Supplements and Athletic Performance


For this post, I want to look at how specific dietary supplements can affect (and improve) athletic performance. Appropriate dietary intake not only impacts body weight and composition (which can indirectly affect athletic performance), but also:

  • available energy stores and fuel utilization

  • rate and efficiency of recovery

  • muscular contraction

  • preventing and repairing injuries

  • maintaining or enhancing the immune system

...just to name a few.

While obtaining appropriate intake through whole foods is seen as the gold standard for athletes and physically active individuals, there are a few key dietary components that may be beneficial with additional supplementation. In this case, supplementation may be warranted where whole food sources likely provide a relatively low amount compared to therapeutic dosages. Let's make this clear: no you do NOT need to take supplements if your dietary intake is adequate, but there is some evidence behind specific supplementary nutrients that can aid in enhancing athletic performance.

But first, let's define 'enhancing athletic performance' as including:

  • Any quantitative improvement in athletic abilities (increased strength, speed, endurance, training volume capacity, etc), body composition (changes in lean body mass/muscle mass vs body fat), recovery (increased time/efficiency for muscle protein synthesis or cartilage repair post-exercise)

  • Any qualitative improvements (enhanced quality of training or recovery, i.e. not feeling like you're going to die during or after a workout)

Also, when I say athletes, I am referring to any individual seeking physical activity-related goals (so even if you are just an average exerciser that wants to get stronger or faster, congratulations- I am now calling you an athlete!)

**The nutrition supplements that are included in this post contain the most viable research for enhancing athletic performance, body composition, and/or recovery. However, many athletes would agree that there is also a huge psychological impact for seeing improvements in athletic performance. To this respect, just because there is a placebo effect (improvements in performance are seen despite the actual supplement/nutrient NOT being present, but rather the belief that it is working) really would not matter much as long as the athlete is seeing the improvements they want to see. (A la 'Michael's secret stuff' in Space Jam...)

PLEASE TAKE NOTE: I am NOT including 'pre-workout' powders/supplements as there is little control over the amounts of ingredients present in a 'proprietary blend' nor are there substantial research findings on the implications of mixtures of these ingredients. The biggest issue with determining significant evidence for a pre-workout supplement is the fact that supplements are NOT regulated, and therefore the ingredients are NOT controlled for. This means that there is NO guarantee that what is on the label is present in the supplement (or that the product being tested is actually what you are taking), nor are there any specific amounts of ingredients but rather a generalized 'propriety blend'. This makes for a disaster when it comes to testing its efficacy in controlled trials because the supplement itself is NOT controlled for. *It is your decision to use pre-workout supplements if you want to, but take note that the evidence I am sharing in this post is based on the individual nutrients acting alone, NOT in a mixture with other dietary components.

Let's start first with the most commonly used sports nutrition supplement: protein powders.

Protein powders should be seen as a dietary supplement where they are providing protein, of which you can (and should) be getting through your diet anyway (like from meats, eggs, dairy, grains+legumes, etc). A protein powder supplement can therefore be used as an aid to ensure that you are getting the appropriate total protein intake for your needs. As mentioned in my previous post on dietary protein, the suggested recommendations for athletes may be between 1.2-2.0g/kg body weight (although higher intakes have shown NO adverse effects, there is also a lack of noted benefits when protein intake exceeds needs.) (McArdle, et al. 2013) That being said, if you are meeting your protein requirements through food intake alone, then there is no need to also supplement with a protein powder. HOWEVER, due to comparatively increased protein requirements for athletes and highly active individuals, it is not uncommon to fail to meet these protein requirements through dietary intake alone, and thus the use of a protein supplement could provide a benefit. (McArdle, et al. 2013) [Dietary protein, particularly animal proteins, are likely to be your most expensive items at the grocery store, and may be associated with digestive issues for some. Not to mention the fact that diets that are high in animal foods TEND to also be low in fiber, if fiber content is NOT being controlled for, which can be associated with further health complications. If this is the case, including some complementary plant proteins can provide some additional fiber and may save some money. Notably, the use of a protein powder supplement can aid in reducing costs, reducing possible digestive issues, and reducing prep/cook time and fridge/freezer space.]

Athletes notably have a higher protein requirement due to excessive protein breakdown from exercising muscles and enzyme utilization from increased metabolic processes. (McArdle, et al. 2013) There is also an increased risk for additional protein breakdown (more than what would normally be broken down from exercise) when glycogen stores are depleted during high intensity exercise to where a HIGH carbohydrate diet is noted to aid in conserving muscle during chronic high intensity training. (McArdle, et al. 2013) This means that if you are depleted in glycogen (like from low carbohydrate diet+chronic high intensity exercise) then you are utilizing PROTEIN for energy (NOT fat because fat oxidation only occurs at lower intensities) which means that you are sacrificing your muscle while you exercise. This is a huge takeaway point for athletes that undergo high intensity exercise: carbohydrates are your friend! They provide your fuel source AND prevent muscle degradation which further promotes lean body mass and REE (resting energy expenditure). *You may see some individuals who follow a low carbohydrate diet supplementing with BCAAs to provide an alternative (amino acid) cellular energy source for high intensity exercise. (more about that in a bit)

The most widely recognized protein powder is whey protein (whey comes from milk/dairy) due to its high bioavailability and quality (complete protein, high in leucine) however there is no notable difference in athletic performance between supplementation with whey protein powder, beef protein isolate, or chicken protein isolate according to a recent study. (Sharp, et al. 2017) These proteins are all complete protein sources (from animal protein) and where this study found that all three supplements were associated with similar improvements in strength and body composition in the tested subjects compared to placebo, but with no significant differences between the different proteins. (Sharp, et al. 2017) Plant protein supplements also come in a variety from soy, to pea+rice, hemp, and more. There are study findings to suggest that when total protein content is controlled for, there are no significant differences between a whey protein supplement and a plant-based protein but where both proteins showed similar improvements in lean body mass, muscle mass, strength, and power with decreased fat mass when ingested post-exercise during an 8 week resistance training regimen. (Joy, et al. 2013) Plant proteins however are primarily incomplete proteins by themselves (legumes lack methionine, grains lack leucine) to where combinations of complementary proteins (legumes+grains) would therefore provide all of the essential amino acids. *Soy is a plant protein that is already complete. The combination of pea+brown rice protein is suggested to be the highest quality for plant protein supplements.

As far as improving athletic performance...

Protein itself is NOT going to directly improve your athletic performance, but where maintaining appropriate protein intake can offset for excessive protein utilization from training and can help to maintain lean body mass and metabolic functioning (and where body composition may indirectly affect athletic performance depending on the activity). (McArdle, et al. 2013) It has been suggested that dietary protein content consisting of 25-35% of total calories is associated with maximizing muscle protein synthesis with implications for increased energy expenditure, enhanced functional capacity of skeletal muscles, and an increase in lean body mass (which also increases REE/BMR or the energy expenditure when at rest). (Arciero, et al. 2015) It is further theorized that timed protein intake throughout the day (at least 20g per meal, ~6 times per day) is associated with increased lean body mass compared to fewer meals (and thus less frequent protein intake throughout the day). (Arciero, et al. 2015) In this study, individuals were given either a high protein diet (~35% of calories from protein, ~40% from carbohydrates) for 3 meals per day, 6 meals per day, OR a control diet (~15% of calories from protein, ~60% from carbohydrates) with all diets being controlled for total calories. (Arciero, et al. 2015) During this trial, the high protein 6x day group exhibited significantly decreased total body fat and abdominal fat, and increased lean body mass compared to the high protein 3X day group AND the control diet (i.e. even when protein content is controlled for, it was the frequency of intake that mattered). (Arciero, et al. 2015) *Take note: in this study, calories were controlled for, and the high protein conditions contained the same macronutrient ratios, but with different frequency of feedings. This study suggested that more frequent intake of protein is associated with decreased fat mass and increased lean body mass.

What about BCAAs, do I need to take those too?

BCAAs are the branched-chain amino acids leucine, isoleucine, and valine, which are ESSENTIAL for muscle protein synthesis AND energy metabolism (i.e. may be used as an energy source). (Arciero, et al. 2015) (I mentioned how BCAAs can provide an alternative energy source during high intensity exercise when glycogen is depleted, but take note that due to their essential role in muscle protein synthesis, if the BCAAs are also depleted, like being used as an energy source during exercise, then muscle protein synthesis may also be impacted. More reason to not let glycogen get depleted to the point that BCAAs are used for energy and not for muscle protein synthesis.)

These branched-chain amino acids are just three of the nine essential amino acids that are present in all complete proteins which means that they are already present in animal proteins/whey protein and in complete/complementary plant proteins. Leucine however is the most notable amino acid for contributing to muscle protein synthesis through it's actions on mTOR (which regulates protein synthesis). (Arciero, et al. 2015) Supplementation with just 5g of leucine alone was shown to have similar effects to 25g whey protein. (Arciero, et al. 2015) Let me repeat that: 5g of just leucine by itself has been shown to have similar effects for muscle protein synthesis as 25g of whey protein (or 1 average serving of a complete protein). Pre-exercise supplementation (of leucine) is suggested to aid in promoting muscle growth (if whole food sources are being limited due to weight loss or weight maintenance diets). (Arciero, et al. 2015) Whole-food sources of leucine includes a 3.5 oz serving of most animal proteins (beef, pork, chicken, turkey, salmon, cod or tuna) containing between 1.3-2.3g leucine, while a serving of 2 eggs, or 100g of haddock, shrimp or scallops contains less than 1g leucine. (Arciero, et al. 2015) Based on these estimations, it would take approximately 8-10oz of meat/day to obtain the suggested leucine concentration for favorable effects on muscle protein synthesis. However, depending on the individual and their diet, this amount can also be easily reached with a protein powder (like whey) where the leucine content is generally 2.3-3.5g per 1 serving, in addition to normal dietary protein intake from whole foods.

So should you take a supplement?

If you are taking in adequate protein already to meet your needs, then you are ALSO getting appropriate amounts of BCAAs and leucine. The big takeaway here: If your dietary intake is NOT already meeting your protein requirements, then supplementation may help. If you supplement with a whey protein, then you are ALSO already getting enough leucine and BCAAs so no need to further supplement. IF you are in a glycogen-depleted state (like a low-carb diet with chronic high intensity training), additional BCAAs, and specifically leucine, may aid in reducing muscle catabolism.

When it comes to improving blood flow (vasodilation)...

Surprise surprise: having adequate blood flow is important! When it comes to blood flow during exercise, the efficiency with which you can pump blood (carrying oxygen and nutrients like glucose) to the tissues, and carrying waste (carbon dioxide, etc) away from tissues, the better for your overall athletic performance and recovery. *Most pre-workout formulas will contain one or more vasodilators and one or more substances to increase energy (will cover stimulants and cellular energy sources in a bit) for this reason: improving blood flow can increase exercise duration, efficiency, and improve recovery.

Nitric oxide is the principle compound responsible for vasodilation ('dilating the blood vessels') but it is a gas produced in the body (you can't just ingest it from food or a supplement). There are precursors to nitric oxide that you can ingest though, particularly nitrates, and the amino acids arginine and citrulline-malate. (Bescos, et al. 2012) It is important to note that while these dietary supplements may show some effects in improving athletic performance, that training status can be largely associated with these effects where for example it was often the untrained individuals that showed improvements with supplementation in controlled trials while the more highly trained athletes did NOT show any improvements. (Bescos, et al. 2012) *Improved blood flow is a training adaptation, meaning the more highly trained the athlete, the more finely tuned their system (like efficient blood flow), and therefore the less room for improvement via supplements.

First let's talk about nitrates...

Nitrates and nitrites are present in vegetables like beets, lettuce, and spinach, but where there has been some negative connotations around foods containing nitrates like processed meats that contain sodium nitrate (you may have seen nitrate-free bacon for example). (Bescos, et al. 2012) The proposed fear behind dietary nitrates is due to the association between nitrosating agents having carcinogenic effects in animal studies, yet extensive studies have found NO association between dietary nitrate intake and cancer in humans. (Bescos, et al. 2012)

The intake of dietary nitrates from beetroot juice has been studied extensively however where most results suggest an INCREASED capacity for endurance work by decreased VO2max at variable intensities, which equates to increased economy during exercise. (Dominguez, et al. 2017) Improved economy of exercise means that there is a higher power output at the same VO2 level (i.e. doing more work without extra effort). (Dominguez, et al. 2017) Studies that look at the potential impact of dietary nitrates from beetroot juice have shown an increased time to exhaustion (i.e. increased endurance) and a reduction in the amplitude of the pulmonary response (i.e. less cardiovascular effort for a task, and longer duration before feeling tired). (Bescos, et al. 2012) A meta-analysis has summed up the available evidence as suggesting a role of beetroot juice supplementation with increasing efficiency, time to exhaustion, and may improve anaerobic threshold intensities and VO2max. (Dominguez, et al. 2017) It is suggested that acute intake (1-5 days) of beetroot juice may decrease blood pressure and increase VO2max and peak power output however these effects may depend on the training status of the individual. (Arciero, et al. 2015) *The dosages studied were approximately 16oz of beetroot juice, or the equivalent of 2-3 beets. Effects were noted to take place 2-3 hours after ingestion, which would imply for example taking it at least 90 minutes before a long endurance event.

What about the amino acids arginine and citrulline-malate?

Arginine is a precursor to nitric oxide, and thus can indirectly act as a vasodilator. Arginine supplementation has been associated with improved sport performance (namely increased VO2max) in doses as low as 2g/day for 45 days in a sample of trained athletes, but without any effects on body composition. (Pahlavani, et al. 2017) Studies of arginine supplementation have shown that higher dosages of 14g/day for 6 months were associated with increased maximal power in women and where acute intake of 6g/day for 14 days was associated with increased phase II VO2 kinetics in men (which means less oxygen debt after exercise and less lactic acid accumulation) i.e. increased tolerance for endurance exercise. (Bescos, et al. 2012) HOWEVER these effects were NOT seen in already highly trained athletes. *As a point of reference, usual dietary intake to meet protein needs often equates to approximately 4-5g arginine/day (meaning eating a diet that meets your protein needs will likely already get you this much arginine in a day).

Citrulline is a precursor to arginine, and thus a precursor to nitric oxide. There may be some merit in supplementation with citrulline + malate (citrulline-malate) where some study findings have shown significant increases in total number of repetitions performed and decreased RPE (rate of perceived exertion) in those who took citrulline-malate (8g CM+8g dextrose) compared to placebo (8g dextrose). (Glenn, et al. 2017)

Another popular amino acid used in 'pre-workout' formulas...

B-alanine is a precursor to carnosine which can buffer intracellular H+ and therefore reduce the acidic load in the muscle to allow for prolonged anaerobic (high intensity) work. (Arciero, et al. 2015) Conflicting results from various studies suggest that the role of B-alanine may depend on training where for example a dose of 6.4g/day for 4 weeks in 800m runners showed improvements in running time trials, but where 4.8g/day for 4 weeks in 400m runners did not show a significant improvement in running times. (Arciero, et al. 2015) A proposed theory behind differences in effectiveness of B-alanine supplementation improving athletic performance may be due to reduced sensitivity in those who are already highly trained as these individuals would already have effective muscle buffering capacity as a training adaptation. (Arciero, et al. 2015) *This essentially means that the possible effectiveness of B-alanine may depend on both your training status and training modality. The more highly trained, the more efficient your body is at buffering this acidic load already.

What about energy?

When we talk about improvements in energy, we are looking at both a stimulant effect (enhancing the central nervous system response) as well as cellular energy (providing a cellular energy substrate).

Caffeine is a stimulant that has been shown to influence endurance, strength, power, and other aspects of high intensity exercise notably through its associations with increasing energy expenditure, fat oxidation (and thus glycogen sparing), and increased central nervous system activity. (Arciero, et al. 2015) A meta-analysis shows that caffeine is associated with mild benefits for short duration high intensity exercise but with a much stronger influence on endurance activities. (Arciero, et al. 2015) There are also some study findings to suggest that caffeine can attenuate for performance declines that can happen due to glycogen depletion which means that in a state where glycogen is depleted (like fasting, very low carb diet, long endurance events, etc) caffeine can help to maintain athletic performance to a degree. (Arciero, et al. 2015) *It should be noted that most of the studies of caffeine are based on a high dose of 3-6mg/kg body weight from a caffeine supplement, NOT from that equivalent in coffee.

And when it comes to a cellular energy substrate...

Creatine is a naturally occurring compound that is found in meats and seafood and is primarily present in skeletal muscle. (Kreider, et al. 2017) Creatine phosphate plays a key role in ATP formation during short duration, sprint/explosive movements (lasting up to 10 seconds) until those creatine stores are depleted and anaerobic respiration (glycolysis) can take over. (Kreider, et al. 2017) (Yes, we ALL already have creatine in our cells, and it is already being put to use immediately when we initiate activity/short-term work). The amount of stored creatine you have/can use will depend on muscle mass with requirements varying from 1-3g of creatine/day up to 5-10g/day in those with larger muscle mass. (Kreider, et al. 2017) Approximately 1lb of beef or salmon contains ~2g creatine and the liver and kidneys can also synthesize creatine (in order to make up the difference from dietary intake) to refill these stores daily. (Kreider, et al. 2017) (Again, WE ALL have creatine and use creatine-it is not specific for muscle-bound athletes or males or young people. It is present in all bodies of all ages, genders, and activity levels. The only differences will come from the relative amounts that we contain/can store based on individual differences in muscle mass.)

Creatine supplementation is therefore suggested to provide for filling a larger reserve, and for fueling these sprint/explosive movements as well as increases in lean muscle mass, strength, and anaerobic performance (may facilitate greater training volume). (Arciero, et al. 2015) Creatine loading is the suggested method for successfully building up reserves by taking in up to 20g/day for the first week, followed by 5g/day for 4-8 weeks. (Arciero, et al. 2015) This method of creatine loading showed increases in lean muscle mass and training efficiency. (Arciero, et al. 2015) It is even suggested that 2-5g 1 hour before resistance exercise can enhance muscular and physical performance. (Arciero, et al. 2015) Food sources of creatine include animal proteins like salmon, pork, beef, cod and herring but in relatively low amounts (compared to a supplement) where for example beef contains 0.8g in a 6oz serving. (Arciero, et al. 2015) [It would take about 2lbs of beef/day to equal the amount of creatine shown to have these muscular performance benefits.] **The International Society of Sports Nutrition has deemed creatine to be SAFE for both short term and long term (Up TO 30g/DAY FOR 5 YEARS; that's a lot, and still safe!) for healthy individuals in populations ranging from infants to elderly. (Kreider, et al. 2017)

Let's talk about recovery...

Recovery from exercise is important to not only allow for training adaptations to occur (it is during recovery when your body reaps the benefits from the workout) but importantly for athletes, where appropriate recovery can help to prevent injury.

Some of the key factors to recovery include:

  • Adequate protein intake

  • Fuel replenishment

  • Rest

However, there may be some merit in additional factors like aiding in connective tissue repair, as well as the controversial topic of controlling for inflammation.

For connective tissue repair, vitamin C is a notable nutrient due to its role in collagen synthesis, (among it's many other roles like carnitine synthesis, tyrosine synthesis and subsequent neurotransmitter synthesis, as well as acting as an antioxidant). (Gropper and Smith, 2013) For connective tissue repair, vitamin C is responsible for the cross-linking in the synthesis of new collagen, which is a structural protein of the connective tissues like tendons and cartilage, as well as bones, teeth, and even skin. (Gropper and Smith, 2013) Regular dietary intake of fruits and vegetables should supply the recommended amount of vitamin C (~90mg/day for general population; as a reference: 1 cup of strawberries contains about 90mg vitamin C), but where additional supplementation may be helpful in those who are deficient (from low dietary intake or high demand in the body). (Gropper and Smith, 2013) There are some findings to suggest that supplementation with 15g of a vitamin C-enhanced gelatin product (gelatin is a dietary form of animal collagen) prior to exercise can stimulate collagen synthesis in humans. (Shaw, et al. 2017) These findings suggest a possible association with improved connective tissue repair and recovery from exercise or injury. (Shaw, et al. 2017) * As a side note, you may have heard about glucosamine/chondroitin (found in shellfish) as a supplement for joint support, HOWEVER the results are contradictory where some findings suggest possible effects from high dose for a long duration (for osteoarthritis pain management) but where the most recent studies show NO difference between the glucosamine/chondroitin supplement and placebo during rehabilitation following ACL surgery in athletes. (Eraslan and Ulkar, 2015)

Now let's finish up by addressing inflammation...

Inflammation is the natural recovery response to physical activity (this is the influx of blood carrying nutrients, amino acids, fluid, etc to the damaged tissues in order to repair those damages and thus reap the benefits of the workout). This inflammatory process is therefore not only a NORMAL response, but should be welcomed and left uninterrupted (recovery can last between 24-72 hours in most people). Methods aimed at blunting this inflammatory response (like taking anti-inflammatory supplements/foods, or using an ice bath post-workout) will not only NOT equate to quicker or more effective recovery from a workout, but can actually HINDER your full recovery from the workout.

In extreme cases, like a competition day with multiple events, or with high volume training (like during a short-term training camp with 2x/days) where there is a high amount of muscle damage with minimal amount of rest/recovery time, the addition of some aid to reduce inflammation can help to alleviate discomfort and allow for continued physical activity. Anti-inflammatory supplements like tart cherry juice are noted for these circumstances where cherries are rich in antioxidants and bioactive compounds that can elicit anti-inflammatory effects, of which can aid in reducing pain and inflammation post-exercise during recovery. (Arciero, et al. 2015) The use of tart cherry juice as a recovery aid has been suggested to be most effective for recovery from high intensity, muscle-damaging resistance exercise and endurance exercise. (Arciero, et al. 2015) Most of the study results are based on 12-16oz of tart cherry juice, or the equivalent of 90-120 cherries per day.

Ice baths have been used in the past for cases where continual physical activity is needed within a narrow window of time. The cold water constricts blood vessels which reduces blood flow, and inflammation of those tissues, but most importantly means delaying the recovery process. Study findings suggest that the use of 5 minute ice baths post-exercise not only does NOT decrease DOMS (delayed onset muscle soreness), it can actually be associated with detrimental effects in post-trial athletic performance compared to contrast baths (alternating between hot and cold tubs). (Higgins, et al. 2011)

*Take note: blunting the inflammatory response is NOT the same as RECOVERY, but rather allowing for continued activity.

"Allowing for continued activity" can be seen as:

  • 'just get the job done' (like during a competition day)

  • training for a high volume stimulus physically and psychologically (i.e. NOT training to improve your skill/strength/speed, but rather increasing the volume to push your 'comfort level').

If you want to reap the benefits of a workout and actually see improvements in your physical activity, then allowing adequate time for uninterrupted recovery is KEY.

References:

Arciero P, Miller V, Ward E. Performance-Enhancing Diets and the PRISE Protocol to Optimize Athletic Performance. Journal of Nutrition and Metabolism. 2015; https://www-ncbi-nlm-nih-gov.proxy.lib.fsu.edu/pmc/articles/PMC4408745/

Bescos R, Sureda A, Tur J, et al. The Effect of Nitric-Oxide-Related Supplements on Human Performance. Sports Medicine. 2012; 42(2):99-117. https://link-springer-com.proxy.lib.fsu.edu/content/pdf/10.2165%2F11596860-000000000-00000.pdf

Dominguez R, Cuenca E, Mate-Munoz J, et al. Effects of Beetroot Juice Supplementation on Cardiorespiratory Endurance in Athletes: A Systematic Review. Nutrients. 2017; 9(1): https://www-ncbi-nlm-nih-gov.proxy.lib.fsu.edu/pmc/articles/PMC5295087/

Eraslan A, Ulkar B. Glucosamine supplement after anterior cruciate ligament reconstruction in athletes: a randomized placebo-controlled trial. Research in Sports Medicine. 2015; 23(1):14-26. http://resolver.ebscohost.com.proxy.lib.fsu.edu/openurl??sid=Entrez%3aPubMed&id=pmid%3a25630243&site=ftf-live

Glenn J, Gray M, Wethington L, et al. Acute citrulline malate supplementation improves upper- and lower- body submaximal weightlifting exercise performance in resistance-trained females. European Journal of Nutrition. 2017; 56(2): 775-784. https://link-springer-com.proxy.lib.fsu.edu/article/10.1007%2Fs00394-015-1124-6

Gropper S, Smith J. Advanced Nutrition and Human Metabolism. 6th edition. Wadsworth- Cengage Learning. 2013.

Higgins T, Heazlewood I, Climstein M. A random control trial of contrast baths and ice baths for recovery during competition in U/20 rugby union. Journal of Strength and Conditioning Research. 2011; 25(4): 1046-1051. https://insights-ovid-com.proxy.lib.fsu.edu/pubmed?pmid=20661161

Joy J, Lowery R, Wilson J, et al. The effects of 8 weeks of whey or rice protein supplementation on body composition and exercise performance. Nutrition Journal. 2013; 12:86. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3698202/

Kreider R, Kalman D, Antonio J, et al. International Society of Sports Nutrition position stand: safety and efficacy of creatine supplementation in exercise, sport, and medicine. Journal of the International Society of Sports Nutrition. 2017; 14:18. https://www-ncbi-nlm-nih-gov.proxy.lib.fsu.edu/pmc/articles/PMC5469049/

Mcardle W, Katch F, Katch V. Sports and Exercise Nutrition. 4th edition. Lippincott, Williams, and Wilkins. Philadelphia, PA. 2013.

Pahlavani N, Entezari M, Nasiri M, et al. The effect of L-arginine supplementation on body composition and performance in male athletes: a double-blinded randomized clinical trial. European Journal of Clinical Nutrition. 2017; 71(4):544-548. http://www.nature.com.proxy.lib.fsu.edu/ejcn/journal/v71/n4/full/ejcn2016266a.html?foxtrotcallback=true

Sharp M, Lowery R, Shields K, et al. The Effects of Beef, Chicken, or Whey Protein Post-Workout on Body Composition and Muscle Performance. Journal of Strength and Conditioning Research. 2017; https://insights-ovid-com.proxy.lib.fsu.edu/pubmed?pmid=28399016

Shaw G, Lee-Barthel A, Ross M, et al. Vitamin C-enriched gelatin supplement before intermittent activity augments collagen synthesis. American Journal of Clinical Nutrition. 2017; 105(1): 136-143. http://ajcn.nutrition.org.proxy.lib.fsu.edu/content/105/1/136