SUMMARY This Position Stand provides guidance on fluid replacement to sustain appropriate hydration of individuals performing physical activity. The goal of prehydrating is to start the activity euhydrated and with normal plasma electrolyte levels. Prehydrating with beverages, in addition to normal meals and fluid intake, should be initiated when needed at least several hours before the activity to enable fluid absorption and allow urine output to return to normal levels. The goal of drinking during exercise is to prevent excessive (>2% body weight loss from water deficit) dehydration and excessive changes in electrolyte balance to avert compromised performance. Because there is considerable variability in sweating rates and sweat electrolyte content between individuals, customized fluid replacement programs are recommended. Individual sweat rates can be estimated by measuring body weight before and after exercise. During exercise, consuming beverages containing electrolytes and carbohydrates can provide benefits over water alone under certain circumstances. After exercise, the goal is to replace any fluid electrolyte deficit. The speed with which rehydration is needed and the magnitude of fluid electrolyte deficits will determine if an aggressive replacement program is merited. INTRODUCTION People perform physical activity throughout a range of environmental conditions (temperature, humidity, sun, wind exposure). Depending upon the metabolic rate, environmental conditions and clothing worn, exercise can induce significant elevations in body (core and skin) temperatures. Body temperature elevations elicit heat loss responses of increased skin blood flow and increased sweat secretion (120,121). Sweat evaporation provides the primary avenue of heat loss during vigorous exercise in warm hot weather; therefore sweat losses can be substantial. Besides containing water, sweat contains electrolytes that are lost. If not appropriately replaced, water and electrolytes imbalances (dehydration and hyponatremia) can develop and adversely impact on the individuals exercise performance and perhaps health (27,72). This Position Stand summarizes current knowledge regarding exercise with respect to fluid electrolyte needs and the impact of their imbalances on exercise performance and health. This position statement replaces the prior Position Stand on exercise and fluid replacement published in 1996 (39). The new Position Stand includes a Strength of Recommendation Taxonomy (SORT) to document the strength of evidence for each conclusion and recommendation (50). Table 1 provides a description of strength of evidence category employed, based on the quality, quantity and consistency of the evidence for each statement. Occasionally review papers have been cited, to reduce the number of references, which provide extensive documentation regarding supporting studies. Recommendations are provided for practical hydration assessment techniques and rehydration strategies for before, during and after exercise. It is recognized that considerable variability exists between individuals, different physical activities and environmental conditions regarding water electrolyte losses so that each person will need to customize these recommendations. Importantly, it is emphasized that during exercise individuals should avoid drinking more fluid than the amount needed to replace their sweat losses.TABLE 1: Strength of recommendation taxonomy.Throughout this Position Stand, the term "euhydration" refers to "normal" body water content, while the terms "hypohydration" and "hyperhydration" refer to body water content deficits and excesses beyond the normal fluctuation in body water content, respectively. The term "dehydration" refers to the loss of body water. The hypohydration that occurs during exercise is usually characterized as hyperosmotic hypovolemia (because sweat is hypotonic to plasma), although iso osmotic hypovolemia can occur when taking some medications (e.g., diuretics) or exposure to cold and hypoxia. For simplicity, the term dehydration will be used to describe both the process of body water loss and hypohydration in this position statement, unless stated otherwise. FLUID AND ELECTROLYTE REQUIREMENTS Physical Activity and Individual Variability Participation in physical activity exposes individuals to a variety of factors that influence sweat losses; these include the duration and intensity of exercise, the environmental conditions and the type of clothing/equipment worn. Sometimes, these factors are standardized for a specific activity or event within a sport (e.g., the temperature of an air conditioned indoor stadium or the uniform worn by a sporting team). In other cases, these factors occur in a predictable manner (e.g., running speeds in a 10,000 m race are higher than in a marathon, Nordic skiing, and other outdoor winter sports are undertaken in colder environments than summer sports). Nevertheless, in most activities, there is considerable variability in exposure to the factors that contribute to sweat rates between participants. Individual characteristics, such as body weight (11), genetic predisposition, heat acclimatization state (120), and metabolic efficiency (economy at undertaking a specific exercise task) will influence sweat rates for a given activity. As a result, there is a large range in sweat rates and total sweat losses of individuals between and within activities, and in some cases even in the same event on a given day. For example, elite marathon runners may have higher sweating rates but similar total sweat losses (run for shorter duration) as recreational runners who finish the race at the rear of the field. In a soccer match, sweat rates will vary between players according to their position and playing style as well as the total time spent on the field (130). Likewise, American football players (large body mass and wearing protective clothing) will have markedly greater daily sweat losses (~8.8 L·d−1) than cross country runners (~3.5 L·d−1) training in the same hot environmental for the same duration (62). Table 2 summarizes sweat rates observed among serious competitors across a range of sports, both in training and in competition (14-16,18,21,22,41,62,89,130,133). These data show that individuals often achieve sweating rates from 0.5 to 2.0 L·h−1. The differences in sweat rates between individuals, different sports and climatic season demonstrate the difficulties in providing a single one size fits all recommendation. Sweating rate differences between persons for a given event and environment are likely reduced when body size (body mass or surface area corrections) is considered, but marked individual differences still persist.TABLE 2: Observations of sweat rates, voluntary fluid intake and levels of dehydration in various sports. Values are mean, plus (range) or [95% reference range].Environment Muscular contractions produce metabolic heat that is transferred from the active muscles to blood and then the body core. Subsequent body core temperature elevations elicit that heat from within the body core to the skin it can be to the between the skin and the environment is by by the and air and and clothing In and the for heat loss and so sweat losses are As the environmental heat there is a greater on sweating for The wearing of or such as a football the heat and while in to hot Likewise, wearing or clothing while in cold can elicit sweat rates The the sweating rate needed to provide for persons performing (e.g., metabolic rate intensity exercise in hot If the exercise is then of metabolic is to heat in the intensity exercise will or or of metabolic to be to avoid heat the heat of evaporation is the individual will need to or or L·h−1. If the environment is and greater heat loss the sweating rates be If sweat from the body and is not higher sweating will be needed to achieve the increased air will evaporation and sweat acclimatization an individual to achieve higher and more sweating rates, if needed (120,121). exercise training a on sweating rate responses (120,121). such as skin (e.g., from and dehydration can to the sweating rate Sweat electrolyte losses on the total sweat losses and sweat electrolyte Sweat and upon genetic predisposition, sweating rate, and heat acclimatization state Sweat of 1 and or to have marked on sweat electrolyte although dehydration can the sweat of and Sweat and but the to these electrolytes not with the sweating As a result, the of sweat and as a of sweating rate acclimatization the to and heat individuals usually have sweat (e.g., for any given sweating rate statement. can elicit sweat rates and water and electrolyte losses during exercise, in is considerable variability for water and electrolyte losses between individuals and between different If sweat water and electrolyte losses are not replaced, then the person will water balance on the between water and water loss occurs from and and while water losses occur from and sweat The of metabolic water during is to water losses so this in water with in total body water. losses are unless the individual Sweating provides the primary avenue of water loss during The water balance by urine with and urine of and During exercise and heat both and blood flow are markedly in urine output when are over during exercise there may be a reduced to produce urine to the activities these may not be as on urine a (e.g., if fluid and electrolytes are the water losses will usually be to the "normal" total body water is within to of daily body mass of body with a range from to These differences are to body mass is to water, while is water These water content are of and race an person of total body water, with a range of have by of a mass and body and a training individuals who may a in but this is not observed the water with is when the mass and water The of water as is is but the that any water to is of the it is of to fluid intake recommendations. an hydration there is one that and need to be of body water beyond a range that have the hydration should be and to body water of of water content to of body weight for the In the should be practical and to be used by individuals and Table provides an assessment of a variety of hydration of with plasma provide the most and of body hydration but are not practical for by most such as plasma fluid and are not can determine their hydration by several and body that by have marked but when these are used in the can provide of hydration of body weight after in with a of urine should allow to in fluid of hydration can allow of an individual is euhydrated or specific and are urine and urine are often and be of is of euhydrated is more but are of euhydrated can provide regarding hydration if during rehydration For example, if persons large of hypotonic will have urine before is during this will be in and have and that when in the person This the need to urine or after several hours of hydration to allow between and Body weight provide and to fluid balance For who are in a will be and by least should be to a which in active consuming and fluid may need more to a their body water For example, can body water and by is by changes in and changes in during exercise can be used to sweating rates and in hydration that occur in different environments This that 1 of sweat loss a loss in body weight specific of sweat is The are used with the for urine losses and should be used to avoid for sweat in the clothing factors to loss during exercise include water and factors will over sweat rate but not for exercise If are changes can provide a of changes to hydration changes during exercise. statement. can their hydration by urine and body weight individual with a or can be as of body can be used to body that Body weight changes can sweat losses during exercise and can be used to individual fluid replacement needs for specific exercise and environmental and can while performing physical activity and prior to on rehydration during exercise, fluid deficits may have been more often start an exercise with normal total body water and over an in some sports the person the exercise such as when the between exercise is for rehydration or when body weight is an For example, in sports (e.g., individuals may to in weight In some individuals undertaking a or daily of exercise in hot may a fluid from their the (62). individuals with may be prior to exercise. loss is the most of dehydration during exercise in the heat If large deficits occur during exercise then the fluid will and of the dehydration for any water there is in and performance as by core rate and responses during The greater the body water the greater the in for a given exercise exercise and performance in environments levels of dehydration will exercise performance The water (>2% for most and the magnitude of performance are likely to the environmental exercise and the (e.g., to some individuals will be more or to influence on exercise performance when cold is not strength or performance factors that contribute to exercise performance include increased body core increased increased metabolic and perhaps each is evidence that to contribute in than in to exercise performance The of each may on the specific environmental heat acclimatization and but to the performance which is and are is by dehydration and The evidence is for a of than that of dehydration on performance but the are when performing exercise in can be by with an that water within the body These include and that can induce for will usually urine and body water will return to within several hours as this is during exercise and there is a of Likewise, over of with most will still urine output well normal levels. not provide any but can the of dehydration which may be for any performance benefits that are statement. and to perform the same exercise and this is in (>2% can exercise in The greater the dehydration the greater the and exercise performance (>2% performance. influence on exercise performance when cold is not performance or and The water and the magnitude of exercise performance are to the heat exercise and the can be by several but provides benefits and several in individuals can from dehydration or greater than sweat In dehydration is more but more can exercise performance and contribute to serious heat and while can produce or the for heat and is a for heat is with other factors as of heat genetic predisposition, and in of all heat in the over a In a of cases of heat in dehydration in of the cases with this providing for American football players during summer have observed that by with the of heat In dehydration been with reduced and reduced blood flow responses to are with electrolyte deficits and and are in American football players summer in soccer and can occur in winter and to are to be often with large sweat losses have been to not have significant different electrolyte than of is most often observed with and evidence that dehydration can the of For example, it that dehydration the or of with who for serious heat and likely large fluid and electrolyte and of cases provides evidence that with heat and can induce serious health In at a training and running in hot during the of with water intake who from heat while and for by from the of heat and other for and and for In all some by at the marathon in runners and that time a number of from a variety of and recreational activities have been for this with several can occur when plasma to and The the plasma the it and the it the greater the of and individuals have plasma levels as as and have with levels over plasma and and include and and to and to plasma well the for with and factors to include of hypotonic and excessive loss of total body In is more likely to occur in and individuals who sweat and and other hypotonic and after the race In (e.g., some may have been both and based upon with for may be to and In in that is from before, during and even after the event In losses can induce to levels with the of if the individual is or so some of the losses is occurs in American football and players who water to or to prevent heat or when a is given hypotonic fluid with have been with who as from dehydration such as and to large of water statement. is a for both heat and heat and can the or of to and deficits are with can occur in that sweating rate is the primary to sweat losses and body mass total body can contribute to the have sweating rates and electrolyte losses than The sweating rates are have body size and metabolic rates when performing a given exercise In to have sweat when their skin is differences in water and electrolyte are and not of The to a water can be greater in than that water over more than show reduced responses to osmotic which should in water and electrolyte losses within both and to and both and water and electrolyte to be at greater than to develop when in marathon and marathon the for this increased may be to a number of and the for greater for not been with regarding fluid intake to have often been based on sweat loss data from and as are for and may have to to their total body water This position statement provides some sweat rate data from the is in the of the for and are the and to the for differences in the imbalances be in During have greater in the the of the activity in the this Likewise, have been to activity in the and for increased and from statement. have sweating rates than differences in water and electrolyte are and not of are at greater than to develop persons are there is an of to water persons more to have an in plasma and are to body fluid in to water and exercise than If given time and to water and will body of body persons are to water fluid This water and and can to in blood but not of the responses to water or or dehydration can be to the rate to a in the number of to a given fluid loss is reduced in The osmotic and that from for and drinking in should be to during or after exercise, but should the of water hyponatremia) or may be to both the water and have sweating rates than and with These sweating rates are the of body mass and metabolic Sweat electrolyte content is similar or in than statement. have when to voluntary have responses to water and and may be at greater for and have sweating rates than is to hydration on a fluid intake and Sweat electrolyte (e.g., and losses need to be to total body water and this can be during meals with most persons a influence on urine losses during and even a influence during exercise not daily fluid needs for individuals is in beverages and and evidence if in it will likely not daily urine output or dehydration The influence of on urine output during exercise or in individuals is not well but urine is by exercise and heat it is that during exercise urine output and induce dehydration during exercise. can as a at and urine it should be in during the when rehydration is a goal statement. Sweat electrolyte and losses should be to will not markedly daily urine output or hydration can urine output and FLUID The goal of prehydrating is to start the physical activity euhydrated and with normal plasma electrolyte levels. If beverages are with meals and a the exercise then the person should be to euhydrated if the person fluid deficits and not time or to then an aggressive program may be merited. The program will that any is prior to the exercise prior to exercise the individual should beverages example, body at least before the exercise If the individual not produce or the urine is or should more example, 2 before the several hours prior to exercise there is time for urine output to return normal before the beverages with of or at meals will to and the to with that of the and (e.g., water and will the of to during competition and provides or performance over In can and plasma before exercise and therefore the of if are during exercise of the fluid is one to fluid before, or after exercise. is by several factors content and The water temperature is often between and but this and between individuals and Prehydrating with beverages, if should be initiated at least several hours before the exercise to enable fluid absorption and allow urine output to return normal levels. beverages with or meals with beverages can and needed During The goal of drinking during exercise is to prevent excessive dehydration (>2% loss from water deficit) and excessive changes in electrolyte balance to avert compromised exercise performance. The amount and rate of fluid replacement upon the individual sweating rate, exercise and to should during exercise, if it is will should be in fluid replacement rates, in exercise greater than The the exercise duration the greater the of between fluid needs and which can excessive dehydration or It is to a specific fluid and electrolyte replacement of different exercise and other factors (e.g., genetic predisposition, heat acclimatization and training a sweating rate and sweat electrolyte Table provides sweating rates for individuals of different running at different speeds in and warm conditions These sweating rates range from to and individual sweating rates for any of these conditions have a normal with it is that individuals should body weight changes during to their sweat during a exercise with respect to the This customized fluid replacement programs to be for each this may not be and electrolyte replacement strategies will be different for a large football in season summer when with a running at a sweating rates for running to in and warm for marathon runners are euhydrated at the is from to with the higher rates for individuals in warm environments and the rates for the persons in environments Table provides the body weight changes or of during a marathon for persons of different running at different speeds in The the sweating rates provided in Table and fluid replacement rates For drinking at in and for drinking at in excessive dehydration body weight this that it is to a single fluid replacement rate for all the of activity specific can the of For example, a to plasma levels for the conditions in Table that if the for speed and environmental conditions are the are for individuals in marathon or different of physical more and may have different fluid replacement For example, some American football players with large body wearing in hot are to have sweating losses of these individuals will fluid to on a to to the runners Table body weight loss to dehydration at of marathon in temperature for individuals of body weight drinking while running at American of exercise and fluid replacement Position Stand evidence of the can be The of provided guidance for of for persons performing physical activity in hot that these of fluid replacement beverages as the and The need for these different and will on the specific exercise (e.g., intensity and duration) and The and are to replace sweat electrolyte while to and provides These can be by such as and other can be to sustain exercise intensity during exercise of or as well as exercise for sports beverages are used to while to replace sweat water and electrolyte at a rate of been to blood levels and sustain exercise performance For example, to achieve a intake to sustain an individual to one of a sports each which provide of with water to avoid excessive The rates of are with a of (e.g., If both fluid replacement and are to be with a single the should not or even be as beverages reduce to sustain exercise performance and likely will not hydration during exercise should develop customized fluid replacement programs that prevent excessive body weight from body The of and body is for sweat rates and customized fluid replacement of beverages containing electrolytes and carbohydrates can sustain balance and exercise performance. After After exercise, the goal is to replace any fluid and electrolyte deficit. The to be on the speed that rehydration be and the magnitude of the deficit. If time and of normal meals and with a of water will provided the contains to replace sweat losses If dehydration is with a then aggressive rehydration programs may be to replace losses will prevent the return to euhydrated state and excessive urine during the will and losses are more to than water and it is well that individuals sweat electrolytes at different containing such as sports beverages may be but can the needed may be to meals and when sweat losses are to achieve and from dehydration should of fluid for each of body weight The is needed to for the increased urine the of large of fluid when should be over time with than in large to fluid fluid replacement after exercise may be in individuals with dehydration body weight with or or who for some For most fluid replacement not provide an over drinking in fluid and electrolyte deficits If time of normal meals and beverages will and from excessive dehydration can of fluid for each of body weight lost. beverages and with will and by and fluid fluid replacement is not unless merited. Physical exercise can elicit sweat rates and water and electrolyte in If sweat water and electrolyte losses are not then the individual will during physical activity. dehydration can exercise performance and of heat can to and may be at greater for imbalances during and after vigorous exercise. The goal of prehydrating is to start of physical activity euhydrated and with normal body electrolyte Prehydrating with beverages should be initiated at least several hours before exercise to enable fluid absorption and allow urine output to return to normal levels. The goal of drinking during exercise is to prevent excessive (>2% body weight loss from water deficit) dehydration and excessive changes in electrolyte balance from performance and health. Because there is considerable variability in sweating rates and between individuals, fluid replacement programs are recommended. of and body weight to determine sweat rates is a and to sweat During exercise, consuming beverages containing electrolytes and carbohydrates can provide benefits over water under certain circumstances. After exercise, the goal is to replace fluid and electrolyte The speed with which rehydration is needed and the magnitude of deficits will determine if an aggressive replacement program is merited. This Position Stand replaces the 1996 Position Stand and This for the American of by the and by and and from the for for which the is a of the and is a of the of the for which an is a of the from an to the The a from the