Dietary Supplements for Exercise and Athletic Performance
According to a publication in the Journal of Dietary Supplements, 78% of the 200 endurance athletes who were surveyed were found to be current consumers of dietary supplements (DS). Additionally, nearly 54% of these athletes disclosed the usage of a minimum of three supplement products.
The University of Southern Mississippi and Texas Christian University scientists have reported that the top 10 supplements utilized include Multivitamins, Electrolytes, Vitamin D, Protein, B vitamins, Fish oil, Probiotics, Melatonin, Amino Acids/ BCAAs’, and Glucosamine-chondroitin.
According to the scientists, older athletes had a much higher usage rate. Specifically, 67.5% of athletes aged 40 to 49 and 76.2% of athletes aged 50 to 59, compared to only 33% of athletes aged 18 to 29.
According to Austin Graybeal from the University of Southern Mississippi, the authors suggest that although there might be advantages to using DS in endurance athletes, it is necessary to investigate the prevalence and trends of DS consumption in a specific group of endurance cyclists, runners, and triathletes. This investigation is needed to assess the benefits and risks of using DS based on age-specific needs to develop customized DS regimens for recreational competitive purposes.
Higher Usage Compared To The General Population?
The Council for Responsible Nutrition’s annual Consumer Survey on Dietary Supplements has reported similar overall usage levels as indicated by the data.
According to CRN’s 2021 survey, it was found that the usage of dietary supplements by Americans has increased by 7% when compared to 2020, reaching 80%. Additionally, there has been a rise in the percentage of Americans who perceive the dietary supplements industry as trustworthy, with 79% in 2021 compared to 74% in 2020.
75% of all supplement users use multivitamins, making them the most widely used supplements.
Dietary Supplements for Exercise and Athletic Performance
This fact sheet offers an overview of certain components found in dietary supplements intended or claimed to improve exercise and athletic performance. Manufacturers and sellers advertise these products, also known as “ergogenic aids,” by asserting that they enhance strength or endurance, enhance the efficiency of exercise, expedite the achievement of performance goals, and increase the ability to handle more intense training. The fact sheet primarily concentrates on these effects. Additionally, some individuals utilize ergogenic aids to prime the body for exercise, decrease the risk of injury during training, and improve post-exercise recovery.
Various forms of dietary supplements are available for enhancing exercise and athletic performance, such as tablets, capsules, liquids, powders, and bars. These products often consist of multiple ingredients in different combinations and quantities. Amino acids, protein, creatine, and caffeine are some of the commonly used ingredients. According to an estimation, sales of sports nutrition supplements accounted for $5.67 billion in 2016, which is equivalent to 13.8% of the total sales of dietary supplements and related nutrition products, amounting to $41.16 billion for that year.
Several surveys have revealed the level of usage of dietary supplements for bodybuilding and to improve exercise and athletic performance.
- International surveys found that two-thirds of 3,887 adult and adolescent elite track and field athletes participating in world championship competitions took one or more dietary supplements containing such ingredients as vitamins, minerals, creatine, caffeine, and amino acids. Supplement use increased with age and was significantly more common among women than men.
- A survey of 1,248 students aged 16 years or older in five U.S. colleges and universities in 2009–2010 found that 66% reported use of any dietary supplement. The reasons for use included enhanced muscle strength (20% of users), performance enhancement (19% of users), and increased endurance (7% of users). Products taken for these purposes included protein, amino acids, herbal supplements, caffeine, creatine, and combination products.
- In a national survey of about 21,000 U.S. college athletes, respondents reported taking protein products (41.7%), energy drinks and shots (28.6%), creatine (14.0%), amino acids (12.1%), multivitamins with caffeine (5.7%), beta-hydroxy-beta-methylbutyrate (HMB; 0.2%), dehydroepiandrosterone (DHEA; 0.1%), and an unspecified mix of “testosterone boosters” (1.6%). Men were much more likely to take performance-enhancing products than women, except for energy drinks and shots. Among the sports with the highest percentage of users of performance-enhancing products were ice hockey, wrestling, and baseball among the men and volleyball, swimming, and ice hockey among the women.
- In a review of studies on adolescent use of performance-enhancing substances, the American Academy of Pediatrics concluded that protein, creatine, and caffeine were the most commonly used ingredients and that use increased with age. Although athletes used these ingredients more than nonathletes, teenagers not involved in organized athletic activities often took them to enhance their appearance.
- A survey of 106,698 U.S. military personnel in 2007–2008 found that 22.8% of the men and 5.3% of the women reported using bodybuilding supplements, such as creatine and amino acids, and 40.5% of the men and 35.5% of the women reported using energy supplements that might contain caffeine and/or energy-enhancing herbs. Use of these products was positively associated with deployment to combat situations, being younger than 29 years, being physically active, and reporting 5 or fewer hours of sleep a night.
The extent of dietary supplement use by athletes is challenging to generalize due to the diverse nature of studies on this topic. However, the available data indicate that:
- A larger proportion of athletes than the general U.S. population takes dietary supplements.
- Elite athletes (e.g., professional athletes and those who compete on a national or international level) use dietary supplements more often than their non-elite counterparts.
- The supplements used by male and female athletes are similar, except that a larger proportion of women use iron and a larger proportion of men take vitamin E, protein, and creatine.
To perform at their best, individuals must have a nutritionally adequate diet and maintain proper hydration. This type of eating plan is recommended for everyone by the Dietary Guidelines for Americans and MyPlate. Athletes specifically need the right amount of calories, fluids, carbohydrates (to maintain blood glucose levels and replace muscle glycogen), protein, fat, vitamins, and minerals. The recommended amounts are typically 1.4 to 4.5 grams of carbohydrates per pound of body weight (or 3 to 10 grams per kilogram of body weight), 0.55 to 0.9 grams of protein per pound of body weight (or 1.2 to 2.0 grams per kilogram of body weight), and 20% to 35% of total calories from fat.
Some dietary supplements can boost performance, but only if they are added to the existing diet rather than replacing it. Endurance athletes who participate in activities lasting over an hour or in extreme conditions such as hot temperatures or high altitudes may need to replenish fluids and electrolytes and consume extra carbohydrates for energy. However, the effects of taking dietary supplements for exercise and athletic performance can differ based on the individual’s training level, the nature, intensity, and duration of the activity, and the environmental circumstances, even with proper nutritional preparation.
Sellers assert that numerous elements found in dietary supplements have the potential to improve exercise and athletic performance. Advanced athletes, including both well-trained elite athletes and recreational ones, may opt for products containing these ingredients to intensify their training, enhance their performance, and gain a competitive advantage. However, the National Athletic Trainers’ Association acknowledges in a position statement that the effectiveness of studies on different performance-enhancing substances is frequently inconclusive, leading to controversy and confusion regarding their use.
Most studies that evaluate the effectiveness and safety of supplements to enhance exercise and athletic performance only involve trained athletes. As a result, it is often unclear whether the supplements discussed in this fact sheet may benefit recreational exercisers or individuals who only participate in athletic activities occasionally. Additionally, the majority of research on these supplements focuses on young adults, particularly males, and not on adolescents who may use them despite recommendations from pediatric and high-school professional associations. The quality of many studies is compromised due to their small sample sizes and short durations, as well as their use of performance tests that do not reflect real-world conditions or are not reliable or relevant. Confounding variables are also poorly controlled. Furthermore, the benefits and risks demonstrated for these supplements may not apply to their use in enhancing other types of physical performance that were not assessed in the studies. In most instances, further research is necessary to fully comprehend the effectiveness and safety of specific ingredients.
Selected Ingredients in Dietary Supplements for Exercise and Athletic Performance
Most exercise and athletic-performance dietary supplements on the market contain multiple ingredients, especially those advertised for muscle growth and strength. However, most of the research conducted has focused on individual ingredients. Therefore, without clinical trials investigating specific combinations, it is impossible to determine the effects and safety of these multi-ingredient products. Additionally, the amounts of these ingredients vary greatly among different products. Sometimes, products include proprietary blends of ingredients, listed by weight, but the labels do not disclose the quantity of each ingredient in the blend. Manufacturers and sellers of exercise and athletic-performance dietary supplements rarely invest in or carry out scientific research on their proprietary products that meet the standards required for publication in reputable biomedical journals.
Antioxidants (vitamin C, vitamin E, and coenzyme Q10)
Exercise increases oxygen consumption and causes oxidative stress, resulting in the production of free radicals and oxidized molecules in different tissues, including the muscles. It is believed that these free radicals could hinder muscle force production, leading to muscle damage, fatigue, inflammation, and soreness. Some scientists propose that antioxidant supplements like vitamins C and E and coenzyme Q10 (CoQ10) could decrease free radical formation, thus reducing muscle damage and fatigue and aiding in recovery.
Studies indicate that the use of high doses of antioxidant supplements, specifically vitamins C and E, may actually hinder the positive effects of exercise rather than enhance them. For instance, one study enrolled 54 healthy Norwegian individuals, mostly recreational exercisers aged 20-30 years, who were randomly assigned to receive a daily dose of 1,000 mg of vitamin C and 235 mg (equivalent to about 520 IU) of vitamin E as DL-alpha-tocopherol or a placebo for 11 weeks while participating in an endurance training program primarily focused on running. It was observed that the supplements had no impact on maximal oxygen consumption (VO2max), which measures aerobic fitness and endurance capacity, or running performance. However, they did significantly decrease levels of biochemical markers associated with the creation of mitochondria and exercise-induced cell signalling, thereby diminishing the desired adaptations that occur as a result of skeletal muscle training. The same group of researchers conducted another trial involving 32 young men and women who followed a strength-training program for 10 weeks while taking the same doses of vitamins C and E. In comparison to the placebo, the supplements did not affect muscle growth, but did have a notable impact on the increase in arm strength as evaluated through bicep curls, and also weakened cellular signalling pathways related to muscle hypertrophy. Additionally, another study randomly assigned 18 young men aged 20 to 34 years to either receive a daily dose of 120 mg of CoQ10 for 22 days or a placebo. Following 7 days of intense cycling sprints, it was observed that the group taking CoQ10 experienced a significantly smaller improvement in mean power output compared to the placebo group, indicating a poorer adaptation to the training.
Based on the current research, it is generally believed that exercise-induced reactive oxygen species and nitric oxide have positive effects. These free radicals are responsible for triggering adaptations in muscle, resulting in increased production of mitochondria and hypertrophy of myofibers. When cells are exposed to high amounts of antioxidant supplements (such as vitamins C and/or E, which have the most supporting evidence), it seems to interfere with cell signalling, preventing certain beneficial physiological and physical changes that occur with exercise. However, these adaptations may not necessarily hinder improvements in VO2 max or endurance performance.
Arginine
L-arginine, which is an amino acid, can be found in various protein-rich foods such as animal products and nuts. On average, people consume around 4-5 grams of L-arginine per day through their diet. Additionally, the body can synthesize arginine in the kidneys, primarily from citrulline.
Some experts propose that the consumption of arginine supplements can enhance exercise and athletic performance through several mechanisms. To begin with, a portion of the arginine is converted into nitric oxide, a potent vasodilator that can boost blood flow and facilitate the transportation of oxygen and nutrients to the skeletal muscles. Additionally, intensified vasodilation can expedite the elimination of metabolic waste products associated with muscle fatigue, such as lactate and ammonia, which the body generates during physical activity. Moreover, arginine acts as a precursor for creatine synthesis, aiding in the provision of energy to the muscles for short-term, high-intensity movements. Lastly, arginine has the potential to increase the release of human growth hormone (HGH), consequently elevating insulin-like growth factor-1 (IGF-1) levels, both of which promote muscle growth.
The available research on supplemental arginine as a performance enhancer is limited and contradictory. It indicates that doses of 2–20 g/day of arginine do not significantly impact performance in either anaerobic or aerobic exercise. Additionally, arginine generally does not affect nitric oxide levels, blood flow, or exercise byproducts (such as lactate and ammonia), especially when taken by well-trained athletes (such as cyclists, tennis players, and judo practitioners) for 1–28 days. A recent review examined 54 clinical studies that investigated the effects of arginine supplementation on strength, endurance, muscle blood volume and flow, cardiorespiratory measures, and nitric oxide production in healthy, active adults. The authors concluded that arginine supplements (used alone or in combination with other ingredients like branched-chain amino acids [BCAAs] and lysine) provide little to no enhancement in athletic performance and do not improve recovery from exhaustion. Most of these studies had a small number of participants, predominantly young men aged 18–25 years (with only four including women), and lasted for 4–8 weeks (without any lasting for 3 months or longer). In the 18 studies that compared arginine to a placebo, the most common daily doses ranged from 2–10 g as a single dose or up to 20 g divided into three doses.
Studies examining the effects of supplemental arginine on HGH and IGF-1 levels have yielded contradictory results. The outcome appears to depend on various factors, including the age and fitness level of the participants, their use of other supplements, and the type and duration of exercise they engage in. Additional arginine may potentially decrease HGH secretion or increase both HGH and IGF-1 secretion. However, even if HGH secretion is increased, it may not necessarily lead to improved blood flow in the muscles or enhanced protein synthesis. There is limited evidence suggesting that arginine supplementation alone can raise muscle creatine levels or is more effective than consuming creatine directly.
Beetroot or beet juice
Beets contain a high amount of inorganic nitrate, which is a valuable source of nutrients. When nitrate is consumed, it can improve athletic performance by converting into nitric oxide in the body. Nitric oxide acts as a powerful vasodilator, increasing blood flow and delivering more oxygen and nutrients to the muscles. This increased blood flow can be especially beneficial during exercise when oxygen levels decrease. By dilating blood vessels in active muscles, nitrate enhances oxygen and nutrient delivery, reduces the oxygen required for submaximal exercise, and decreases the energy costs associated with muscle force production. Furthermore, it improves oxidative phosphorylation in mitochondria. Beetroot can be obtained in various forms such as juice, concentrate, or powder, but the nitrate content may differ significantly between different products.
Since 2007, there has been a significant increase in the number of clinical trials investigating the efficacy of beetroot juice or concentrate as an ergogenic aid. Generally, beetroot has been shown to enhance performance and endurance to varying degrees compared to placebo among runners, swimmers, rowers, and cyclists in time trials and time-to-exhaustion tests. However, not all studies have yielded the same results. The performance benefits of beetroot are more likely to be observed in recreationally active non-athletes rather than elite athletes. A study conducted on 10 recreationally active young male cyclists indicated a dose-response relationship, where consuming beetroot juice concentrate with a nitrate supply of 4.2 mmol (70 ml) on each of 4 days did not improve performance compared to a placebo. However, larger amounts of juice with a nitrate supply of 8.4 mmol (140 ml) did result in performance benefits. Nevertheless, consuming even larger quantities of beetroot juice with a nitrate supply of 16.8 mmol (280 ml) did not yield any additional performance benefits. There is limited research on the effects of beetroot on anaerobic performance, such as high-volume resistance exercise with multiple repetitions.
Further investigation is required to establish the potential advantages of supplementing with beetroot juice for nitrate intake in terms of exercise and athletic performance, as well as to ascertain the most effective dosages and protocols. The effects of prolonged beetroot-derived nitrate supplementation beyond a few weeks as an ergogenic aid have not been evaluated in any studies.
Beta-alanine
Beta-alanine is an amino acid that is not used by the body to create proteins. It is a precursor to the synthesis of carnosine, which is a dipeptide made up of histidine and beta-alanine, in skeletal muscle. The presence of carnosine helps to regulate changes in muscle pH that occur during high-intensity exercise, specifically from the anaerobic glycolysis process. This process produces energy but also leads to an accumulation of hydrogen ions, resulting in the formation of lactic acid and subsequently, lactate. This buildup can lead to a decrease in force and muscle fatigue. Having more carnosine in the muscle allows for better control of the pH levels during exercise, which can potentially improve performance in activities such as rowing and swimming that require intense efforts but are of short to moderate duration.
In terms of production, beta-alanine is synthesized in the liver and can also be found in animal-based foods like meat, poultry, and fish, although in relatively small amounts. The estimated intake of beta-alanine in the diet varies, ranging from none for vegans to approximately 1 g per day for heavy meat consumers. On the other hand, carnosine is present in animal-based foods such as beef and pork. However, orally consuming carnosine is not an efficient method of increasing muscle carnosine levels because it gets broken down into its individual amino acids during digestion. In contrast, consuming beta-alanine reliably increases the carnosine levels in the body. For instance, taking four to six grams of beta-alanine daily for 10 weeks can lead to an increase of up to 80% in muscle carnosine levels, particularly in trained athletes. However, the extent of this increase varies greatly between individuals. A study involving young, physically active but untrained adult men who took 4.8 g/day of beta-alanine for 5-6 weeks showed that the percentage increase in muscle carnosine content after 9 weeks of follow-up ranged from 2% to 69%. Among those considered “low responders,” the time it took for beta-alanine concentrations to return to baseline values during the washout period was less than half of that compared to the “high responders” (6 weeks vs. 15 weeks).
When evaluating beta-alanine as a potential ergogenic aid, studies have examined its efficacy with various participants, exercise protocols, activity protocols, and dosing regimens. Some studies suggest that consuming beta-alanine could lead to small performance benefits in competitive events that require high-intensity effort over a short period, such as rowing, swimming, and team sports like hockey and football, which involve repeated sprints and intermittent activity. However, other studies have not found such benefits. There is conflicting evidence on whether beta-alanine improves performance in endurance activities like cycling. Experts have not reached a consensus on whether beta-alanine primarily benefits trained athletes or recreationally active individuals. Studies have not consistently demonstrated a relationship between the dose of beta-alanine and its effect on performance.
Based on a review sponsored by the Department of Defense, the authors found limited evidence from 20 human trials that did not support the use of beta-alanine, whether consumed alone or in combination products, by active adults to enhance athletic performance or improve recovery from exercise-related exhaustion. The majority of the studies involved young men between the ages of 18 and 25, who consumed beta-alanine supplements ranging from 1.6 to 6.4 g/day, divided into two to four servings, throughout 4 to 8 weeks. In contrast, the International Society of Sports Nutrition (ISSN) conducted its own literature review and concluded that beta-alanine supplements, when consumed at a dosage of 4 to 6 g/day for a minimum of 2 to 4 weeks, can enhance high-intensity exercise performance lasting over 60 seconds, particularly in activities that focus on time-to-exhaustion. However, the performance benefits are less significant in exercises lasting more than 4 minutes, as the body increasingly relies on aerobic metabolic pathways to provide energy. The ISSN recommended further research to determine if beta-alanine can enhance the strength and muscle mass that are typically developed through regular resistance exercise, such as weightlifting.
The authors of the latest study on the effects of beta-alanine in exercise found that supplementation has a significant and positive impact on performance. This applies to both isolated-limb and whole-body exercises, particularly in protocols lasting 30 seconds to 10 minutes. However, the review also pointed out that the scientific literature on this topic mainly consists of small studies of short duration, with different exercise and supplement methods. In total, the 40 placebo-controlled studies that were reviewed used 65 exercise protocols and 70 exercise measures, involving 1,461 participants. Moreover, the beta-alanine dosage consumed by participants ranged from 84 to 414 g in studies lasting 28-90 days.
Beta-hydroxy-beta-methylbutyrate
HMB, which is derived from leucine, a branched-chain amino acid, makes up about 5% of the body’s leucine content. In the liver, HMB is converted to a precursor called beta-hydroxy-beta-methylglutaryl coenzyme A, which is necessary for cholesterol biosynthesis. Some experts suggest that stressed and damaged skeletal muscle cells, caused by exercise, require an external coenzyme source to restore structure and function in their cellular membranes for cholesterol synthesis. Furthermore, experts believe that the conversion of leucine to HMB stimulates muscle protein synthesis and reduces protein breakdown. To obtain 3 g/day of HMB, supplementation is the only practical option, as consuming over 600 g/day of high-quality protein, such as that found in 5 lb of beef tenderloin, would be required to obtain enough leucine (60 g) for conversion into HMB.
The efficacy of HMB has been studied for two decades, with variations in supplementation periods (ranging from 1 day to 6 weeks) and daily doses (ranging from 1.5 g to 6 g, with 3 g being the most common based on evidence indicating equivalent results to 6 g and better results than 1.5 g). Furthermore, studies have involved participants of varying ages (19 to 50 years), training status (e.g., untrained or trained athletes), training protocols (e.g., with machines or free weights), training duration (10 days to 12 weeks), consumption of other supplements (such as creatine), and other factors. Therefore, it is challenging to predict the potential benefits of HMB consumption for an individual engaging in exercise.
There is a consensus that HMB can aid in the recovery process following exercise that causes enough damage to the skeletal muscles. Therefore, to potentially experience the advantages of using the supplement, trained athletes must put in more effort compared to untrained individuals. Several studies propose that the usage of HMB has supplementary benefits, such as improving strength, power, skeletal muscle hypertrophy, and aerobic performance, for both trained and untrained individuals.
Betaine
Betaine, which is also referred to as trimethylglycine, can be found in foods like beets, spinach, and whole-grain breads. The estimated daily consumption of betaine ranges from 100 to 300 mg/day. The specific ways in which betaine could potentially improve exercise and athletic performance are still unclear, although several hypotheses exist. One hypothesis suggests that betaine may increase the synthesis of creatine, levels of blood nitric acid, and/or cellular water retention.
Betaine in supplemental form has been assessed as a potential ergogenic aid in a few small studies involving men. These studies primarily focused on bodybuilders and occasionally cyclists, evaluating strength- and power-based performance. However, the findings from these studies were inconsistent, and the observed performance enhancements were generally minor. The betaine dosage used in these studies varied between 2 and 5 g per day, administered for a maximum of 15 days.
Branched-chain amino acids
The branched-chain amino acids (BCAAs), leucine, isoleucine, and valine, are three essential amino acids. Their name is based on their chemical structure. BCAAs are present in approximately 25% of amino acids in foods that have complete proteins, which includes animal products like meat, poultry, fish, eggs, and milk. BCAAs make up about 14%–18% of amino acids in skeletal muscle proteins in humans. Unlike other essential amino acids, mitochondria in skeletal muscle can metabolize BCAAs to provide energy during exercise. Additionally, the BCAAs, especially leucine, may stimulate protein synthesis in muscles that have been exercised.
Research on the potential ergogenic effects of BCAAs is limited, and to date, there is little evidence indicating that these amino acid supplements improve performance in endurance-related aerobic events. BCAAs may delay fatigue or help maintain mental focus by competing with tryptophan, an amino acid that is a precursor to the neurotransmitter serotonin, which regulates mood and sleep. However, this effect has not been extensively studied. Some short-term studies lasting approximately 3 to 6 weeks suggest that taking around 10-14 g/day of supplemental BCAAs may enhance muscle mass and strength gains during training. Nevertheless, overall, the studies conducted so far have provided inconsistent evidence regarding the ability of BCAAs to stimulate muscle protein synthesis beyond what can be achieved through sufficient dietary protein intake. Additionally, it remains unclear from existing research whether consuming protein and BCAAs before or after a workout impacts their ability to optimize muscle protein synthesis and reduce protein breakdown.
Caffeine
Caffeine is a naturally occurring methylated xanthine that can be found in coffee, tea, cacao pods, and other herbal and botanical sources like guarana, kola nut, and yerba mate. By binding to adenosine receptors on cells, caffeine stimulates the central nervous system, muscles, and other organs including the heart. This blocking of adenosine activity, a neuromodulator with sedative-like properties, increases arousal, and vigour, and reduces fatigue. Caffeine may also lessen perceived pain and exertion. In the early stages of endurance exercise, caffeine may help use free fatty acids for energy and preserve muscle glycogen.
Caffeine is frequently utilized in energy drinks and “shots” that are praised for their ability to enhance performance. It is also present in energy gels that contain carbohydrates and electrolytes, as well as in anhydrous caffeine-only pills.
Numerous studies indicate that caffeine may improve athletic performance in individuals consuming approximately 2-6 mg/kg body weight before exercise, resulting in enhanced endurance, strength, and power during high-intensity team sports. For a person weighing 154 pounds (70 kg), this dosage equates to 210-420 mg of caffeine. Consuming a higher amount, though, is unlikely to yield further performance enhancement while also increasing the likelihood of encountering side effects.
After analyzing the available literature, it was found that the consumption of caffeine had an impact on performance specific to different sports, such as running, cycling, swimming, and rowing, as measured through time trials. Out of the 33 trials, 30 showed positive enhancements in performance, but only half of them were statistically significant. The studies indicated that performance improvement ranged from a decrease of 0.7% to an increase of 17.3%, suggesting that while caffeine was highly beneficial for some individuals, it slightly hindered performance for others. The varied effects on performance could be attributed to factors like the timing of caffeine ingestion, the mode or form of caffeine intake, and an individual’s habituation of caffeine.
Caffeine supplementation is more effective in supporting endurance-type activities (like running) and activities that involve long durations with intermittent activity (such as soccer) compared to short, intense exercise sessions such as sprinting or weightlifting. Some studies indicate that individuals who are not accustomed to caffeine may experience greater performance improvement from its consumption. It is recommended to limit caffeine intake to 50 mg per day or refrain from consuming it entirely for 2–7 days before participating in an athletic event to maximize any potential performance enhancement. However, conflicting evidence suggests that habitual caffeine consumption does not have an impact on performance.
Creatine
Creatine is a dietary supplement that has been extensively researched and is widely utilized for improving exercise and sports performance. It is naturally produced within the body and can also be obtained in small quantities from food. The main role of creatine is to produce ATP, which supplies energy to the muscles, especially during short-term activities. There are four potential ways in which creatine may enhance muscle performance: by increasing phosphocreatine stores used for ATP production at the start of intense exercise, speeding up the replenishment of phosphocreatine after exercise, reducing the breakdown of adenine nucleotides and the buildup of lactate, and/or improving glycogen storage in skeletal muscles.
The synthesis of creatine from the amino acids glycine, arginine, and methionine by the liver and kidneys results in approximately 1 g/day [114]. Creatine is also present in animal-based foods like beef (2 g/lb), pork (2.3 g/lb), and salmon (2 g/lb). In an individual weighing 154 pounds, the body contains around 120 g of creatine and phosphocreatine, predominantly located in the skeletal and cardiac muscles. However, it is only when individuals consume significantly higher quantities of creatine as a dietary supplement over an extended period that it may have ergogenic effects. Metabolized creatine is converted into creatinine, a waste product, and is excreted through the kidneys.
Short-term creatine supplementation (5 to 7 days) has been shown to significantly increase strength and power in both men and women in various settings, including the laboratory and sports. This includes improvements in bench press strength, cycling power, multiple sets of maximal effort muscle contractions, and performance in sprinting and soccer. For instance, in one study, 14 healthy, resistance-trained men aged 19-29 were randomly assigned to receive either 25 g of creatine monohydrate or a placebo for 6-7 days. Those taking the supplement experienced significant enhancements in peak power output during jump squats and repetitions during bench presses in all five sets, on three different occasions. Another study involved 18 well-trained male sprinters aged 18-24 who were given either 20 g/day of creatine or a placebo for 5 days. The participants taking creatine demonstrated improved performance in both 100-meter sprints and six intermittent 60-meter sprints, compared to those taking the placebo.
Supplementing with creatine for weeks or months enhances the ability to adapt to increased workloads during training. A study was conducted on 14 female collegiate soccer players during the off-season, where some participants were given creatine (15 g/day for 1 week and then 5 g/day for 12 weeks). These participants experienced significantly greater improvements in muscle strength, as assessed through bench press and full-squat maximal strength testing, but did not show any significant increase in lean tissue compared to those who received a placebo.
The effects of creatine supplementation can vary among individuals, depending on factors such as diet and muscle fibre types. For instance, vegetarians who have lower levels of creatine in their muscles may experience greater benefits from supplementation compared to meat eaters. In general, creatine is known to enhance performance in activities that involve short bursts of intense exertion, like sprinting and weight lifting, where the primary source of energy is the ATP-creatine phosphate system.
Creatine supplementation has minimal benefits for endurance sports like distance running or swimming that do not rely on the short-term ATP-creatine phosphate system for immediate energy. Additionally, it can lead to weight gain which may affect performance in these sports. Moreover, during aerobic exercise lasting more than 150 seconds, the body primarily depends on oxidative phosphorylation as the main energy source, a metabolic pathway that does not necessitate creatine.
Iron
Iron is a crucial mineral and plays a role in the structure of haemoglobin, a protein found in red blood cells that transports oxygen from the lungs to the body’s tissues. It is also a component of myoglobin, a muscle protein that supplies oxygen to the muscles. Furthermore, iron is needed for metabolizing substances to generate energy as part of cytochromes and dehydrogenase enzymes involved in substrate oxidation. When there is a deficiency of iron, it can lead to reduced capacity to carry oxygen and impaired muscle function, thus limiting an individual’s ability to engage in physical activity. The negative effects of iron deficiency include fatigue, lethargy, decreased aerobic capacity, and slower performance times in trials.
Athletes need to be mindful of their iron intake and loss to maintain iron balance. Teenage girls and premenopausal women face a higher risk of not getting enough iron from their diets. They require more iron than teenage boys and men because of the significant iron loss during menstruation, and there is a possibility that they do not consume enough iron-containing foods.
There are several reasons why athletes of both genders experience additional iron loss. The process of physical activity causes inflammation, which reduces the absorption of iron from the intestines and the utilization of iron through a peptide called hepcidin, which regulates iron balance. Furthermore, iron is lost through sweating. The repeated impact on hard surfaces during activities can result in the destruction of red blood cells in the feet, known as foot-strike hemolysis. Additionally, the consumption of anti-inflammatory drugs and painkillers can cause some blood loss from the digestive system, resulting in a decrease in iron reserves.
Highly bioavailable heme iron can be found in lean meats and seafood, making them the richest dietary sources. On the other hand, non-heme iron, found in plant-based foods like nuts, beans, vegetables, and fortified grain products, is less bioavailable than heme iron.
The efficacy of iron treatments in improving iron status and aerobic capacity in iron-deficient but non-anaemic endurance athletes was examined through a systematic review and meta-analysis. This review included 19 studies with 80 men and 363 women, who had a mean age of 22 years. The results demonstrated that iron treatments effectively improved iron status but did not necessarily lead to improved aerobic capacity or endurance performance. Additionally, another systematic review and meta-analysis evaluated the effects of iron supplementation on exercise performance in women of reproductive age. A majority of the 24 identified studies were small and had a risk of bias due to their limited sample sizes. However, the study authors suggested that preventing and treating iron deficiency could potentially enhance the performance of female athletes participating in endurance, maximal power output, and strength-based sports.
Protein
Protein is indispensable for muscle construction, upkeep, and repair. When exercising, there is a rise in intramuscular protein oxidation and breakdown. Subsequently, muscle-protein synthesis escalates for approximately one or two days. Consistent resistance exercise yields an accumulation of myofibrillar protein (the predominant proteins in skeletal muscle) and an augmentation in the size of skeletal muscle fibres. On the other hand, aerobic exercise induces a comparatively less substantial build-up of protein in active muscles, primarily within the mitochondria. This augments the oxidative capacity (utilization of oxygen) for subsequent workout sessions.
To meet their nutrient needs, athletes must consider both the quality and quantity of protein. They must obtain essential amino acids (EAAs) either from their diet or through supplementation. This is crucial to support muscle growth, maintenance, and repair. The nine EAAs include histidine, isoleucine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan, and valine. Most complete proteins, which contain all EAAs, consist of approximately 40% EAAs. Therefore, a meal or snack containing 25 g of total protein would provide around 10 g of EAAs.
For muscle-protein synthesis to occur and muscle-protein breakdown to be minimized, it is essential to consume enough protein in the diet. Consuming dietary protein raises the levels of amino acids in the bloodstream, which are then absorbed by muscle cells. Satisfactory protein intake is primarily important for maximizing the training response and facilitating recovery after exercise.
The consumption of high-quality protein, providing approximately 10 g of EAAs, within 0-2 hours after exercise appears to be the most effective way to increase muscle strength and mass through muscle protein synthesis. However, a meta-analysis of randomized clinical trials discovered that consuming protein within an hour before or after exercise does not significantly enhance muscle strength or size or aid in muscle repair or remodelling. The “window of anabolic opportunity,” which occurs after exercise and involves reducing muscle protein breakdown, building muscle, and increasing mitochondrial proteins to enhance oxygen usage in working muscles, can last for up to 24 hours.
Multiple studies have indicated that consuming protein before bedtime can enhance protein synthesis during sleep and potentially promote muscle growth and strength in individuals engaged in resistance training. In these studies, participants ingested a nighttime beverage containing either 27.5 or 40 g of casein protein derived from milk, which resulted in elevated levels of circulating amino acids throughout the night. This increase in muscle protein synthesis has been observed in studies where the plasma amino acid levels were raised.
