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5 Common Athletic-Performance Supplements: What’s the Evidence?

Check the science behind these popular supplements so you can give clients facts.

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The nutritional‐supplements industry brought in $32 billion in 2012, and sales are estimated to nearly double—to $60 billion—by 2021 (Lariviere 2013). This comes as no surprise to anyone who has walked into a supplement store to find walls lined with everything from multivitamins and fish oil pills to preworkout formulas and protein powders.

With so much ambiguous marketing and pseudoscience these days, it's hard to discern which supplements are effective and worth your clients' hard‐earned money. Find out what the science says about five of the most common athletic‐performance supplements on the market: creatine, L‐arginine, beta‐alanine, glutamine and branched‐chain amino acids.

Be mindful of what your primary certification sanctions in regard to talking about or recommending nutritional supplements to clients. Operating within your nutritional scope of practice is not just a matter of professional ethics; in some states it's a matter of law, and violators can be prosecuted. While it's your duty to inform and provide evidence‐based information, "recommending" or "prescribing" supplements to clients without proper credentialing is beyond scope of practice. As ever, "when in doubt, refer out" to a qualified professional.

Creatine: Skip the Loading

Creatine supplements aim to elevate creatine storage in muscle in order to promote faster regeneration of ATP between high‐intensity bouts of exercise (Cooper et al. 2012). Cooper and colleagues note that earlier research (Branch 2003) found creatine supplementation was most effective during short‐burst exercise (typically lasting up to 30 seconds).

Creatine monohydrate (CM) is the most frequently used form of creatine cited in research (Cooper et al. 2012). Athletes often start loading up on CM for 5–7 days, taking 5 grams four times a day. After loading, they consume 3–5 g maintenance dosages once daily, usually after a workout.

However, Cooper et al. say the loading phase is unnecessary. Those who start with the maintenance dose of 3–5 g per day will reap similar benefits, usually 21–28 days after initiating supplementation.

Citing Rawson & Volek (2003), Cooper and associates say exercisers who combine CM and resistance training experience an average increase of 8% in 1‐repetition maximum (1RM) exercise and an average improvement of 14% in endurance strength compared with exercisers who take a placebo during resistance training. Though previous creatine supplementation studies found mixed results, Cooper et al. say these outcomes happened mostly because each study used different dosing protocols. The large body of scientific evidence suggests that CM taken concurrently with resistance training increases muscle mass and strength.

Creatine supplementation may also help with high‐intensity sprints, but the benefit appears to diminish the longer (in terms of workout duration) an athlete keeps exercising (Cooper et al. 2012). From a safety standpoint, creatine does slightly raise levels of creatinine, a chemical waste produced by muscle metabolism that the kidneys filter out of the blood. However, creatine supplementation has not been shown to threaten kidney function/health in healthy people when proper dosage recommendations are followed. Alas, the long‐term effects of creatine supplementation are unclear—no definitive negative or positive effect has been recognized.

L‐Arginine: No Help for Exercisers

Another popular preworkout supplement is L‐arginine, a "conditional" essential amino acid (conditional typically means a nonessential amino acid that can become essential during periods of muscle growth). L‐arginine is purported to raise nitric oxide (NO) levels because it is a NO precursor (Fahs, Heffernan & Fernhall 2009). Oral supplementation with L‐arginine has proven benefits for people with reduced endothelial NO production, including those with cardiovascular disease, diabetes and hypertension (McConell 2007).

Because of this clinical use of L‐arginine, it has been theorized that increasing NO levels would produce more vasodilation, thus increasing oxygen and energy substrates to 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 study participants performed bench press and biceps curls, respectively. To date, a majority of studies have failed to find an increase in vasodilation and blood flow to working musculature with L‐arginine supplementation. The body of literature seems to suggest there is no real benefit to supplementing with L‐arginine in a healthy exercising population.

Beta‐Alanine: Better for 1‐ to 4‐Minute Bouts of Exercise

Beta‐alanine is an amino acid that binds with histidine to create carnosine. Beta‐alanine supplementation tries to raise intramuscular carnosine levels to increase the intracellular pH buffering capacity of 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.

Based on the current literature, Trexler and colleagues report that beta‐alanine will increase time to exhaustion in exercise bouts lasting 60–240 seconds, but have no effect on exercise capacity in bouts lasting less than 60 seconds, such as traditional weight training. This shows that the supplement can help athletes who normally need to perform bouts lasting 1–4 minutes. However, it will not be especially beneficial for exercise bursts lasting under 1 minute, like many traditional weight training sets, despite how the supplement is often marketed.

For athletes who want to use beta‐alanine, a dose of 4–6 g per day for a minimum of 4 weeks has been shown to raise muscle carnosine levels by an average of 55% (Trexler et al. 2015). The only known side effect of beta‐alanine supplementation is a tingling sensation in the hands and face (Trexler et al. 2015). More studies are needed to determine the effects of beta‐alanine supplementation on strength, on endurance performance and for any other health‐related benefits of carnosine.

Glutamine: No Help for Recovery

Any exercise enthusiast familiar with supplements has probably heard someone touting glutamine's recovery benefits. Glutamine is the most abundant amino acid in skeletal muscle and blood, and is involved in the immune response (Gleeson 2008). Glutamine plays an important role in protein synthesis and can reduce the levels of inflammatory biomarkers (Rahmani‐Nia et al. 2014). Though taking glutamine is a popular recovery tactic, the body of literature does not support the idea that glutamine enhances exercise recovery (Gleeson 2008). For example, in a well‐designed 4‐week eccentric‐training study (6 sets of eccentric leg extensions to exhaustion at 75% of 1‐RM) by Rahmani‐Nia et al. (2014), glutamine supplementation was no better than a placebo for increasing power or in reducing markers of muscle soreness (after the eccentric exercise). In light of research findings, it's probably best that clients save their money when it comes to glutamine supplementation.

Branched‐Chain Amino Acids: Your Diet May Already Have Plenty

Branched‐chain amino acids (leucine, isoleucine and valine) are three of the nine essential amino acids. "Branched chain" means their chemical structure includes an extra carbon atom bound to three hydrogen atoms. Branched‐chain amino acids (BCAAs) have a high concentration in skeletal muscle: approximately 14%–18%. Leucine is the primary BCAA of interest because of its roles in initiating muscle protein synthesis and inhibiting protein breakdown (Shimomura et al. 2006).

Many competitive and recreational exercisers use BCAAs to aid in recovery. BCAAs also reduce delayed‐onset muscle soreness and postworkout muscle fatigue (Shimomura et al. 2006) when taken after resistance exercise.

It is worth noting, however, that BCAAs are abundant 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 of BCAA supplementation may be minor.

Facts vs. Hype

Many popular supplements do not live up to the advertising hype. Clearly, glutamine and arginine supplementation have little scientific support, though creatine's low cost and decent effectiveness can make it a viable option for some clients—depending on their specific performance goals. A final word of caution: There is no research on the long‐term safety outcomes of any supplement.


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