science nutrition blog

By Robert Schinetsky

Pre workout supplements come in all shapes, sizes, and flavors. And while they seem fairly “mainstream” these days, there was a time not too long ago that the general public had no idea what a pre workout supplement was. They were mostly relegated to the pages of bodybuilding magazines and the “hardcore” lifting crowd.

However, with the massive increase in the number of sports nutrition and “lifestyle” brands as well as the “normalization” of supplements, the number of options that an individual can choose from is simply dizzying; so how do you find the best pre workout supplement for you? 

Before you start exploring the most effective pre workout supplements for your routine, It’s important to know that not all supplements are created equal. 

Today, we discuss the best pre workout (and post workout) nutrients to keep an eye out for when shopping around for your supplements.

Creatine Monohydrate

So what is creatine and what is the best pre workout with creatine in it? Creatine is, quite simply, the most well-studied and consistently shown effective supplement for improving athletic performance and lean mass gains. It stands alone and is the metric by which all other sports nutrition supplements are measured. In no specific order, supplementation with creatine, in combination with resistance training, has been shown to lead to better outcomes (compared to resistance training alone) in:1

• Energy production
• Power
• Strength output
• Lean mass gains

Creatine also supports recovery by reducing muscle damage following exercise.2 The International Society of Sports Nutrition also remarked about creatine in its position paper:1

“Creatine monohydrate is the most effective ergogenic nutritional supplement currently available to athletes with the intent of increasing high-intensity exercise capacity and lean body mass during training…

“Creatine monohydrate supplementation is not only safe, but has been reported to have a number of therapeutic benefits in healthy and diseased populations ranging from infants to the elderly. There is no compelling scientific evidence that the short- or long-term use of creatine monohydrate (up to 30 g/day for 5 years) has any detrimental effects on otherwise healthy individuals or among clinical populations who may benefit from creatine supplementation …

“At present, creatine monohydrate is the most extensively studied and clinically effective form of creatine for use in nutritional supplements in terms of muscle uptake and ability to increase high-intensity exercise capacity.”

Regarding the “best” time to take creatine, there is some data that suggests that post-workout may be slightly better than pre-workout, but the much more important factor is that creatine monohydrate is consistently taken. Again, remembering to take your creatine supplement each day will have much more impact than getting mired down in fretting over the most optimal time to take it.

This is why both AML Preworkout (as well as AML Preworkout X-treme) and AML Postworkout contain a full 5,000mg of creatine monohydrate per serving.

L-Citrulline/Citrulline Malate

Citrulline is an amino acid found in a number of foods, watermelon in particular, that has been shown to be a superior supplement for increasing blood levels of arginine than even L-arginine supplements.

Why is this beneficial?

Arginine is the “fuel” that the body uses to generate nitric oxide – an important signaling molecule that affects numerous aspects of physiology. The most pertinent of these, at least in terms of athletic performance, is vasodilation (the “widening” of blood vessels), which allows for greater blood flow, oxygen and nutrient delivery to working muscles. Note: Greater NO production also supports better muscle pumps! The end result is a greater work capacity. In fact, studies note that supplementation with citrulline malate or L-Citrulline may help improve VO2 kinetics, boost energy production, enhance time to exhaustion, and increase the number of repetitions performed while also reducing an individual’s rate of perceived exertion (RPE) versus placebo.3,4,5,6,7 Citrulline malate may also promote better recovery and relieve muscle soreness, too.⁵

Now, much of the focus on citrulline/citrulline malate centers around increasing NO production; however, citrulline also serves as an important part of the urea cycle (along with l-ornithine and l-arginine). The urea cycle helps remove metabolic waste products generated from intense exercise, including lactate, hydrogen (H+ ions) and ammonia. As these byproducts accumulate, fatigue builds and ultimately forces you to end your set. Citrulline supplementation may help increase buffering capacity of skeletal muscle, helping you delay fatigue and complete more total work during your training session (i.e., progressive overload).

There is some debate as to which form of citrulline is “superior” – Citrulline Malate or L-Citrulline. Truth be told, so long as you’re getting an efficacious dosage of L-Citrulline (between 2.4-10 grams), you’re good. Research supports the inclusion of 8-10 grams of Citrulline Malate in pre-workout supplements to boost resistance training performance.

Most citrulline malate supplements on the market are either 1:1 (meaning the supply equal amounts of citrulline and malic acid) or 2:1 (two parts citrulline to one part malic acid).

AML Pre Workout X-treme supplies 10,000mg of Citrulline Malate 2:1, yielding 6,620mg (>6grams) of L-Citrulline.

Caffeine

Did you really think you’d get through an article on the best pre-workout supplements for 2022 without seeing the king of psychostimulants?

Caffeine is as synonymous with pre-workout supplements as training montages in ‘80s movies – they belong together and are made better when used together.

As you likely know, caffeine increases feelings of wakefulness and alertness. This occurs via antagonism of adenosine (a neurotransmitter that promotes feelings of lethargy and sleepiness).

But, that’s not all.

Caffeine also stimulates the release of dopamine, which increases feelings of reward, mood, motivation, motor control and decision-making.

There’s also no shortage of studies investigating the safety and efficacy of caffeine, particularly regarding sports performance. Specifically, caffeine has been noted to consistently improve performance regarding:

• Sport-specific endurance⁸
• Power-based sports⁹
• Resistance exercise¹⁰

In fact, caffeine has not only been found to be beneficial for sports performance when dosed between 3-6mg/kg, but also safe (the same cannot be said of other stimulants sometimes found in pre-workout supplements).

Moreover, doses as high as 9mg/kg (upwards of 900mg caffeine for a 100kg athlete!) have been studied and found to benefit performance; however, doses ranging between 3-6mg/kg have been studied more frequently.^12,13

If you’ve had a bad night’s sleep, caffeine may also be helpful as it has been shown to reduce poor training performance due to sleep deprivation as well as exhaustive exercise.¹¹

Caffeine may also enhance central drive and has the potential to increase strength or muscular endurance performance.

AML Preworkout as well as AML Preworkout X-Treme contain 400mg of caffeine anhydrous, which is in line with the research noting improvements in strength and power output in athletes.

Dopamine Precursors

As we just mentioned above, dopamine is the neurotransmitter that’s most often associated with feelings of reward; however, it also affects a variety of other things, including mood, motivation, memory, learning and motor control.

Dopamine can also play an important role in exercise and sports performance. And, as you can tell if you’ve spent even a modicum of time reading AML’s article section, we’re fans of dopamine and helping the body make the most of this primetime neurochemical. During very stressful situations (such as intense physical activity), dopamine can become depleted, leading to a decline in motivation and performance while simultaneously accelerating the onset of fatigue.¹⁴

In fact, researchers have noted that fatigue is due, in part, to an increase in serotonergic activity and a decrease in dopaminergic activity. Moreover, administration of dopamine reuptake inhibitors can prolong the time to fatigue and help individuals maintain power output during exercise as well as improve performance in hotter environments.¹⁵

It stands to reason that by staving off this reduction in dopamine (by supplying the body with the nutrients it needs to support dopamine synthesis), you would be able to delay the onset of fatigue, maintain a high level of performance, increase time to exhaustion, and attain new heights in strength, power and athleticism.

For these reasons, AML Preworkout and Preworkout X-treme (as well as our entire DopaRush lineup) include prominent dopamine-support agents, including:

• L-Tyrosine
• Velvet bean (mucuna pruriens)
• Folic Acid

Tyrosine

You’re probably wondering, “if tyrosine is non-essential, how could it possibly be included as one of the best pre workout supplements?”

Allow us to explain…

From a physiological point of view, tyrosine is non-essential as it can be created from the essential amino acid phenylalanine. However, in regards to performance, focus, and combating stress, tyrosine is anything but non-essential.

The reason we say this is that the body uses tyrosine to produce the catecholamines/neurotransmitters: epinephrine, norepinephrine, and dopamine.

If you remember from our discussion of caffeine above, dopamine is vitally important to maintaining a high level of performance during training or competition. And, as we also stated above being under siege by stress (physical or mental) can drain your catecholamine “bank account”. Anyone who’s ever faced a thermodynamics final or a set of 20-rep squats can attest that stress does leave you feeling completely drained and in a constant daze.

Supplementing with tyrosine helps replenish these key neurotransmitters before stress can deplete them, allowing you to stay focused longer without becoming stressed or “burned out.”

In other words, supplementing with tyrosine supports better focus, less fatigue and reduced stress along with heightened mood and motivation which yields superior mental and physical performance in your training sessions.

Velvet Bean

Building on the best dopamine supplements is velvet bean. Also known as mucuna pruriens, velvet bean is a tropical legume indigenous to Asia and Africa that is chock full of L-Dopa -- the direct precursor to dopamine production.

L-Dopa is produced from the amino acid L-tyrosine by the enzyme tyrosine hydroxylase. The reason to supplement with L-Dopa is that readily crosses the protective blood–brain barrier, something dopamine itself cannot do.

We’ve beaten the importance of dopamine in regards to performance enough, so we won’t beleaguer the point further. Just know that L-Dopa is a well-studied, and powerful, activator of dopamine. L-Dopa is so potent that it’s even been explored as a possible treatment for Parkinson’s disease which is caused by declining dopamine.

L-Dopa also mediates neurotrophic factor release by the brain and CNS. In case you weren’t aware, neurotrophic factor are a collection of small peptides that support the growth, survival, and differentiation of young and old neurons.

Betaine Anhydrous

Betaine is an organic compound derived from choline that is both naturally produced by our bodies and found in a number of foods, beets being the best known (from which betaine derives its name).

In regards to exercise performance, betaine helps increase cell volumization and hydration via its actions as an osmolyte. Betaine also supports the body’s production of creatine via its methylation of homocysteine to methionine – one of the amino acids the body uses to produce creatine. This provides two mechanisms by which betaine can enhance performance – better hydration and improved creatine production.

Human research has noted that supplementation with 2.5 grams of betaine per day may increase:^16,17,18,19

• Muscle protein synthesis
• Power output (bench press and vertical jump)
• Force production
• Muscular endurance
• Lean mass gains
• Reductions in fat mass

As stated above, betaine (as an osmolyte) can increase intracellular water¹⁷,

which encourages cell volumization and cellular swelling. This supports muscle growth by way of stimulating muscle protein synthesis.

Similar to creatine monohydrate, there is some discussion as to the “most optimal” time to consume betaine – pre-workout, post-workout, first thing in the morning, etc. As discussed above, the most important thing is to take it consistently as the body of research to date investigates the consistent intake of betaine daily over the course of several weeks. Therefore, when you consume betaine during the day is secondary to actually taking it each day.

AML includes the full 2.5g dose of betaine anhydrous in AML Preworkout, AML Preworkout X-treme and AML Postworkout.

Beta-Alanine

Beta Alanine is the supplement most often associated with improving resistance to fatigue and boosting endurance exercise performance. This is because supplementation with beta-alanine has been found to increase levels of the intracellular buffer, carnosine.

This ultimately improves a muscle’s capacity to buffer H+ ions and delays the onset of fatigue, thereby helping athletes complete more repetitions and more total work before succumbing to fatigue.

Research notes that daily supplementation with beta-alanine may lead to improvements in:^20,21 

• Muscle endurance
• Muscle growth
• Resistance to fatigue
• Time-to-exhaustion

It should be noted that beta-alanine is most beneficial to those individuals who engage in endurance activities or those who perform repeated bouts of effort with limited rest (<60 seconds), as the endurance-boosting effects are typically best experienced when physical demand exceeds >60 seconds of effort.

As for the “best” time to take beta-alanine, it’s similar to creatine and betaine. Its effects are cumulative, which means that it needs to be taken consistently in order to derive benefit. The saturation dose of beta-alanine is 179, which means if you’re supplementing with between 2.4-6.4 grams per day (the dosage range used in research studies), it will take between 4-8 weeks to reach the 179 gram threshold, at which point the carnosine content of your muscles will be improved enough to boost performance.

Polyphenols

Listen to enough commercials and you’ll be inundated with the word “polyphenols” and the myriad of benefits they offer. But, how many individuals actually know what the heck polyphenols actually are?

To keep things simple, polyphenols are a large family of bioactive compounds naturally occurring in plants. There are over 8,000 polyphenols, and they can be subdivided into four groups, including:

• Flavonoids (e.g., quercetin, catechins, anthocyanins, etc.)
• Phenolic acids (e.g., stilbenes, lignans, etc.)
• Polyphenolic amides (e.g., capsaicin)
• “Other” polyphenols (e.g., ellagic acids, resveratrol, curcumin, etc.)

Polyphenols offer a number of health-promoting benefits, including:

• Glycemic support
• Cardiovascular support
• Cognitive function
• Digestive health

Grape and beetroot are among the richest sources of polyphenols (both of which are commonly included in pre-workout supplements).

Polyphenols may benefit exercise performance through two main mechanisms:²²

• Enhancing vascular function (e.g., vasodilation, vasorelaxation, nitric oxide production)
• Limiting oxidative damage during exercise by upregulating endogenous antioxidant capacity

Research from 2017 found that supplementation with a polyphenol-rich extract significantly increased average power developed (5%), maximal peak power output (3.7%) and total power output (5%).²³

A 2019 review on the influence of polyphenol supplementation for performance and recovery found that:²⁴

“acute supplementation with polyphenols 1-2 h prior to exercise may enhance exercise capacity and/or performance during endurance and repeated sprint exercise via antioxidant and vascular mechanisms.”

“supplementation with polyphenols for 3 or more days prior to and following exercise will enhance recovery following muscle damage via antioxidant and anti-inflammatory mechanisms.”

Peak ATP^®

ATP (adenosine triphosphate) is the cellular currency of energy production, and the body’s ability to regenerate ATP lies at the heart of sustaining a high level of performance.

Certain supplements over the years have been investigated in an attempt to increase blood levels of ATP; however, the vast majority of them have been found to be ineffective due to a lack of bioavailability, even when dosed as high as 5,000mg.^25,26,27

Peak ATP is a clinically researched, patented form of adenosine 5’-triphosphate (ATP) disodium that is identical in structure to human ATP. Research has shown that Peak ATP supplementation not only is bioavailable, but it may also improve athletic performance and body composition. This occurs via its ability to support increased blood flow, muscular excitability and recovery.

Studies note that Peak ATP can provide benefits after just a single dose, and has been shown in human studies to result in:^28,29

• 147% increase in strength
• 30% increase in power
• 96% greater muscle thickness

Supplementation may also help reduce protein breakdown and prevent performance drop-off as an individual gets deeper into their workout.^30,31,32

p-Synephrine

p-Synephrine is an alkaloid found in citrus aurantium (bitter orange) that is structurally similar to ephedrine but comes without the adverse cardiovascular effects due to its lack of affinity for Beta-1 and Beta-2 receptors in the body (which is a good thing).

P-synephrine does show affinity for beta-3 receptors, which has been noted to increase:

• Energy expenditure
• Fat oxidation (“fat burning”)
• Post-exercise oxygen uptake

This leads to improvements in repetition performance and volume load during training. Other research indicates there is an additive effect when stacking p-synephrine with caffeine (as is the case with AML Preworkout X treme).^33,34 Specifically, the combination of caffeine with 100mg p-synephrine was found to help athletes achieve faster, more powerful repetitions with no additional perceived exertion or lactate accumulation!³³ To top it off, p-Synephrine may also help reduce food intake, benefiting those seeking weight loss.

BEST POST WORKOUT INGREDIENTS

Leucine

During intense exercise, muscle tissue is damaged and broken down. Following exercise it stands to reason that you would want to consume nutrients that stimulate muscle protein synthesis so as to initiate muscle repair and recovery.

Typically, post workout supplements include BCAA to stimulate protein synthesis, but the majority of BCAA supplementation benefits are solely attributed to the “king” of amino acids -- leucine.

Leucine is the “anabolic trigger” that ignites body’s muscle building pathways via stimulation of the mechanistic target of rapamycin (mTOR) pathway.

In fact, studies show that leucine consumption immediately post-workout increased mTOR activity for several hours following exercise, resulting in elevated muscle protein synthesis.[25] Another noteworthy piece of research documented that ingestion of leucine immediately after exercise increased muscle protein synthesis by as much as 33%![26]

In addition to its anabolic properties, leucine also exerts some fairly impressive anti-catabolic properties too. Specifically, the essential amino acid has been shown to reduce muscle protein breakdown following exercise (via activation of mTOR). This activation of mTOR also causes the inactivation of the energy-sensing molecule, AMPK.[27,28]

In case you didn’t know, AMPK stimulates the conversion of protein into amino acids for energy during periods of low energy, such as during exercise. AMPK does this to restore the energy status of the muscle cell. But that’s not all. AMPK also encourages the breakdown of muscle glycogen into glucose.

Leucine’s ability to nullify the actions of AMPK-mediated protein and glycogen breakdown halt muscle breakdown and promote glycogen resynthesis following exercise.[29]

MOST EFFECTIVE PRE WORKOUT & POST WORKOUT INGREDIENTS

Betaine

Betaine, a.k.a. trimethylglycine, is a compound naturally occurring in wheat, spinach, shellfish and sugar beets (from which its name is derived). It serves a number of roles in the body, the most important of which is its role as a methyl donor.

Betaine contains three methyl groups and it donates one of them to methylate an inflammatory chemical called homocysteine. In case you weren’t aware, homocysteine is one of the big risk factors used to identify and track coronary artery disease.

The versatile compound also operates as an important fluid regulator in the body due to is osmolytic properties. As an osmolyte, betaine encourages cells to draw in additional water and nutrients, which promotes better hydration, stamina, and performance. As you’re probably aware, intense exercise causes significant water loss. The cell-saturating properties of betaine help encourage preserve and restore hydration before, during, and after exercise.

Human research has documented that supplementation with 2.5 grams per day of betaine increased power output (bench press and vertical jump), force production, muscular endurance and lean mass gains.[21,22,23]

Additional studies have noted that betaine supplementation leads to 7.8% increase in IGF-1 levels and a 6.1% reduction in the catabolic hormone cortisol.

Researchers also believe that betaine’s ability to serve as a methyl donor also enhances creatine uptake into muscle tissue by stimulating the conversion of homocysteine into methionine. Since elevated homocysteine levels have been noted to impair insulin signaling[24], lower homocysteine levels (caused by betaine) should enhance insulin sensitivity, thereby improving insulin-mediated uptake of creatine into the muscle cell.

Electrolytes

Electrolytes are minerals that help regulate the amount of water in your body as well as balance your body's pH level. They also serve important roles in optimal function of skeletal muscles.[43]

As you’ve seen for yourself, intense exercise brings with it buckets of sweat. And, in addition to all the water lost during training also comes the loss of valuable electrolytes. Failure to replace these essential minerals can lead to increased feelings of fatigue, impaired performance, decreased focus, and lots and lots of cramping.

In fact, even as little as 2% dehydration can lead to declines in exercise performance.[42]

Two of the most important electrolytes to consume pre workout and post workout are potassium and magnesium citrate. These two compounds enhance hydration and muscle cell volume as an osmolyte, and they work synergistically with creatine and betaine to enhance muscle recovery and growth.

Furthermore, several studies have shown that higher potassium and magnesium intake lowers the risk of stroke and other cardiovascular diseases, likely due to their capacity to increase nitric oxide production and vasodilation, which reduces blood pressure and enhances blood flow.[45,46]

Citrate has also been shown to improve exercise performance and reduce fatigue. This is most likely due to its ability to buffer lactic acid buildup in the muscle and support TCA cycle functioning.[44]

Most Overhyped Pre Workout and Post Workout Ingredients 

Agmatine Sulfate

When looking at the nitric oxide-boosting portion (a.k.a. “pump matrix”) of most pre workouts, chances are pretty good you’ll come across agmatine sulfate.

Derived from l-arginine, agmatine sulfate is a popular choice for those looking to enhance and prolong their nitric oxide-fueled muscle pumps. This is due to some research indicating that agmatine may indirectly support nitric oxide production via inhibition of arginase[52] -- the enzyme that breaks down arginine.

Theoretically speaking, by limiting the actions of arginase, blood levels of arginine should remain elevated longer leading to stronger, longer-lasting NO production, and with it muscle pumps.

However, research demonstrating the NO-boosting effects of agmatine when consumed orally in humans is severely lacking. There is some research may have some neurological and endocrine benefits, including a reduction in perceived pain[51], but it terms of improving athletic performance the evidence isn’t there yet.

Taurine

Taurine is one of the most common ingredients included in pre workouts supplements and energy drinks. It is a non-essential amino acid located mostly in the brain, heart, and skeletal muscle system that maintains cell volume, aids muscle contraction and promotes antioxidant defense systems in skeletal muscle.

Similar to our next ingredient (BCAA), taurine isn’t exactly something you want to see in your pre workout if you’re wanting to increase energy levels, performance, or productivity.

A number of research trials conducted in humans indicate that that the combination of taurine + caffeine does not improve performance, energy, or attention.[47,48,49,50] Yet, these two ingredients are routinely paired together in countless pre workout supplements.

But there’s more...

The combination has been documented to reduce feelings of vigor and dampen the stimulating effects of caffeine. And, to top it off, some research even notes that the combination of taurine + caffeine actually increases feelings of fatigue.

In other words, if you want to make your caffeine less effective and less stimulating while also inducing greater fatigue, then go ahead and combine taurine with caffeine.

But, if you want to make your pre workout dose of caffeine work for you, avoid taurine pre workout. This is why AML Pre Workout DOES NOT contain taurine.

BCAAs (Leucine, Isoleucine, and Valine)

You’re not seeing things.

Despite being one of the most popular, best-selling products on the market, BCAAs are one of the most overhyped pre workout (or intra workout) supplements you can take.

Above, we did list leucine as one of the best post workout supplements you can use. However, you would be better served to avoid supplementing with BCAA (as well as free form leucine) immediately prior to training.

Why is that?

Well, there’s some solid evidence indicating that supplementation with the BCAAs decreases dopamine levels.[36,37] This is due to the fact that branched-chain amino acids, leucine in particular, competitively inhibits L-Tyrosine -- the dopamine precursor.

Additionally, as we mentioned above when discussing leucine in the best post-workout supplements, it stimulates glycogen replenishment, which meals it also hinders the breakdown of glycogen into glucose. This leads to decreased cellular energy -- something you don’t really want before heading into a tough training session.

All of this drives home the point that leucine supplementation should take place post workout, but certainly not pre-workout.

And, if you’re concerned about going catabolic during your workout, just realize that so long as you’ve had a meal at least 2-3 hours prior to training, you’re not at risk of losing excessive muscle tissue. Furthermore, the need to supplement with BCAA is entirely unnecessary if you’re consuming adequate dietary protein during the day.

Glutamine

L-Glutamine is one of the oldest supplements around, and it’s also one of the most overrated and overhyped ones too.

Glutamine is the most abundant amino acid in the body, with roughly 61% of body stores located in skeletal muscle tissue. As an amino acid, glutamine is rich in nitrogen and carbon, and it’s involved in protein synthesis, which has led many to believe it can be an effective “muscle building” or post-workout recovery supplement. It serves as a sort of “fuel” for various cells in the body, including lymphocytes and macrophages.

However, multiple studies have documented that in otherwise healthy individuals (e.g. those not suffering from severe trauma or horrific burn wounds) glutamine supplementation has absolutely no benefit on recovery, muscle growth, athletic performance, or strength.[38,39,40]

The reason l-glutamine is so ineffective is that it suffers from terrible bioavailability. You see, the stomach, liver, and intestines love them some glutamine, which means that any free form glutamine you ingest is likely to be broken down and gobbled up by those organs before it ever gets a chance to enter the bloodstream and reach your muscles.

To make matters worse, supplementation with l-glutamine actually may impede recovery and muscle growth.

A 2014 review noted that glutamine supplements did not reduce muscle protein breakdown and they also increased de novo glutamine production, suggesting that consuming supplemental L-glutamine may accelerate muscle breakdown.[41]

FYI, that same study also found that glutamine supplementation may potentially increase the inflammatory response, which could result in excessive inflammation and further complications.

Takeaway: What is The Best Pre Workout?

There are a lot of pre workout supplements on the market, many of which are good quality and many that aren’t…so what is the most effective pre workout supplement?

There are very few (if any) supplements on the market that are formulated using the principles that AML implements when creating its premium-quality products.

AML Pre Workout supplements were engineered with the singular goal of cultivating the best pre workout supplements (backed by science) and assembling them into one comprehensive product.

©Published by Advanced Research Media, Inc. 2022
©Reprinted with permission from Advanced Research Media, Inc.

REFERENCES:

1. 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.

2. Cooke, M.B., Rybalka, E., Williams, A.D. et al. Creatine supplementation enhances muscle force recovery after eccentrically-induced muscle damage in healthy individuals. J Int Soc Sports Nutr 6, 13 (2009). https://doi.org/10.1186/1550-2783-6-13

3. Wax, B., Kavazis, A. N., Weldon, K., & Sperlak, J. (2015). Effects of supplemental citrulline malate ingestion during repeated bouts of lower-body exercise in advanced weightlifters. Journal of Strength and Conditioning Research, 29(3), 786-792. https://doi.org/10.1519/JSC.0000000000000670

4. Glenn, J. M., Gray, M., Wethington, L. N., Stone, M. S., Stewart, R. W. J., & Moyen, N. E. (2017). Acute citrulline malate supplementation improves upper- and lower-body submaximal weightlifting exercise performance in resistance-trained females. European Journal of Nutrition, 56(2), 775-784. https://doi.org/10.1007/s00394-015-1124-6

5. Perez-Guisado, J., & Jakeman, P. M. (2010). Citrulline malate enhances athletic anaerobic performance and relieves muscle soreness. Journal of Strength and Conditioning Research, 24(5), 1215-1222.

6. Bailey SJ, Blackwell JR, Lord T, et al. L-citrulline supplementation improves O2 uptake kinetics and high-intensity exercise performance in humans. J Appl Physiol 119: 385-395, 2015

7. Suzuki T, Morita M, Kobayashi Y, Kamimura A. Oral L-citrulline supplementation enhances cycling time trial performance in healthy trained men: Double-blind randomized placebo-controlled 2-way crossover study. J Int Soc Sports Nutr 13: 6, 2016.

8. Ganio MS, Klau JF, Casa DJ, Armstrong LE, Maresh CM. Effect of caffeine on sport-specific endurance performance: a systematic review. J Strength Cond Res. 2009;23(1):315–324. doi: 10.1519/JSC.0b013e31818b979a.

9. Astorino TA, Roberson DW. Efficacy of acute caffeine ingestion for short-term high-intensity exercise performance: a systematic review. J Strength Cond Res. 2010;24(1):257-265. doi: 10.1519/JSC.0b013e3181c1f88a.

10. Davis JK, Green JM. Caffeine and anaerobic performance. Sports Med. 2009;39(10):813. doi: 10.2165/11317770-000000000-00000.

11. Goldstein ER, Ziegenfuss T, Kalman D, et al. International society of sports nutrition position stand: caffeine and performance. J Int Soc Sports Nutr. 2010;7(1):5. doi:10.1186/1550-2783-7-5

12. Pickering C, Grgic J. Caffeine and Exercise: What Next?. Sports Med. 2019;49(7):1007-1030. doi:10.1007/s40279-019-01101-0

13. Pasman WJ, van Baak MA, Jeukendrup AE, de Haan A. The effect of different dosages of caffeine on endurance performance time. Int J Sports Med. 1995;16(4):225-230. doi: 10.1055/s-2007-972996.

14. Selasi Attipoe, Stacey A. Zeno, Courtney Lee, Cindy Crawford, Raheleh Khorsan, Avi R. Walter, Patricia A. Deuster, Tyrosine for Mitigating Stress and Enhancing Performance in Healthy Adult Humans, a Rapid Evidence Assessment of the Literature, Military Medicine, Volume 180, Issue 7, July 2015, Pages 754-765, https://doi.org/10.7205/MILMED-D-14-00594

15. Cordeiro LMS, Rabelo PCR, Moraes MM, et al. Physical exercise-induced fatigue: the role of serotonergic and dopaminergic systems. Braz J Med Biol Res. 2017;50(12):e6432. Published 2017 Oct 19. doi:10.1590/1414-431X20176432

16. Lee EC, Maresh CM, Kraemer WJ, Yamamoto LM, Hatfield DL, Bailey BL, Armstrong LE, Volek JS, McDermott BP, Craig SA: Ergogenic effects of betaine supplementation on strength and power performance. J Int Soc Sports Nutr. 2010, 7: 27-10.1186/1550-2783-7-27.

17. Hoffman JR, Ratamess NA, Kang J, Rashti SL, Faigenbaum AD: Effect of betaine supplementation on power performance and fatigue. J Int Soc Sports Nutr. 2009, 6: 7-10.1186/1550-2783-6-7

18. Trepanowski JF, Farney TM, McCarthy CG, Schilling BK, Craig SA, Bloomer RJ: The effects of chronic betaine supplementation on exercise performance, skeletal muscle oxygen saturation and associated biochemical parameters in resistance trained men. J Strength Cond Res. 2011, 25: 3461-3471. 10.1519/JSC.0b013e318217d48d.

19. Cholewa JM, Hudson A, Cicholski T, Cervenka A, Barreno K, Broom K, Barch M, Craig SAS. The effects of chronic betaine supplementation on body composition and performance in collegiate females: a double-blind, randomized, placebo controlled trial. J Int Soc Sports Nutr. 2018 Jul 31;15(1):37. doi: 10.1186/s12970-018-0243-x. PMID: 30064450; PMCID: PMC6069865.

20. Smith AE, Walter AA, Graef JL, Kendall KL, Moon JR, Lockwood CM, Fukuda DH, Beck TW, Cramer JT, Stout JR. Effects of beta-alanine supplementation and high-intensity interval training on endurance performance and body composition in men; a double-blind trial. J Int Soc Sports Nutr. 2009 Feb 11;6:5. doi: 10.1186/1550-2783-6-5. PMID: 19210788; PMCID: PMC2649036.

21. Trexler ET, Smith-Ryan AE, Stout JR, Hoffman JR, Wilborn CD, Sale C, Kreider RB, Jäger R, Earnest CP, Bannock L, Campbell B, Kalman D, Ziegenfuss TN, Antonio J. International society of sports nutrition position stand: Beta-Alanine. J Int Soc Sports Nutr. 2015 Jul 15;12:30. doi: 10.1186/s12970-015-0090-y. PMID: 26175657; PMCID: PMC4501114.

22. d'Unienville NMA, Blake HT, Coates AM, Hill AM, Nelson MJ, Buckley JD. Effect of food sources of nitrate, polyphenols, L-arginine and L-citrulline on endurance exercise performance: a systematic review and meta-analysis of randomised controlled trials. J Int Soc Sports Nutr. 2021;18(1):76. Published 2021 Dec 29. doi:10.1186/s12970-021-00472-y

23. Cases J, Romain C, Marín-Pagán C, et al. Supplementation with a Polyphenol-Rich Extract, PerfLoad®, Improves Physical Performance during High-Intensity Exercise: A Randomized, Double Blind, Crossover Trial. Nutrients. 2017;9(4):421. doi:10.3390/nu9040421.

24. Bowtell J, Kelly V. Fruit-Derived Polyphenol Supplementation for Athlete Recovery and Performance. Sports Med. 2019;49(Suppl 1):3-23. doi:10.1007/s40279-018-0998-x

25. Arts, I.C., Coolen, E.J., Bours, M.J. et al. Adenosine 5′-triphosphate (ATP) supplements are not orally bioavailable: a randomized, placebo-controlled cross-over trial in healthy humans. J Int Soc Sports Nutr 9, 16 (2012). https://doorg/10.1186/1550-2783-9-16

26. Coolen EJ, Arts IC, Bekers O, Vervaet C, Bast A, Dagnelie PC. Oral bioavailability
    of ATP after prolonged administration. Br J Nutr. 2011;105:357-66

27. Herda TJ, Ryan ED, Stout JR, Cramer JT. Effects of a supplement designed to increase ATP levels on muscle strength, power output, and endurance. J Int Soc Sports Nutr. 2008;5:3.

28. Wilson JM, et al. Effects of oral adenosine-5’-triphosphate supplementation on athletic performance, skeletal muscle hypertrophy and recovery in resistance-trained men.Nutrition and Metabolism. 2013, 10:57.

29. Lowery RP, et al. Oral ATP administration improves blood flow responses to exercise in both animal and human training models.Presented at 10th Annual ISSN Conference. Colorado Springs, CO. June 2013.

30. Rathmacher JA, et al. Adenosine-5’-triphosphate (ATP) supplementation improves low peak muscle torque and torque fatigue during repeated high intensity exercise sets. Journal of the International Society of Sports Nutrition. 2012, 9:48.

31. Martin Purpura PhD, John A. Rathmacher PhD, Matthew H. Sharp MS, Ryan P. Lowery MS, Kevin A. Shields MS, Jeremy M. Partl MS, Jacob M. Wilson PhD & Ralf Jäger PhD, MBA (2017): Oral Adenosine-5′-triphosphate (ATP) Administration Increases Postexercise ATP Levels, Muscle Excitability, and Athletic Performance Following a Repeated Sprint Bout, Journal of the American College of Nutrition, DOI: 10.1080/07315724.2016.1246989

32. Ratamess NA, Bush JA, Kang J, et al. The effects of supplementation with P-Synephrine alone and in combination with caffeine on resistance exercise performance. Journal of the International Society of Sports Nutrition. 2015;12:35. doi:10.1186/s12970-015-0096-5.

33. Ratamess NA, Bush JA, Kang J, et al. The Effects of Supplementation with p-Synephrine Alone and in Combination with Caffeine on Metabolic, Lipolytic, and Cardiovascular Responses during Resistance Exercise. J Am Coll Nutr. 2016;35(8):657-669. doi:10.1080/07315724.2016.1150223.

34. Stohs SJ, Preuss HG, Shara M. A review of the receptor-binding properties of p-synephrine as related to its pharmacological effects. Oxid Med Cell Longev. 2011;2011:1. doi: 10.1155/2011/482973.