KEY POINTS

• Athletes and others who begin exercise with a less than normal volume of body water are likely to experience adverse effects on cardiovascular function, temperature regulation, and exercise performance.
• Increasing body water stores above normal, well-hydrated levels by drinking fluids shortly before exercise is also likely to improve cardiovascular function and temperature regulation when it is impossible to ingest sufficient fluids during exercise.
• Under most circumstances, it is wise to drink at least 500 ml (16 oz) of fluid before sleeping on the night before exercise and at least another 500 ml first thing in the morning to help ensure a state of euhydration. Next, one should drink another 500-1000 ml about 1 h before and an additional 250-500 ml about 20 min before exercise to “top off’ fluid stores.
• The type of fluid consumed before exercise is important. Fluids containing carbohydrate (to supply energy) and small amounts of sodium chloride (to help maintain thirst and reduce urine formation) are likely to have more beneficial effects than plain water. The addition of glycerol to a pre-exercise hydration beverage usually is ineffective and can produce headaches and nausea.

INTRODUCTION
The maintenance of adequate stores of body water is extremely important for cardiovascular and thermoregulatory function and for exercise performance. Roughly 60% of the body mass is water—42 L (92 lb) in a person who weighs 70 kg (154 lb), and that water is critical to cardiovascular function and temperature regulation. Blood (5-6 L) is needed to deliver oxygen and nutrients to the working muscles and to transport heat from the muscles to the skin, where evaporation of the water in sweat helps dissipate heat to the environment. If fluids lost through sweating, urine production, and other avenues are not replaced by drinking, human beings will die from dehydration in a few days. In sport competitions, inadequate blood supply to the muscles or excessive heat storage due to insufficient heat dissipation can lead to poor performance and to heat illness.
When the body has normal stores of body water, it is said to be in a state of euhydration. Hypohydration is a state of reduced body fluids, and hyperhydration is a condition of greater than normal body water. The term dehydration refers to a more-or-less rapid reduction in body water as the body progresses from a euhydrated to a hypohydrated state. For example, a soccer player who is unable to replenish sweat loss in a match will gradually become dehydrated as body water is lost. The rate of sweat loss can be as great as 2 L/h or more in athletes who compete at high intensities in hot environments, and a sweat loss of 1 L/h is common in more temperate environments. In sports such as wrestling, judo, lightweight crew, and boxing, athletes often undergo acute dehydration of 5% of their body weights or more to become certified to compete at lower body weight classifications. Furthermore, many people commonly fail to replace their daily body fluid losses because of an inadequate thirst drive. Thus, many athletes undoubtedly begin their competitions in a hypohydrated condition, either because they have failed to replenish fluids lost in training or previous competitions or because they have purposely undergone dehydration. Therefore, it seems intuitively obvious that these athletes should drink copious amounts of fluids before exercise if they are to perform well and minimize the risk of heat illness.

Even if the body water stores are normal before exercise begins, it seems reasonable to think that increasing the body fluids, i.e., undergoing hyperhydration, before exercise might improve cardiovascular and thermoregulatory function, thereby leading to improved exercise performance. Accordingly, the purpose of this article is to address the following questions:

• Is pre-exercise fluid consumption effective in improving cardiovascular and thermoregulatory function and enhancing exercise performance when one is already in a hypohydrated condition? If so, is the effect diminished by replacement of sweat loss during the exercise?
• Is pre-exercise fluid consumption effective in improving cardiovascular and thermoregulatory function and enhancing exercise performance when one initiates the exercise in a euhydrated state? If so, is the effect diminished by fluid replenishment during the exercise?
• If pre-exercise drinking is advantageous, what is the optimal volume and formulation of fluid that should be consumed, and when should it be consumed?
• What are the potential adverse effects of drinking before exercise and how can these effects be minimized?

RESEARCH REVIEW
Adverse Effects Of Undertaking Exercise In A Dehydrated State
As reviewed by Sawka and Pandolf (1990), hypohydration of as little as 1-2% of body weight, i.e., 700 ml (24 oz) in a 70-kg person, can impair the performance of endurance exercise. Hypohydration is associated with a decrease in plasma volume, which can lead to a decrease in stroke volume of the heart. The heart rate then increases in an attempt to compensate for the decreased stroke volume, but this compensation is often inadequate, resulting in a fall in cardiac output. These adverse effects of dehydration on performance are less common in brief-duration, high-power activities such as weight lifting, are more severe as strenuous exercise is more prolonged, and are worse in hotter than in cooler environments.
Regardless of whether a reduction of body water occurs before exercise (Greenleaf & Castle, 1971; Nadel et al., 1980; Sawka et al., 1985) or during exercise (Montain & Coyle, 1992), the adverse effects of losing body water on cardiovascular function and temperature regulation become progressively greater with increasing decrements of body fluids. Furthermore, Sawka and Pandolf (1990) reviewed over 20 available reports on the effects of dehydration on various tests of athletic performance and concluded that dehydration adversely affects performance, with the effects being more severe with more extreme dehydration, with more prolonged exercise tests (e.g., strength performance is less likely to be harmed by dehydration than is prolonged cycling), and in hotter environments (Figure 1). They found no evidence that dehydration improved exercise performance of any kind.
Because dehydration before exercise is associated with increases in heart rate and body core temperature and decreases in blood volume, stroke volume, cardiac output, sweating, blood flow to the skin, and exercise performance, it makes sense that drinking extra fluids before exercise might minimize these adverse effects and perhaps improve exercise performance. In fact, in its position stand on exercise and fluid replacement, the American College of Sports Medicine (1996) recommends the ingestion of 400-600 ml of water 2 h before exercise to optimize body fluid levels and help delay or avoid detrimental effects of dehydration during exercise.

Hydration Between Sessions of Exercise
Wrestlers and others who purposely lose weight by dehydration, athletes who do not replace sweat lost in prior exercise bouts, forest-fire fighters who work strenuously on consecutive days, and military personnel engaged in sustained operations in the field may begin exercise in a hypohydrated state. Achievement of a state of euhydration, should be the goal in each of these circumstances in order to minimize strain on the cardiovascular and thermoregulatory systems, minimize the risk of heat illness, and improve exercise performance (Castellani et al., 1997; Melin et al., 1994). However, if time is short before the subsequent exercise, it may be nearly impossible to achieve a euhydrated state. Even drinking nearly 2 L of water 45 min before exercise may be effective in replacing only about 60% of the fluid lost previously by dehydration (Castellani et al., 1997).
When a large volume of fluid is consumed in an attempt to increase body water, much of it is rapidly lost in the urine. Therefore, Shirreffs et al. (1996) have shown that it is important to ingest a volume of fluid equivalent to 150% or more of the body weight lost through dehydration if one hopes to achieve a state close to euhydration. In addition, they showed that it is important to have adequate sodium in the rehydration beverage to attenuate fluid losses in urine. Similar conclusions about the physiological advantages of rehydration before exercise, but with more emphasis on the beverage’s osmotic properties—caused not only by sodium but also by any other electrolytes plus carbohydrates in the drink—were reached by Greenleaf et al. (1998) and by Dearborn et al. (1999)
The advantage to performance of rehydrating with carbohydrate-electrolyte beverages compared to water was shown by Fallowfield et al. (1995), whose subjects ran on a treadmill at 70% VO2max for 90 min or until fatigue. Immediately after the run, they ingested 1 L of a water placebo or a beverage containing electrolytes and 6.9% carbohydrate. A second liter of the same beverages was consumed 2 h later. This volume of fluid, which was 109-116% of the volume lost as sweat in the first run, was sufficient to restore 63-66% of the lost sweat. After 4 h of recovery from the first run, the subjects repeated the treadmill run to exhaustion. Partially rehydrating with the carbohydrate-electrolyte drink led to an improved endurance time (62 min) for the second run when compared to the water placebo trial (39.8 min). Similarly, in an early report Costill and Sparks (1973) found that a consuming a carbohydrate-electrolyte drink before treadmill running was better than water in partially restoring cardiovascular and thermoregulatory function that had deteriorated following acute dehydration prior to the exercise.
In summary, there is a high probability that when one begins to exercise in a hypohydrated state, physiological function and performance will be adversely affected, and partial restoration of body fluids before exercise begins will attenuate these adverse effects. Also, substantially more fluid must be consumed than is lost in prior dehydration if a state of euhydration is to be achieved. Finally, beverages containing sodium and carbohydrate are more effective in restoring body water than is plain water.

Hyperhydration Before Exercise: Effects on Cardiovascular Function and Temperature Regulation
Whether or not increasing the stores of body water from an already euhydrated condition positively affects physiology is controversial. One of the principal factors contributing to this controversy is the degree to which fluid is consumed during the exercise task. Positive effects of hyperhydration are less likely to be detected if sweat loss is fully replaced during the exercise. It is widely accepted that fluid replenishment during prolonged exercise is more critical than is hyperhydration before exercise, but it is less certain that there is any advantage to pre-exercise hyperhydration if sweat loss is fully replenished during exercise. However, it should be recognized that total replacement of sweat loss during exercise is rare among athletes, who typically replenish less than 50% of their sweat during exercise (Sawka & Pandolf, 1990).
There are at least ten published studies of physiological responses to hyperhydration 30 to 150 min before exercise that included a control trial in which presumably euhydrated subjects were not allowed to drink shortly before exercise. Either treadmill walking/running or cycle ergometry was employed as an exercise mode and exercise intensity varied from 40-75% VO2max.
No Fluid Replacement During Exercise. The literature shows that when little or no drinking was permitted during exercise, hyperhydration before exercise improved at least one measure of cardiovascular function or temperature regulation (Gisolfi & Copping, 1974; Grucza et al., 1987; Lyons et al., 1990; Nadel et al, 1980; Nielsen, 1974). Plain water (Lyons et al., 1990) or both plain water and a solution of water plus glycerol (which caused two of eight subjects to vomit; Latzka et al., 1998), were essentially ineffective in only two investigations. The subjects in the study of Latzka et al. (1998) walked on a treadmill in chemical protective clothing, but the heat stress was so severe, the subjects were unable to achieve a stable core temperature. In such a circumstance, hyperhydration will delay the onset of dehydration during the exercise somewhat, but it cannot overcome the adverse effects of progressive hyperthermia. On the other hand, in less stressful environments, hyperhydration with 1-2 L appears to be a good strategy if no fluid is to be consumed during exercise. Finally, if only a small volume of fluid, e.g., 500 ml, is consumed before exercise, it appears that any minor hyperhydration achieved will have no meaningful effect on cardiovascular function or temperature regulation, whether or not any fluid is provided during exercise (Candas et al., 1988).
Partial Fluid Replacement During Exercise. When partial rehydration at a rate of ~900 ml/h was accomplished during an exercise trial, one report (Moroff & Bass, 1965) showed a clear physiological advantage to pre-exercise hyperhydration with plain water, whereas one did not (Gisolfi & Copping, 1974). Both of these studies were performed in the heat, but the former employed relatively unfit subjects who walked on a treadmill, whereas Gisolfi and Copping studied fit subjects who ran on the treadmill at 75% VO2max. When hyperhydration was attempted with carbohydrate-electrolyte solutions that contained rather high concentrations of carbohydrates (9.7-19.4%), there was no advantage to drinking 768 ml within 105 min of the start of exercise (Greenleaf et al., 1998). Interestingly, in a trial in which glycerol was added to a 19.4% carbohydrate-electrolyte beverage, the glycerol seemed to cause a decrease in sweating and an increase in urine volume when compared to the drink without glycerol (Greenleaf et al., 1998). These results were opposite to those of Lyons et al. (1990), who did not replace fluids during exercise.
Complete Fluid Replacement During Exercise. In the only study in which all sweat loss was replaced during exercise, Latzka et al. (1997) were unable to detect any beneficial effect of hyperhydration with 1.8 L water or a solution of water plus glycerol in nine fit, heat-acclimated men who walked on a treadmill at 45% VO2max for 2 h in a hot environment (35 (C (95 (F), 60% rh. Once again, glycerol supplementation was not superior to plain water. Furthermore, the addition of glycerol to the water did not enhance the hyperhydration effect, and two of the subjects became nauseated in one of the glycerol trials, which had to be aborted and repeated on a subsequent day. This investigation clearly establishes the importance of replacing as much sweat loss as possible during exercise. Still, full rehydration during exercise is very unlikely in an athletic setting.

Hyperhydration Before Exercise: Effects on Exercise Performance
Strictly speaking, a true test of hyperhydration on exercise performance would compare a hyperhydration treatment with a no-fluid treatment before exercise, and all subjects would have all sweat loss replaced during exercise. In other words, the interpretation of the test results would not be confounded by the dehydration of subjects during exercise. Surprisingly, there are no readily accessible published studies of performance that meet both of these criteria.
Studies With a No-Fluid Control Group. In their study of severe heat stress in eight trained, heat-acclimated men, Latzka et al. (1998) did compare hyperhydration and no-fluid treatments, but sweat loss was not replaced during exercise, probably because the subjects wore chemical protective clothing that made drinking difficult. Heart rates, cardiac outputs, arterial pressures, sweating rates, rectal temperatures, skin temperatures, and mean body temperatures were little affected by hyperhydration with 1.84 L of water or water plus added glycerol. The exercise-heat strain was so severe that the subjects stopped because of impending heat illness or fatigue (10 of 24 individual tests). Thus, the endurance time in this test is not a realistic marker of performance in athletic competition. These subjects stopped walking on the treadmill after only 29.9 min (no fluid/euhydration), 33.8 min (glycerol-hyperhydration), and 31.3 min (water-hyperhydration). The authors concluded that under conditions of severe exercise-heat stress, hyperhydration with water or a glycerol solution provides no advantage over euhydration except that hyperhydration delays the onset of dehydration during exercise.
Water Versus Other Beverages. Numerous performance studies have been published that compared water and other beverages consumed before exercise. In most of these studies, provision of supplementary energy, not hyperhydration, was the principal variable of interest; thus, there was no control group in which no fluid was consumed before exercise. Furthermore, the assumption that all subjects were euhydrated before beginning the pre-exercise drinking regimen was usually not verified. Nevertheless, comparisons of water and other beverages ingested before exercise should provide some valid information pertaining to the optimal formulation of a pre-exercise beverage. Many pre-exercise feeding studies have been summarized previously by Sherman (1991) and most of the results demonstrate that beverages containing carbohydrate have a distinct advantage over plain water in improving energy supply and enhancing performance. The remaining studies discussed in this section have included beverages containing glycerol, a presumed hyperhydrating agent.
Glycerol as a Hyperhydrating Agent. In the last decade, many studies have tested the efficacy of glycerol as a hyperhydrating agent. When glycerol is ingested, it is distributed throughout the body water; if additional water is consumed, it can be temporarily retained in the body by the osmotic effect of the glycerol, thereby expanding total body water. The presumed advantage of glycerol solutions is that glycerol purportedly reduces the rate of elimination of water in the urine so that the extra body water is retained longer than if plain water is used as the rehydrating agent (Freund et al., 1995; Riedesel et al., 1987). In a relatively early study of glycerol as a hyperhydrating agent in an exercise setting, Lyons et al. (1990) provided untrained but presumably heat-acclimatized subjects (four men and two women) with about 2 L of water with or without glycerol (1 g/kg body weight) during a 2.5-h period before walking on a treadmill in the heat. Compared to plain water, the authors found that glycerol ingestion reduced urine production, improved body water stores at the start of exercise by about 700 ml, increased sweat production, and reduced core temperature without affecting heart rate. Only a small amount of fluid was provided during the exercise, so the subjects became dehydrated over the course of the experiment. Exercise performance was not measured.
Subsequently, neither Greenleaf et al. (1998) nor Latzka et al. (1997; 1998) could verify any advantage of including glycerol in a pre-exercise beverage. In fact, Greenleaf et al. (1998) reported that the addition of glycerol seemed to decrease sweating rate and increase urine formation and rectal temperature, and Latzka et al (1997) found that a solution of water plus glycerol did not significantly reduce urine output when compared to plain water. Neither of these two studies tested exercise performance.
A report by Montner et al. (1996) is one of the few that has claimed a positive effect on exercise performance of adding glycerol to a pre-exercise hyperhydration beverage; the exercise was completed in a temperate environment. The subjects were moderately-trained cyclists, and the cycle-ergometer performance tests were conducted at about 75% VO2max. In the 2 h before exercise, they drank about 1.8 L of flavored water or water with glycerol (1.2 g glycerol/kg body weight). There was no pre-exercise, no-fluid, euhydration control group. In one experiment, subjects received no fluid replacement during exercise; in a second, they replaced about 60% of the sweat loss during exercise with a 5% glucose beverage. Thus, in both experiments, the subjects underwent dehydration during the performance trials. Oddly, in the first experiment the water hyperhydration treatment increased body weight by only 70 g versus 800 g in the glycerol trial, whereas in the second experiment, the water trial increased body weight before exercise by 900 g versus 1000 g in the glycerol trial. Thus, urine output during the hyperhydration period in the first experiment was much lower in the glycerol trial, but there was no significant effect of glycerol on urine production in the second experiment. Heart rates were a few beats/min lower in the glycerol trials, but sweating rates, core temperatures, plasma volumes, and ratings of perceived exertion were not different between trials. Given the apparent absence of important physiological effects of the hyperhydration treatments, it is surprising that large differences in exercise duration were shown. In the experiment without fluid replacement during exercise, subjects hyperhydrated with water alone were exhausted in 77 min, whereas they lasted 94 min when glycerol was added to the water. In the fluid-replacement trial, the corresponding values were 99 and 123 min. Unfortunately, no data were provided about the reliability of the performance test in these subjects; remarkably, three subjects improved their performances by about 1 h in the glycerol versus water trials.
Eight highly-trained male triathletes were the subjects of a glycerol-versus-water hydration experiment reported by Inder et al. (1998). In the 4 h before exercise the subjects consumed about 1.25 L of fluid, with the last 200 ml being ingested 90 min before exercise. In one trial, glycerol (1 g/kg body weight) was added to 500 ml of water consumed 4 h before exercise. (It had been claimed by Riedesel et al. (1987) that glycerol could sustain hyperhydration for at least 4 h.) There were no significant differences between drink treatments on pre-exercise body weights, urine volumes, sweat volumes, or cycling performance times. Accordingly, no advantage for glycerol versus plain water was detected in this study; furthermore, three of the eight athletes experienced gastrointestinal discomfort in the glycerol trial.
In several investigations of the potential benefits of glycerol feedings, relatively small volumes of fluids were ingested before exercise, so it is doubtful that any meaningful hyperhydration occurred in these studies. Still, they can provide evidence of the relative efficacy of glycerol solutions versus other beverages. In one of these reports, Miller et al. (1983) examined glycerol (1 g/kg body weight) added to 300 ml of water versus plain water for their effects on exercise performance when the beverages were consumed 30 min before exercise. The 10 highly trained cyclists were instructed to complete as much cycle ergometer work as possible in 150 min. Heart rates, ratings of perceived exertion, total energy expenditure, and total work outputs were nearly identical in both trials, i.e., glycerol provided no advantage over plain water.
To compare the effects of pre-exercise 400-ml feedings of water with solutions of glycerol or glucose (1 g glycerol or glucose/kg body weight), Gleeson et al. (1986) required subjects to perform cycle ergometry at 73% VO2max to exhaustion in a cool environment. In the glucose trial, the subjects exercised for 109 min, which was significantly longer than during both water (96 min) and glycerol (86 min) trials. Moreover, all subjects experienced headaches in the glycerol trial. The same group conducted a follow-up study essentially identical to that reported by Gleeson et al. (1986) but with fasting for 36 h before drinking the pre-exercise beverages; Maughan and Gleeson (1988) recorded endurance times of 78 min for the water trial, 81 min for the water-plus-glycerol trial, and 92 min for the water-plus-glucose trial. However, although the pattern of changes was similar to that found in their previous study, in this experiment the difference between the water and water-plus-glucose treatments did not reach statistical significance.
Chronic Hyperhydration. In a study of untrained, heat-acclimatized, desert-dwelling men, Kristal-Boneh et al. (1988) compared the effects of doubling the subjects’ daily fluid intake for one week (with additional water or a saline solution) on cycle ergometry performance in a hot environmental chamber. Daily fluid intake was increased from 1981 ml/d to 4100 ml/d, and this extra fluid increased pre-exercise body mass by 700-900 ml and increased plasma volume by 7-9 %. The sweating rate was about 0.1 L/h greater in the saline trial than in the other two trials. Exercise performance times were 39 min for the control trial, 49 min for the water hyperhydration trial, and 51 min for the saline trial. Although performance for both hyperhydration trials was significantly better than for the control trial, interpretation of this result is confounded by the fact that the trials were performed in sequence, i.e., control, water, and saline. Thus, it is possible that the subjects learned to perform the exercise test better as a result of their first trial in the control condition.
Field Studies of Hyperhydration. It should be noted that nearly all studies of hyperhydration before exercise have been conducted in controlled laboratory environments. Only one was found in which hyperhydration was investigated in an applied sport or occupational labor setting. Using heat-acclimatized, elite male soccer players, Rico-Sanz et al. (1996) compared a required 6-d fluid intake of 4.6 L/d with a voluntary intake of 2.7 L/d on physiological variables during a soccer match and on soccer-specific performance tests following the match. Only voluntary fluid intake occurred 12 h before the match, which was conducted at 26.8° C (80° F), 81% rh. Urine output in the voluntary hydration condition was only about 1.1 L/d, but it is uncertain if this difference between fluid intake and output reflects a state of hyperhydration, euhydration, or hypohydration at the start of the soccer match. However, total body water was increased by 1.1 L when subjects were required to drink more fluids. Heart rates, sweating rates, and plasma volume changes during the match were similar for both treatments, but there appeared to be a slightly lower increase in core temperature with extra fluid consumption. The brief (<60 s) performance tests were unaffected by pre-match hydration treatments.
In summary, there is insufficient evidence to support the claim that pre-exercise hyperhydration from a euhydrated condition will improve exercise performance. There are simply too few studies in which hyperhydration was compared to a no-fluid condition before exercise. Still, it is clear that adding glycerol to a pre-exercise drink should be avoided and that beverages containing carbohydrate and sodium chloride are likely to be superior to plain water.

POTENTIAL ADVERSE EFFECTS OF HYPERHYDRATION
Many athletes can attest to the fact that drinking excessive volumes of fluid immediately prior to a sport competition can lead to gastrointestinal discomfort, including vomiting, if the fluid has not emptied sufficiently from the stomach. For most competitors, a volume of about 250-500 ml of water or a moderately concentrated (5-7%) carbohydrate-electrolyte beverage ingested 20 min before exercise can be tolerated. Nonetheless, athletes should practice hydration regimens during training before trying them in competitive situations. Supplementing beverages with glycerol (Gleeson et al., 1986; Inder et al., 1998; Latzka et al., 1997, 1998; Murray et al., 1991) can cause headaches and gastrointestinal problems; drinking beverages that contain high concentrations of carbohydrate (Maughan, 1991), especially fructose (Fruth & Gisolfi, 1983), can also result in gastrointestinal difficulties.
To the extent that hyperhydration causes an athlete to slow down or stop to urinate during competition, it could be disadvantageous. However, during strenuous exercise, e.g., >60% VO2max, very little urine is formed in any case (Wemple et al., 1997), so this should not be a problem. Excess urination could cause difficulty in ultraendurance events, but this problem should be counteracted by the advantages of hyperhydration in attenuating or preventing the onset of dehydration.
Finally, hyperhydration before brief weight-bearing events (e.g., 20-30 min of running, skating, roller-blading) conducted in temperate environments will not provide any advantage over euhydration. Such events are unlikely to cause more than 1% dehydration, and the addition of a 500-1000 g load of water by pre-exercise drinking will simply add to the energy cost of the event and could conceivably be detrimental to performance.

REFERENCES
American College of Sports Medicine (1996). Exercise and fluid replacement. Med. Sci. Sports Exerc. 28:i-vii.

Candas, V., J. P. Libert, G. Brandenberger, J.C. Sagot, and J.M. Kahn (1988). Thermal and circulatory responses during prolonged exercise at different levels of hydration. J. Physiol. Paris 83:11-18.

Castellani, J.W., C.M. Maresh, L.E. Armstrong, R.W. Kenefick, D. Riebe, M. Echegaray, D. Casa, and V.D. Castracane (1997). Intravenous vs. oral rehydration: effects on subsequent exercise-heat stress. J. Appl. Physiol. 82:799-806.

Costill, D.L., and K.E. Sparks (1973). Rapid fluid replacement following thermal dehydration. J. Appl. Physiol. 34:299-303.

Dearborn, A.S., A.C. Ertl, C.G.R. Jackson, P.R. Barnes, J.L. Breckler, and G.E. Greenleaf (1999). Effect of glucose-water ingestion on exercise thermoregulation in men dehydrated after water immersion. Aviat. Space. Environ. Med. 70:35-41.

Fallowfield J.L., C. Williams, and R. Singh (1995). The influence of ingesting a carbohydrate-electrolyte beverage during 4 hours of recovery on subsequent endurance capacity. Int. J. Sport Nutr. 5:285-299.

Freund, B.J., S.J. Montain, A.J. Young, M.N. Sawka, J.P. DeLuca, K.B. Pandolf, and C.R. Valeri (1995). Glycerol hyperhydration: hormonal, renal and vascular fluid responses. J. Appl. Physiol. 79:2069-2077.

Fruth, J.M., and C.V. Gisolfi (1983). Effects of carbohydrate consumption on endurance performance: fructose versus glucose. In: E.L. Fox (ed.) Nutrient Utilization During Exercise. Columbus, OH: Ross Laboratories, pp. 68-77.

Gleeson, M., R.J. Maughan, and P.L. Greenhaff (1986). Comparison of the effects of pre-exercise feeding of glucose, glycerol and placebo on endurance and fuel homeostasis in man. Eur. J. Appl. Physiol. 55:645-653.

Greenleaf, J.E., and B.L. Castle (1971). Exercise temperature regulation in man during hypohydration and hyperhydration. J. Appl. Physiol. 30:847-853.

Greenleaf, J.E., R. Looft-Wilson, J. L. Wisherd, C.G.R. Jackson, P.P. Fung, A.C. Ertl, P.R. Barnes, C.D. Jensen, and J.H. Whittam (1998). Hypervolemia in men from fluid ingestion at rest and during exercise. Aviat. Space Environ. Med. 69:374-386.

Grucza, R. M. Szczypaczewska, and S. Kozlowski (1987). Thermoregulation in hyperhydrated men during physical exercise. Eur. J. Appl. Physiol. 56:603-607.

Kristal-Boneh, E., J.G. Glusman, C. Chaemovitz, and Y. Cassuto (1988). Improved thermoregulation caused by forced water intake in human desert dwellers. Eur. J. Appl. Physiol. 57:220-224.

Inder, W.J., M.P. Swanney, R.A. Donald, T.C.R. Prickett, and J. Hellemans (1998). The effect of glycerol and desmopressin on exercise performance and hydration in triathletes. Med. Sci. Sports Exerc. 30:1263-1269.

Latzka, W.A., M.N. Sawka, S.J. Montain, G.S. Skrinar, R.A. Fielding, R.P. Matott, and K.B. Pandolf (1997). Hyperhydration: theromoregulatory effects during compensable exercise-heat stress. J. Appl. Physiol. 83:860-866.

Latzka, W.A., M.N. Sawka, S.J. Montain, G.S. Skrinar, R.A. Fielding, R.P. Matott, and K.B. Pandolf (1998). Hyperhydration: tolerance and cardiovascular effects during uncompensable exercise-heat stress. J. Appl. Physiol. 84:1858-1864.

Lyons, T.P., M.L. Riedesel, L.E. Meuli, and T.W. Chick (1990). Effects of glycerol-induced hyperhydration prior to exercise in the heat on sweating and core temperature. Med. Sci. Sports Exerc. 22:477-483.

Maughan, R.J. (1991). Carbohydrate-electrolyte solutions during prolonged exercise. In: D.R. Lamb and M. Williams (eds.) Perspectives in Exercise Science and Sports Medicine, Vol. 4, Ergogenics: Enhancement of Performance in Exercise and Sport. Carmel, IN: Benchmark Press, pp. 35-76.

Maughan, R.J., and M. Gleeson (1988). Influence of a 36 h fast followed by refeeding with glucose, glycerol or placebo on metabolism and performance during prolonged exercise in man. Eur. J. Appl. Physiol. 57:570-576.

Melin, B., M. Cure, C. Jimenez, N. Koulmann, G. Savourey, and J. Bittel (1994). Effect of ingestion pattern on rehydration and exercise performance subsequent to passive dehydration. Eur. J. Appl. Physiol. 68:281-284.

Miller, J.M., E.F. Coyle, W.M. Sherman, J.M. Hagberg, D.L. Costill, W.J. Fink, S.E. Terblanche, and J.O. Holloszy (1983). Effect of glycerol feeding on endurance and metabolism during prolonged exercise in man. Med. Sci. Sports Exerc. 15:237-242.

Montain, S.J., and E.F. Coyle (1992). Influence of graded dehydration on hyperthermia and cardiovascular drift during exercise. J. Appl. Physiol. 73:1340-1350.

Montner, P., D.M. Stark, M.L. Riedesel, G. Murata, R. Robergs, M. Timms, and T.W. Chick (1996). Pre-exercise glycerol hydration improves cycling endurance time. Int. J. Sports Med. 17:27-33.

Moroff, S.V., and D.E. Bass (1965). Effects of overhydration on man’s physiological responses to work in the heat. J. Appl. Physiol. 20:267-270.

Murray, R., D.E. Eddy, G.L. Paul, J.G. Seifert, and G.A. Halaby (1991). Physiological response to glycerol ingestion during exercise. J. Appl. Physiol. 71:144-149.

Nadel, E.R., S.M. Fortney, and C.B. Wenger (1980). Effect of hydration state on circulatory and thermal regulations. J. Appl. Physiol. 49:715-721.

Nielsen, B. (1974). Effect of changes in plasma Na+ and Ca++ ion concentration on body temperature during exercise. Acta Physiol. Scand. 91:123-129.

Rico-Sanz J., W.R. Frontera, M.A. Rivera, A. Rivera-Brown, P.A. Molé, and C.N. Meredith (1996). Effects of hyperhydration on total body water, temperature regulation and performance of elite young soccer players in a warm climate. Int. J. Sports Med. 17:85-91.

Riedesel, M.L., D.Y. Allen, G.T. Peake, and K. Al-Qattan (1987). Hyperhydration with glycerol solutions. J. Appl. Physiol. 63:2262-2268.

Sawka, M.N., and K.B. Pandolf (1990). Effects of body water loss on physiological function and exercise performance. In: C.V. Gisolfi and D.R. Lamb (eds.) Perspectives in Exercise Science and Sports Medicine, Vol. 3, Fluid Homeostasis During Exercise. Carmel, IN: Benchmark Press, pp. 1-30.

Sawka, M.N., A.J. Young, R.P. Francesconi, S.R. Muza, and K.B. Pandolf (1985). Thermoregulatory and blood responses during exercise at graded hypohydration levels. J. Appl. Physiol. 59:1394-1401.

Sherman, W.M. (1991). Carbohydrate feedings before and after exercise. In: D.R. Lamb and M. Williams (eds.) Perspectives in Exercise Science and Sports Medicine, Vol. 4, Ergogenics: Enhancement of Performance in Exercise and Sport. Carmel, IN: Benchmark Press, pp. 1-34.

Shirreffs, S.M., A.J. Taylor, J.B. Leiper, and R.J. Maughan (1996). Post-exercise rehydration in man: effects of volume consumed and drink sodium content. Med. Sci. Sports Exerc. 28:1260-1271.

Wemple, R.D., D.R. Lamb, and K.H. McKeever (1997). Caffeine vs caffeine-free sports drinks: Effects on urine production at rest and during prolonged exercise. Int. J. Sports Med. 18:40-46