== Introduction ==The advice given to runners on science of hydration has changed over time for exercise is complex and looks set to continue to changecontroversial. There are competing forces at work - sports drink manufacturers, event organizers (often sponsored by While dehydration can cause problems, the real risk is [[Hyponatremia]] where the manufacturers) and scientists (some also sponsored by level of sodium in the manufacturers)blood is too low. One thing is clear about hydration - it is important. Incorrect hydration The science shows that sodium losses increase exponentially with sweat rate, so exercise in the heat can lead to impaired performance, and result in extreme cases, deathlevels of sodium loss. For a simpler look at hydration, see [[Practical Hydration]]. =Introduction=A condition related The advice given to dehydration is Hyponatremia, which is where the sodium runners on hydration has changed over time and looks set to continue to change. There are competing forces at work - sports drink manufacturers, event organizers (saltoften sponsored by the manufacturers) level in and scientists (some also sponsored by the blood becomes too dilute. This manufacturers). One thing is clear about hydration - it is a dangerous condition that has killed a number of runnersimportant. More on this laterIncorrect hydration can lead to impaired performance, and in extreme cases, death. This blog entry A condition related to dehydration is a follow on to [['Practical HydrationHyponatremia]]' , which should be read firstis where the sodium (salt) level in the blood becomes too dilute. This is a dangerous condition that has killed a number of runners. This entry is a follow on to [[Practical Hydration]] which should be read first. == Effects of dehydration ==Everyone knows While it's commonly believed that even small levels of dehydration is bad. But how bad? Current impacts performance, the research indicates that some level of real world performance is not impacted by dehydration (up to 34%) does not impact performance, or impacts performance much less than expected [7]of body weight<ref name="Goulet2012"/><ref name="Goulet2011"/>. (Dehydration Greater levels of 5% does dehydration will impact performance [11]<ref name="González-Alonso-1995"/>.) This may be due to the fact that carbohydrate (glycogen) is stored with waterWhile authorities have recommended aggressive drinking<ref name="Convertino-1996"/>, these guidelines are now recognized as erroneous<ref name="WallWatson2013"/>, in though they are still promoted by the ratio of about 1g glycogen to 2beverage industry<ref name="beverageWWW"/>.5g water [8]=Glycogen Depletion, Dehydration and Body Weight =A common method of calculating dehydration is simply from body weight. This means While it's true that 2000 calories of glycogen depletion that are likely to occur in marathon distance runs would result in about 4lb an athlete's weight loss during exercise will be predominantly from water, this is not the same as dehydration, nor does it necessarily imply this weight loss with no reduction in hydration needs to be restored quickly though drinking. This is because a carbohydrate (2000Kcal/4=500g glycogen + 1250g [[Glycogen]]) is stored with water = 1750g). In practice moving from a high carbohydrate , in the ratio of about 1g [[Glycogen]] to high fat diet can see 6lb weight loss, believed to be glycogen + water depletion [8]. 3-4g water<ref name="OlssonSaltin1970"/><ref name= Salt loss through sweat ==The amount "Nilsson-1973"/>. This means that 2000 calories of salt [[Glycogen]] depletion that is lost through sweating varies a lot. It varies from individual are likely to individual, and for an individual it will vary depending on fitness and heat acclimation occur in marathon distance runs would result in about 4lb/2Kg [[9Weight Loss]]. This means that you may have to experiment with your salt intake, both during and after no reduction in hydration (2000Kcal/4=500g [[Glycogen]] + 1500g to 2000g water = 2000g to 2500g). To restore the weight lost in endurance exercisethe Glycogen reserves must also be restored, something that may take days. Anecdotal tip: If your skin is crusty with salt after Even moving from a run, you are probably someone who sweats out a lot of salthigh carbohydrate to high fat diet can see 6lb [[Weight Loss]] from [[Glycogen]] depletion. =Sodium Intake and Rehydration= More on Hyponatremia ==Hyponatremia is where the sodium Several studies have shown that drinks containing sodium provide better rehydration by reducing urine output. * Consuming drinks with 61 mmol/l (~1/2 teaspoon saltper quart/liter) levels becomes too dilute. Initial symptoms tend to be a gain in weight reduced urine output and a general swelling improved hydration when compared with 23 mmol/l (~1/4 teaspoon salt per quart/liter)<ref name="Shirreffs-1996"/>* When comparing drinks with 2, 26, 52 and 'puffiness'100 mmol/l, urine output was inversely proportional to sodium concentration, most noticeable in and the hands2 & 26 mmol/l cases resulting in dehydrated subjects after 5. More severe symptoms are caused by a swelling of 5 hours, where the brain others were rehydrated<ref name="Maughan-1995"/>. (cerebral edema) including nauseaThese cases are roughly equal to water, vomiting1/4, headache and malaise [10]1/2, 3/4 teaspoon of salt per quart/liter.) The cause of Hyponatremia is poorly understood, but believed to be related to excessive water intake [1]* Drinks containing 0.45g salt/100ml reduced urine output and improved hydration<ref name="Nose-1988"/>. (I believe that this 0.45g/100ml is excessive fluid intake in the absence about 1/10 teaspoon of sufficient electrolytessalt per quart/liter.) Hyponatremia can be common in endurance athletes=Sodium loss through sweat=The amount of salt that is lost through sweating varies a lot. In a 1997 Ironman triathlonIt varies from individual to individual, almost 4% of competitors received attention and for Hyponatremia [4]. In a study of the 2002 Boston Marathon, 13% of finishers had some level of Hyponatremia, an individual it will vary depending on fitness and 0heat acclimation.6% had critical Hyponatremia [2]. The study revealed This means that the risk factors for Hyponatremia include a slow finish time (>4 hour) you may have to experiment with your salt intake, both during and consumption after exercise.==Anatomy of Sweating==[[File:Sweat Gland.jpg|right|thumb|500px|A drawing of >6 pints the sweat gland. (3 litersC=clear cells, D=dark cells, IC=Intracellular canaliculi, M=Myoepitherial cell, Mc=Mitochondria. ) of water during the race; BAA suggests a 'slight build' is also a risk factor[12]. Healthy kidneys can excrete about ]Humans have 2 pints (1 liter-4 million sweat glands over nearly their whole body surface, and though each is tiny, together they weigh as much as a kidney (~100g) <ref name="Fitzpatrick"/>. Sweat glands are most numerous on the soles of the feet. Sweat is produced in two steps<ref name="Fitzpatrick"/>:# A coil generates an ultra-filtrated fluid per hour, but this may be reduced by exertion or illness [3]. So drinking >6 pints in 4 hours could easily exceed This fluid has the same sodium concentration (isotonic) as the kidneys capacity to copeblood. # The recent rise in Hyponatremia may be due to earlier advice to athletes to "drink as much as possible" fluid travels from the coil up the sweat duct which reabsorbs sodium and chloride (but not [[13Potassium|potassium]], combined with a general concern about salt intake). == HypERnatremia - the opposite of HypOnatremia ==Generally, Hypernatremia This reabsorption is via active transportation (too much sodium i.e. it requires energy from ATP). The [[Glycogen]] stored in the blood) seems to be a result of dehydration rather sweat glands will only support the reabsorption for less than excessive salt intake 10 min., so the energy is predominantly supplied by the blood. Glucose is the preferred energy source, though [[17Lactate]]and pyruvate can also be used. It should be noted that taking electrolyte capsules bypasses Fatty acids, ketones, and amino acids are very poorly used. The reabsorption process also acidifies the body's tastefinal sweat. This sense The rate of taste seems to reflect our sweat production depends on the local skin temperature and core body's internal sensors; our desire for salty foods reflects our salt requirementstemperature. A rise in the localized skin temperature will produce an increased sweat rate within 60 seconds<ref name="Fitzpatrick"/>. == Salt and High Blood Pressure Sodium Loss Table==If you have high blood pressure, you may need to be careful The table below is based on the research showing that sweat sodium concentration increases with your salt intakesweat rate. There The table below is for a runner who is evidence that increased salt intake 174cm/70inches high and weighs 60Kg/132lbs, but you can increase blood pressure create a customized chart at [[4Sodium Loss]]. If you have high blood pressureTo check your sweat rate, discuss these issues with your doctorsimply weigh yourself before and after a run. Dropping 1 Kg or 2. If your doctor is not an athlete, I would highly recommend changing 2 pounds equates to one that is1 liter of sweating. If (Obviously you don't know what your blood pressure is, get it checked. (As an aside, if you have low blood pressure, which I do, increasing your salt need to adjust for any fluid intake can really helpand avoid urination.) {| class="wikitable" style="margin-left: auto; margin-right: auto; border: none;"! ! ! colspan="3"|'''Heat Acclimated'''! colspan= Caffeine and Alcohol =="3"|'''Heat Non-Acclimated'''The scientific evidence shows that caffeine is generally not a diuretic [5, 14, 15]. Previous studies have shown that if you don|-| '''t normally take caffeine and then get a large dose, there is some diuretic effect. However normal intakes of caffeine by non-users and use by regular users is not a diuretic Sweat Rate'''| '''Sweat Rate'''| '''Sweat Concentration'''| [[Sodium Loss]]| [[16Sodium Loss]]. (If you urinate more because you drink a 20oz Latte, it is because of the 20oz of fluid, not the caffeine.| '''Sweat Concentration'''| [[Sodium Loss]]| [[Sodium Loss]]|-| '''(l/hr)'''Alcohol is another story; drinking anything stronger than 2% will cause dehydration. Because alcohol takes 36 hours to clear the body, it should be avoided for 48 hours before you wish to avoid impaired performance [5].| '''(mg/cm2/min)'''| '''(mmol/l)''' | '''(mg/hr)'''== Muscle Cramps ==The common wisdom that muscle cramps are caused by lack of electrolytes or dehydration does not appear to be supported by science [6].| '''(tsp/hr)''' | '''(mmol/l)'''== Blisters and black toe nails ==| '''(mg/hr)'''| '''(tsp/hr)'''|-Dehydration reduces body weight, which can reduce the size of your feet| '''0. This in turn changes the fit of your shoes, causing blisters. Hyponatremia can cause swelling, which increases the size of your feet and can cause blisters. Both conditions can also increase the chance of black toe nails5'''| '''0.49'''| 22| 249| 0.1| 31 | 355== References ==| 0.2[1]Exercise|-Associated Hyponatremia[http://cjasn.asnjournals.org/cgi/content/abstract/2/| '''1/151 http://cjasn'''| '''0.asnjournals98'''| 32| 732| 0.org/cgi/content/abstract/2/1/151]3| 46| 1044| 0.4[2]Hyponatremia among Runners in the Boston Marathon|-[http://content| '''1.nejm5'''| '''1.org/cgi/content/abstract/352/15/1550 http://content47'''| 43| 1450| 0.nejm6| 61| 2066| 0.org/cgi/content/abstract/352/15/1550]9[3]Water Intoxication|-| '''2'''[http://en| '''1.wikipedia96'''| 53| 2402| 1| 75| 3423| 1.org/wiki/Water_intoxication http://en5|-| '''2.wikipedia5'''| '''2.org/wiki/Water_intoxication]45'''| 63[4]Micronutrient Information Center - Sodium| 3589[http://lpi| 1.5| 90| 5113| 2.oregonstate.edu/infocenter/minerals/2|}This table is based on the research quoted below showing a linear relationship between sweat rate and sweat sodium/ http://lpiconcentration.oregonstate.edu/infocenter/minerals/sodium/][5]Caffeine dehydration : Caffeine ==Sodium Loss and alcohol - just how dehydrating are they?Sweat Rate==[http://wwwThe concentration of sodium in sweat depends on the sweat rate. This is believed to be because the sweat is released with a high sodium concentration, then the sodium is reabsorbed before it reaches the surface.pponlineThe faster the sweating, the less chance for reabsorption.co[[File:Sweat Rate Sodium Concentration - adjusted.ukjpg|none|thumb|400px|Sweat rate and sodium concentration<ref name="Buono-2008"/encyc/caffeine>, adjusted using the formula for regional patch collection<ref name="Baker-dehydration.htm http:2009"//www>.pponline.co.uk/encyc/caffeine-dehydration.htm][6]Muscle Cramps : No link between hydration and cramps===Converting per-area sweat rates to whole body sweat rates===We can convert from per-area sweat rates to whole body sweat rates by using a [http://www.pponlinehalls.co.ukmd/encyc/musclebody-surface-cramps.htm http:area//www.pponline.co.uk/encyc/muscle-crampsbsa.htmBody Surface Area Calculator][7]Hydration - fluid intake advice and tips[http:. For example, a 135 pound, 70 inch high person has a skin surface area of 1.74 m<sup>2</sup>, which is 17,400 cm<sup>2</wwwsup>.pponline.co.ukTherefore 1 mg/cm<sup>2</encycsup>/hydration-fluid-intake-advice-and-tips-40789 http:min is 17,400 mg/min, or 17.4 g/www.pponline.co.ukmin or 1,044 g/encychour, or 1 liter/hydration-fluid-intake-advice-hour. ==Sodium Loss andFitness==While some sources suggest that increased fitness reduces the sodium concentration in sweat research<ref name="Hamouti-tips-40789][8]The Relation Of Glycogen To Water Storage In The Liver[http:2011"//www> shows this is not the case.jbcFor both trained and untrained individuals sodium concentration depends mainly on sweat rate.org/cgi/reprint/96/In fact, for a given relative intensity (% of [[VO2max|V̇O<sub>2</367.pdf http://www.jbc.org/cgi/reprint/96/2/367sub>max]]) trained individuals will be performing a greater absolute work rate and therefore have a greater sweat rate and sodium concentration.pdf][9]Cracking the Code on Hydration[httpFile://wwwSodium in sweat trained and untrained.active.com/cycling/Articles/Cracking-jpg|none|thumb|400px|Sweat sodium concentration against sweating rate, showing for three different work intensities and for trained and untrained individuals. Note that this data is not adjusted for regional patch collection, so the-Code-on-Hydrationrates are too high and should be scaled by 0.htm http://www67.active.com]]==Sodium Loss and Heat Acclimation==A study<ref name="Buono-2007"/cycling/Articles/Cracking-> shows that the-Code-on-Hydration.htmsodium concentration of sweat is reduced by [[Heat Acclimation Training][10]Hyponatremia[http://en.wikipediaThe study used three bouts of 30 min.org/wiki/Hyponatremia http://enof exercise in environmental chamber with 10 min.wikipediaof rest between each bout.org/wiki/Hyponatremia][11]Dehydration reduces cardiac output [File:Sweat Rate Sodium Concentration for heat adaptation - adjusted.jpg|none|thumb|400px|Sweat sodium concentration against sweating rate, before and increases systemic and cutaneous vascular resistance during exercise[http:after 10 days of heat acclimation training, adjusted using the formula for regional patch collection<ref name="Baker-2009"//www>.edb.utexas]]==Sodium Loss and Skin Temperature==A study<ref name="Shamsuddin-2005"/> of sweating great sodium concentration for different temperatures has shown that sodium reabsorption is greater at high temperatures.edu/coyle/pdf%20library/%2863%29%20Dehydration%20reduces%20cardiac%20output%20&%20increases%20systemic%20&%20cutaneous%20vascular%20resistance%20during%20exerciseUnfortunately the units used in this study are not comparable with other studies. The mechanism behind this is unclear,%20J%20Appl%20Physiol%2079,%201487-96,%201995.pdf httpbut the implication is that the sodium concentration of sweat in cooler weather may be higher than expected from the above studies. [[File://wwwSweat Rate Sodium Concentration for skin temperatures.edbjpg|none|thumb|400px|Sweat sodium concentration against sweating great, shown for two different skin temperatures.utexas.edu/coyle/pdf%20library/%2863%29%20Dehydration%20reduces%20cardiac%20output%20&%20increases%20systemic%20&%20cutaneous%20vascular%20resistance%20during%20exercise]]=Sodium Retention=The human body has mechanisms to try to maintaining its sodium balance. Greater sodium intake results in the excess being excreted in the sweat and urine. Conversly,%20J%20Appl%20Physiol%2079,%201487restricted sodium intake will result in a reduction of the sodium concentration of the sweat<ref name="CONN-96,%2019951946"/>.pdf][12]BAA - HYDRATIONThis reduction in the sodium concentration occurs at all sweating rates, DEHYDRATION AND HYPONATREMIA[http:but the relationship between sodium concentration and sweat rate remains a straight line<ref name="Sigal-1968"//www>.bostonmarathonSo at any given sweat rate, a restricted sodium intake will result in less sodium in the sweat.org/BostonMarathon/WelcomeBooklet.asp#hydration http://wwwHowever, even on a restricted sodium intake, the more you sweat, the greater the sodium concentration.bostonmarathon.orgComparing the maximum sodium concentration of sweat between a salt intake of 500mg/BostonMarathonday and 20,000mg/WelcomeBooklet.asp#hydration]day, the low salt intake reduced the sodium concentration by 30-48%<ref name="Sigal-1968"/>. [13]USATF Announces Major Changes in Hydration Guidelines for Long Distance Runners[httpFile://wwwSodiumIntakeSweatConcentration.rrm.comjpg|none|thumb|500px|The effect of high (20,000mg/archive03day NaCL) and low (500mg/042803n2.htm http:day NaCL) on the sodium concentration of sweat at various sweat rates<ref name="Sigal-1968"//www>.rrmThree subjects were put on the diet for a week, then tested for five days while remaining on that diet.com/archive03/042803n2The two tests were separated by a month.htm]][14]Metabolic and exercise endurance effects =Sodium Intake=Below are some sample sources of coffee and caffeine ingestionSodium, with the concentrations defined. [http{| class="wikitable" style="margin-left: auto; margin-right: auto; border://jap.physiology.org/cgi/content/full/85/3/883 http://jap.physiology.org/cgi/content/full/85/3/883]none;"! Source [15]Effects of caffeine ingestion on body fluid balance and thermoregulation during exercise! Sodium - mmol per liter ! Sodium - grams per liter ! Sodium - grams per pint ! Salt - grams per pint |-| Gatorade| 18[http://www| 0.4| 0.ncbi2| 0.5 |-| Water + 1/4 Teaspoon salt per quart| 27| 0.6| 0.nlm3| 0.75 |-| Gatorade+ 1/4 Teaspoon salt per quart| 45| 1.0| 0.5| 1.2 |-| S-Caps + 8oz water*| 65| 1.4| 0.7| 1.7 |-| Salt Stick + 8oz Water| 38| 0.84| 0.4| 0.98 |-| Salt Stick + 16oz Water| 19| 0.42| 0.2| 0.49 |}Note: S-Caps does not specify the amount of fluid to take with each capsule, but does mention 'at least one cup', so this ratio is used. The per-pint and per-liter equivalents assume a constant ratio of one capsule per 8oz of water. See also [[Comparison of Gels]].==Example Sodium Losses==Here are some hypothetical examples* Adam, a heat acclimatized runner, weighs himself before and after his four hour run and the difference is 8 pounds, which is roughly equivalent to 8 pints/4 liters of sweat. Based on 1 liter/hour of sweating we estimate Adam lost 4 grams of sodium, which is about 2 teaspoons. * Bob is not heat acclimatized runner, and losses 9 pounds in three hours (9 pints/4.5 liters). From the sweat rate we estimate that Bob has lost 7.5 grams of sodium, which is about 3.3 teaspoons.=Sweat Rates While Running=Sweat rates in male runners have been measured in the range from 0.75-2.23 in winter to 0.99-2.55 in the summer (Liters per hour)<ref name="acsm"/>. At the low end, we can imagine a fit runner finishing a 3-hour marathon in winter and sweating only 2.25 Liters. Assuming they are also heat acclimated, they would only lose 2 grams of sodium, which is 5 grams of salt, less than a teaspoon. On the other end of the scale, a fit, but unacclimatized runner completing a 5 hour marathon in summer would sweat out nearly 13 Liters, 18 grams of sodium, which is 45 grams of salt or more than 7 teaspoons. There is a table showing a range of values at [[Sodium Loss]].=Hyponatremia=[[Hyponatremia]] is where the sodium (salt) levels in the blood become too dilute. The symptoms of mild hyponatremia tend to be a gain in weight and a general swelling and 'puffiness', most noticeable in the hands. However, mild Hyponatremia may have no clinical symptoms, or just weakness, dizziness, headache, nausea/vomiting, but more severe Hyponatremia is likely to have symptoms of cerebral edema, including altered mental status, seizures, pulmonary edema, coma, and death<ref name="RosnerKirven2006"/>.=HypERnatremia - the opposite of HypOnatremia=Generally, Hypernatremia (too much sodium in the blood) seems to be a result of dehydration rather than excessive salt intake<ref name="Kratz-2005"/>. It should be noted that taking [[Electrolyte Capsules]] bypasses the body's taste. This sense of taste seems to reflect our body's internal sensors; our desire for salty foods reflects our salt requirements.=Salt and High Blood Pressure=There is evidence that increased salt intake can increase blood pressure<ref name="ref4"/>, and the common recommendation is to restrict your salt intake if you have high blood pressure. However, a recent study<ref name="Stolarz-Skrzypek-2011"/> has shown that reducing your salt intake may increase your risk of a heart attack rather than lower it. For more on the health risks of low salt diets see http://www.drmirkin.com/public/ezine050811.html As an aside, if you have low blood pressure, which I do, increasing your salt intake can really help.=Caffeine=The scientific evidence shows that [[Caffeine]] is generally not a diuretic<ref name="Graham-1998"/><ref name="Falk-1990"/>. Previous studies have shown that if you don't normally take [[Caffeine]] and then get a large dose, there is some diuretic effect. However normal intakes of [[Caffeine]] by non-users and use by regular users is not a diuretic<ref name="Maughan-2003"/>. (If you urinate more because you drink a 20oz Latte, it is because of the 20oz of fluid, not the [[Caffeine]].)=Alcohol=Alcohol is a diuretic due to the suppression of vasopressin secretion<ref name="ROBERTS-1963"/><ref name="RubiniKleeman1955"/>, and the volume of urine produced is proportional to the alcohol consumed<ref name="Eggleton-1942"/>. However, the diuretic effect of alcohol may be reduced when consumed when suffering from post-exercise dehydration. A study looked at consuming water or an alcoholic beverage of 1%, 2%, and 4% after 1 hour of moderate exercise<ref name="Shirreffs-1997"/>. The study found that urine production tended to increase with alcohol content, but the difference was not statistically significant. The alcohol tended to reduce the rate of recovery for both blood and plasma volume, though tendency was only statistically significant at 4%. In summary, alcoholic beverages of up to 2% appear to have little impact on rehydration rate compared with the equivalent volume of water, but 4% beverages tend to delay recovery. =Cramps =The evidence for hydration and electrolyte status causing [[Cramps]] is somewhat ambiguous, but supplementing your electrolyte intake may help. =Blisters and black toe nails=Dehydration reduces body weight, which can reduce the size of your feet. This in turn changes the fit of your [[Shoes]], causing blisters. [[Hyponatremia]] can cause swelling, which increases the size of your feet and can cause blisters. Both conditions can also increase the chance of black toe nails.=Sodium and Water in the Body=Approximately 60% of the human body weight is water, though this varies primarily with body fat as adipose (fat) tissue contains a lower percentage of water. Total Body Water (TBW) can be divided up into<ref name="CLINC"/>: * Intracellular fluid (ICF) which is 40% of body weight * Extracellular fluid (ECF) which is the other 20% of body weight* Plasma is 25% of ECF/5% body weight* Interstitial fluid which is 75% of ECF/15% of body weight, typically 11 Liters/22 pints.The volume of extracellular fluid is typically 15 liters in a 70 kg human, and the 50 grams of sodium it contains is about 90% of the body's total sodium content.=Symptoms of Dehydration=These symptoms are for the general public<ref name="CLINC"/>, and there is evidence<ref name="SYMPT"/> that they may not apply to athletes suffering from dehydration.{| class="wikitable" style="margin-left: auto; margin-right: auto; border: none;"! symptom ! mild dehydration (3-5% body weight) ! Moderate dehydration (6-9% body weight) ! Severe dehydration (>10% body weight) |-| Level of consciousness| Alert | Lethargic | Obtunded |-| Capillary Refill| 2 seconds| 2-4 seconds| >4 seconds |-| Blood Pressure| Normal| Normal supine, lower standing| lower |-| Skin Turgor| Normal| Slow| Tenting |-| Eyes| Normal| Sunken| Very Sunken |}=References =<references><ref name="RosnerKirven2006">M. H. Rosner, J. Kirven, Exercise-Associated Hyponatremia, Clinical Journal of the American Society of Nephrology, volume 2, issue 1, 2006, pages 151–161, ISSN [http://www.worldcat.org/issn/1555-9041 1555-9041], doi [http://dx.doi.org/10.2215/CJN.02730806 10.2215/CJN.02730806]</ref><ref name="CLINC">Clinical Studies in Fluid and Electrolyte Balance</ref><ref name="SYMPT">J. McGarvey, J. Thompson, C. Hanna, T. D. Noakes, J. Stewart, D. Speedy, Sensitivity and specificity of clinical signs for assessment of dehydration in endurance athletes, British Journal of Sports Medicine, volume 44, issue 10, 2008, pages 716–719, ISSN [http://www.worldcat.org/issn/0306-3674 0306-3674], doi [http://dx.doi.org/10.1136/bjsm.2008.053249 10.1136/bjsm.2008.053249]</ref><ref name="Nilsson-1973">LH. Nilsson, Liver glycogen content in man in the postabsorptive state., Scand J Clin Lab Invest, volume 32, issue 4, pages 317-23, Dec 1973, PMID [http://www.ncbi.nlm.nih.gov/pubmed/2383801 http://www.ncbigov/pubmed/4771101 4771101]</ref><ref name="González-Alonso-1995">J. González-Alonso, R. Mora-Rodríguez, PR. Below, EF. Coyle, Dehydration reduces cardiac output and increases systemic and cutaneous vascular resistance during exercise., J Appl Physiol (1985), volume 79, issue 5, pages 1487-96, Nov 1995, PMID [http://www.ncbi.nlm.nih.gov/pubmed/8594004 8594004]</ref><ref name="Graham-1998">TE. Graham, E. Hibbert, P. Sathasivam, Metabolic and exercise endurance effects of coffee and caffeine ingestion., J Appl Physiol (1985), volume 85, issue 3, pages 883-9, Sep 1998, PMID [http://www.ncbi.nlm.nih.gov/pubmed/9729561 9729561]</ref><ref name="Falk-1990">B. Falk, R. Burstein, J. Rosenblum, Y. Shapiro, E. Zylber-Katz, N. Bashan, Effects of caffeine ingestion on body fluid balance and thermoregulation during exercise., Can J Physiol Pharmacol, volume 68, issue 7, pages 889-92, Jul 1990, PMID [http://www.ncbi.nlm.nih.gov/pubmed/2383801 2383801]</ref><ref name="Maughan-2003">RJ. Maughan, J. Griffin, Caffeine ingestion and fluid balance: a review., J Hum Nutr Diet, volume 16, issue 6, pages 411-20, Dec 2003, PMID [http://www.ncbi.nlm.nih.gov/pubmed/19774754 19774754]</ref><ref name="Kratz-2005">A. Kratz, AJ. Siegel, JG. Verbalis, MM. Adner, T. Shirey, E. Lee-Lewandrowski, KB. Lewandrowski, Sodium status of collapsed marathon runners., Arch Pathol Lab Med, volume 129, issue 2, pages 227-30, Feb 2005, doi [http://dx.doi.org/10.1043/1543-2165(2005)129<227:SSOCMR>2.0.CO;2 10.1043/1543-2165(2005)129<227:SSOCMR>2.0.CO;2], PMID [http://www.ncbi.nlm.nih.gov/pubmed/15679427 15679427]</ref><ref name="acsm">http://journals.lww.com/acsm-msse/_layouts/oaks.journals/ImageView.aspx?k=acsm-msse:2007:02000:00022&i=TT2</ref><ref name="ref4">Micronutrient Information Center - Sodiumhttp://lpi.oregonstate.edu/infocenter/minerals/sodium/</ref><ref name="Stolarz-Skrzypek-2011">K. Stolarz-Skrzypek, T. Kuznetsova, L. Thijs, V. Tikhonoff, J. Seidlerová, T. Richart, Y. Jin, A. Olszanecka, S. 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