sweat pH can be correlated to sodium concentration and sweat rate in order to indicate to users the proper time to hydrate during physical exercise and avoid the risk of muscle cramps. Salivary pH below a critical threshold is correlated with enamel decalcification, an acidic breakdown of calcium in the teeth. We conduct a number of human trials with the device on a treadmill to demonstrate the ability to monitor changes in sweat pH due to exercise and electrolyte intake and predict optimal hydration. Additionally, we perform trials to measure salivary pH over time to monitor the effects of diet on oral health risks.

Snacking may improve physical function among older Americans

BACKGROUND/OBJECTIVES

Snacking was reported to provide nutritional benefits among older adults, but the association between such dietary behavior and health outcomes has not been clearly established. The purpose of this study is to examine the associations between snacking and gait speed, a performance-based measure of physical function.

DESIGN

Cross-sectional population-based survey.

SETTING

The 1999-2002 National Health and Nutrition Examination Survey (NHANES).

PARTICIPANTS

A nationally representative sample of Americans aged 60 and older（n = 2,333).

MEASUREMENTS

Participants were classified by snacking frequency (0, 1, 2, 3, ≥4 snacks/d) and by the contribution of snacking to their daily energy intake (0 to <10%, 10% to <20%, 20% to <30%, ≥30%). Physical function was assessed by measurement of gait speed over 20 feet.

RESULTS

After adjusting for age, gender, education, race/ethnicity, smoking status, and marital status, older adults who snacked four times or more daily had a faster gait speed (P = 0.033) than non-snackers. Snacking that contributed 20% to <30% (P = 0.017) of energy was associated with a faster gait speed than snacking that contributed 0 to <10% of energy. Similar associations were observed after further adjustment for potential confounders.

CONCLUSION

Both snacking frequency and percentage of energy from snacking are positively associated with gait speed among older adults. The benefits of snacking on older adults' physical function may warrant their inclusion in this population's diet.

Sports nutrition needs: before, during, and after exercise

This article discusses how athletes should properly fuel their bodies before, during, and after exercise to maximize athletic performance. Emphasis is placed on hydration status and glycogen stores being maintained above deficits that negatively affect sport performance. Timing of nutrient intake is as important as composition.

Body mass change and ultraendurance performance: a decrease in body mass is associated with an increased running speed in male 100-km ultramarathoners

We investigated, in 50 recreational male ultrarunners, the changes in body mass, selected hematological and urine parameters, and fluid intake during a 100-km ultramarathon. The athletes lost (mean and SD) 2.6 (1.8) % in body mass (p < 0.0001). Running speed was significantly and negatively related to the change in body mass (p < 0.05). Serum sodium concentration ([Na⁺]) and the concentration of aldosterone increased with increasing loss in body mass (p < 0.05). Urine-specific gravity increased (p < 0.0001). The change in body mass was significantly and negatively related to postrace serum [Na⁺] (p < 0.05). Fluid intake was significantly and positively related to both running speed (r = 0.33, p = 0.0182) and the change in body mass (r = 0.44, p = 0.0014) and significantly and negatively to both postrace serum [Na⁺] (r = -0.42, p = 0.0022) and the change in serum [Na⁺] (r = -0.38, p = 0.0072). This field study showed that recreational, male, 100-km ultramarathoners dehydrated as evidenced by the decrease in >2 % body mass and the increase in urine-specific gravity. Race performance, however, was not impaired because of the loss in body mass. In contrast, faster athletes lost more body mass compared with slower athletes while also drinking more. The concept that a loss of >2% in body mass leads to dehydration and consequently impairs endurance performance must be questioned for ultraendurance athletes competing in the field. For practical applications, a loss in body mass during a 100-km ultramarathon was associated with a faster running speed.

Heat illness surveillance in schoolboys participating in physical education class in tropical climate: an analytical prospective descriptive study

OBJECTIVES

This study aimed to determine thermoregulatory and cardiovascular responses as well as the occurrence of heat illness in children exercising outdoors in physical education class under hot and humid climate. Little information regarding this issue under real-life situation is available, especially in the Southeast Asia.

DESIGN

Analytical, prospective descriptive study.

SETTING

A primary school in Bangkok, Thailand.

PARTICIPANTS

A total of 457 schoolboys (aged 5.5-12 years) were observed while exercising outdoors during their physical education classes throughout the academic year of 2009, including semester 1 (between July and September 2009) and semester 2 (between November 2009 and February 2010).

PRIMARY AND SECONDARY OUTCOME MEASURES

Primary outcome measure was tympanic temperature. Secondary outcome measures included blood pressure, heart rate, hydration status and the occurrence of heat-related illness.

RESULTS

Outdoor physical activity consisted of skill practice (duration 24.11±11.04 min, intensity <3 metabolic equivalent of tasks) and playing sports (duration 11.48±5.53 min, intensity 2.6-8.8 metabolic equivalent of tasks). After exercise, tympanic temperature increased by 0.66±0.41°C. There were 20 (4.4%) students whose ear temperature exceeded 38°C, 18 of whom did not consume water. The RR of increasing body temperature up to 38°C in overweight students was 2.1-fold higher than normal-weight students. The per cent change in mean arterial pressure and heart rate increased by 20.16±15.34% and 23.94±19.78%, respectively. Sweat and dehydration rates were 391.16±186.75 ml/h and 0.63±0.26%, respectively. No evidence of heat illness was found. Wet bulb globe temperatures of semesters 1 and 2 were 29.95±1.87°C and 28.32±2.39°C, respectively.

CONCLUSIONS

There is an increased risk for heat illness during outdoor activities in physical education class in primary school children, especially those who are overweight and have poor hydration status.

A faster running speed is associated with a greater body weight loss in 100-km ultra-marathoners

In 219 recreational male runners, we investigated changes in body mass, total body water, haematocrit, plasma sodium concentration ([Na(+)]), and urine specific gravity as well as fluid intake during a 100-km ultra-marathon. The athletes lost 1.9 kg (s = 1.4) of body mass, equal to 2.5% (s = 1.8) of body mass (P < 0.001), 0.7 kg (s = 1.0) of predicted skeletal muscle mass (P < 0.001), 0.2 kg (s = 1.3) of predicted fat mass (P < 0.05), and 0.9 L (s = 1.6) of predicted total body water (P < 0.001). Haematocrit decreased (P < 0.001), urine specific gravity (P < 0.001), plasma volume (P < 0.05), and plasma [Na(+)] (P < 0.05) all increased. Change in body mass was related to running speed (r = -0.16, P < 0.05), change in plasma volume was associated with change in plasma [Na(+)] (r = -0.28, P < 0.0001), and change in body mass was related to both change in plasma [Na(+)] (r = -0.36) and change in plasma volume (r = 0.31) (P < 0.0001). The athletes consumed 0.65 L (s = 0.27) fluid per hour. Fluid intake was related to both running speed (r = 0.42, P < 0.0001) and change in body mass (r = 0.23, P = 0.0006), but not post-race plasma [Na(+)] or change in plasma [Na(+)] (P > 0.05). In conclusion, faster runners lost more body mass, runners lost more body mass when they drank less fluid, and faster runners drank more fluid than slower runners.

Fluid Balance and Dehydration in the Young Athlete

Many young athletes train and compete under conditions that put their body fluid balance at risk, and hypohydration is usually the major concern. Another less frequent condition is hyperhydration that—if accompanied by other risk factors—may cause hyponatremia. Water and electrolyte losses during physical activities occur primarily from sweat. Such losses have been identified mostly in active (but nonathletic) young populations under laboratory settings. Studies have been trying to estimate fluid losses in the athletic population under field conditions, taking into account the sport modality and environmental conditions. Besides these external conditions, young athletes adopt different drinking attitudes, which may depend on knowledge, education, and the opportunities to drink during the break periods as well as fluid availability. Focusing on the young athlete, this review will discuss water and sodium losses from sweat, the effects of hypohydration on performance, and fluid intake attitudes within and during practices and competitions. Some considerations related to the methods of identifying hydration status and guidelines are also given, with the understanding that they should be individually adapted for the athlete and activity. The young athlete, parents, coaches, and athletic/health professionals should be aware of such information to prevent fluid imbalances and the consequent hazardous effects on performance and health.

Body composition and hydration status changes in male and female open-water swimmers during an ultra-endurance event

Body mass changes during ultra-endurance performances have been described for running, cycling and for swimming in a heated pool. The present field study of 20 male and 11 female open-water swimmers investigated the changes in body composition and hydration status during an ultra-endurance event. Body mass, both estimated fat mass and skeletal muscle mass, haematocrit, plasma sodium concentration ([Na+]) and urine specific gravity were determined. Energy intake, energy expenditure and fluid intake were estimated. Males experienced significant reductions in body mass (-0.5 %) and skeletal muscle mass (-1.1 %) (P < 0.05) during the race compared to females who showed no significant changes with regard to these variables (P > 0.05). Changes in percent body fat, fat mass, and fat-free mass were heterogeneous and did not reach statistical significance (P > 0.05) between gender groups. Fluid intake relative to plasma volume was higher in females than in males during the ultra-endurance event. Compared to males, females' average increase in haematocrit was 3.3 percentage points (pp) higher, urine specific gravity decrease 0.1 pp smaller, and plasma [Na+] 1.3 pp higher. The observed patterns of fluid intake, changes in plasma volume, urine specific gravity, and plasma [Na+] suggest that, particularly in females, a combination of fluid shift from blood vessels to interstitial tissue, facilitated by skeletal muscle damage, as well as exercise-associated hyponatremia had occurred. To summarise, changes in body composition and hydration status are different in male compared to female open-water ultra-endurance swimmers.

Hydration and Health

Daily adequate water intake to maintain euhydration is arguably the most important nutrient requirement for humans. Within a margin of error, the body regulates the maintenance of body fluid balance and especially that of the plasma volume, through mechanisms that stimulate thirst and/or modify the rate of urine production. However, there are circumstances such as with excessive sweating during exercise in the heat, osmotic diarrhea, or excessive fluid consumption, or water intoxication where normal mechanisms of regulation may be inadequate to compensate for acute changes in hydration status and result in life threatening consequences. Health and onset of disease may be affected by the chronic hydration state of individual. The risks of colorectal cancer, nephrolithiasis in those with a history of kidney stones, and bladder cancer may be reduced by more frequent water consumption. Recent research suggests that appropriate timing of water intake around meal occasions may help reduce energy intake and contribute to maintenance of body weight in overweight individuals. Definitive benefits of hydration on cardiovascular and oral health and general immune system function remain to be determined. It is also unclear whether the health benefits of water and fluid ingestion are a function of the process of frequent fluid intake or the maintenance of a potentially expanded state of hydration.

Passing the anaerobic threshold is associated with substantial changes in the gene expression profile in white blood cells

High and moderate intensity endurance exercise alters gene expression in human white blood cells (WBCs), but the understanding of how this effect occurs is limited. To increase our knowledge of the nature of this process, we investigated the effects of passing the anaerobic threshold (AnT) on the gene expression profile in WBCs of athletes. Nineteen highly trained skiers participated in a treadmill test with an incremental step protocol until exhaustion (ramp test to exhaustion, RTE). The average total time to exhaustion was 14:40 min and time after AnT was 4:50 min. Two weeks later, seven of these skiers participated in a moderate treadmill test (MT) at 80% peak O(2) uptake for 30 min, which was slightly below their AnTs. Blood samples were obtained before and immediately after both tests. RTE was associated with substantially greater leukocytosis and acidosis than MT. Gene expression in WBCs was measured using whole genome microarray expression analysis before and immediately after each test. A total of 310 upregulated genes were found after RTE, and 69 genes after MT of which 64 were identical to RTE. Both tests influenced a variety of known gene pathways related to inflammation, stress response, signal transduction and apoptosis. A large group of differentially expressed previously unknown small nucleolar RNA and small Cajal body RNA was found. In conclusion, a 15-min test to exhaustion was associated with substantially greater changes of gene expression than a 30-min test just below the AnT.

Hydration and independence in activities of daily living in people with multiple sclerosis: a pilot investigation

PURPOSE

Bladder dysfunction and disability may cause people with multiple sclerosis (pwMS) to limit fluid intake. However, hydration is rarely considered in the multiple sclerosis literature. We investigated the hydration status of people with pwMS and its association with independence in activities of daily living.

METHODS

 Twenty-six (six men) pwMS over 18 years old and able to walk with or without an aid took part in the study. Hydration status was measured via urine osmolality, with adequate hydration defined as an osmolality ≤500 (mOsm kg(-1)). Independence in daily activities was measured using the Barthel index.

RESULTS

 Mean urine osmolality was 470 ± 209 mOsm kg(-1) and indicated 11 (42%) participants were not adequately hydrated. Independence in daily activities could partly explain hydration status (R(2) = 0.209, p < 0.05). Additionally there was a trend for men to be less well hydrated than women.

CONCLUSIONS

 The results indicate that some pwMS were not adequately hydrated and that this could be partly explained by disability. Implications of reducing and maintaining fluid levels on function and quality of life in relation to bladder dysfunction and disability in pwMS should be investigated.

Preventing heat-related illness among agricultural workers

Hyperthermia from exertion and environmental conditions during agricultural work manifests itself by various symptoms and may lead to death. From 1992 through 2006, 68 workers employed in crop production and related services died from heat-related illness. The crop worker fatality rate averaged 4 heat-related deaths per one million workers per year-20 times higher than the 0.2 rate for US civilian workers overall. Many of the agricultural workers who died were foreign-born. Foreign-born workers tend to have limited English language skills and often are not acclimatized to exertion in hot weather when beginning seasonal jobs. Increased recognition of heat hazards to agricultural workers, in particular, has stimulated concern among employers, workers, and public policy makers. California and Washington have led the nation in adopting workplace safety standards designed to prevent heat-related illnesses. These state regulations include new specific requirements for employer provision of drinking water, shade for rest or other sufficient means to recover from heat, worker and supervisor training, and written heat safety plans. Agricultural employers face practical challenges in fulfilling the purpose and complying with these standards. By their very nature the standards impose generic requirements in a broad range of circumstances and may not be equally protective in all agricultural work settings. It is vital that employers and supervisors have a thorough knowledge of heat illness prevention to devise and implement safety measures that suit local conditions. Ongoing risk-based assessment of current heat conditions by employers is important to this safety effort. Workers need training to avoid heat illness and recognize the symptoms in themselves and coworkers. Innovative management practices are joining time-honored approaches to controlling heat stress and strain. Research targeted to answer questions about heat accumulation and dissipation during agricultural work and audience-sensitive education to promote understanding of basic physiology and recognition of hyperthermia symptoms can aid in heat illness prevention. This review was prepared for the Agricultural Safety and Health Council of America/ National Institute for Occupational Safety and Health conference, "Be Safe, Be Profitable: Protecting Workers in Agriculture," Dallas/Fort Worth, Texas, January 27-28, 2010.

Water, hydration, and health

This review examines the current knowledge of water intake as it pertains to human health, including overall patterns of intake and some factors linked with intake, the complex mechanisms behind water homeostasis, and the effects of variation in water intake on health and energy intake, weight, and human performance and functioning. Water represents a critical nutrient, the absence of which will be lethal within days. Water's importance for the prevention of nutrition-related noncommunicable diseases has received more attention recently because of the shift toward consumption of large proportions of fluids as caloric beverages. Despite this focus, there are major gaps in knowledge related to the measurement of total fluid intake and hydration status at the population level; there are also few longer-term systematic interventions and no published randomized, controlled longer-term trials. This review provides suggestions for ways to examine water requirements and encourages more dialogue on this important topic.

Weight Management Strategies for Recreational Athletes: What Do We Tell Them?

The 2008 Physical Activity Guidelines for Americans provide clear recommendations for health care professionals to share with their patients and clients. The guidelines clearly lay out what the general public needs to do to improve their fitness level and manage their weight. The physical activity guidelines need to be reviewed in conjunction with appropriate dietary advice found in the Dietary Guidelines for Americans. Patients and clients who increase their physical activity to light or moderately active, the recreational athlete, can meet their nutrition needs by consuming a well-balanced, varied diet of nutrient-dense foods. Sports drinks and bars, which are heavily marketed to all levels of athletes and sedentary people, are not necessary for the recreational athlete in most situations and may negatively affect body weight.

Aspectos relacionados com a otimização do treinamento aeróbio para o alto rendimento

O objetivo deste trabalho foi apresentar recomendações visando à otimização do treinamento aeróbio, a partir do conhecimento dos índices de aptidão funcional e seus mecanismos fisiológicos. Em atletas altamente treinados, a precisão na elaboração do treinamento pode ser o meio mais seguro para a melhora do rendimento, pois nesses indivíduos é comum a carga de treinamento oscilar entre o estimulo insuficiente e o aparecimento do excesso de treinamento. Existe, portanto, uma variedade muito grande de fatores que devem ser considerados na elaboração de um programa de treinamento. O entendimento dos mecanismos de fadiga e das respostas fisiológicas associadas às diferentes durações e intensidades de exercício é essencial para uma correta elaboração das sessões de treinamento. Além disso, treinos intervalados de alta intensidade são imprescindíveis para melhora de rendimento em atletas altamente treinados, porém, é recomendado que ele seja realizado após um razoável período de recuperação das sessões de treino anteriores. Assim, o contato entre o atleta e o treinador é importante para um planejamento cuidadoso dos períodos de recuperação antes da ocorrência de fadiga excessiva. O treinador deveria arquivar um histórico das cargas de treino e recuperações, aprendendo com a própria experiência os tipos de cargas que podem ser toleradas individualmente. Entre os fatores que podem afetar o rendimento aeróbio, o planejamento de um aquecimento apropriado e as condições ambientais adversas são aspectos muito importantes. Após reunir todas essas informações, é possível elaborar as bases do treinamento (frequência, volume, intensidade e recuperação) visando melhora contínua do rendimento aeróbio.

Water as an essential nutrient: the physiological basis of hydration

How much water we really need depends on water functions and the mechanisms of daily water balance regulation. The aim of this review is to describe the physiology of water balance and consequently to highlight the new recommendations with regard to water requirements. Water has numerous roles in the human body. It acts as a building material; as a solvent, reaction medium and reactant; as a carrier for nutrients and waste products; in thermoregulation; and as a lubricant and shock absorber. The regulation of water balance is very precise, as a loss of 1% of body water is usually compensated within 24 h. Both water intake and water losses are controlled to reach water balance. Minute changes in plasma osmolarity are the main factors that trigger these homeostatic mechanisms. Healthy adults regulate water balance with precision, but young infants and elderly people are at greater risk of dehydration. Dehydration can affect consciousness and can induce speech incoherence, extremity weakness, hypotonia of ocular globes, orthostatic hypotension and tachycardia. Human water requirements are not based on a minimal intake because it might lead to a water deficit due to numerous factors that modify water needs (climate, physical activity, diet and so on). Water needs are based on experimentally derived intake levels that are expected to meet the nutritional adequacy of a healthy population. The regulation of water balance is essential for the maintenance of health and life. On an average, a sedentary adult should drink 1.5 l of water per day, as water is the only liquid nutrient that is really essential for body hydration.

Fluid replacement following dehydration reduces oxidative stress during recovery

To investigate the effects of hydration status on oxidative DNA damage and exercise performance, 10 subjects ran on a treadmill until exhaustion at 80% VO(2max) during four different trials [control (C), 3% dehydration (D), 3% dehydration+water (W) or 3% dehydration+sports drink (S)]. Dehydration significantly decreased exercise time to exhaustion (D<C and S). Plasma MDA levels were significantly higher at pre-exercise in D than C. Plasma TAS was significantly lower at pre-exercise in C and S than in D, and was significantly lower in S than D at 60min of recovery. Dehydration significantly increased oxidative DNA damage during exercise, but fluid replacement with water or sports drink alleviated it equally. These results suggest that (1) dehydration impairs exercise performance and increases DNA damage during exercise to exhaustion; and (2) fluid replacement prolongs exercise endurance and attenuates DNA damage.