American College of Sports Medicine Roundtable on Hydration and Physical Activity

Abstract

Introduction An international panel of experts convened for an American College of Sports Medicine (ACSM) Roundtable dealing with Hydration and Physical Activity on December 8–9, 2003, in Boston, MA. The purpose of the meeting was to conduct an evidence-based analysis of hydration-related issues that have recently generated controversy or confusion in the scientific and lay communities. Some of the questions addressed by the Roundtable Panel included the following: How are euhydration and dehydration accurately determined in both laboratory and field settings? Are we unintentionally encouraging athletes to over-drink? How much fluid should an athlete consume each day? Under what circumstances does dehydration negatively affect health and performance? What are the best recommendations for fluid, electrolyte, and carbohydrate replacement before, during, and after exercise? Does dehydration contribute to collapse during and after exercise? Does dehydration contribute to the genesis of exertional heat stroke? How does exercise-related hyponatremia develop? and finally, How is hyponatremia best prevented? This document summarizes the outcome of the Roundtable presentations and discussions using a format that reflects the evidence-based approach used during the 2-day meeting. Each of the consensus statements in this document bears a designation of A, B, C, or D (Table 1). These designators reflect strength of evidence determinations as noted below. The related references are not comprehensive, but are meant to provide key citations in support of the consensus statements. The Roundtable panel focused primarily on hydration issues related to athletes, but many of the consensus statements may also be applicable to military, occupational, fitness, and recreational settings.Table 1: Level of evidence guideFluid and Electrolyte Requirements Assessing body hydration status During prolonged or strenuous physical activity, body water flux is primarily caused by sweat losses, although urine and respiratory fluid losses contribute to the final total body water status. Maintaining baseline euhydration status is important for day to day training safety and performance of athletes and active people. Dehydration is a body water deficit that occurs during physical activity and in athletes is usually characterized by hyperosmotic hypovolemia, although hypo-osmotic hypovolemia can occur in some situations. During hot weather training, dehydration occurs more frequently and has more severe consequences. A practical approach to monitor day to day fluid status is important for athletes who are training strenuously, especially in hot weather conditions or when wearing insulating clothing or equipment. 1. When fluid intake matches fluid loss, daily body mass will fluctuate by less than 1% and hydration status can be reliably estimated using as few as three consecutive days of first-morning body weights measured after voiding. i. Level of evidence: B ii. References: Cheuvront et al.[1], Casa et al.[2] 2. A body water deficit of greater than 2% of body weight marks the level of dehydration that can adversely affect performance. i. Level of evidence: A ii. References: Sawka [3], ACSM [4], Cheuvront et al.[5] 3. Several techniques have been used to measure and monitor hydration in the laboratory setting. A. Total body water is best measured by isotope techniques. i. Level of evidence: A ii. References: Ritz [6] B. Plasma osmolality is a reliable indication of hydration status. A euhydrated athlete should have a plasma osmolality between 280 mOsm/kg and 290 mOsm/kg. i. Level of evidence: A ii. References: Senay [7], Robertson et al.[8], Popowski et al. [9] C. Fluid regulatory hormones can be confounded and alone are not good markers of hydration status. i. Level of evidence: B ii. References: Francesconi et al.[10], Montain et al. [11] 4. Several techniques have been used to estimate hydration in the field setting. A. Urine-specific gravity, urine color, and urine osmolality are useful screening measures of hydration status. A euhydrated athlete will usually have a urine specific gravity of less than 1.020, a pale yellow urine color, and a urine osmolality of less than 700 mOsm/kg. i. Level of evidence: A ii. References: Adolph [12], Popowski et al.[9], Armstrong et al. [13], Armstrong et al.[14], Shirreffs and Maughan [15], Bartok et al. [16] B. Bioelectric impedance can provide an indication of total body water, but is a poor indicator of hydration status or of changes in hydration status. i. Level of evidence: A ii. References: O'Brien et al.[17,18], Armstrong et al.[19] 5. Practical field measurements of hydration should be used to measure or monitor hydration status in athletes. A. Day to day body weight changes are an acute estimate of hydration changes, if careful baseline measures are obtained and confounding factors are controlled. i. Level of evidence: A ii. Reference: Cheuvront et al.[20] B. A day to day decrease in body mass of greater than 1% below the baseline is a marker of dehydration. i. Level of evidence: B ii. References: Adolph and Dill [21], Adolph [22], Cheuvront et al.[1] C. A combination of baseline first-morning, postvoiding weight and plasma osmolality of less than 290 mOsm/kg, urine osmolality of less than 700 mOsm/kg, urine specific gravity of less than 1.020, or pale yellow urine (the color of lemonade, 1–3 on the Urine Color Chart) can give a prediction of a euhydrated condition in most athletes. i. Level of evidence: A ii. References: Ritz [6], Popowski et al.[9], Senay [7], Armstrong et al.[13], Bartok et al.[16], Shirreffs and Maughan [15], Casa et al.[2], Cheuvront et al.[1] D. The difference in pre- and postactivity body weight is a reasonable estimate of acute body water losses and estimates the volume of fluid replacement needed to approximate euhydration, assuming that exercise began in a euhydrated state. i. Level of evidence: B ii. Reference: Cheuvront et al.[20] E. Clinical signs and symptoms such as thirst, dizziness, headache, tachycardia, oral mucosal surface moisture, skin turgor, and others should not be ignored, but are too generalized to be of predictive use and the assessment of dehydration via these signs and symptoms is too imprecise to accurately assess the presence of hydration in an athlete. i. Level of evidence: D ii. References: Barkin and Ward [23], Engel et al.[24] Daily fluid and electrolyte requirements Individual fluid and electrolyte needs are widely variable during physical exercise due to differences in metabolic rate, body mass and size, environmental conditions (eg, temperature, humidity, wind, solar load, clothing worn), heat acclimatization status, physical fitness, activity duration, and genetic variability. For example, during a marathon, sweat rates may vary from less than 500 mL/h to more than 2 L/h. Similarly, sweat sodium concentration may vary from less than 20 mEq/L (460 mg/L) to more than 80 mEq/L (1840 mg/L). An individualized replacement recommendation is prudent for athlete safety during activities where a large sweat loss (eg, > 1L) is expected. Athletes should learn to estimate sweat rate to optimize hydration strategies for long-duration activities. 1. Dehydration results from sweat, respiration, urine, and insensible skin losses that are not replaced. A. For inactive persons in temperate conditions, daily water needs can be as small as 1 to 2 L, but extended periods of intense exercise can increase daily water requirements to more than 10 L. However, for most moderately active people, daily water needs typically range between 3 and 5 L. i. Level of evidence: B ii. References: Institute of Medicine [25], Lentner [26], Leiper et al.[27,28] B. During vigorous physical activity, hourly sweat losses from 0.5 to 2.0 L/h are common, with other extremes possible. i. Level of evidence: A ii. References: Rehrer and Burke [29] C. Athletes often dehydrate involuntarily during exercise. Thus, during intense physical activity and environmental stress, fluid losses commonly exceed replacement, resulting in an acute fluid deficit. i. Level of evidence: A ii. References: Rehrer and Burke [29], Maughan et al.[30], Adolph [12] 2. Exercise in specific environments or conditions can further exacerbate fluid loss. A. Athletes involved in long-duration activities should attempt to replace sweat losses during activity, but should not exceed the volume of sweat lost during the activity. The minimum fluid replacement goal during most activities is to limit fluid deficits to less than 2% of baseline, euhydrated body weight. i. Level of evidence: B ii. Reference: Cheuvront et al.[5] B. Sweat sodium concentration during exercise can range from about less than 20 to more than 80 mmol/L or about 1 to 5 g of table salt per liter of sweat. An athlete with an average sweat rate of 1 L/h can lose approximately 2 to 10 g of table salt in a 2-hour practice. i. Level of evidence: B ii. References: Maughan et al.[30], Shirreffs et al.[31] C. An endurance athlete with a sweat rate of 1 L/h who exercises for 5 hours can lose 5 to over 30 g of table salt during the event. i. Level of evidence: C ii. References: Maughan et al.[30], Shirreffs et al.[31] D. General prescriptive guidelines for fluid and electrolyte replacement practices for athletes are not meaningful across or even within sports due to considerable variability in the sweat losses of athlete and sports-specific differences in the factors that influence fluid intake during exercise. Education messages should encourage athletes to recognize their individual needs based on sweat losses and to target issues that influence fluid intake during activity, For example, opportunities to drink, availability of fluids, and the culture and rules of the sport can all influence intake and these factors should be taken into account when designing fluid and electrolyte replacement regimens. i. Level of evidence: D Diet effects on water requirements Body water is replaced by beverage consumption and by ingestion of foods that contain water. A balanced diet that provides about 2500 to 3000 kcal will generally provide about 1 liter of water per day from food alone. In addition, the consumption of food stimulates drinking. Although foods and beverages provide fluids, their composition can influence fluid requirements by altering fluid retention. 1. A normal balanced diet will usually replace sodium lost in activity except for low-sodium diets (less than about 3 g/d) early in heat exposure and for athletes with very high sweat sodium losses. i. Level of evidence: A ii. References: Armstrong et al.[32], Glace et al.[33], Rehrer [34], Twerenbold et al.[35] 2. Caffeine, alcohol, and protein can modestly increase urine water losses. A. Caffeine ingestion has a modest in some but does not affect water replacement in beverages (eg, can be during the day by athletes who are not i. Level of evidence: B ii. References: and Armstrong Institute of Medicine [25], Maughan and B. are not when after exercise is can modest in some i. Level of evidence: B ii. Reference: et C. or have a and should not be used when and is i. Level of evidence: C ii. References: et et D. in may not adversely affect status in athletes, but should not be when and is i. Level of evidence: C ii. References: et Shirreffs and Maughan 3. diets than g/d) can increase water loss and increase water i. Level of evidence: B ii. Reference: et 4. diets an to water intake to each of is The fluid loss is normal but may increase dehydration in athletes who are fluid intake in an attempt to lose weight. i. Level of evidence: B ii. Reference: et Fluid replacement after activity Fluid and replacement after activity is to An athlete involved in vigorous training or with that are less than hours more replacement strategies than the athlete who has more than hours between fluid intake activity urine the fluid intake in even over periods In to body water, sodium losses also to be replaced these 1. The difference in pre- and body weights is a measure of dehydration for a exercise Assessing Body Hydration i. Level of evidence: A ii. Reference: Cheuvront et al.[20] 2. strategies on the of the fluid deficit and the for to the exercise A. Athletes often to replace water and electrolyte losses. normal food and fluid intake is usually to replace water and electrolyte losses when exercise are more than i. Level of evidence: B ii. Reference: Casa et al.[2] B. within hours of exercise ingestion of water and sodium in of the body deficits to for normal fluid needs and urine loss. This an replacement volume of to of the decrease in body mass with the of to mmol/L of sodium will most replace the deficit. i. Level of evidence: B ii. References: et Shirreffs et Adolph C. 2 of fluid in 500 20 to 30 is more for than the volume in a after the exercise replacement of fluid after exercise stimulates urine resulting in less body water retention. i. Level of evidence: B ii. References: et et and Shirreffs Adolph 3. concentration of the beverage is an important A. foods (eg, or such as and or with other sports mmol/L or provide a sodium fluid and fluid i. Level of evidence: B ii. References: Maughan et et Adolph B. should attempt to the for sodium with the of i. Level of evidence: B ii. References: et Maughan and Leiper Adolph C. The for is replacement, but such as and also are important in hydration and can be replaced by a balanced i. Level of evidence: D ii. References: Leiper et Shirreffs 4. fluid replacement may be and prudent in A. fluid replacement may be activity in athletes who or or who for some the signs of dehydration are not on sodium level should be fluid i. Level of evidence: C ii. References: Maughan and et et and B. fluid replacement is not generally but is during in American and other sports for athletes who are due to and the to fluid intake with sweat losses. be a of the i. Level of evidence: D ii. References: Casa et Maughan and Athletes who fluid deficits during physical activity may some loss of performance especially in long-duration that in the factors contribute to the performance with dehydration and in physical and changes in and heat 1. performance can be by dehydration and during exercise. A. and body performance. The is greater with and and are the to be i. Level of evidence: B ii. References: and et and B. Dehydration negatively and and i. Level of evidence: B ii. References: et et et et Sawka et C. Dehydration of more than 2% to of body mass the of the exercise i. Level of evidence: A ii. References: and Montain et al. et Montain and et D. carbohydrate beverages provide g during vigorous exercise can and and than the volume of water. i. Level of evidence: B ii. References: et and and Montain et et et et et et et et et E. Caffeine or during exercise in of 2 body mass or more (eg, 2 in a can some deficits in performance and during prolonged intense exercise and heat However, is a in individual to such that effects of and may with performance in some not adversely i. Level of evidence: C ii. References: et Maughan and Armstrong 2. Dehydration of more than 2% of body mass can and exercise performance of dehydration further exacerbate the A. Dehydration skin and sweat and the in body with exercise in the i. Level of evidence: A ii. References: Armstrong et Sawka and B. The greater the level of the greater the and i. Level of evidence: A ii. References: Sawka et Montain and Montain et C. are or performance to or during activity, fluid can be during exercise. i. Level of evidence: B ii. References: et et et Sawka and D. Maintaining hydration less than a 2% body mass deficit during exercise rate, skin normal temperature, and i. Level of evidence: A ii. Reference: Armstrong et E. hydration to less than 2% body mass and carbohydrate total physical to and related to sports performance (eg, and i. Level of evidence: A ii. References: Armstrong et et et will performance over if an athlete fluid intake to fluid losses during exercise. i. Level of evidence: B ii. References: Casa et Montain and beverages performance with the volume of water during prolonged exercise or in exercise. In the performance of hydration and carbohydrate intake are and i. Level of evidence: A ii. References: et et et and and Montain et et et et et 3. performance can be by dehydration. A. Dehydration of more than a 2% loss in body mass heat and when heat i. Level of evidence: B ii. References: and et Sawka et et B. dehydration by fluid and during exercise and when heat i. Level of evidence: B ii. References: and et and and Sawka et C. fluid replacement the body that can be to heat and during heat i. Level of evidence: B ii. References: et and D. beverages that and sodium increase fluid intake with water in both and i. Level of evidence: A ii. References: et et et Hydration and that occur during exercise are often heat occur more frequently with heat The of during and after exercise is not but is to be related to salt loss, and exercise. These are during of but are more in matches in hot and in can occur in such as in and in This in that even when the is the of some athletes can be and that heat can be sweat An be that salt loss, and fluid losses by prolonged exercise and not on environmental heat severe 1. that occur during exercise are related to large losses of salt in sweat, and A. Athletes to during and after exercise to sweat more and lose more sodium in sweat than who not i. Level of evidence: C ii. References: et B. The of during and after exercise in hot conditions can be by salt and during exercise by beverages i. Level of evidence: D ii. References: and C. usually occur during or as a i. Level of evidence: D ii. References: D. is evidence that with or is in the of with exercise. i. Level of evidence: D ii. Reference: 2. can be with oral beverages that contain to mmol/L of sodium of normal i. Level of evidence: D ii. References: and exertional heat heat the conditions of heat and heat heat can occur during physical exercise when the combination of heat from metabolic and environmental the to heat as a the In addition, some of heat are with of body to heat than an to Although severe exertional heat occurs more frequently in and environments during or activity, heat can occur as as and that body heat loss increase body heat and fluid losses. of heat are and hot or or headache, and body to status, changes, tachycardia, and to The symptoms of heat although by and usually by evidence of other and are often and can be as severe heat if is not measured to body changes with exertional heat are headache, to dizziness, and but are possible. 1. heat can occur in hot conditions dehydration if the heat from be from the body a rate to a in i. Level of evidence: B ii. References: Armstrong et et et et 2. Dehydration the of heat and heat during and after activity. A. Dehydration and the of the to metabolic heat to the body i. Level of evidence: A ii. References: Sawka and et Montain and Casa et al.[2], et Montain et B. Dehydration the of heat by more to i. Level of evidence: B ii. References: et and et C. Fluid loss from or the of exertional heat i. Level of evidence: D ii. References: 3. Maintaining normal hydration the of exertional heat A. Maintaining normal hydration heat and i. Level of evidence: A ii. References: Sawka et Montain and Adolph [12], 4. Athletes with severe heat and exertional heat during or prolonged often a large volume of fluid to replace losses. heat are often and have i. Level of evidence: C ii. References: et al. et al. Adolph [12] 5. important factors for exertional heat are acclimatization to heat and humidity, consumption the day to training or high body poor fitness, a of and training in on the i. Level of evidence: B ii. References: Armstrong et et et et et Armstrong and et Athletes to heat have a of heat A. to 10 days of heat exposure and training will athletes to with that sweat volume and over the and sodium concentration in sweat. i. Level of evidence: A ii. References: Armstrong et et et Armstrong et et and and et et B. Dehydration will many of the by heat acclimatization and physical i. Level of evidence: A ii. References: et Sawka et The and for exertional heat is when the is and with of the and or alone in an or water is the to body In addition, skin the by from the to to the such as the and or in water or are less but often i. Level of evidence: B ii. References: Armstrong et al. et et et Casa and Armstrong Casa and on hyponatremia The of sodium from normal of to mEq/L to below mEq/L may to to a During prolonged activity, sodium can be by fluid intake alone or with a sodium deficit of the fluid due to sweat loss. of hyponatremia are to exertional heat and exertional heat and may headache, and of severe hyponatremia and that can in and Although exertional hyponatremia is generally have when sodium to (eg, than 1. hyponatremia can occur as a of fluid ingestion alone or fluid ingestion with high sweat sodium losses. A. periods of can in that the sodium to i. Level of evidence: A ii. References: Twerenbold et et Armstrong et et Montain et et O'Brien et B. salt loss in sweat, such as occurs in will contribute to the of sodium and will the of fluid intake to i. Level of evidence: A ii. References: and Rehrer et Montain et C. who a for may lose salt in sweat and be more to sodium with drinking. i. Level of evidence: B ii. References: et et et 2. hyponatremia is and to be most during endurance activities such as than than to and prolonged A. hyponatremia is more in as to more of water availability and consume when than i. Level of evidence: C ii. References: et et et et B. to be greater of exertional hyponatremia their fluid intake their sweat rate and their body mass total body can be more by i. Level of evidence: C ii. References: et et et C. The of hyponatremia during endurance exercise such as the and is generally less than in although have rates in i. Level of evidence: C ii. References: et et et Armstrong 3. of hyponatremia should be to and recreational athletes as as prolonged in of 3 to A. Fluid intake during exercise should exceed sweat loss. The difference between body weight and after exercise an estimate of sweat rate and of fluid replacement during activity fluid i. Level of evidence: A ii. Reference: ACSM B. Athletes prolonged exercise in of 3 to hours should or sodium to the loss of salt in sweat. This is especially for who that lose of salt in their sweat. i. Level of evidence: C ii. Reference: Montain et and Hydration is a for and the these are more to heat due to less The of and the to dehydration is from that of are often not to hydration as during exercise and are for 1. in are not as as in and are less heat than to a high heat Sweat rate and sweat rate per body surface are less in than heat loss for when in a hot the large surface to body mass in their rate of heat from hot i. Level of evidence: B ii. References: et 2. often not of fluid during physical activity and can dehydrate during activity. A. than in the i. Level of evidence: B ii. Reference: et B. a 1% to 2% in body mass performance in to i. Level of evidence: C et C. will more fluid during exercise in or hot environments when with a sports than when water is is further with the of carbohydrate and mmol/L i. Level of evidence: B ii. Reference: et D. with less during exercise their high sweat sodium loss the to i. Level of evidence: B ii. References: et et E. A mmol/L and carbohydrate stimulates in with i. Level of evidence: B ii. Reference: et 3. are less heat than in to exercise heat and have skin and and sweat rates than i. Level of evidence: A ii. References: and and 4. usually to in However, when rate their of than and less as a i. Level of evidence: B ii. References: and et of the ACSM Roundtable on Hydration and Physical Activity are as E. Armstrong of Institute of Institute of MA. of of of Exercise E. of Maughan of Exercise Medicine and Montain Institute of MA. Sports Institute of Medicine MA. of Exercise of of of of Exercise