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.

Putting Protein in Its Place

newfoodpyramid_largeProtein powders, bars, and drinks are often touted as the key to enhancing muscle growth, increasing energy, and losing excess body fat. Nutrition science indicates that excess protein intake can cause a decrease in the intake of other essential macronutrients. It can also saturate the body’s protein supply and result in depleted calcium stores, adversely affected kidney function, and damage to other critical systems of the body, including the cardiovascular system. Scientists recommend meeting the majority of nutritional needs from a nutrient-rich diet that balances the intake of carbohydrates, fats, and protein.

Learn the basics of how protein affects your performance or read the more technical explanation.

Articles by Jamie Saunders

Putting Protein in its Place (Basic)

newfoodpyramid_largeThe three macronutrients- carbohydrate, protein, and fat- tend to rotate through periods of time in the sports nutrition spotlight. Each of these nutrients performs numerous important functions in the body, and all are required in the diet of athletes. Of these nutrients, protein is often promoted as the most important in relation to athletes’ requirements. In fact, the Greek word proteos, from which the term protein is derived, translates to mean “primary” or “taking first place”.  In order to put protein in its proper place in sports nutrition, a look at the current research and recommendations is needed.

Protein has several important functions in the body, such as transporting nutrients and oxygen in the blood. Protein also plays a role in tissue growth and repair, the immune system, fluid balance, wound healing, and many chemical reactions in the body. These functions are unique to protein. Protein can also provide energy for the body; however the body prefers to use carbohydrates and fat for energy.

Athletes need to consume enough protein to meet their needs. It is recommended that protein provide 10% to 35% of an individual’s total calories. Another form of protein recommendations is based on an individual’s body weight. These recommendations are shown in Table 1, and are usually given in ranges. With each of these ranges, athletes exercising longer and harder should aim for the upper end of the range, while athletes exercising shorter and at lower intensities should aim for the lower end of the range. Table 2 shows appropriate protein requirements per day according to body weight and various protein recommendation levels.

Although many athletes believe they need protein supplements to meet their protein needs, most athletes can get enough protein simply by eating a healthy diet. Foods rich in protein include meat, poultry, fish, dairy products, eggs, beans, nuts, and some grains. Because protein is readily available in many foods, protein powders are generally unnecessary for athletes. Protein bars and protein drinks may be a convenient alternative in certain situations, however obtaining protein from food sources is always the recommended approach.

Many athletes believe they need excess amounts of protein to help them build muscle. In fact, no benefit has been demonstrated for protein intakes above 2.0 grams per kilogram, and there are several possible negative effects to bone, kidney, and cardiovascular health with excess protein intake. Eating extra protein also likely means that the athlete is not getting enough carbohydrates and fat. All three of these nutrients are important for athletes, and all are needed for athletes to perform at their best. If any of the three represent a disproportionately high amount in the body, the athlete may not be getting enough of the other two. Thus, it is in the appropriate balance of the three macronutrients that athletes can maximize their performance.

Table 1. Daily protein recommendations in grams per kilogram body weight by population type.

Population

Protein Recommendations

General Population

0.8 grams per kilogram body weight

Recreational Athlete

0.8-1.0 grams per kilogram body weight

Endurance Athletes

1.2-1.4 grams per kilogram body weight

Ultra-Endurance Athletes

1.2-2.0 grams per kilogram body weight

Strength Athletes

1.2-1.7 grams per kilogram body weight

 

Table 2.  Daily protein recommendations in grams according to body weight and varying protein recommendation levels.

0.8 g/kg

1.0 g/kg

1.2 g/kg

1.4 g/kg

1.6 g/kg

2.0 g/kg

125 lbs.

45 g pro

57 g pro

68 g pro

80 g pro

91 g pro

114 g pro

150 lbs.

55 g pro

68 g pro

82 g pro

96 g pro

109 g pro

136 g pro

175 lbs.

64 g pro

80 g pro

95 g pro

111 g pro

127 g pro

159 g pro

200 lbs.

73 g pro

91 g pro

109 g pro

127 g pro

145 g pro

182 g pro

225 lbs.

82 g pro

102 g pro

123 g pro

143 g pro

164 g pro

205 g pro

Learn more technical details about protein.

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. 

 

Putting Protein in Its Place (Technical)

The three macronutrients- carbohydrate, protein, and fat- tend to rotate through periods of time in the sports nutrition spotlight. Each of these nutrients performs numerous important functions in the body, and all are required in the diet of athletes. Of these nutrients, protein is often touted as the most important in relation to athletes’ requirements. In fact, the Greek word proteos, from which the term protein is derived, translates to mean “primary” or “taking first place” (Gropper et al. 2008).  In order to put protein in its proper place in sports nutrition, an examination of the current research literature and recommendations is warranted.

The basic units of proteins are amino acids. There are twenty different amino acids, which connect by peptide bonds in varying combinations and lengths, to form polypeptides (Albert et al. 2002). Proteins are organized into primary, secondary, tertiary, and quaternary levels of structure, with each subsequent level becoming more complex in nature. The structure of protein is important because the functional role of protein is determined by its organization and structure (Gropper et al. 2008).

Proteins in the body function as catalysts, enzymes, hormone messengers, and transporters of nutrients and oxygen in the blood (Gropper et al. 2008).Protein is involved in the synthesis, maintenance, growth, and repair of tissue (Zieve et al. 2011). Protein also plays a role in the immune system as it is involved in the formation of enzymes, hormones, and antibodies. Protein can act as a buffer in the body, and it assists in the maintenance of fluid, electrolyte, and acid-base balance. Another function of protein is the role it plays in blood clotting, and therefore wound healing. Lastly, protein plays a role in the provision of energy. More precisely, one gram of protein provides four calories of energy (Gropper et al. 2008).

A review of the listed functions of protein reveals the importance of this macronutrient in the realm of athletics. Another important note is that aside from the function of providing energy, all of the functions discussed are unique to protein, meaning carbohydrates and fat cannot carry out these functions (Gropper et al. 2008). Thus, the necessity of protein is certain; however, it is essential to determine how much of this nutrient is required in order to assure the proper functioning of these roles in the body.

newfoodpyramid_largeThe Recommended Dietary Allowance (RDA) for protein is 0.8 grams of protein per kilogram of body weight, and this recommendation is defined as the average daily amount of protein sufficient to meet the nutrient needs of approximately 97% to 98% of healthy individuals. The Acceptable Macronutrient Distribution Range demonstrates that protein should provide 10% to 35% of total energy (Otten et al. 2006). Both of these recommendations are geared toward the general healthy population, and a topic of popular debate is to what extent athletes require greater than this general recommendation for protein (Fuhrman and Ferrerl 2010).

According to a Joint Position Stand of the American Dietetic Association, Dietitians of Canada, and the American College of Sports Medicine, athletes have varying levels of protein needs depending on the type, duration, and intensity of exercise (Rodriguez et al. 2009). For recreational athletes, protein needs range from 0.8 to 1.0 grams per kilogram body weight per day. For endurance athletes, the recommendation is 1.2 to 1.4 grams per kilogram of body weight, with the needs of ultra endurance athletes ranging from 1.2 to 2.0 grams per kilogram of body weight. Strength athletes require approximately 1.2 to 1.7 grams of protein per kilogram of body weight (Rodriguez et al. 2009). With each of these ranges, athletes participating at higher intensities or longer durations within the particular sport type will have requirements toward the upper end of the range, while athletes performing at lower intensities or shorter durations should meet their protein needs if they follow the recommendations given for the lower end of the range (Dunford and Doyle 2012). Table 1 shows appropriate protein requirements per day according to body weight and various protein recommendation levels.

Table 1. Daily protein recommendations in grams according to body weight and varying protein recommendation levels.

0.8 g/kg

1.0 g/kg

1.2 g/kg

1.4 g/kg

1.6 g/kg

2.0 g/kg

125 lbs.

45 g pro

57 g pro

68 g pro

80 g pro

91 g pro

114 g pro

150 lbs.

55 g pro

68 g pro

82 g pro

96 g pro

109 g pro

136 g pro

175 lbs.

64 g pro

80 g pro

95 g pro

111 g pro

127 g pro

159 g pro

200 lbs.

73 g pro

91 g pro

109 g pro

127 g pro

145 g pro

182 g pro

225 lbs.

82 g pro

102 g pro

123 g pro

143 g pro

164 g pro

205 g pro

 

Numerous research endeavors were examined to determine the protein recommendation ranges for athletes, and these levels of protein intake are thought to allow sufficient protein amounts for the body to perform its essential roles (Otten et al. 2006). The  numerical recommendations must be translated into actual food intake. Protein is found in a wide variety of foods, including both animal and plant sources. Animal sources include meat, poultry, fish, dairy products (milk, yogurt, cheese, etc.), and eggs. Plant sources of protein include beans, lentils, legumes, nuts, nut butters, seeds, some grains, and certain vegetables (Zieve et al. 2011).

Competitive athletes involved in heavy training commonly believe they cannot meet their protein requirements through food sources alone. Such athletes frequently turn to protein supplements, which come in the form of protein powders, protein bars, and protein drink or shake options. Popular protein bars range from approximately 8 to 20 grams of protein per bar, and protein drink or shake products (premixed or powder) range from about 4 to 50 grams of protein per serving (High protein drinks 2009, Protein bars 2009). Such protein levels can easily be met by consuming regular foods, such as meat. One three-ounce serving of beef provides 30 grams of protein, a similar serving of chicken or turkey provides 26 grams of protein, and three ounces of fish provides 20 grams of protein (Dunford and Doyle 2012). In reality, most individuals consume larger portions of meat, poultry, and fish than three ounces, and therefore may easily get double or more the amount of protein listed. Other protein sources such as dairy products and beans typically provide about 8 grams of protein per serving.  Nuts, such as almonds or peanuts, provide 32 to 40 grams of protein per cup (Dunford and Doyle 2012). As is demonstrated by these examples, athletes should generally not have a difficulty meeting their protein needs through food sources alone.

A few exceptions should be noted, such as in the case of athletes who are not consuming sufficient overall calories, and therefore likely have inadequate protein intakes. In certain cases, consuming adequate protein may be a concern for vegetarian or vegan athletes (Association, Dietitians of Canada 2003). However, it is possible to obtain sufficient protein from a plant-based diet. Thus, protein powders are generally unnecessary for athletes (Mahan and Escott-Stump 2008). Protein bars and protein drinks may be a convenient alternative in certain cases of sport nutrition; however, obtaining needed protein from food sources is always the recommended approach.

Most athletes are able to meet their protein requirements quite easily if they are eating sufficient calories. A common notion is the idea that excess amounts of protein must be consumed in order to assist in muscle gains (Maughan and Shirreffs 2012). In fact, no benefit has been demonstrated for protein intakes above 2.0 grams per kilogram body weight, and there are several possible negative effects with excess protein intake. These include a potentially negative effect on calcium stores, bone health, kidney function in individuals with impaired renal function, and cardiovascular health (Frank et al. 2009).

When considering issues related to excess protein, it is illuminating to examine the processes involved in hypertrophy and net protein balance. The process of hypertrophy, or muscle growth, requires a positive net protein balance (NPB). NPB is comprised of muscle protein synthesis and muscle protein breakdown. If the rate of synthesis exceeds that of breakdown, positive NPB will result, thereby leading to hypertrophy (Phillips and van Loon 2011). As protein intake plays a key role in promoting muscle protein synthesis, many athletes erroneously believe that as their protein intake increases, their muscle protein synthesis increases linearly, indefinitely.  This, however, is not the case. Excess protein will not continue to promote protein synthesis, but rather will be used as a substrate for the process of oxidative metabolism (Frank et al. 2009). As was discussed earlier, protein has numerous unique roles. Thus it is advantageous for protein to be used for executing these roles, rather than acting as an energy substrate- a role filled far better by carbohydrates and fat. Along these lines, if protein is in excess, it follows that fat, carbohydrate, or both are consequently lessened in the diet (Gibala 2007). This displacement of other macronutrients by protein points to another concern with excess protein consumption, as fat and carbohydrates fulfill numerous important functions in the body.

Carbohydrates are the preferred energy source for the body, and they are a required energy source for certain tissues such as the brain, white blood cells, and red blood cells (Dunford and Doyle 2012). Carbohydrates also provide numerous essential vitamins and minerals. If sufficient carbohydrates are consumed, they also provide a protein-sparing effect, in that carbohydrates will be used for energy production rather than protein being used for energy through the process of gluconeogenesis (Gropper et al. 2008). The current recommendations for daily carbohydrate intake are 3 to 5 grams of carbohydrate per kilogram body weight for low intensity, skill-based sports and 5 to 7 grams of carbohydrate per kilogram body weight for moderate intensity exercise less than one hour in duration. For moderate to high intensity endurance or stop and go sports lasting one to three hours in duration, 6 to 10 grams per kilogram body weight is recommended. For high intensity endurance events lasting greater than four hours, the recommendation is 8 to 12 grams carbohydrate per kilogram body weight (Rodriguez et al. 2009). Carbohydrates are found in numerous foods, including grains, cereal, pasta, rice, milk, yogurt, fruit, and starchy vegetables (Dunford and Doyle 2012).

Fats, or lipids, are also an important source of energy for the body (Gibala 2007). Fat also provides essential fatty acids, which are omega-three and omega-six fatty acids. These fatty acids are not made by the body and therefore must be obtained through the diet (American Dietetic Association, Dietitians of Canada 2007). Fat is also a source of fat soluble vitamins (vitamins A, D, E, and K), and fat is required for the absorption of these vitamins (Mahan and Escott-Stump 2008). A few other key roles include insulation, protection of vital organs, and shock absorption. There is not a recommendation in grams per kilogram of body weight for fat, as there is for protein and carbohydrate. However, the Acceptable Macronutrient Distribution Range for fat is 20 to 35% of total energy, with suggested recommendation of 10 to 25% for endurance athletes and 15 to 20% for strength athletes (Phillips and van Loon 2011). Although many athletes believe fat should be minimized in the diet, it is not recommended that athletes ever go below 10% of total energy from fat (Rodriguez et al. 2009).

The three macronutrients- protein, fat, and carbohydrate- all play key roles in the body, and all are necessary for promoting optimal athletic performance. Consuming any of these nutrients in excess above the recommended amounts frequently leads to displacement of one or both of the other macronutrients. Though protein does perform numerous essential functions required for physical activity processes, carbohydrates and fat are similarly important for the athlete. Thus, it is in the appropriate balance of the three macronutrients, rather than the disproportionate ranking of one above the others, that athletes can maximize their 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

Alberts, B., A. Johnson, and J. Lewis, et al. 2002. Molecular biology of the cell 4th edition. Garland Science, New York, NY, USA.

American Dietetic Association, Dietitians of Canada. 2007. Dietary Fatty Acids. Journal of the American Dietetic Association. 107: 1599-1611.

Association, Dietitians of Canada. 2003. Vegetarian diets. Journal of the American Dietetic Association. 103:748-765.

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

Frank, H., J. Graf, and U. Amann-Gassner. 2009. Effect of short-term high protein compared with normal-protein diets on renal hemodynamics and associated variables in healthy young men. American Journal of Clinical Nutrition.  90(6):1509-16.

Fuhrman, J., and D.M. Ferrerl. 2010. Fueling the vegetarian (vegan) athlete. Current Sports Medicine Reports. 9(4): 233-241.

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