Athletes have many factors to consider when it comes to improving performance. An element that is commonly overlooked is hydration. Fueling the body involves not only choosing nutritious food options, but also consuming the required fluids and nutrients to remain hydrated. With numerous hydration options available to athletes, it is requisite to examine the existing research and recommendations to promote proper hydration for athletic participation.
The importance of attaining and maintaining an adequate hydration status cannot be overstated. The human body weight is comprised of approximately 60 percent water, and water takes part in a number of chemical reactions within the cells of the body. Water also serves as a medium for allowing nutrients to pass from the blood to the cells, and for metabolic products to transfer from the cell to the blood (Gropper et al. 2008). Water also plays an important role in thermoregulation and maintaining the body’s temperature. In addition to these roles, water is necessary for most other physiological processes (Dunford and Doyle 2012). As physical activity leads to additional physiological stress, hydration is an essential consideration for athletes and individuals participating in physical activity.
Because the body functions best when homeostatic conditions are maintained, the goal in regard to hydration status is euhydration. Euhydration refers to a state in which there is a sufficient volume of water to meet the physiological requirements of the body (Dunford and Doyle 2012). Deviations from the euhydrated condition include hypohydration and hyperhydration. Hyperhydration is a condition in which there is increased body water content, and hypohydration refers to a decreased body water content (Sawka et al. 2001). Both of these conditions can lead to detrimental symptoms, particularly in relation to exercise and sport performance. These conditions will be discussed next.
Hypohydration occurs by the process of decreasing total body water, or dehydration. Dehydration leads to several unfavorable symptoms due to the increase it causes in physiological strain. Measures of physiological change include heart rate, core temperature, and perceived exertion responses. These measures have been demonstrated to be increased during exercise or heat stress in the dehydrated condition (Sawka et al. 2001). Another effect of dehydration, particularly when the level of dehydration is greater than two percent, is a decrease in both cognitive performance and aerobic exercise performance (Cheuvront et al. 2003). The greater the extent of the body water deficit, or the greater the dehydration level, the greater the impairment in aerobic exercise performance and increased physiological strain (Montain et al. 1992, Institute of Medicine 1994). Thus, the importance of avoiding the dehydrated condition is great, particularly in the case of athletes, as dehydration impairs body functions and athletic performance.
Hyperhydration refers to increased body water content, and has sometimes been touted as a method for improving exercise performance. The hyperhydrated state is not accomplished by merely overdrinking, but combines overdrinking with an agent that binds water in the body, such as glycerol or a hypertonic drink. The reason for this is that overdrinking alone prior to exercise will likely lead to increased urine production, and will not achieve a hyperhydrated condition (American College of Sports Medicine et al. 2007). Another concern in this realm is that during exercise, urine production is less and sweat rate is increased, leading to a consequently heightened risk of hyponatremia. Hyponatremia is a condition in which plasma sodium levels are decreased to a level of 130 mmol/L or less, either by increased fluid diluting the plasma, or inadequate sodium (Rehrer 2001). Symptoms of hyponatremia include headache, fatigue, confusion, vomiting, wheezing, and swollen feet or hands (American College of Sports Medicine et al. 2007). In more severe cases, seizures, coma, respiratory arrest, and even death are possible (Zambraski 2005). As has been described, there are a number of potential negative effects of hyperhydration, and research has demonstrated limited benefit to hyperhydrating. Any performance benefits observed may be associated with the delay in dehydration onset, however there are no thermoregulatory advantages of hyperhydrating (American College of Sports Medicine et al. 2007). Thus, it is generally not recommended to aim for hyperhydration, but rather athletes are encouraged to strive for a euhydrated state.
As is demonstrated by the previous descriptions, excessive deviations from a condition of fluid balance in the body can have detrimental effects on health and athletic performance. Thus, a key concept to examine is the source of fluid losses from the body, as well as various means of fluid gains or fluid replacement to the body. The primary routes of fluid losses include respiratory, renal, gastrointestinal, and sweat. Respiratory and gastrointestinal losses tend to be quite low, while urine fluid losses are regulated by the kidneys to aid in maintaining water balance. Fluid losses via sweat vary considerably based on factors such as individual sweat rate, environmental temperature and conditions, intensity and duration of physical activity, clothing, and equipment. Individual sweat rates also vary based upon characteristics such as weight, heat acclimatization, metabolic efficiency, and genetic factors (American College of Sports Medicine et al. 2007).
Due to the increased fluid losses incurred during participation in physical activity, and the importance of maintaining fluid balance, specific recommendations for replacing fluid losses have been set in place by the American College of Sports Medicine. These recommendations include guidelines and goals for hydration before, during, and after exercise. The recommendations are summarized in Table 1. Note that these are general guidelines that should be used as a starting point for developing an individualized hydration plan for each athlete.
Table 1. Fluid Replacement Recommendations.8
|Start physical activity euhydrated, with normal plasma electrolyte levels||4 hr prior: Slowly drink fluids (5-7 mL/kg)2 hr prior: If do not produce urine, or urine is dark- drink more fluid (3-5 mL/kg)||Consuming sodium (either in the beverage or from food) will help increase thirst and assist in fluid retention|
|Prevent greater than 2% body weight loss, excessive dehydration, and extreme alterations in electrolyte balance||Individualized fluid replacement program based on duration, intensity, environmental conditions, opportunities to drink, and individual sweat rate.||<60 minutes: Water and perhaps electrolytes should meet needs>60 minutes: 30-60 grams/hour carbohydrate (from food or fluid). Caffeine may help sustain performance|
|Replenish all fluid and electrolyte losses||If recovery time not limited: Normal meals, snacks, and water should sufficeLimited recovery time or excessive dehydration: 1.5 L fluid for each kilogram body weight lost (consume over time rather than large bolus)||Sodium from food or beverage to replace losses. Carbohydrates and protein from food or beverage to replenish glycogen stores and promote muscle anabolism|
Numerous beverages and sports drinks are promoted as being beneficial or necessary for fluid replacement in relation to athletic participation. The recommendations in Table 1 summarize the fluid and nutrient requirements before, during, and after exercise; however there are many potential routes that can be taken to accomplish an appropriate hydration status. Beverages and products often touted in association with exercise and fluid replacement include water, sports beverages (Gatorade, Powerade, etc.), protein drinks, milk, chocolate milk, and caffeinated beverages. The research relating to each of these will be detailed next.
For exercise in moderate environmental conditions, water should be sufficient for meeting hydration needs for activities lasting less than one or two hours. For activities of greater duration or more extreme environmental conditions, electrolyte (particularly sodium) and carbohydrate replacement are in order (Dunford and Doyle 2012). These needs can be met by a variety of methods, such as foods, gels, or beverages. If a sports beverage is used to help meet these needs, the Institute of Medicine advises that the composition of the beverage should be as follows: 20-30 meq/L sodium, 2-5 meq/L potassium, and about 5-10% carbohydrate (Institute of Medicine 1994). The role of the sodium and potassium is to replace electrolytes lost in sweat. Sodium also plays a role in increasing thirst, which aids in fluid replacement. The primary role of carbohydrate is the provision of energy, and when carbohydrate containing beverages are consumed during exercise, it is recommended that they contain 6-8% carbohydrate (American College of Sports Medicine et al. 2007).
Milk and chocolate milk have been promoted as potentially effective recovery beverages for post-exercise use (Roy 2008). Chocolate milk is the more commonly researched beverage due to the increased flavor desirability, particularly following exercise. Chocolate milk contains carbohydrate in similar amounts to many sports beverages, and also contains the proteins casein and whey. Protein in the recovery period may assist with muscle anabolism, and has been recommended to be consumed following exercise, either in food or beverage form (van Loon 2000). Chocolate milk also assists with hydration and fluid replacement following exercise, and provides the electrolytes sodium and potassium, which can aid in replacing electrolytes lost in sweat (spaccarotella and Andzel 2011). Due to potential intolerance immediately before or during exercise, it appears the composition of chocolate milk is best suited for the post-exercise recovery period.
As mentioned previously, it is recommended that protein be consumed in addition to carbohydrates following exercise. Thus, numerous protein beverages have been promoted as recovery beverages for the post-exercise period. Products such as the Gatorade G Series Pro Protein Recovery Shake, High-protein Boost, Endurox R4 Powder, and several others are high-protein beverage options commonly promoted for post-exercise use (Dunford and Doyle 2012). Each of these products varies in their precise content, but all provide both protein and carbohydrate, which seem to have a synergistic effect when used together in recovery beverages. Potential benefits include rehydration, replenishing glycogen stores, and protein turnover, all of which may be beneficial for subsequent athletic performance (Goh et al. 2012). The exact macronutrient distribution does not seem as influential on the effects of the beverage, provided the beverages compared are isocaloric and contain both carbohydrate and protein (Goh et al. 2012).
Caffeinated beverages have also been used for their stimulatory effects to aid in athletic performance. A common concern associated with caffeine and hydration is the potential diuretic effect of caffeine. A review of the existing research on caffeine and sports performance summarized the research in this area and concluded that caffeine, when taken in appropriate and not excessive amounts, does not impair overall fluid status, and athletes may choose to use caffeine prior or perhaps during exercise for its potentially beneficial performance effects (Burke 2008). In the realm of recovery beverages however, there is some evidence to suggest that caffeine consumption can increase urine output and therefore negatively affect rehydration status (Gonzalez-Alonso et al. 1992).
In sum, hydration is a critical element affecting athletic performance, as well as overall health. Excessive deviations from the euhydrated state, either in the direction of hypohydration or hyperhydration can potentially lead to detrimental effects. Recommendations have been established for hydration before, during, and after exercise, and these should be used as a guide for developing an individualized hydration plan for each athlete. Numerous beverages and products are available for assisting with meeting the athlete’s hydration needs, and several have been reviewed here. Regardless of the products selected for the means of hydration, athletes should make maintaining appropriate hydration levels a priority in order to maximize their health and athletic performance.
By: Jamie Saunders, University of Utah
Jamie Saunders has always been interested in the area of nutrition and wellness. Saunders graduated from Southern Utah University with a Bachelor’s degree in Human Nutrition, and from the University of Utah’s Coordinated Master’s Program in Dietetics, with an emphasis in Sports Dietetics. She is a Registered Dietitian and currently works as the Outpatient Dietitian for the University Health Care’s South Jordan Health Center.
American College of Sports Medicine, Sawka M. N., L. M. Burke, E. R. Eichner, R. J. Maughan, S. J. Montain, and N. S. Stachenfeld. 2007. American college of sports medicine position stand: Exercise and fluid replacement. Medicine and Science in Sports and Exercise 39: 377-390.
Burke, L. M. 2008. Caffeine and sports performance. Appl Physiol Nutr Metab 33: 1319-1334.
Cheuvront, S. N., E. M. Haymes, and M. N. Sawka. 2003. Fluid balance and endurance exercise performance. Curr Sports Med Rep 2: 202-208.
Dunford, M. and J. A. Doyle. 2012. Nutrition for Sport and Exercise, 2nd edition. Wadsworth, Belmont, California, USA.
Goh, Q., C. A. Boop, N. D. Luden, A. G. Smith, C. J. Womack, and M. J. Saunders. 2012. Recovery from cycling exercise: Effects of carbohydrate and protein beverages. Nutrients 4: 568-584.
Gonzalez-Alonso, J., C. L. Heaps, and E. F. Coyle. 1992. Rehydration after exercise with common beverages and water. Int J Sports Med 13: 399-406.
Gropper, S. S., J. L. Smith, and J. L. Groff. 2008. Advanced Nutrition and Human Metabolism, 5th Edition. Thompson Wadsworth, Belmont, California, USA.
Institute of Medicine. 1994. Fluid replacement and heat stress.
Institute of Medicine. 1994. Fluid replacement and heat stress.
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.
Rehrer, N. J. 2001. Fluid and electrolyte balance in ultra-endurance sport. Sports Medicine 31: 701-715.
Roy, B. 2008. Milk: The new sports drink? A review. J Int Soc Sports Nutr 5.
Sawka, M. N. and E. F. Coyle. 1999. Influence of body water and blood volume on thermoregulation and exercise performance in the heat. Exercise and Sports Science 27: 167-218.
Sawka, M. N., S. J. Montain, and W. A. Latzka. 2001. Hydration effects on thermoregulation and performance in the heat. Comparative Biochemistry and Physiology Part A 128: 679-690.
Spaccarotella, K. J. and W. D. Andzel. 2011. The effects of low fat chocolate milk on postexercise recovery in collegiate athletes. The Journal of Strength and Conditioning Research 25: 3456-3460.
Van Loon, L., M. Kruijshoop, H. Verhagen, W. Saris, A. Wagenmakers. 2000. Ingestion of protein hydrosylate and amino acid-carbohydrate mixtures increases postexercise plasma insulin responses in men. J Nutr 130: 2508-2513.
Zambraski, E. J. 2005. The renal system. Pages 521-532 in C. M. Tipton, M. N. Sawka, C. A. Tate, and R. L. Terjung. American college of sports medicine: Advanced exercise physiology. Lippincott, Williams and Wilkins, Baltimore, Maryland, USA.
Articles by Jamie Saunders.