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5 Common Athletic-Performance Supplements: What's the Evidence?
By Matthew T. Stratton and Len Kravitz, PhD

In 2012 the nutritional supplements industry brought in $32 billion and is estimated to nearly double to a staggering $60 billion by 2021 (Lariviere, 2013). This comes as no surprise to anyone who has walked into any supplement store recently to find walls lined with everything from multivitamins to fish oil pills to pre-workout formulas and protein powders. With the extensive ambiguous marketing and pseudoscience these days, it can be hard to discern what is indeed effective and worth your client's hard earned money. That is why we decided to look into what the science says about five (creatine, arginine, beta-alanine, glutamine, and branched chain amino acids) of the most common athletic performance supplements on the market.

The purpose of creatine supplementation is to elevate creatine storage levels in muscle in order to promote a faster regeneration of ATP between high intensity bouts of exercise (Cooper et al., 2012). Cooper and colleagues summarize that creatine supplementation is proposed to be most effective during short burst exercise that typically lasts up to 30 seconds. Creatine monohydrate (CM) is the most frequently used form of creatine in research (Cooper et al.). Creatine monohydrate is commonly consumed by starting with a loading period of 5-7 days where the user takes 5 grams four times a day. Following the loading period, CM is consumed in 3-5 grams of maintenance dosages once daily, usually after workout. However, as reported in a systematic review by Cooper et al., the loading phase is not necessary. Individuals who start with the maintenance dose of 3-5 grams/day will reap similar benefits, typically between 21-28 days after initiating supplementation.

Cooper and associates (2012) summarize that exercisers who combine CM and resistance training experience an average increase of 1-repetition maximum (1RM) exercise of 8% and 14% greater endurance strength as compared to a placebo (a substance that has no proposed beneficial effect). While it is worth noting that previous studies have demonstrated mixed results with creatine supplementation, these outcomes can largely be explained by the variance in dosing protocols of the investigations (Cooper et al.). Presently, the large body of scientific evidence suggests that CM, when taken concurrently with resistance exercise training, will increase muscle mass and muscular strength. Creatine supplementation may also be beneficial for high intensity sprints, but its benefit appears to diminish as the length of the time spent exercising increases (Cooper et al.). From a safety standpoint, creatine has been shown to slightly raise creatinine (a chemical waste product produced by muscle metabolism that is filtered out of the blood by the kidneys) levels. However, creatine supplementation has not been shown to have negative consequences to kidney function and health in already healthy individuals (when proper dosage recommendations are followed). Alas, the long-term effects of creatine supplementation are unclear, with no definitive negative or positive effect currently recognized.

Another popular supplement commonly found in pre-workout formulas is l-arginine. L-arginine is a 'conditional' essential amino acid (meaning it is typically nonessential amino acid, but can become essential during periods of muscle growth) that is purported to raise nitric oxide (NO) levels due to it being a NO precursor (Fahs, Heffernan, and Fernhall, 2009). Oral supplementation with l-arginine has shown to benefit populations with reduced endothelial NO production, including persons with cardiovascular disease, diabetes, and hypertension (McConell, 2007). Because of its clinical use it has been theorized that this increase in NO levels would lead to greater levels of vasodilation in skeletal muscle during resistance exercise; however, this theory has yet to be supported. A 2009 study by Fahs and colleagues found no increase in vasodilation or blood flow to muscles of the chest or biceps when performing bench press or bicep curls, respectively. To date, the majority of studies have failed to report an increase in vasodilation and blood flow to working musculature. The body of literature seems to suggest that there is no real benefit to supplement with l-arginine in a healthy, exercising population.

Beta-alanine is an amino acid that binds with histidine to create carnosine. The main goal of beta-alanine supplementation is to raise intramuscular carnosine levels in order to increase the intracellular pH buffering capacity of the muscle (Trexler et al., 2015). Thus beta-alanine supplementation is taken to minimize the effect of acidosis (i.e., the burn) in exercise. There may be a particularly pronounced effect in vegetarians, as the body's natural carnosine levels are largely affected by regular consumption of animal proteins, such as beef, pork, poultry, and fish. In a systematic review, Trexler and colleagues report that beta-alanine will increase time to exhaustion in exercise bouts lasting 60 to 240 seconds, however there was no effect on exercise capacity in bouts lasting less than 60 seconds, such as traditional weight training. This shows that the supplement can be beneficial for athletes who normally need to perform bouts between 1-4 minutes. However it will not be very beneficial for exercises whose bursts exercise are less than one minute, much like traditional weight training sets, despite how the supplement is often marketed.

For athletes who want to use beta-alanine, a dose of 4-6 grams per day for a minimum of 4 weeks has shown to raise muscle carnosine levels by an average of 55% (Trexler et al., 2012). Trexler and colleagues report the only known side effect of beta-alanine supplementation is a tingling sensation in the hands and face. The authors conclude that more studies are needed to determine the effects of beta-alanine supplementation on strength, endurance performance and for any other health-related benefit associated with carnosine.

Any exercise enthusiast who has been around supplements has probably heard someone touting the recovery benefits of glutamine. Glutamine is the most abundant amino acid in skeletal muscle and blood is involved in the immune response (Gleeson, 2008). Glutamine plays an important role in protein synthesis and can reduce the levels of inflammatory biomarkers (Rahamin-Nia et al, 2013). Glutamine is most popularly used in an attempt to aid recovery from exercise. Unfortunately the body of literature does not support the purposed benefits of glutamine on enhancing exercise recovery (Gleeson). For example, in a well-designed 4-week eccentric training (6 sets of eccentric leg extensions to exhaustion with 75% of the 1RM) study by Rahamin-Ni et al. (2013), glutamine supplementation was no better then the placebo in measures of power increase or in reducing markers of muscle soreness (after the eccentric exercise). In light of research findings we would suggest that you encourage your clients to save their money when it comes to glutamine supplementation.

Branched Chained Amino Acids
Branched chain amino acids (leucine, isoleucine, and valine) are three of the nine essential amino acids. They are called 'branched chain' because of their chemical structure includes an additional carbon atom bound to three hydrogen atoms. The branched chain amino acids (BCAA) have a high concentration in skeletal muscle, which is approximately 14-18% (Shimomura et al., 2006). Leucine is the primary BCAA of interest because of its role in the initiation of muscle protein synthesis (Shimomura). Leucine is also involved in inhibiting protein breakdown (Shimomura).

BCAA supplementation is very commonly used to aid in recovery. More specifically, BCAAs have been shown to have a beneficial role in reducing delayed onset muscle soreness and post-workout muscle fatigue (Shimomura et al., 2006) when taken following resistance exercise.

It is worth noting however that BCAAs are found in great abundance in high protein foods. For example, whey protein is approximately 11% leucine. If a client's whole food protein intake is adequate, then the benefits realized from BCAA supplementation may be minor.

Final Thoughts
As this brief review of 5 commonly used athletic performance supplements demonstrates, not all of them truly live up to the advertising hype. For instance, from this review it is clear that glutamine and arginine supplementation has very little scientific support. However, in the case of creatine, due to its low cost and decent effectiveness, it may be a viable option for some clients to consider (depending on their specific performance goals, of course). A final word of caution is warranted. Presently there is no long-term safety outcome research with any supplement.

Matthew T. Stratton, BS completed his undergraduate exercise science degree at the University of New Mexico and is pursuing a Masters degree in Exercise Science. His research interests are in performance enhancing supplementation and skeletal muscle hypertrophy.

Len Kravitz, PhD, CSCS is the program coordinator of exercise science and a researcher at the University of New Mexico, where he received the Outstanding Teacher of the Year award. In addition to being a 2016 inductee into the National Fitness Hall of Fame, Len was awarded the 2016 CanFitPro Specialty Presenter Award.

Cooper, R., Naclerio, F., Allgrove, J. et al. (2012). Creatine Supplementation with specific view to exercise/sports performance: An update. Journal of the International Society of Sports Nutrition 9.33, doi:10.1186/1550-2783-9-33
Fahs, C.A., Heffernan, K.S, & Fernhall, B. (2009). Hemodynamic and vascular response to resistance exercise with L-arginine. Medicine & Science in Sports & Exercise, 41(4), 773-779.
Gleeson, M. (2008). Dosing and efficacy of glutamine supplementation in human exercise and sport training. The Journal of Nutrition, 138, 2045S-049S.
Lariviere, D. (2013). Nutritional Supplements Flexing Muscles As Growth Industry. Forbes. Forbes Magazine.
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