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Nutritional Considerations for Muscular Strength
This is an excerpt from Science and Development of Muscular Strength by Timothy J Suchomel.
Beyond the design of training programs, strength and conditioning professionals must consider the energy levels of their athletes. Simply, if the athlete does not have the caloric input to be able to complete or withstand the prescribed training, the desired adaptations may suffer. From this standpoint, it is important to consider how athletes fuel themselves and how this may affect their ability to train and recover. Thus, macronutrient, micronutrient, and ergogenic aid consumption should be considered to develop a sound nutrition plan for athletes. The purpose of this chapter is to provide readers with insight on various nutritional factors and how they may affect muscular strength characteristics and recovery from different training stimuli.
ENERGY BALANCE
Before addressing the nutritional needs of an athlete, it is important to determine their energy requirements; this can be accomplished by calculating their total daily energy expenditure, which includes the resting metabolic rate, non-exercise activity thermogenesis, thermic effect of food (i.e., dietary-induced thermogenesis), and thermic effect of exercise (i.e., exercise energy expenditure) (71). An in-depth discussion on the procedures for calculating each energy expenditure factor is beyond the scope of this chapter. Put simply, energy balance may be determined as the difference between energy intake and energy expenditure, or “calories in versus calories out.” Readers should note that the energy requirements for specific activities (e.g., training, practice, competition) may vary, and the metabolic cost and rate of energy expenditure may be based on training variables such as volume, intensity, duration, and frequency (249, 284). Regarding the frequency of training sessions, it is important to consider the accumulated amount of work performed by the athlete and whether they have consumed enough kilocalories to combat the energy expended to reduce the potential for negative training effects (247) or losses in body mass, lean body mass, or both. In general, more kilocalories are used as more overall work is completed, but this may also depend on an athlete’s body size, mass, and composition (250) as well as their position in sport (e.g., American football lineman vs. skill player). Readers should also note that the energy expended during exercise may affect post-exercise consumption and recovery parameters (37); this, in turn, provides a justification for including post-exercise nutrition planning, because the summative effects of energy expenditure from training may relate to various training adaptations, including body mass and composition, cardiovascular function, and sport performance (245).
Key Point
The energy requirements for specific activities (e.g., training, practice, competition) may vary, and the metabolic cost and rate of energy expenditure may be based on training variables such as volume, intensity, duration, and frequency.
Energy availability can be calculated using the following equation (169). Different levels of energy availability based on Cabre and colleagues (38) are displayed in table 11.1.
Energy availability = [Energy intake (kcal) − Exercise energy expenditure (kcal)]/Fat free mass (kg)
MACRONUTRIENTS
Three primary macronutrients provide energy to the body while maintaining the body’s structure and systems; these include carbohydrates, proteins, and fats. The following sections provide an overview of how each macronutrient contributes to the development of muscular strength.
CARBOHYDRATE
Carbohydrates are chemical compounds that are made up of carbon, hydrogen, and oxygen and serve as the primary fuel source for moderate- to high-intensity exercise (269), making carbohydrate an essential component of an athlete’s diet. Based on their structure, they may be classified as either simple carbohydrates, where they may take the form of either monosaccharides (i.e., single sugar) or disaccharides (composed of two monosaccharides), or complex carbohydrates, where polysaccharides are formed with potentially thousands of monosaccharides. Examples of simple and complex carbohydrates are displayed in table 11.2. While polysaccharides may consist of the storage form of carbohydrate (i.e., glycogen), they generally must be broken down into the monosaccharide glucose to be used as a substrate for the usable form of energy in the human body, adenosine triphosphate (ATP). For additional context, carbohydrate provides an athlete with 4 kcal/g of energy. Although low-carbohydrate diets may be used in certain scenarios, diets with less than 30% of total kilocalories consisting of carbohydrate may be associated with symptoms of fatigue (28) and may contribute to overtraining and a reduction in performance (247).
Carbohydrates may be classified based on their glycemic index (GI), which refers to the ability of a given food to raise blood glucose levels. Briefly, white bread serves as the primary reference food for the GI and has a value of 100. Thus, high, moderate, and low GI foods are classified with values of greater than 70, 55 to 70, and less than 55, respectively. Examples of high, moderate, and low GI foods are displayed in table 11.3, and readers are referred to Atkinson and colleagues for more comprehensive information (6, 7). The GI of various foods is important because it relates to how, when, and to what extent glucose levels become elevated and to the use of different substrates for energy (65). For example, low GI foods consumed in the hours prior to training may have a metabolic advantage over high GI foods because they produce a smaller insulin response, which may increase free fatty acid availability and allow a more stable glucose concentration during training, thus sparing muscle glycogen (46). However, because low GI foods may be high in fiber content, it is important that athletes allow for the necessary time to digest such foods to prevent gastrointestinal issues during training or competition. Interestingly, two meta-analyses indicated that there may be no difference between high and low GI foods when it comes to glycogen sparing (75, 118); however, high GI foods may be advantageous to consume after exercise because they promote glycogen resynthesis, thus benefiting recovery (32).
While there is little doubt that carbohydrate intake can significantly benefit endurance performance (209, 273), less research supports additional carbohydrate intake beyond a typical diet for resistance training performance. For example, the authors of a 2022 systematic review concluded that carbohydrate intake may not affect an athlete’s resistance training performance while in a fed state during workouts that included up to 10 sets per muscle group (113). However, the authors also noted that higher-volume resistance training workouts may benefit from carbohydrate intake, although further research is needed. Additional researchers indicated that carbohydrate ingestion before or during a resistance training session may allow individuals to perform a greater volume of work during sessions that are longer than 45 minutes in duration and include at least 8 to 10 sets (151). The authors also concluded that carbohydrate ingestion after an 8-hour fast may improve resistance training performance. Despite these results, it should be noted that carbohydrate restriction may negatively affect an athlete’s ability to consistently perform high-intensity training sets (165), indicating the importance of still having adequate levels of carbohydrates readily available for activity. To counteract carbohydrate restriction, some researchers have investigated the use of carbohydrate mouth rinsing, defined as distribution of carbohydrate fluid in the mouth for 5 to 10 seconds before spitting it out (57). Researchers concluded that carbohydrate mouth rinsing did not benefit repeat and all-out running and cycling sprint performance (58); however, others found that mouth rinsing with carbohydrate and caffeine may enhance exercise capacity (145). Collectively, the available literature suggests that additional carbohydrate intake prior to training may not benefit strength performance when activities are shorter in duration. Thus, athletes and strength and conditioning professionals should consider the amount of carbohydrates that are necessary for different types of training and competition.
Key Point
Carbohydrate restriction may negatively affect an athlete’s ability to consistently perform high-intensity training sets, indicating the importance of still having adequate levels of carbohydrates readily available for activity.
Daily carbohydrate requirements for athletes should be periodized to ensure adequate availability for training and competition; however, athletes and strength and conditioning professionals should consult sport nutritionists or registered dietitians to improve their knowledge of best practices. While many have suggested that an athlete’s diet should consist of a specific percentage of carbohydrate, this method does not seem to be supported because it is poorly correlated with the amount of carbohydrate consumed during activity as well as the fuel requirements of said activities (34). Thus, it is recommended that the amount of carbohydrate needed for each athlete should be based on the activities that they are performing on any given training day. For example, it has been suggested that athletes ingest [less than] 2 g/kg, 2-4 g/kg, 4-6 g/kg, 6-8 g/kg, or 8-12 g/kg of carbohydrate if they are participating in little to no activity, low-intensity activities with minimal energy use (e.g., recovery session), moderate- to high-intensity activities that last about an hour per day (e.g., resistance training session), moderate- to high-intensity activities that last between 1 to 3 hours per day (e.g., sport practices or competitions), or moderate- to high-intensity activities that last more than 4 hours per day (e.g., combined sport practice, resistance training session, and recovery session), respectively (46).
Regarding carbohydrate consumption during training or competition, additional recommendations suggest that well-trained athletes competing in events lasting 1 to 2 hours, 2 to 3 hours, or more than 2.5 hours should consume approximately 30, 60, or 90 g of carbohydrate per hour, respectively; less-trained athletes may adjust these values downward (137). Regarding post-training or competition recommendations, researchers have suggested consuming 1.2 g/kg of carbohydrate per hour (136) starting within the first 2 hours of cessation to optimize glycogen resynthesis (133); however, consumption should also be based on how long the training session or event was and when the next one will occur.
The previous recommendations are quite general, but it is important that carbohydrate intake is based on the activities that will be performed. However, flexibility should be exercised, especially when schedules change on short notice. Finally, educating athletes on specific portion sizes and nutrition software programs or apps that remind athletes about specific feeding times may help create an autonomous athlete (71). Readers interested in additional information on how to periodize carbohydrates are directed to a previous review by Impey and colleagues (131).
PROTEIN
Beyond serving as contractile elements for force production (e.g., actin, myosin, titin, nebulin), proteins may be structural (e.g., keratins), part of the immune system (e.g., antibodies), or regulatory (e.g., enzymes) in their functions. This diverse range of actions may ultimately be the result of the large variation in structure among different proteins. Each protein is made up of a wide variety of amino acids, of which 9 are considered essential and 11 are considered non-essential (see table 11.4). Simply, essential amino acids must be consumed within an athlete’s diet, whereas non-essential proteins are naturally made within the human body. Because proteins are in a constant state of turnover, being broken down and rebuilt throughout any given day, a diet with adequate protein allows new proteins to be formed to replace damaged ones following a given training stimulus (46). Although protein consumption may not directly affect maximal strength (166), athletes and strength and conditioning professionals should recognize its contribution to the underlying mechanisms and recovery of muscular strength characteristics.
Key Point
Although protein consumption may not directly affect maximal strength, athletes and strength and conditioning professionals should recognize its contribution to the underlying mechanisms and recovery of muscular strength characteristics.
The nitrogen balance reflects the ratio of nitrogen intake compared to what is lost and provides an indication of gain or loss of total-body protein (a nitrogen-containing molecule). In 2007, the World Health Organization indicated that 0.8 to 0.9 g/kg of protein per day is required to maintain a nitrogen balance in adults (282); however, this conclusion was primarily based on research focused on sedentary individuals. As a result, researchers have concluded that athletes require significantly higher values than the previous recommendations (164, 198), with a minimum intake at around 1.2 to 1.6 g/kg/day (257) to maintain nitrogen balance.
Although the nitrogen balance represents the minimum protein intake for an athlete, this may not be optimal based on specific training goals and demands; moreover, the previous recommendations may not account for different types of athletes. Close and colleagues (46) suggested that endurance athletes should consume 1.2 to 1.4 g/kg of protein day, whereas strength athletes may need to consume 1.8 to 2.0 g/kg/day. It should be noted that these values may be elevated to 2.0 to 2.5 g/kg/day based on the frequency and intensity of training and competitions (3, 182). Additional research has suggested consuming approximately 0.4 g/kg of protein every 3 to 4 hours throughout the day, rather than consuming much larger boluses at individual meals (187). This, in turn, may promote a positive nitrogen balance, leaving the athlete in a more anabolic (building) state rather than a catabolic (breakdown) state throughout the day.
Key Point
Researchers have suggested consuming approximately 0.4 g/kg of protein every 3 to 4 hours, rather than consuming much larger boluses at individual meals; this may promote a positive nitrogen balance, leaving the athlete in a more anabolic (building) state rather than a catabolic (breakdown) state throughout the day.
Beyond the amount of protein that an athlete may consume, the type of protein, including animal based (e.g., whey and casein) and plant based (e.g., soy), should be considered. Researchers have concluded that animal-based protein generally has higher bioavailability (percentage digested and used) and contains a higher percentage of essential amino acids (21, 228), including leucine, the amino acid responsible for activating the mammalian target of rapamycin complex-1 (mTOR) pathway and subsequent upregulation of protein synthesis (199). Consuming 2.5 to 5 g of leucine within a single meal may be required to activate the mTOR pathway and initiate muscle protein synthesis (200). Consumption of leucine alone, however, is not sufficient to synthesize complete muscle proteins, which requires adequate availability of all nine essential amino acids (74). In contrast to animal sources of protein, athletes and strength and conditioning professionals should note that plant-based proteins include incomplete protein, containing insufficient amounts of one or more essential amino acids. This can be overcome by consuming greater overall amounts and varied sources of plant proteins to achieve adequate intake to increase the bioavailability of the essential amino acids required to support muscle protein synthesis. It should, however, be noted that consumption of greater amounts of plant-based protein may lead to greater carbohydrate and caloric consumption as well (e.g., 120 g of chicken breast = 38 g of protein and 0 g of carbohydrates; 520 g mixed beans = 38 g of protein and 84 g of carbohydrate) (71, 203). Beyond the bioavailability of amino acids, consumers may also consider the rate that different protein types increase amino acid concentrations within the blood, a primary driver of muscle protein synthesis (43). For example, researchers showed that whey protein increased protein synthesis to a greater extent after exercise compared to both milk (80% casein and 20% whey) and soy-based protein, while milk was also superior to soy (199). Although these findings support the use of specific forms of protein for protein synthesis, it should be noted that the type of protein may be linked to the timing of ingestion (described later in this subsection).
Another form of protein that should be considered within an athlete’s diet is collagen. Briefly, collagen is the most abundant protein in connective tissue and serves as the primary structural component of tendons, ligaments, and intramuscular connective tissue (10), which may then dictate the strength and stiffness of such tissue. Researchers have shown that 15 g of gelatin consumed with vitamin C–rich blackcurrant juice led to a 2-fold increase in collagen synthesis (230). However, additional research showed that ingesting 30 g of collagen protein following 6 sets of a high-volume (8-15 repetitions) barbell squat using 60% of the 1RM resulted in no increase in connective protein synthesis rates (8), indicating that the literature appears to be inconclusive on this topic and that further research is needed (127).
Athletes have the option of consuming protein in a variety of concentrations (e.g., solid, liquid, gels), especially due to food manufacturers adding protein to many of their existing products. It should be noted that liquid forms of protein may produce a faster increase in plasma amino acids compared to other forms (36), especially following training or competition; these findings are likely due to time needed to digest and absorb solid forms of protein. However, as mentioned previously, different forms of protein have their place within the athlete’s overall diet plan.
Another aspect of protein consumption that must be discussed is the timing of ingestion relative to activity. As noted previously, it has been suggested that protein should be consumed throughout the day at a rate of 0.4 g/kg every 3 to 4 hours (187), which may place an athlete in a more anabolic state. In fact, researchers have shown that performing resistance training in a fasted state may result in a net loss of protein (201). Thus, based on the time of a given training session, it is important for athletes to consume amino acids either before (261) or immediately after (199) exercise to prevent a net loss of muscle protein. This may be challenging, especially with training sessions that occur early in the morning or late at night, which is why athletes should have snack options containing protein prior to training that do not result in gastrointestinal distress. As a workout commences, athletes begin to experience a breakdown in muscle protein. While this is a normal occurrence, it would seem logical to implement strategies to counteract these activities and set the athlete up for the rebuilding of proteins after exercise. Unfortunately, limited research on intraworkout protein consumption exists; however, Beelen and colleagues (17) indicated that whole-body and muscle protein synthesis rates increased during a workout and early post-workout when a protein and carbohydrate drink was consumed during the training session. Based on these findings, it would appear advantageous to begin consuming protein prior to the end of the resistance training workout to increase protein synthesis and potentially slow protein breakdown.
Following a training session, athletes are generally in a catabolic state that is characterized by greater levels of protein breakdown, and they are therefore in need of protein intake to counteract these effects and promote adaptation. In a classic study, Cribb and Hayes (52) examined the effect of consuming meals before and following resistance training with morning and evening meals that both consisted of 32 g of protein, 34 g of carbohydrate, less than 0.4 g of fat, and 5.6 g of creatine for 10 weeks. The authors showed that pre- and post-training meals produced improvements in lean body mass, body fat percentage, cross-sectional area of Type IIa and IIx fibers, contractile protein content, phosphocreatine (PCr) and total creatine content, muscle glycogen content, and increases in both bench press and squat strength. A previous systematic review and meta-analysis supports the previous findings, and the authors concluded that at least 6 weeks of resistance training and post-training protein supplementation may benefit maximal strength characteristics (41).
Although it has previously been suggested that a “metabolic window” (i.e., anabolic window) exists for approximately 45 minutes after training (134), the literature has indicated that total protein intake may be more important for muscular strength and hypertrophy, to an extent, following a workout (228). In fact, further research showed that muscle protein synthesis remained increased several hours following exercise (210) and that 40 g of protein consumed immediately after exercise and over 3 subsequent hours may produce greater protein synthesis effects compared to 20 g. It should be noted that consuming a combination of carbohydrate and protein following a workout may also promote increased muscle glycogen resynthesis (35). Finally, although discussed less frequently, researchers have suggested that consuming approximately 0.4 to 0.5 g/kg of protein prior to the overnight sleeping period may benefit resistance training adaptations (237, 265). In this light, it is suggested that athletes use casein protein to allow amino acids to be absorbed over a longer duration.
Key Point
It is important for athletes to consume amino acids either before or immediately after exercise to prevent a net loss of muscle protein.
FAT
The third macronutrient that generally comprises the smallest portion of an athlete’s diet is fat (i.e., lipids). Although fat within diets is typically viewed in a negative light, fats are an essential nutrient that contributes to a variety of functions within the human body. For example, fats may be used to protect internal organs, absorb vitamins, and facilitate cell membrane, hormone, and prostaglandin production. In addition to carbohydrates, fats are also one of the primary substrates for energy production, especially during long-duration exercise, and may provide 9 kcal/g of energy. Fats are classified based on their structure as either saturated or unsaturated, and the latter may be further subdivided into monounsaturated or polyunsaturated fats. It should, however, be noted that all classifications of fat include a mixture of different fatty acids, and they are classified based on the majority of the fat source they contain (46). Although saturated and unsaturated fats are frequently discussed as bad fats and good fats, respectively, this may be an oversimplification; in some instances, replacing the former with the latter may affect other nutrient levels (e.g., the removal of dairy products may negatively affect calcium intake) (46, 71). However, when possible, it is recommended that athletes avoid consumption of trans fats, because this form of fat may increase low-density lipoprotein (i.e., bad) cholesterol and decrease high-density lipoprotein (i.e., good) cholesterol, which in turn may increase the risk of cardiovascular disease (188). Examples of foods that may contain trans fats include baked goods, margarine, and frozen pizza.
It is important to note that certain fatty acids (i.e., n-3 and n-6 fatty acids, also known as omega-3 and omega-6 fatty acids, respectively) are considered essential because they are not naturally made in the human body. In fact, it has been suggested that a diet that consists of too little dietary fat may negatively affect an individual’s overall health (46). Western diets have been reported to include relatively high levels of n-6 fatty acid (e.g., poultry, eggs, nuts, peanut butter, avocado) but much lower levels of n-3 fatty acid (233). This may relate to a reduced consumption of oily fish, such as salmon, tuna, mackerel, herring, and swordfish, all of which are significant sources of n-3 fatty acids. Given that some athletes may not enjoy eating oily fish, n-3 supplements may be beneficial to both their health and performance; however, it is important that athletes consult with a sport nutrition professional to determine whether supplementation is necessary. A 2023 study indicated that 10 weeks of progressive resistance training combined with a fish oil supplement (4 g/day) may lead to greater improvements in absolute and relative bench press and squat strength and reductions in fat mass (112). Additional research concluded that n-3 supplementation may significantly reduce muscle soreness following resistance training (141), which in turn may enhance the recovery process between training sessions (202). Collectively, the previous research findings suggest that greater maximal strength and enhanced recovery may be by-products of fish oil supplementation. It should be noted that the research in this area is evolving, and further research is needed to provide more concrete recommendations.
Some researchers have promoted the idea of high-fat diets for athletes, with the mindset of sparing muscle glycogen and improving the use of fat for energy. For example, Yeo and colleagues (288) suggested that a high-fat, low-carbohydrate diet consumed for up to 2 weeks paired with normal training, followed by 1 to 3 days of a high-carbohydrate diet and taper in training volume, may lead to “fat adaptation,” in which greater fat use remains elevated even after carbohydrate availability increases. Although this may be beneficial for endurance-trained athletes, this type of diet may reduce the activity of pyruvate dehydrogenase during rest as well as during submaximal and supramaximal exercise (243), which in turn may negatively affect high-intensity efforts in which carbohydrate is the primary fuel source. Additional research has also shown that high-fat diets may negatively affect protein synthesis (102). Therefore, it is suggested that high-fat diets should be avoided when the goal is to enhance muscular strength.
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