Hot or Cold: How Temperature Affects Sports (Technical)

Fig1Crespo

Fig. 1. Organization of vertebrate skeletal muscles (From ref. 1).

Like other tissues, skeletal muscle tissue consists of cells (muscle fibers). The size of these cells ranges from 5 to 100 μm in diameter, and they are up to several centimeters long (Randall et al. 2002). Their parallel arrangement allows for the fibers in a muscle to pull together in a specific direction to exert force. This muscle force is achieved by parallel subunits inside muscle fibers (myofibrils) which in turn consist of sarcomeres, the longitudinally repeated functional units of muscle. The importance of the sarcomere is that its arrangement helps us understand the molecular basis for muscle function. Each sarcomere contains two proteins arranged in a particular geometric pattern, namely actin and myosin, and the interaction between these two proteins explains how a muscle is able to contract (current mechanism known as the sliding-filament theory; see Fig. 1). This contraction requires energy and it is obtained from glucose and lipids that are in turn transformed into adenosine triphosphate (ATP), the energy currency of the cell. Both ATP production (see how chemistry fuels running) and hydrolysis release heat, and it is this heat that contributes to the body’s temperature.

ATP is necessary for muscle work because of two major processes that are energy-dependent. The first process has to do with the cycling of attachment and detachment of myosin cross-bridges to actin, which is mediated by an enzyme called actomyosin ATPase. Without ATP, the myosin heads cannot detach from the actin filament for a new cycle. The second process involves the pumping of Ca2+ (calcium ions) back into the sarcoplasmic reticulum of the muscle fiber by an enzyme called sarcoplamic reticulum ATPase. Free Ca2+ induces muscle contraction by binding to troponin (a muscle protein) which changes the configuration of another protein, tropomyosin, allowing for the myosin heads to access myosin binding sites on the actin filament. During strenuous exercise, muscle energy consumption can surpass that of a resting muscle 100-fold and achieve rates of energy consumption greater than 1.5 kg ATP per minute of activity (McIntosh et al. 2006). If we reflect on the facts that skeletal muscle constitutes about 40% of our total body weight and that muscle contraction is only ~25% efficient, we immediately realize that a lot of expended energy must be released as heat (Sawka and Young 2006). In fact, about 3 joules of energy are released as heat for every joule of chemical energy that is converted into mechanical work4. This extra heat produced during activity is added to the heat generated by our basal metabolism and increases body temperature (2-4°C increase in core temperature is common after strenuous exercise; Randall et al. 2002). Excessively high body temperatures threaten enzymatic activity and thus, avoiding excessive heat storage is of paramount importance when exercising.

Athletes performing different types of exercise rely on the strength of specific muscles. This strength depends on muscle morphology and architecture and myosin isoform composition (see genetic aspects in How Much do Genes Affect Your Athletic Potential?). The phenotypic profiles of muscle fibers cannot only be affected by neuromuscular activity, hormones and aging, but also by the athletic training a person undergoes. Broadly speaking we can define two types of exercise: high-resistance exercise and endurance exercise. The first one results in greater muscle mass and strength by involving some form of high-intensity weightlifting for a short duration (8-12 repetitions) two to three days a week. In contrast, muscular endurance is achieved by low-intensity exercise regimes during 30-60 minutes on an almost daily basis (McCarthy and Esser 2012). Thus, athletes usually bear this in mind when exercising. But, irrespective of the type of exercise, we always feel an increase in body temperature associated with activity. How is it then that our body copes with the excess heat generated during sports or other physically-demanding activities?

Metabolic heat generated by active muscles is transferred to the bloodstream and then to the body core. Whether this heat increases our body temperature or not will depend on different environmental variables, particularly ambient temperature. For example, in cold climates we can suffer from heat loss, which will lower our body temperature and cause our metabolic rate to slow down. If body heat generation cannot keep up with the dissipation of heat to the environment, our body temperature will eventually decrease to dangerous low levels, and may even end in death. The opposite can happen in hot climates. If we cannot dissipate enough heat, we accumulate heat causing our metabolic rate to increase (which generates even more heat) and leads to overheating. This can also end in death. Fortunately, since most of us do not experience extreme weather on a regular basis, our bodies are able to handle this interplay between internal and external temperature in different ways.

Fig2Crespo

Fig. 2. Avenues of heat exchange for an athlete performing exercise in air (From ref. 3).

Humans can be classified as endotherms, which means that our own energy metabolism produces the heat that determines our body temperature. Endothermy allows us to also be homeotherms, because our body temperature is relatively constant and independent of ambient temperature (core body temperature in humans is about 37°C). Thermoregulation in homeotherms occurs through two collaborative processes, namely behavioral and physiological temperature regulation. The first consists of conscious and unconscious behavioral changes influencing heat storage, like modifying activity levels, seeking shade or sunlight, reducing surface area for heat exchange and even changing clothes. Physiological temperature regulation encompasses responses that are unconscious. Our bodies can control the rate of metabolic heat we produce (e.g., by shivering), as well as heat loss by sweating and blood flow distribution (e.g., cutaneous vasodilatation and vasoconstriction). This last mechanism facilitates heat transfer from the skin to the surrounding air or water and is highly dependent on environmental temperature, air humidity, air or water motion, radiation and clothing (Gavin 2003). Biophysically speaking, this heat transfer can be achieved by non-evaporative avenues (conduction, convection, and radiation) called “dry heat exchange” or via evaporative cooling (see Fig. 2). Evaporation is induced by sweating (it can begin after just 2 seconds of engaging in heavy physical work; Randall et al. 2002) when we exercise, and it is the only known mechanism for dissipating heat against a thermal gradient. For example, on a hot day in the desert, our exocrine glands can produce over 12 liters of sweat, effectively cooling our bodies to tolerable temperatures (Jablonski 2006). However, the effectiveness of sweating is low in very humid environments, making it extremely difficult to get rid of excess heat.

Usually our motivation to win or complete a certain task leads us to ignore effective thermoregulatory strategies, and this usually causes lower performance, injuries and/or heat related illnesses. On top of thermoregulatory strategies during activity, there are also several pre- and post-exercise strategies that aid us in performing better and avoiding injuries (Noonan et al. 2012, Ross et al. 2013, Very et al. 2013). For example, warming up and stretching prior to exercising has been shown to deter muscular injuries. In general, warm-up is defined as activities that make us sweat mildly but do not fatigue us, with the purpose of improving muscle dynamics and preparing us for more stringent demands of subsequent exercise. There are two types of warm-up, active and passive. Active warm-up is the most common type of warm-up for both amateur and professional athletes and involves some kind of non-specific body movement (e.g., jogging, cycling or callisthenics). In contrast, passive warm-up results from the increase of muscle temperature or core body temperature by external means, like heating pads, vibrational devices (Cochran 2013), hot showers, saunas, etc. Stretching, as part of warm-up, is recommended within 15 minutes prior to activity to obtain the best results (Woods et al. 2007). Post-exercise strategies are more commonly used by professional athletes after very demanding activities that may lead to muscular fatigue and injuries. These usually involve some kind of muscle cooling technique (DeGroot 2013). Finally, every athlete knows that good nutrition (see Putting Protein in Its Place)  and hydration (see Hydration and Sports Beverages) are essential for safe and effective exercising. In particular, hydration is strongly linked to thermoregulation. Although sweating allows us to get rid of excessive heat efficiently, it also presents the risk of dehydration, if not enough water is consumed.

Regular physical activity enhances and maintains health, but we need to take special considerations (like the ones we saw above) when engaging in sports or other vigorous physical activities. This is particularly true in hot and humid weather, which cannot only lead to poor athletic performance but also to heat stress and even death. Besides inadequate hydration, excessive heat retention can be caused by physical exertion, insufficient recovery time in-between activities, and inappropriate clothing. Heat stress can come in the form of heat cramps (painful cramps in abdominal muscles and muscles of the extremities), heat syncopes (weakness, fatigue and fainting), heat exhaustion due to water and/or salt depletion (causing exhaustion, muscle cramps, nausea, vomiting, dizziness, elevated temperature, weakness headaches, etc.), and heat strokes due to failing thermoregulation (causing nausea, seizures, disorientation, and in severe cases unconsciousness or comatosis). There are also serious risks associated with exercising in cold weather (Castellani and Young 2012). For example, sprains and strains are common, and in very cold-weather, frostbite and hypothermia (core body temperature dropping below that required for normal metabolism) can present a challenge to unprepared athletes.

All of these health related issues can be avoided by learning on the one hand, about the different strategies that our bodies use to control body temperature and, on the other hand, ways of helping our bodies to thermoregulate when external conditions are too harsh. We should always reduce the risks of heat-related illness, by hydrating and eating appropriately, adjusting exercise activity levels according to our current fitness status, having adequate recovery periods between bouts of exercises, and realizing when it is better to cancel athletics and stay home (Heat-Related Illnesses 2014).

By Jose G. Crespo
Jose G. Crespo is a researcher in the field of animal physiology and behavior with an emphasis on insect thermoregulation and neuroscience. He is currently a Postdoctoral researcher at the University of Utah – Department of Biology.

References

Castellani, J. W., & A. J. Young. 2012. Health and performance challenges during sports training and competition in cold weather. British Journal of Sports Medicine. 46: 1-5.

Cochrane, D. 2013. The sports performance application of vibration exercise for warm-up, flexibility and sprint speed. European Journal of Sport Science. 13: 256-271.

DeGroot, D. W., R. P. Gallimore, S. M. Thompson, & R. W. Kenefick. 2013. Extremity cooling for heat stress mitigation in military and occupational settings. Journal of Thermal Biology.   38: 305-310.

Gavin, T, P. 2003. Clothing and thermoregulation during exercise. Sports Medicine. 33: 941-947.

Heat-Related Illnesses (Heat Cramps, Heat Exhaustion, Heat Stroke). University of Utah Health Care, n.d. Web. 1 April 2014. Available at: https://healthcare.utah.edu/healthlibrary/centers/ortho/doc.php?type=90&id=P01611

Jablonski, N.G. 2006. Sweat. In Skin: A Natural History, pp. 39-55. Berkley: University of California Press.

MacIntosh, B. R., P. F. Gardiner, & A. J. McComas. 2006. Muscle Metabolism. In Skeletal Muscle: Form and Function (2nd Ed.), pp. 209-223. Chelsea, MI: Sheridan Books.

McCarthy, J. J., & K. A. Esser. 2012. Skeletal Muscle Adaptation to Exercise. In Muscle: Fundamental Biology and Mechanisms of Disease (ed. J.A. Hill & E.N. Olson), pp. 911-        920. San Diego: Elsevier.

Noonan, B., R. W. Bancroft, J. S. Dines, & A. Bedi. 2012. Heat- and Cold-induced Injuries in Athletes: Evaluation and Management. Journal of the American Academy of Orthopaedic Surgeons. 20: 744-754.

Randall, D., W. Burggren, & K. French. 2002. Energetic Costs of Meeting Environmental Challenges. In Animal physiology: Mechanisms and adaptations (5th Ed.), pp. 699-736. New York: W. H. Freeman.

Randall, D., W. Burggren, & K. French. 2002. Muscles and Animal Movement. In Animal physiology: Mechanisms and adaptations (5th Ed.), pp. 361-424. New York: W. H. Freeman.

Ross, M., C. Abbiss, P. Laursen, D. Martin, & L. Burke. 2013. Precooling methods and their effects on athletic performance: a systematic review and practical applications. Sports Medicine. 43: 207-225.

Sawka, M. N., & A. J. Young. 2006. Physiological Systems and Their Responses to Conditions of Heat and Cold. In ACSM’s Advanced Exercise Physiology (ed. C.M. Tipton),    pp. 535-563. Baltimore: Lippincott Williams & Wilkins.

Versey, N. G., S. L. Halson, & B. T. Dawson. 2013. Water immersion recovery for athletes: effect on exercise performance and practical recommendations. Sports Medicine. 43:       1101-1130.

Woods, K., P. Bishop, & E. Jones. 2007. Warm-up and Stretching in the Prevention of Muscular Injury. Sports Medicine. 37: 1089-1099.

Hot or Cold: How Temperature Affects Sports (Basic)

Fig2CrespoWe wonder whether the day ahead of us is going to be hot or cold in order to decide if we should do certain activities, like practice our favorite outdoor sports. We might think that no matter how hot or cold it gets, we should still go on our running routine because exercise is always good for us. However, we should always remind ourselves that excessive heat or cold can not only make us uncomfortable during exercise, but even put our health at risk.

Based on morphological characteristics, muscles can be classified into two major types, smooth muscle (e.g., the type of muscle found in the walls of hollow organs such as blood vessels) and striated muscle (including heart muscle and skeletal muscle). Skeletal muscles generate most of the heat that causes body temperature to rise during exercise, and thus, it is the main focus of this article.

Muscle contraction requires energy. In muscle cells, like in any other cells, adenosine triphosphate (ATP) is the molecule that stores energy. This energy is transformed into work by the muscles that we use during a specific activity. However, not all the energy is transformed into work. Both the production and hydrolysis (water-mediated cleavage of chemical bonds) of ATP release heat as a by-product, and it is this heat that contributes to the body’s temperature.

Since we are homeotherms (our body temperature is kept relatively constant with respect to ambient temperature), our basal metabolism is higher than that of non-homeotherm animals. When we engage in any type of activity, our body produces extra heat that is added to the heat generated by our basal metabolism and thus, our body temperature increases. If our bodies could not regulate internal temperature, we would store great amounts of heat compromising cell function.

We can regulate body temperature via behavioral and physiological means. For example, we can exercise in the shade to avoid direct sunlight (behavioral) and depending on ambient temperature, we can experience vasodilation (widening of blood vessels) and vasoconstriction (narrowing of blood vessels) to facilitate or restrict heat transfer from the skin to the surrounding air. Thus, thermoregulation can profoundly affect how we perform in different sports and under different ambient conditions.

Furthermore, we need to be extra careful when engaging in sports or other vigorous physical activities in hot and humid weather. Hot weather means that we may accumulate heat more rapidly than what our body can dissipate, and humid conditions imply that sweating (the only known mechanism for dissipating heat against a thermal gradient) may not be possible. Under these circumstances we are prone to suffer from heat stress. Heat stress can lead to cramps, syncopes, exhaustion, and even stroke.

All of these can be avoided by learning about the different strategies to reduce the risks of heat-illness, always hydrating appropriately, adjusting exercise activity levels according to current fitness status, having adequate recovery periods between bouts of exercise, and realizing when it is better to cancel athletics and stay home.

Read the technical details about body temperature and sport.

By Jose G. Crespo
Jose G. Crespo is a researcher in the field of animal physiology and behavior with an emphasis on insect thermoregulation and neuroscience. He is currently a Postdoctoral researcher at the University of Utah – Department of Biology.

Hydration and Sport Beverages

sports-drinks-athleteAthletes have many factors to consider when it comes to improving their performance, and one of these critical aspects is maintaining proper water levels, or hydration. Water makes up about 60 percent of the human body, and is critical to transport nutrients and maintain body temperature, among other physiological processes.

Numerous beverages and sports drinks have been promoted as being beneficial for fluid replacement or retention in athletes. For moderate exercise (less than two hours), water should be sufficient to meet hydration needs. For longer periods, sports beverages, drinks, or gels can help replace electrolytes lost in sweat. Some products are also recommended after exercise to replace the proteins and carbohydrates consumed. It is important for athletes to have proper hydration and nutrient levels before, during, and after exercise for both performance and overall health, and specialized products can help fulfill these needs.

Learn the basics of staying hydrated or read the more technical explanation.

Articles by Jamie Saunders

Hydration and Sport Beverages (Technical)

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

Goal

Fluid Recommendation

Other Nutrients

Before Exercise

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

During Exercise

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

After Exercise

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.

References

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.

Hydration and Sport Beverages (Basic)

Athletes have many factors to consider when it comes to improving performance, and a critical aspect is hydration. The human body is about 60 percent water, and water takes part in several chemical reactions within the body (Gropper et al. 2008). Water also allows for transport of nutrients, is essential for maintaining the body’s temperature, and is necessary for most other physiological processes (Dunford and Doyle 2012). Physical activity leads to additional physiological stress, further increasing the need for adequate hydration. With numerous hydration options available to athletes, it is necessary to examine the existing research and recommendations to promote proper hydration for athletic participation.

The goal for hydration status is euhydration, which is a sufficient volume of water to meet the body’s requirements (Dunford and Doyle 2012). Deviations from this condition include hypohydration and hyperhydration, and both can lead to detrimental symptoms (Sawka et al. 2001). Hypohydration occurs by the process of decreasing total body water, or dehydration. Exercise in the dehydrated state leads to several unfavorable symptoms due to the increase it causes in heart rate, core temperature, and perceived exertion responses (Sawka and Coyle 1999). Dehydration, particularly when greater than two percent, can decrease cognitive and exercise performance. The greater the dehydration level, the greater the impairment in functioning (Cheuvront et al. 2003). Hyperhydration involves overdrinking in combination with an agent that binds water. Though sometimes promoted as a means for improving exercise performance, this practice has many risks and is generally not recommended.5 Another concern in this realm is hyponatremia, a condition in which plasma sodium levels are decreased. Symptoms include headache, fatigue, confusion, seizures, coma, and even death (Zambraski 2005).

As has been demonstrated, excessive deviations from fluid balance can have detrimental effects on health and athletic performance. Fluid balance is comprised of fluid loss and fluid gains of the body. The primary routes of fluid losses include respiratory, renal, gastrointestinal, and sweat. In regard to fluid gains or replacement for athletes, recommendations have been developed by the American College of Sports Medicine.

Numerous beverages are promoted as being beneficial for athletes for fluid replacement purposes. Beverages and products often touted include water, sports beverages (Gatorade, PowerAde, etc.), protein drinks, milk, chocolate milk, and caffeinated beverages. Water is likely the best option for before and during exercise when activities are less than sixty minutes. For exercise of longer duration or in extreme environmental conditions, electrolytes and carbohydrates may need to be replaced during exercise in addition to fluid losses. Caffeinated beverages may have potential stimulatory benefits, and do not appear to excessively negatively affect hydration status when used in appropriate amounts. In the post exercise period, recovery beverages such as chocolate milk, protein drinks, and sports beverages may be viable options (Dunford and Doyle 2012). 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.

Learn the technical details of hydration and sports drinks.

References

Gropper, S. S., J. L. Smith, and J. L. Groff. 2008. Advanced Nutrition and Human Metabolism, 5th Edition. Thompson Wadsworth, Belmont, California, USA.

Dunford, M. and J. A. Doyle. 2012. Nutrition for Sport and Exercise, 2nd edition. Wadsworth, Belmont, California, USA.

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