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Methods to Evaluate Electrolyte and Water Turnover of Athletes

2009; Volume: 1; Issue: 4 Linguagem: Inglês

10.3928/19425864-20090625-06

1942-5872

Lawrence E. Armstrong, Douglas J. Casa,

Sports Performance and Training

Original Research freeMethods to Evaluate Electrolyte and Water Turnover of Athletes Lawrence E. Armstrong, PhD, FACSM, ; and , PhD, FACSM Douglas J. Casa, PhD, ATC, FACSM, FNATA, , PhD, ATC, FACSM, FNATA Lawrence E. Armstrong, PhD, FACSM Address correspondence to Lawrence E. Armstrong, PhD, FACSM, Unit 1110, EKIN, Storrs, CT 06269-1110; e-mail: E-mail Address: [email protected]. and Douglas J. Casa, PhD, ATC, FACSM, FNATA Athletic Training & Sports Health Care, 2009;1(4):169–179Published Online:June 25, 2009https://doi.org/10.3928/19425864-20090625-06Cited by:22PDFAbstract ToolsAdd to favoritesDownload CitationsTrack Citations ShareShare onFacebookTwitterLinkedInRedditEmail SectionsMoreAbstractFluid-electrolyte deficiencies may accumulate over several days in athletes whose diets contain nutrients (eg, water, sodium, potassium) in quantities that are smaller than the losses that occur in sweat and urine. Individualized assessment and personalized dietary recommendations are necessary, especially in cases of water or salt depletion, heat exhaustion, and heat cramps. Unfortunately, no composite source of these techniques exists. The purpose of this article is to describe methods that validly assess urine and sweat volumes, electrolyte concentrations, dietary fluid and electrolyte intake, and 24-hour water and electrolyte balance for athletes who train and compete in hot environments. Reference (ie, expected) values, sample data sheets, and a case report are presented. These techniques allow motivated professionals to validly characterize the fluid-electrolyte status of athletes and thereby suggest modifications of diet and training habits. Without these techniques, professionals must resort to inaccurate or indirect estimates of whole-body fluid and electrolyte balance.IntroductionThe skin of a person weighing 70 kg contains 200 to 300 eccrine sweat glands per cm2, each of which has a length of approximately 1.3 mm.1,2 Acting under the control of the preoptic area of the anterior hypothalamus, efferent nerve impulses stimulate the body's sweat glands to collectively secrete between 0.8 and 1.5 L of fluid per hour during a moderate-intensity workout.3 Sweat that appears on the skin contains over 40 compounds, including key mineral salts such as sodium and chloride (extracellular ions) or potassium and magnesium (intracellular ions).4 For most athletes, a balanced western diet provides ample nutrients that easily offset sweat electrolyte and water losses during exercise. However, when training or competition occurs in a hot environment or involves multiple exercise sessions per day or when the individual has a very large sweat rate or sweat salt concentration, fluid-electrolyte losses can exceed 24-hour dietary intake. In these extreme situations, clinical signs and symptoms (eg, skeletal muscle cramps, heat exhaustion) may arise that prompt athletes to seek medical assistance.Unfortunately, even experienced clinicians find it difficult to precisely diagnose and treat these illnesses because fluid and electrolyte assessment requires accurate measurements of sweat rate (volume of sweat produced per hour), sweat electrolyte concentration (mg per L of sweat), urinary output, fluid consumption, and dietary nutrient intake (mg of electrolyte per 24 hours), as well as calculations of the resulting whole-body balance. In addition, the dynamic and complex nature of body fluids complicates diagnoses,5 necessitating an individualized approach to fluid-electrolyte evaluation.6,7 Therefore, the primary purpose of this article is to describe numerous factors that athletic trainers must consider when assessing the electrolyte and water turnover of athletes who have an increased risk of exertional heat illness or a fluid-electrolyte imbalance.Since the early observations of eccrine sweat gland function during the 1930s,8 numerous sweat collection methods have been used, including local sampling methods (ie, filter paper or gauze absorption, skin scraping, multisite pipette suction, sweat gland cannulation, rubber glove and arm bag collection)9 and the whole-body rinse technique.10,11 Several comparisons of local sweat collections versus the whole-body rinse technique have been published, but no previous publication has described completely the necessary methods and calculations.4,10–17 Virtually all investigators have reported that local sweat samples have resulted in higher electrolyte concentrations than samples analyzed via whole-body rinse and were not valid representations of the entire skin surface. Acknowledging the whole-body rinse as the method of choice, the secondary purpose of this article is to describe the whole-body rinse technique of sweat electrolyte analysis and to provide details regarding the techniques that allow athletic trainers to characterize an athlete's fluid-electrolyte status on any given day. To our knowledge, this is the first publication to delineate these methods in a detailed, composite document.Evaluating Whole-Body Fluid BalanceTable 1 presents the factors involved in calculating fluid and electrolyte balance. Equation 1 incorporates the gain of fluid from dietary sources (ie, in beverages, water, and solid food). This is measured simply by recording the volume (mL or oz) of water, fluid-electrolyte replacement beverages, tea, coffee, juice, or soft drinks that an athlete consumes per 24 hours. To this volume, the water contained in solid food should be added. However, this is not feasible in most situations because a precise measurement requires weighing each food item, drying it in an oven, weighing the dried food, and calculating the water weight by subtraction (a 1-g weight change equals 1 mL of water). Because time, personnel, or facilities usually do not allow desiccation of food, the water content can be estimated as 20% of the volume consumed as fluid.18 For example, if an athlete consumes a total of 3 L of fluid per day, the moisture content of solid food is estimated to be 0.6 L (3.0 L×0.20 L = 0.6 L). Some elite athletes are exceptional in this regard, as the water content of their solid food has been reported to be 37% of total dietary water.19Table 1 Fluid Electrolyte Equations That May Be Applied to a 24-Hour Period or to a Single Exercise SessionEQUATION 1aEQUATION 2EQUATION 3bEQUATION 4caIn athletes, fecal water and electrolyte losses are small and difficult to measure; therefore, they are not included here.b1 kg body weight = 1 L fluid; 1 g body weight = 1 mL fluid.cContent (total mg or total mEq) = fluid volume (L)×fluid concentration (mg/L or mEq/L).Equation 1 in Table 1 also contains 3 quantities that are difficult to measure, and therefore usually are calculated metabolic-water production, transcutaneous water loss, and respiratory water loss. Metabolic water is produced when the body digests and converts food to chemical energy, as some biochemical reactions generate water within cells during the processing of carbohydrate, fat, and protein. The cellular oxidation of carbohydrate, fat, and protein yields 0.6 mL, 1.1 mL, and 0.4 mL of water per gram, respectively.20 This calculation requires an athletic trainer or dietitian to analyze the diet for the total grams of carbohydrate, fat, and protein consumed. Transcutaneous (ie, across the skin) and respiratory losses occur continuously throughout life as water loss through the skin and lungs, respectively. Fortunately, in most environments and athletic situations, the volume of metabolic water produced (ie, approximately 500 to 800 mL/day)20 is similar to the sum of the transcutaneous plus respiratory water losses.21 Thus, the gain and loss of water via these processes approximately cancel each other and we recommend using the simplified equation 2; this eliminates the need to measure metabolic, transcutaneous, and respiratory water losses.Equation 3 (Table 1) is a field expedient method that requires only 2 body weight measurements (1 kg = 1 L). Urine excretion, metabolic water production, transcutaneous water loss, and respiratory water loss are disregarded. Other inherent assumptions and sources of error have been delineated by Maughan et al.22 As with equations 1 and 2, avoiding water ingestion during the observation period simplifies this technique and the associated calculations.For equations 1 and 2 (Table 1), sweat volume is determined by measuring body weight change during exercise. The simplest method involves voiding the bowel and bladder, weighing the athlete nude (or while wearing undergarments) on a digital floor scale with a precision of 0.1 kg (ie, 0.2 lb), and then simulating the conditions of training or competition by exercising for 1 hour and weighing the athlete nude again. The sweat rate equals the body weight difference expressed per 1 hour. If fluid is consumed or if urine is excreted between the body weight measurements, the final sweat rate should be corrected as: sweat rate (L per hour) = body weight difference (1 kg = 1 L)+water intake (L)−urine volume (L). All factors are measured over a 1-hour or half-hour period; the latter is corrected to 1 hour mathematically.Assessing Whole-Body Electrolyte BalanceEquation 4 in Table 1 considers the gain and loss of electrolytes (ie, mineral turnover, salt balance) that constitutes whole-body balance. Dietary electrolyte intake is usually analyzed on the basis of a 24-hour period, but shorter durations may be used (eg, a prolonged competition or double workout session). Although this equation may be applied to sodium, chloride, potassium, magnesium, or any other nutrient, the following paragraphs focus primarily on sodium.An individualized approach to analysis of fluid-electrolyte balance6,7 requires a computer, software, a complete and accurate record of all food and fluid consumed by the athlete, and an experienced software user. Numerous dietary analysis software packages are commercially available. Prestwood23 has outlined the features that should be considered when purchasing dietary software programs. In addition, the U.S. Department of Agriculture offers free dietary analysis programs and advice through their Web sites ( http://www.nutrition.gov and http://www.nal.usda.gov/fnic/foodcomp/search/). This type of analytical software program contains thousands of food items and provides information to use the techniques described below. Once all food and fluid items have been entered into the computer program, it provides numerous outputs including total kilocalories; grams of carbohydrate, sugars, fat, protein, amino acids; and milligrams of sodium, potassium, chloride, magnesium, and other minerals. We recommend that athletes be trained to record brand names, food quantities (eg, 8 oz, 3 slices, 2 tablespoons), methods of preparation (eg, fried, baked, toasted, in oil, in water), the restaurant or dining facility, and portion size (eg, small, large). Table 2 presents a sample food recall sheet that athletes may use to record the food and fluids they consume during a predetermined 24-hour period.Table 2 Diet Record Instructionsa,bPlease record all foods, water, beverages, and supplements that you consume during a 24-hour period.HELPFUL HINTSBe very specific in your description of the type, the preparation method, and the amount of each food and beverage you consume.Use the label on foods to help you determine portion sizes.Save labels from packages and return them with your food record forms (this will greatly assist and enhance our analysis of your true nutrient intake).Use nutrient descriptors (eg, low-fat, fat-free, light, reduced calorie) and brand names to delineate foods.Record food and beverage consumption after each meal or snack instead of waiting until the end of the day.Date: ___________Name:____________________________________________TIMEFOOD AND BEVERAGE DESCRIPTIONAMOUNTTOTAL KCALcaThese food and fluid items are evaluated with commercial nutritional analysis software.bFree dietary analysis programs and advice may be found at http://www.nutrition.gov and http://www.nal.usda.gov/fnic/foodcomp/search/.cThis can be found on the label.Equation 4 in Table 1 involves sodium or other electrolyte losses in urine, feces, and sweat. All of these measurements require electrolyte analyzers, which are commonly used in hospital laboratories or clinics. Such analyzers use ion-selective electrodes that are based on thin films or membranes; the electrolyte content of a sample is compared with a reference electrode.24 The content of sodium (milliequivalents [mEq]) in urine is calculated by multiplying the concentration (mEq/L) by the volume (L); the concentration is determined with a laboratory electrolyte analyzer, and volume is measured by weighing a 24-hour urine collection on a scale or balance (1 g = 1 mL; 1 kg = 1 L). This collection represents all urine produced during the 24-hour observation period. The electrolyte analyzer provides concentration in mEq; to convert this unit to mg, multiply mEq of sodium by 22.99 or multiply mEq of potassium by 39.1.As noted above, virtually all published comparisons indicate that local sweat collection methods do not accurately represent the entire body surface, and that the whole-body rinse technique is the preferred method.4,10–17The technique's procedures require both sophisticated laboratory instruments and simple household items (Table 3). If electrolyte analyzers and sensitive balances are not available, the athletic trainer should contact a hospital or university laboratory.Table 3 Supplies Required to Perform One Sweat Electrolyte Analysis Using the Whole-Body Rinse TechniqueITEMS1 pair of exercise shorts,a socks,a and sneakers1 t-shirta1 exercise machineb (ie, treadmill, elliptical trainer, stair climber, stationary bike)2 pairs of nitrile or latex examination gloves1 electrolyte-free plastic sheeta,c2 plastic jugsa (1-gallon capacity) filled with distilled watera2 clean towelsa3 disposable pipettes (2-mL to 5-mL capacity)6 clean plastic test tubes with lid or storage cap (minimum 0.5-mL capacity)1 digital floor scale, 0.2 lb (ie, 0.1 kg) precision1 laboratory electrolyte analyzer1 stop watch1 laboratory bench top pan balance, 0.01-g to 1.0-g resolution1 metal wash tub (1-m diameter; 15-cm to 30-cm height)1 plastic trash bag1 permanent marker1 pair scissors1 data sheet (Table 5)aItem is initially electrolyte free.bExercise equipment is not necessary if the athlete runs outdoors.cA disposable plastic paint tarp (0.2-mm to 0.4-mm thickness; 12×12 ft) serves this purpose well.Table 4 presents the procedures that athletic trainers and investigators can use to evaluate sweat electrolyte concentrations and the total electrolyte loss during exercise. Several hours before exercise, the athletic trainer passes the athlete's shorts, socks, and underwear through one full cycle of an automatic washer, using plain water and no soap or detergent; this removes the electrolytes that were present in the fibers of the clothing. Clothing items are then dried in an automatic clothes dryer, without softening agents or other special care. Two bath towels should be cleaned concurrently; these will be used during exercise to blot sweat droplets that form on the skin, before they fall to the floor. Immediately prior to exercise, the athlete should take a 5-minute shower without soap (which may contain potassium), vigorously scrubbing all hair-covered areas of the body with both hands. In our experience, these procedures ensure that the athlete begins exercise with electrolyte-free clothing and skin.Table 4 Procedures to Evaluate Sweat Electrolyte Concentration (mEq/l) and Content (total mEq or mg) via the Whole-Body Rinse TechniqueaPROCEDUREATHLETEATHLETIC TRAINERCollect and organize supplies.XLaunder all clothing and 2 towels, without detergent, in an automatic washer to remove electrolytes. Run clean clothing through 1 extra rinse cycle with water only.XIf jugs of commercial distilled water are not available from a supermarket, the athletic trainer should prepare two 1-gallon plastic milk containers by washing with soapy water and rinsing >10 times to remove all soap residue. Weigh the empty, dry jugs on a sensitive pan scale to the nearest 1 g to determine the clean jug weight; fill the clean plastic jugs with distilled water (prepared in a distilled water apparatus) and weigh the jugs again to the nearest 1 g; the volume of the water in L is equal to the number of kg of water in each jug (eg, 3.92 kg = 3.92 L). Record the volume of water on the data sheet.XWeigh clothing to the nearest 1 g before exercise.XVoid bowel and bladder.XShower entire body with water. Use no soap or shampoo. Thoroughly scrub all hairy areas.XDress in electrolyte-free shorts, socks, and undergarments. Shoes are not rinsed and need not be cleaned.XMeasure athlete's body weight to the nearest 0.2 lb or 0.1 kg before exercise.XExercise for 30 or 60 minutes in a warm or hot environment. Men wear no shirts and women wear sports bras. Blot the skin frequently with a clean towel to capture sweat that might drip onto the floor. This is more effective during stationary cycling than treadmill running. The towel eventually will be added to the rinse water. Athlete drinks nothing.XXMeasure body weight to the nearest 0.2 lb or 0.1 kg after exercise.XXAthlete disrobes privately and places shorts and socks in a clean, electrolyte-free plastic bag.XIn the locker room shower area, place a circular wash tub (approximately 2-m diameter, 15-cm to 30-cm wall height) near floor drains and line the tub with a new electrolyte-free plastic tarp.b Edges of the tarp should extend well beyond the lip of the tub. Do not soil the tarp on the side that faces the ceiling.XWearing only underclothing, the athlete steps into the tub and squats in a posture resembling a crouched baseball catcher.XXAssistants, wearing gloves, hold the tarp vertically, encircling the athlete in the shape of a plastic cylinder. The goal is to catch all water (approximately 2 gallons or 8 L) that rinses the body.XWhile wearing plastic gloves, the athletic trainer pours distilled water slowly on all skin surfaces, especially on the hair, shoulders, head, chest, back, armpit, and groin areas. Athlete scrubs hairy areas as the rinse water is applied.XXDuring the rinse, the athletic trainer begins at the head and pours a conservative amount of distilled water on the scalp, stopping periodically to allow the athlete to scrub the hair. Most water is applied to hair-covered areas of the body and skin areas that produce the most sweat (eg, head, shoulders, chest, back, armpits). Each zone of the skin surface should be rinsed twice per gallon jug (approximately 3.9 L).cXXThe athlete exits the tarp and tub, while the athletic trainer ensures that all rinse water remains in the tarp.XXWeigh clothing to the nearest 1 g after exercise. Subtract pre-exercise clothing weight to determine the amount of sweat that was trapped in clothing.XWhile wearing gloves, the athletic trainer adds all clothing and towels to the rinse water (approximately 2 gallons, 8 L). All items are saturated with the rinse water, mixed thoroughly, and wrung by hand several times. The rinse water now contains all electrolytes lost in sweat during exercise.XThe athletic trainer collects a sample (1 mL to 2 mL) of the rinse water with a clean pipette and transfers this sample to a clean test tube and seals the tube.XThe rinse water inside the test tube is analyzed for sodium and potassium concentration with a laboratory electrolyte analyzer.XThe athletic trainer calculates sodium lost during exercise (Table 5), expressed as total mEq/hour or mg/hour.XThe dietitian or athletic trainer recommends specific food items to replace sodium and potassium losses.XaAlthough sodium is used as an example, this technique is valid for all nutrients in sweat.bA new polyethylene indoor paint tarp (0.2 mm to 0.4 mm) serves this purpose well.cMultiple consecutive rinses have indicated that a single rinse (using 2 gallons or 8 L of distilled water) captures 96% to 98% of all electrolytes secreted by sweat glands. This is identical to other published data.10,14During exercise, the athletic trainer wears nitrile or latex examination gloves, stands behind the athlete, and periodically blots the athlete's back with a towel to capture electrolytes that otherwise might drip onto the floor; the athlete does the same for the front of the body. Exercise intensity should be strenuous (ie, 70% maximal aerobic power or a simulation of a competitive event) for 30 or 60 minutes to encourage near-maximal sweat production; ideally, air temperature is warm (30°C to 34°C) or hot (35°C to 38°C). After exercise, the athletic trainer blots the entire skin surface with a towel and the athlete moves to the shower room for the rinse procedure. If jugs of commercial distilled water are not easily obtained, the athletic trainer should clean two plastic milk containers, as described in Table 4. In either event, the volume of distilled water in the jugs can be determined accurately by subtracting the weight (g) of the empty jugs from the weight of the jugs filled with distilled water.Table 5 presents the measurements and calculations that are required to determine sweat electrolyte losses during 30 minutes of exercise. Although sodium (Na+) is the only electrolyte mentioned, these calculations also apply to potassium. Row 3 allows the athletic trainer to calculate the amount of sweat (1.0 g = 1.0 mL; 1.0 kg = 1.0 L) that is trapped in the clothing of the athlete. To avoid contamination a clear sheet of commercially available sandwich wrap is placed on the scale before clothing items are added. Rows 4 and 5 allow total sweat volume (L) and sweat rate (L/hour) to be calculated based on body weight difference. If the duration of exercise was not 60 minutes, the sweat rate in row 5 should be expressed per hour. Row 10 provides the total volume (L in 2 plastic jugs) of distilled water that was poured over the skin surface. Row 11 shows the sodium concentration (mg/L) of the rinse water, as determined by a laboratory electrolyte analyzer. Distilled water can be purchased at most supermarkets. Row 13 presents the value for the total amount of sodium (mg) in the rinse water; which is calculated by multiplying the sodium concentration of the rinse water (mg/L) (row 11) by the volume of water used to rinse the body (L) (row 10). Row 17 presents the total sodium (mg) (1 mEq Na+ = 22.99 mg Na+) lost in sweat during exercise; this assumes that all sodium on the skin appeared in the rinse water.Table 5 Sample Whole-Body Rinse Data Worksheet for a 30-Minute Exercise SessionEVENTS AND CALCULATIONSPRE-EXERCISEPOST-EXERCISEDIFFERENCE1. Clock real time8:15 AM8:45 AM0.5 hours2. Athlete body weight (kg), semi-nude7068.91.13. Weight (kg) of clothing worn during weighinga0.880.980.14. Actual sweat volume (L) in 30 minutes1.2b5. Calculated sweat rate (L/hour)2.4c6. Plastic jug A weight (kg) when empty0.507. Plastic jug B weight (kg) when empty0.518. Distilled water weight in jug A (kg)3.949. Distilled water weight in jug B (kg)3.9610. Total rinse water volume (L) in jug A+jug B7.9011. Sodium concentration (mg/L rinse water)147d12. Potassium concentration (mg/L rinse water)18.8d13. Total sodium (mg) in 7.9 L of rinse watere1162f14. Total potassium (mg) in 7.9 L of rinse watere148f15. Sweat sodium concentration (mg/L sweat)968g16. Sweat potassium concentration (mg/L sweat)123g17. Total sodium lost (mg) in sweate1162h18. Total potassium lost (mg) in sweate148haSome sweat is absorbed and trapped in clothing.bThis is the sum of item 2 and item 3 in column 4.cThe measurement is the result of item 4÷item 1 difference.dThe laboratory electrolyte analyzer provides concentration in mEq; to convert to mg, multiply mEq sodium by 22.99 or multiply mEq potassium by 39.1.eAssuming that all sweat electrolytes are captured in the rinse water, towels, and clothing, items 13 and 17 or items 14 and 18 are identical.fThe measurement is the result of item 10×item 11 or item 10×item 12.gThe measurement is the result of item 13÷item 4 or item 14÷item 4.hThe measurement is the result of item 15×item 4 or item 16×item 4.Table 6 depicts a sample report that we presented to physicians, coaches, and athletes. It is different from Table 5 because items 2 through 6 were determined during an actual practice session, by accurately measuring water bottles and body weight. Items 7 through 10 were evaluated in our laboratory, using the whole-body rinse method presented in Tables 4 and 5. Items 11 through 15 focus on urinary sodium and potassium losses; whereas items 16 through 17 provide calculations of the combined electrolyte losses in sweat plus urine. Items 18 and 19 in Table 6 were determined from a record of 24-hour food and fluid intake (Table 2) and nutritional analysis of these food items, using dietary analysis software (described above). This report allows the athletic trainer to communicate useful fluid (items 2, 5, 6, and 11), electrolyte (items 7 through 10 and 12 through 17), and dietary information to physicians, coaches, and athletes. The keys to understanding exertional illnesses (eg, heat exhaustion or heat cramps) include comparing dietary intake to whole-body loss and determining the deficit or comparing the magnitude of dietary intake and whole-body loss to published data and determining whether either falls outside the reference (ie, expected) range.Table 6 Sample Summary Report of a Female Collegiate Basketball Player Prepared for Sports Medicine Physicians, Coaches, and AthletesaAthlete Name_______________________________________Date_________________ITEMMEASUREMENT1. On-court practice time2.75 hours2. Water intake (2.75 hours)b1.94 L3. Urine volume0 L4. Change of body weightc0.81 kgd (−1% body weight)5. Total sweat volume (2.75 hours)e3.19 L6. Sweat rate1.16 L/hour7. Sweat sodium concentrationf966 mg/L8. Total sweat sodium loss3082 mg9. Sweat potassium concentrationf66.5 mg/L10. Total sweat potassium loss212 mg11. 24-hour urine volume1.3 L12. Urine sodium concentrationf1012 mg/L13. Total urine sodium loss1315 mg14. Urine potassium concentrationf704 mg/L15. Total urine potassium loss915 mg16. Total sweat+urine sodium loss4397 mg/day17. Total sweat+urine potassium loss1127 mg/day18. 24-hour dietary intake of sodium (3-day average)3622 mg sodium/day19. 24-hour dietary intake of potassium (3-day average)1228 mg potassium/day20. 24-hour whole-body sodium balanceg−775 mg/day21. 24-hour whole-body potassium balanceg+101 mg/day22. 24-hour sweat+urine water loss4.49 LaThe values are calculated as described in Tables 1 and 5.bWater bottles provided and weighed by the athletic trainer.cThe measurement was the result of prebody weight−postbody weight.d1.0 kg = 1.0 L.eTotal sweat volume is equal to body weight loss+water intake−urine volume.fThe laboratory electrolyte analyzer provides concentration in mEq; to convert to mg, multiply mEq sodium by 22.99 or multiply mEq potassium by 39.1.gDietary intake−loss via sweat+urine.Reference ValuesTo check the validity of data, athletic trainers can compare their measurements and calculations to those published by other research and clinical teams. For example, Rehrer and Burke3 compiled data from 24 studies that described the sweat rates of athletes in various sports. Women experienced sweat losses ranging from 0.7 or 0.8 L/hour (basketball indoor training, 25°C, 43% relative humidity; soccer outdoor training, 9°C, 35% relative humidity; cycling 40 km at 30 km/hour speed, approximately 25°C) to 1.5 L/hour (10 km run at 12.8 km/hour speed, approximately 21°C). Men encountered higher sweat rates, ranging from 0.7 L/hour (soccer training, 9°C, 61% relative humidity; cycling 40 km at 30 km/hour speed, approximately 20°C) to 1.8 L/hour (10 km run at 14.6 km/hour speed, approximately 21°C; Australian football, 27°C, 52% relative humidity) or 2.1 L/hour (soccer training, 33°C, 40% relative humidity). Lemon et al14 observed 6 men during 60 minutes of treadmill running in a 23°C laboratory environment; they reported sweat rates of 0.46, 0.77, and 0.92 L/hour at exercise intensities of 42% (low), 55% (moderate), and 67% (high) of maximal aerobic power, respectively. As a further point of comparison, Stofan et al25 reported that American football linemen, wearing a full uniform and helmet, lost 3.4±1.5 L of sweat during a 2.3-hour training session in a mild environment (19°C to 26°C). Similarly, large football linemen in the U.S. National Football League exhibited a sweat rate of 2.39 L/hour.26 Among the highest sweat rates published in the literature, a female rower experienced a 2.3 L/hour loss during training,27 the sweat rate of a male tennis player was measured at 3.4 L/hour,28 and that of an elite distance runner was 3.7 L/hour.29Virtually all publications that report sweat electrolyte analyses with the whole-body rinse technique (Table 5) were conducted in laboratories. These studies present the following ranges: sweat sodium concentration, 8 to 64 mEq/L,30 13 to 47 mEq/L,31 and 40 to 60 mEq/L32; sweat chloride concentration, 13 to 38 mEq/L,31 30 to 50 mEq/L,32 and 32 to 70 mEq/L.10 The ratio of sodium to sweat potassium concentration, 2 to 5 mEq/L,31 3 to 7 mEq/L,10 and 4 to 5 mEq/L32; sweat magnesium concentration, 2 to 5 mEq/L,32 and 1 to 3 mEq/L 10; sweat calcium concentration, 4 to 9 mEq/L,32 and 1 to 6 mEq/L.10 To convert the unit mEq to mg, multiply the number of mEq by the following factors: sodium, 22.99; chloride, 35.45; potassium, 39.10; magnesium, 12.16; and calcium, 20.03.Daily urine volume (mL per 24 hours) is different for men and women, depending on body size. The range for men is 690 to 2690 mL per day (mean = 1360 mL per day). The range for women is 490 to 2260 mL per day (mean = 1130 mL per day) if they use no hormonal contraceptives, but 320 to 2290 mL per day (mean = 980 mL per d