IN DEPTH DESCRIPTION
Creatine is a peptide molecule found primarily in the skeletal muscle in the body, and has a role in the production of energy in the muscle cells. More specifically, phosphocreatine – which is created from creatine – regenerates ATP that is used up during the first few seconds of muscle contraction, thereby prolonging the initial burst of energy and power in short-term, high intensity exercise.
It has been shown that taking creatine supplements can increase the concentration of both free creatine and phosphocreatine in the muscle [1,2].
Because of the role of phosphocreatine in ATP production, creatine supplementation has been widely researched for its potential to improve exercise performance. Particularly good results are found for high-intensity bursts of physical activity such as sprinting and maximal-effort muscle contractions, showing improvements in power and force [3,4,5].
As well as providing an immediate or ‘acute’ increase in power, creatine supplementation has also been found to favour an increase in muscle strength and size when used regularly over the course of a strength training programme. A randomised controlled trial published in the Medicine and Science in Sports and Exercise journal subjected 23 male volunteers to a 6-week arm flexor strength training programme, giving them either creatine monohydrate (5g four times a day for 5 days, then 2g a day) or a placebo. At the end of the 6 weeks, those taking the creatine had a greater improvement in their arm flexor one repetition maximum (1RM = the maximum amount lifted for one rep) than the placebo group, increasing to 54.7kg for the creatine group but to just 49.3 kg for the placebo group. Upper arm muscle area increased by a mean of 7.9cm for the creatine group but did not change for the placebo group. A review in the Journal of Strength and Conditioning Research looked at 22 studies examining the effect of creatine combined with resistance exercise on muscle strength and weightlifting performance. Combining the results of all the studies, the authors found that the average increase in muscle strength following creatine supplementation was 8% greater than the average increase with placebo (20% vs. 12%), and the average increase in weightlifting performance was 14% greater in those taking creatine than a placebo (when all groups were doing resistance exercise).
In terms of how creatine improves muscle strength and size, one of its actions may be to increase the proportion of satellite cells in the muscle. These are cells that can provide additional nuclei to the enlarging muscle fibres, hence playing an important role in the growth of adult skeletal muscle . In a randomised controlled study on 32 healthy men doing strength training, it was found that creatine supplementation produced greater enhancements in satellite cell proliferation at weeks 4 and 8 compared to supplementation with protein or a placebo. The study also found that creatine supplementation resulted in an increased number of nuclei per fibre and increases of 14–17% in mean muscle fibre area throughout the study. 
Creatine may also support energy by improving glucose uptake into cells and muscle glycogen storage. A study on 20 adults given creatine at a loading dose of 20g for five days followed by 2g a day found that the loading dose increased muscle glycogen content by an average of 18% (although this was not maintained with the dose of 2g a day). Creatine has also been found to improve glucose tolerance: a study on 22 sedentary healthy men found that those taking creatine for three months in conjunction with moderate aerobic training had a greater improvement in glucose tolerance than the group taking placebo and doing the same aerobic activity . This indicates an improvement in glucose uptake into the cells.
Creatine is also thought to be essential for cognitive function, as it is needed to provide energy to the brain. Animal research has shown that creatine is important for normal brain development and function ; and infants born with depletion of creatine in the body and brain due to an inborn defect show mental retardation and learning disabilities, that can be corrected with creatine supplementation [12, 13]. To test its effects on cognitive function in healthy adults, one trial gave 19 adults either creatine at 5g four times a day for 7 days, or a placebo, then tested their cognitive and psychomotor performance and mood before and after 24 hours of sleep deprivation. They found that the creatine group showed less deterioration in performance after the sleep deprivation including tests of reaction time and balance, and less change in mood, concluding that ‘creatine supplementation had a positive effect on mood state and tasks that place a heavy stress on the prefrontal cortex’ .
Beta-alanine is another amino acid that has a role in muscle function – but not in muscle protein synthesis. Beta-alanine combines with L-histidine, another amino acid, to make a dipeptide called carnosine, which is stored in the muscle. Carnosine has various roles in muscle function, as we’ll discuss below. Beta-alanine supplementation has been found to significantly increase carnosine in the muscle – one human study found that giving 3.2g and 6.4g of beta-alanine for four weeks resulted in an increase of 42% and 64% in muscle carnosine.
One of the primary effects of carnosine in muscle is that it buffers lactic acid that builds up during intensive (anaerobic) exercise, delaying the onset of muscle fatigue . This can help to improve endurance. Several studies have examined the effects of beta-alanine in reducing muscle fatigue through this mechanism. One placebo-controlled trial on 15 sprinters gave the participants either beta-alanine (2.4g/day building up to 4.8g/day) or a placebo for 4–5 weeks. Before and after the supplementation period their performance on 5 x 30 bouts of knee extensions and a 400 m race was evaluated. It was found that those taking the beta-alanine had significant improvements in peak torque (force) for bouts 4 and 5 of the knee extensions, relative to their pre-supplementation performance and relative to the placebo group. (The 400-m run performance was not improved.) Another notable placebo-controlled trial gave 22 women either a beta-alanine supplement or a placebo for 28 days, testing several measures of exercise performance before and at the end of the supplementation period. It was found that those taking the beta alanine had a 13.9% improvement in ventilatory threshold (the point when breathing surpasses normal ventilation rate – a measure of anaerobic capacity and lactate accumulation), 12.6% increase in ‘physical working capacity at fatigue’ (a measure of ability to resist fatigue) and a 2.5% increase in time to exhaustion. The placebo group showed no improvements. These studies therefore indicate that beta-alanine can help to delay fatigue in the muscles, especially in intensive exercise.
Beta-alanine supplementation may also specifically improve explosive performance and enhance muscle contractility (capacity of the muscle to contract). A study on nine male elite alpine skiers found that supplementing with 4.8g per day of beta-alanine for five weeks improved measures of explosive and jump performance that were not seen in those taking a placebo. This may happen through a different mechanism than buffering lactic acid: it’s thought that carnosine may improve muscle contractility by increasing free calcium inside the cells (calcium is needed for muscle contraction) and sensitising contractile proteins to calcium.
Carnosine has also been found to have antioxidant and anti-aging activity, as well as hypoglycaemic (blood sugar-lowering) and anti-glycation activity [21, 22, 23]. As an antioxidant, its activities are thought to include scavenging reactive oxygen species and reactive nitrogen species – types of ‘free radical’. Glycation is a process in which sugar molecules bind to protein or fat molecules in an uncontrolled way, preventing the function of those molecules and causing damage to cells and tissues – for example stiffening of the arteries. Carnosine has been found to inhibit protein glycation and even reverse glycated protein, helping to prevent this damage. It has also been found to lower blood sugar in animal studies of diabetes, possibly by increasing insulin secretion to improve uptake of glucose into the cells. 
HMB (Beta-Hydroxy Beta-Methylbutyric Acid)
HMB is a metabolite of the branched-chain amino acid leucine. As a supplement, HMB is most commonly used for increasing the benefits from weight training and exercise. It is thought to have an anti-catabolic effect, inhibiting protein breakdown.
Several human studies have investigated the potential of HMB to increase strength, improve body composition, and reduce muscle damage during resistance training or intensive exercise. A randomised trial on 39 men and 36 women given HMB at 3g per day or a placebo during a four-week resistance training programme found that those taking the HMB had a greater increase in upper body strength than the placebo group (an average of 7.5kg versus 5.2kg). They also decreased their fat percentage by an average of 1.1%, compared to 0.5% for the placebo group.  Another study examined the effects of 0g, 1.5g and 3g a day of HMB for subjects during a three-week weight lifting programme. They found that those taking HMB lifted more weight during each week of the study compared to the participants not taking the supplement, and their levels of creatine kinase (a marker of muscle damage) were reduced at 3 weeks.
HMB and creatine have been found to have a cumulative effect on lean body mass and strength. In a double-blind, three-week study, 40 participants were randomized into four groups, taking either creatine on its own (20g for 7 days then 10g for 14 days), HMB (3g per day), creatine + HMB, or placebo, while doing a resistance exercise programme. The creatine-only group gained 0.92kg more lean mass than the placebo group, the HMB group 0.39kg more than placebo, and the creatine + HMB group gained 1.54kg more than placebo. In addition, both individual supplement groups and the creatine + HMB group showed accumulative strength increases that were greater than placebo across all exercises: 37.5kg (HMG), 39.1kg (creatine), and 51.9kg (combination) greater than the strength increase in the placebo group. These results suggest that both individual creatine and HMB supplements may help increase lean body mass and strength, but the combined effect is greater.
L-tyrosine is an amino acid that is incorporated into proteins in the body. But tyrosine is best-known for its role in the production of the thyroid hormones thyroxine (T4) and triiodothyronine (T3), which are made from tyrosine and the mineral iodine. Thyroid hormones govern metabolism, including the production of energy from the food that we eat. As well as directly affecting energy levels, thyroid hormones have an influence on body weight, muscle strength, mood, cognitive function and memory, and heart rate – amongst others. Tyrosine is also a precursor to other hormones: adrenaline and noradrenaline, which are involved in the ‘fight or flight’ stress response, and have a role in energy, motivation and drive; and dopamine – which is involved in reward and pleasure, amongst other functions.
So the body uses tyrosine to produce hormones that govern energy and metabolism. But does supplementing tyrosine help with energy or performance? There seem to have been very few studies carried out to examine this effect. One double-blind trial published in the European Journal of Applied Physiology examined the effects of tyrosine on exercise performance in the heat. Eight healthy male volunteers performed two separate cycling trials to exhaustion in 30°C heat and 60% relative humidity, after consuming either a drink containing 150mg of tyrosine per kg body weight, or a placebo drink. The volunteers were able to cycle longer after taking the tyrosine compared to the placebo (an average of 80.3 minutes versus 69.2 minutes). Tyrosine is thought to improve exercise tolerance in heat by increasing availability of dopamine in the brain.  However, other similar studies found that tyrosine did not have an effect on performance, even in the heat.
Tyrosine may support growth and repair of muscles via a role in the activity of growth hormone. Although other amino acids such as arginine and ornithine are better known for their role in stimulating growth hormone secretion, tyrosine residues are present in growth hormone receptors and may be necessary for normal responses to growth hormone in the cells. In an animal study it was found that replacing tyrosine residues with another amino acid (phenylalanine) in growth hormone receptors resulted in reduced protein synthesis in the cell. The researchers concluded that tyrosine residues are required for these selected cellular responses to growth hormone.
Tyrosine is also known to have antioxidant activity. A lab study found that tyrosine has scavenging activity against several free radicals, including superoxide and hydrogen peroxide radicals . This may be relevant to exercise performance because one of the contributing factors to muscle fatigue and damage during exercise is the production of free radicals, which are a natural by-product of energy metabolism in cells. Therefore, antioxidants may help to reduce fatigue and muscle damage. . However, there seems to be limited or no research examining this potential effect of tyrosine supplementation.
L-taurine is an amino acid that is not incorporated into proteins, but is one of the most abundant amino acids in almost every tissue in the body, including in the muscle cells . It has roles in many different processes in the body including detoxification, bile acid production (needed to emulsify and efficiently absorb fats and fat-soluble vitamins), and growth and development [33, 34]. Taurine is needed for the normal functioning of skeletal muscle, including calcium-dependent muscle contraction, regulating cell volume, and aiding in antioxidant defence .
L-taurine supplementation has been studied for its potential to improve exercise performance, with some positive results. In a 2013 double-blind study on eight male middle-distance runners, the participants took either a 1000mg taurine supplement or a placebo two hours before performing a 3-km time trial. The average time trial result was slightly improved when taking the taurine: 647 seconds compared to 659 seconds when taking the placebo – an equivalent of 1.7% improvement. However, the authors said that the mechanism behind this improvement (how taurine is improving performance) was not clear. Another trial on 11 men participating in bicycle ergometer exercises until exhaustion found that seven days of taurine supplementation increased their VO2max (maximal oxygen uptake, a measure of aerobic endurance), time to exhaustion and maximal workload. In this case, the researchers theorised that taurine may enhance exercise capacity through protecting against exercise-induced DNA damage and protecting the cells (i.e. acting as an antioxidant).  And an animal study found that giving rats 100mg and 500mg of taurine per kg body weight per day for two weeks improved the rats’ running time to exhaustion by 25% and 50% respectively, compared to those who were not given taurine.
Taurine may also have a role in glucose regulation and insulin sensitivity. Many studies have investigated this link. A study on mice indicated that taurine may control glucose homeostasis (regulation) both by regulating the expression of genes required for glucose-stimulated insulin secretion, and by enhancing insulin sensitivity . Other studies have also indicated that taurine can enhance the action of insulin, and facilitate the interaction of insulin with its receptor, amongst others effects . All this means that taurine may help the cells to take up glucose for energy, as well as other nutrients including amino acids for protein synthesis.
Alpha lipoic acid
Alpha lipoic acid is a molecule that was once classified as a vitamin, but is now known to be made by the body. It acts as a coenzyme in carbohydrate metabolism and in the citric acid cycle which produces ATP (adenosine triphosphate) for energy in the mitochondria of cells.
As well as its direct role in energy production, alpha lipoic acid has several other important functions that may support exercise performance. Firstly, alpha lipoic acid has been found to support glucose uptake into cells and insulin sensitivity. An in-vitro study showed that alpha lipoic acid can increase glucose uptake by muscle cells, comparable to the effect of insulin . Various human studies have also examined this effect, primarily in patients with type II diabetes. A study on 57 diabetic patients found that those taking just 300mg of alpha lipoic acid a day for eight weeks showed significantly decreased fasting blood glucose, 2-hour post-meal glucose levels, and measurements of insulin resistance. Another study on patients with impaired glucose tolerance (but not diabetes) found that those receiving 600mg intravenous dose of alpha lipoic acid for two weeks showed improved insulin sensitivity (insulin sensitivity index was enhanced by 41%) as well as reduced markers of inflammation. Linking all this back to exercise performance, this indicates that alpha lipoic acid supplementation could help cells to take up glucose for energy, as well as other nutrients including amino acids for protein synthesis, and also improve potential for fat loss.
Secondly, alpha lipoic acid is a potent antioxidant. It has demonstrated antioxidant activity in both water-soluble and fat-soluble areas of the body’s cells, as opposed to many other substances that only act in one of these areas (e.g. vitamin C, which is water-soluble only). It can regenerate other antioxidants such as vitamin C (which in turn regenerates vitamin E) and has been found to increase levels of glutathione and coenzyme Q10 inside cells . Alpha lipoic acid has been shown to scavenge some of the most common and most damaging free radicals such as superoxide, hydroxyl and peroxyl radicals and singlet oxygen .
As previously discussed, this antioxidant activity may be relevant to exercise performance because one of the contributing factors to muscle fatigue and damage during exercise is the production of free radicals, which are a natural by-product of energy metabolism in cells. Therefore, antioxidants may help to reduce fatigue and muscle damage . To support the theory that alpha lipoic acid could have this effect, a randomised controlled trial on 16 men found that those taking an alpha lipoic acid supplement at 1200mg for 10 days before an exercise trial had significantly lower peak levels of creatine kinase (a marker of muscle damage) after the exercise compared to placebo, with the authors concluding that alpha lipoic acid may improve skeletal muscle regeneration. 
Inositol is a component of cell membranes. It is sometimes considered as part of the B-vitamin family, but it is not strictly a vitamin as it can be made by the body. Several forms (stereoisomers) of inositol exist in the body, but myo-inositol is the most abundant in the central nervous system .
Inositol is thought to have a role in the action of insulin , helping glucose and other substances to be taken into the cells. Specifically, it is needed for production of a substance called phosphatidylinositol 3,4,5-trisphosphate (PIP3), which is required for insulin signalling and for glucose to be taken into muscle cells.
Both animal and human studies have indicated that inositol supplementation can help to regulate blood glucose levels and improve insulin sensitivity. A recent 2015 double-blind clinical trial on 40 healthy participants found that those taking a drink containing 2.23g of inositol per day for 12 weeks showed a significant reduction in insulin levels, a decrease in measures of insulin resistance, and a mean reduction in blood glucose levels after meals of 14% . Several studies have investigated the effects of inositol supplementation for women with polycystic ovary syndrome (PCOS), in which insulin resistance is often a factor. In a 2014 study, 24 PCOS patients given 3g of myo-inositol per day showed a reduced insulin response to an oral glucose tolerance test, indicating improved insulin sensitivity .
Cinnamon is of course a delicious spice, but it also has several potential health benefits. One of these is its possible role in regulating glucose metabolism and supporting insulin sensitivity.
This glucose-regulating effect has been investigated in many studies, including clinical trials. Most of these trials were on type-II diabetics, but some also on healthy individuals. A small study on seven healthy men found that giving the participants 5g of cinnamon immediately before or 12 hours before an oral glucose tolerance test reduced blood glucose response by 13% and 10% respectively compared to the placebo, and improved insulin sensitivity. This suggests cinnamon can have both an immediate and sustained blood glucose-lowering effect in healthy individuals.  In another small trial published in the European Journal of Applied Physiology, eight healthy volunteers took part in two 14-day programmes taking either a 3g cinnamon supplement or a placebo every day, undergoing oral glucose tolerance tests on day 1 and 14 and for several days after the 14 day treatment. When taking the cinnamon, glucose response to the tolerance test was reduced by an average of 13.1% on day 1 and 5.5% on day 14, and insulin response was reduced by an average 27.1% on day 14. However, this effect was not found when the volunteers stopped taking the cinnamon. This indicates that it needs to be taken regularly to have a good effect! 
As a good summary of cinnamon’s effects in diabetes, a meta-analysis (considered the ‘gold standard’ of scientific studies, as it combines the results of many individual trials) was carried out in 2011 looking at the results of eight randomized, placebo-controlled trials on the effects of cinnamon on fasting blood glucose in type II diabetes or prediabetes. The authors reported that cinnamon intake, either as whole cinnamon or as cinnamon extract, results in a statistically significant lowering in fasting blood glucose – by an average of 0.49mmol/L. 
Banaba leaf comes from a tree or shrub called Lagerstroemia, sometimes known as crepe myrtle, which grows primarily in warmer climates and is native to south Asia. Banaba has been used in traditional medicines for its anti-diabetic effects , and as a result has been widely researched for its potential to support blood glucose control and insulin sensitivity, including in human trials.
In a randomized clinical trial on type 2 diabetic patients, those who took a banaba extract supplement standardized to 1% corosolic acid (thought to be one of the primary active constituents) for two weeks had reduced blood glucose levels of up to 30% . Another trial found similar benefits for nondiabetics with high fasting blood sugar: when patients were given a banaba extract supplement containing 10 mg of corosolic acid for two weeks, their fasting blood glucose decreased by 12%, as did their glucose levels 60 minutes after eating a starchy meal .
Research suggests that banaba leaf could work in several ways to support blood glucose control – including by increasing uptake of glucose into the cells . This is relevant for athletes in terms of supporting energy levels – i.e. the ability of the muscle cells to make use of glucose. But banaba may also improve insulin sensitivity, which is of particular benefit to athletes or those who wish to lose fat or build lean muscle. This was suggested by an animal study on diabetic mice, where it was found that a single dose of corosolic acid from banaba leaf could reduce blood sugar levels in the mice for up to 2 weeks, with the researchers stating that “These results support the hypothesis that CA improves glucose metabolism by reducing insulin resistance.” 
Glycine is one of the three amino acids that are used by the body to make creatine (the others being arginine and methionine). Creatine, as previously discussed, is a peptide stored primarily in the skeletal muscle in the body; it has a role in the phosphocreatine system, which regenerates ATP in the muscle after the first few seconds of muscle contraction, prolonging the immediate burst of energy. Again, creatine may also have several other roles, including supporting an increase in muscle strength and size, supporting glycogen storage in muscles and also supporting cognitive function by providing energy to the brain (see our write-up on Creatine for full details).
As well as being a precursor to creatine, glycine may also have an anti-catabolic effect on muscle. Researchers found that giving glycine to mice could protect against loss of muscle mass (cachexia) associated with cancer . Obviously this study does not provide proof that glycine works in the same way to protect muscle mass in healthy athletes, but does provide an indication of its potential benefit.
Glycine is also one of the amino acids that the body uses to produce glutathione, a vitally important antioxidant molecule that protects cells against damage from free radicals. Supplementing glycine together with cysteine has been found to improve glutathione levels in patients who are deficient.
Lysine is an essential amino acid – one that the body cannot make itself and must be supplied by our diet. It is found primarily in animal proteins; plant proteins generally contain a much lower percentage of lysine, and therefore levels can become deficient in those who eat little or no animal protein.
Supplementing L-lysine has been found to support muscle strength in adult men. In an experiment on 40 men – half of whom were under-nourished and half well-nourished – it was found that increasing the lysine intake of the well-fed men up to a total of 80mg per kilo body weight (which entailed giving them about an extra 2 grams of lysine per day) increased their muscle strength by about 7.5 percent after 8 weeks. [61, 62]
It’s also been found that lysine and arginine together may reduce levels of cortisol – one of the body’s stress hormones. This is interesting for athletes or those trying to build muscle strength or size because cortisol is a catabolic hormone that increases breakdown of muscle; and so reducing cortisol levels – especially post-exercise – may support muscle growth. The study behind this theory was a double-blind, placebo-controlled study of 108 Japanese adults in which supplemented group were given a combination of 2.64g each of lysine and arginine per day. It was found that the men given the supplement showed an 18% reduction in basal cortisol levels (i.e. their cortisol levels before a stressful event), and speeded up their return to normal cortisol levels after a stressful event. What’s more – although this is not as specifically relevant to strength or muscle gain – both male and female participants who took the lysine and arginine supplement showed significantly reduced anxiety levels both before and after the stressful event [63, 64].
Trimethylglycine – also known as betaine – is a natural substance found in foods, and can be made in the body from choline.
One of the primary roles of TMG is as an osmolyte  – a substance that affects osmosis. This means it can help to maintain cell hydration and volume.
The other well-known role of TMG in the body is as a ‘methyl donor’ in the cycle that converts homocysteine to methionine and SAMe (s-adenosyl methionine). This conversion is essential for the proper function of many of our body’s processes – from neurotransmitter production, to DNA repair, to controlling inflammation, to heart protection – meaning TMG could have a wide influence on our health.
TMG’s role in production of SAMe also means it may be important for fat metabolism in the liver – i.e. breaking down, removing or preventing the build-up of fat (which can lead to ‘fatty liver’). This in turn may help to prevent insulin resistance and obesity. In an animal experiment it was found that mice fed a high-fat diet developed insulin resistance, obesity and fatty liver; they also had reduced natural levels of TMG in their livers. But when they were given TMG in supplement form together with the same diet, this produced a reversal of insulin resistance and fatty liver.  Through this same mechanism, TMG supplementation may support body composition in humans too. In a study on 23 strength-trained men who were matched for body fat percentage, those who took 2.5g of TMG a day for 6 weeks while undergoing a training programme showed significantly improved body composition including body fat percentage and lean body mass, whereas the placebo group (doing the same training) showed no improvement in these measures . And in a population study on almost 2,000 older adults in China, those who had higher levels of TMG in their blood tended to have lower body weight, body mass index and waist circumference compared to those with lower levels of TMG , further supporting the idea that TMG may be important for body composition.
TMG may also have an anabolic effect, stimulating muscle growth and repair. Researchers carrying out an in vitro (test tube) study found that TMG could stimulate differentiation and growth of muscle fibres from immature muscle cells, potentially by increasing the activation of IGF-1, an anabolic hormone.  To investigate this further, another group of researchers carried out a clinical trial on 12 trained men. The participants took either a TMG supplement (2.5g per day) or a placebo for two weeks, then took part in an acute exercise session, after which their levels of hormones were measured. They found that after the two weeks of TMG supplementation, the men’s blood levels of IGF-1 and growth hormone increased, and cortisol (a catabolic hormone) had decreased in comparison to placebo. Their levels of muscle Akt, a signalling molecule that triggers protein synthesis, also increased. The TMG seemed to be enhancing the anabolic environment and encouraging protein synthesis. 
Methionine is another essential amino acid – one that the body cannot make itself and must be supplied by our diet. Methionine is used for protein synthesis, and is one of the primary amino acids that make up the contractile tissue in muscles .
As well as playing a role in structural proteins, methionine is one of the three amino acids that are used to make creatine (the others being arginine and methionine). Creatine, as previously discussed, is a peptide stored primarily in the skeletal muscle in the body; it has a role in the phosphocreatine system, which regenerates ATP in the muscle after the first few seconds of muscle contraction, prolonging the immediate burst of energy. Again, creatine may also have several other roles, including supporting an increase in muscle strength and size, supporting glycogen storage in muscles and also supporting cognitive function by providing energy to the brain (see our write-up on Creatine for full details).
Methionine can also be converted in the body to SAMe (s-adenosyl methionine). SAMe is a methyl donor that participates in many of our body’s essential processes, including neurotransmitter production, DNA repair, and producing the antioxidant molecule glutathione. As well as protecting cells against free radical damage, studies suggest that increasing glutathione availability in the muscles can delay muscle fatigue and improve performance during exercise by limiting oxidative stress (build-up of free radicals) and reducing the acidity that results from lactic acid production. [72, 73]
L-Arginine is a non-essential amino acid. Although it is used in protein synthesis, arginine is best known as the precursor or ‘building block’ for nitric oxide in the body. Nitric oxide causes dilation of the blood vessels, allowing better blood flow. This in turn can improve the delivery of glucose, oxygen and other nutrients to the body’s tissues, including the muscles; and improve removal of waste products such as lactate and ammonia.  In this way arginine may improve exercise performance.
As with many other nutrients, studies on arginine supplementation and its benefits for sports performance have had mixed results. However, it has shown some particularly positive results in exercise studies for increasing time to exhaustion (how long the individual can keep exercising) and oxygen cost of exercise (how much oxygen is used up by the body when exercising).
One of these was a double-blind trial carried out by UK researchers on nine healthy men. The men consumed either 6 grams of arginine in a drink, or a placebo, then one hour later had to do a series of moderate- and high-intensity exercise bouts. It was found that after consuming the arginine, the men’s average time to exhaustion in the high-intensity exercise increased from 562 seconds to 707 seconds – an increase of 25.8%. And in the moderate-intensity exercise their oxygen consumption was reduced by 7% when taking the arginine, indicating greater efficiency in utilization of oxygen.  Another small study on nine elite male wrestlers found that when they took arginine (1.5 grams per 10 kg body weight) one hour before a cycling exercise trial, their average time to exhaustion increased by 5.6% compared to when taking a placebo .
A study by Brazilian researchers also found that taking arginine may enhance lean mass gain, strength gain and fat loss when training. Twenty young men were divided into two groups and given either a combination of 3 grams of L-arginine and 1 gram of vitamin C per day, or just the vitamin C, for 8 weeks. Over the same time period both groups did the same lower-body weight-training programme, which they had previously been doing for 12 weeks before starting supplementation. After the 8 weeks, those taking L-arginine showed a significant average increase in lean muscle mass and muscular strength in knee flexion and extension exercises; as well as a reduction in fat mass, and an 8.4% decrease in body fat percentage. The control group, taking just the vitamin C, did not have any significant improvement in any of these areas (which may be expected as their training intensity did not increase).  This indicates that arginine could have beneficial effects for body composition as well as immediate exercise performance.
As well as being a precursor to nitric oxide, arginine has been shown in studies to increase growth hormone release [83, 84]. In fact, it’s been found that taking an arginine supplement alone can increase the body’s resting growth hormone levels by at least 100% . This could provide an alternative explanation for the increases in muscle mass and strength experienced by participants in the Brazilian study who were supplementing with arginine.
L-Citrulline is a non-essential amino acid that can be produced in the body from glutamine and ornithine. Contrary to some of the other amino acids we have discussed, it is not used directly in protein synthesis. Instead, citrulline is converted directly to arginine in the kidneys, and may then provide many of the same benefits as arginine itself in terms of supporting nitric oxide production (or even greater benefits, as we will see below).
Because of this role as an arginine precursor, citrulline has been widely studied for its potential to support exercise performance. In a 2010 randomized placebo-controlled trial on 41 men, researchers at the University of Cordoba found that men who took a single high dose of citrulline malate before training increased their number of repetitions in barbell presses at 80% of their 1-rep max (i.e. 80% of the weight at which they could only do 1 rep) compared to when taking a placebo. The more sets they did, the more the citrulline supplementation seemed to help, with the men achieving almost 53% more reps in the last set when taking citrulline versus placebo, indicating it was reducing fatigue. In this trial the participants also reported a decrease of 40% in muscle soreness at 24 and 48 hours post-exercise when taking the citrulline supplement.  In a similar study by US researchers, 14 resistance-trained men took either a placebo or a citrulline malate supplement and then performed three sets of chin-ups, reverse chin-ups and push-ups to failure (i.e. for as long as they could keep going). The citrulline supplement significantly increased the average number of reps they could do in each exercise – for example, 32.1 versus 26.6 in the reverse chin-ups. 
Citrulline has also been found in some studies to have similar benefits for women. In a 2015 placebo-controlled trial, 15 women took a single dose of citrulline malate before resistance exercise – this time both bench press and leg press to test upper and lower-body performance. The participants did more reps in both exercises when taking the citrulline supplement compared to the placebo – for example, completing an average total of 66.7 reps in leg press versus just 55.1. The women also reported significantly less ‘perception of exertion’ in the bench press exercise when taking the citrulline – i.e. they didn’t feel that they were working as hard to achieve the reps. 
But if the benefits of citrulline are derived from its conversion to arginine, why not just take arginine? Research indicates that while taking arginine can cause larger spikes in blood levels of arginine (i.e. the peak levels after taking the supplement), supplementation with citrulline may be more effective at maintaining higher arginine levels for longer periods of time . In fact, taking the two together is sometimes found be more effective than either alone. As an example, Japanese researchers found that giving rabbits a combination of arginine and citrulline improved nitric oxide availability compared to supplementing either amino acid alone .
L-Carnitine is an amino acid that is not used in protein synthesis. The primary role of carnitine in the body is in energy production – it is needed to transport fats into the mitochondria (the ‘energy-producing factories’) of our cells so they can be used in energy production, in a process called beta-oxidation.
Carnitine is a popular supplement for supporting athletic performance and endurance, and has had positive results in some studies. For example, a 2014 study on 26 professional footballers found that taking 3–4g of L-carnitine before exercise was associated with lower lactic acid production and lower heart rate response during a running test (suggesting more efficient energy utilization) . And in a study on 20 male athletes, those taking 2g of carnitine a day for 10 days showed a significant improvement in performance times in a 1500m running test – and reduced lactic acid build-up – whereas the control group did not improve from their baseline results. 
It was thought that carnitine improves performance by increasing beta-oxidation of fatty acids in the mitochondria – i.e. transporting more fats into the mitochondria to be burned for energy. However some studies suggest that this is not the case. Other possible ways it could be working include increasing blood flow to the muscle tissues, and decreasing ‘hypoxic stress’ – i.e. stress or damage to the cells and tissues due to lack of oxygen. 
Carnitine may also spare muscle glycogen in low or moderate-intensity exercise: in a trial on 14 men, those taking 2g of carnitine in addition to 80g of carbohydrate utilised 55% less muscle glycogen when exercising at 50% of maximum compared to those just taking the carbohydrates. Sparing muscle glycogen may result in improved endurance and time to exhaustion.
Carnitine has been found to help protect against muscle soreness and muscle damage after exercise, supporting recovery. In a study on 21 active men, those taking 2g of carnitine a day for 14 days had significantly lower levels of creatine kinase and lactate dehydrogenase – markers of muscle damage – 24 hours after exercise than those taking a placebo . A double-blind trial on 18 active men and women found that those taking 2g of L-carnitine a day for three weeks had significantly reduced markers of muscle damage, free radical formation and muscle soreness after a squat/leg press exercise challenge .
Taking carnitine supplements taken with carbohydrates may also increase energy expenditure (calorie burning) and prevent body fat gain. In a study of 12 men, it was found that those who took 1.36 g of carnitine together with 80g of carbohydrate twice a day for 12 weeks improved their whole-body energy expenditure by 6%, and did not gain fat; whereas those taking just the carbohydrates gained 1.8kg body fat mass over the 12 weeks and had no increase in energy expenditure . This indicates that carnitine could be helpful in fat loss/weight management too, especially for those who need to have a higher carbohydrate intake to support muscle glycogen replenishment and recovery from exercise.
Carnitine and its metabolites (e.g. acetyl-l-carnitine) may also have significant antioxidant activity. Several in vitro and animal studies have found this to be the case ; and a human study on 12 healthy participants, 2g of L-carnitine a day was found to increase levels of the body’s antioxidant enzymes including superoxide dismutase (SOD) and glutathione peroxidase, and increase total antioxidant capacity (i.e. ability to scavenge free radicals) . In one of the other studies quoted above, participants taking 2g of carnitine for 14 days were also found to have a higher plasma total antioxidant capacity than those taking a placebo .
Branched-chain amino acids (L-Leucine, L-Isoleucine, L-Valine)
The branched-chain amino acids (BCAAs) are leucine, isoleucine and valine. They are a sub-group of the essential amino acids. They may account for only around 18% of muscle proteins, but are thought to be particularly important for muscle protein synthesis and repair, playing more than just a structural role. Supplementing BCAAs may also be helpful for supporting performance and reducing fatigue during exercise.
All three BCAAs – leucine in particular – have been found to both increase protein synthesis and decrease protein degradation in resting human muscles, i.e. have an anabolic effect [93, 94]. As well as acting as a substrate (raw material) for protein synthesis, they seem to affect the signalling pathways that control it [93, 95] – i.e. they act like a ‘switch’ to turn on protein synthesis in the muscle.
Through this mechanism, taking BCAAs before or during training may also reduce muscle damage, reduce muscle fatigue and soreness and promote recovery. In a trial on 30 young men and women, half were given a 5g (5000mg) BCAAs mixture and the other half a placebo drink before performing a squat exercise test designed to induce delayed-onset muscle soreness (DOMS) and muscle fatigue. Those who took the BCAAs reported lower levels of muscle soreness from immediately after the exercise to four days later, with the women actually experiencing a greater reduction than the men. The ratings of muscle fatigue were also lower in the BCAAs groups, from day 2 to day 5 after the exercise . In another study on 12 long-distance runners taking part in a 3-day intensive training, those who took a BCAA-containing drink throughout the training reported 32% reduced muscle soreness and 24% lower muscle fatigue compared to the group taking the placebo drink (that contained the same number of calories). They also had lower levels of creatine kinase and other markers of muscle damage in their blood .
Taking BCAAs may reduce central fatigue during exercise, and therefore improve performance. Central fatigue occurs in the nervous system rather than the muscles, and is thought to be caused by an increase in levels of neurotransmitters such as serotonin in the brain, which tend to make us feel more relaxed, potentially causing feelings of fatigue even when the muscles should still be able to produce energy. But what’s the role of BCAAs here? As BCAAs get pulled into muscle and depleted from the blood during exercise, this allows more tryptophan to be taken into the brain (as there is less competition for uptake), which then converts to serotonin. So supplementing BCAAs may help to maintain their levels in the blood, reducing that influx of tryptophan.  One trial on seven endurance cyclists found that when the participants took a BCAAs drink during exercise, they reported less perceived exertion (how hard they thought they were working) and less mental fatigue than when taking a placebo drink (7% and 15% lower, respectively).  Another small double-blind trial on seven participants found that those who took BCAAs at 300mg/kg body weight for three days prior to exercise showed greater resistance to fatigue (17.2%) when compared to the placebo .
- Balsom PD et al. Creatine in humans with special reference to creatine supplementation. Sports Med. 1994 Oct;18(4):268-80.
- Demant TW, Rhodes EC. Effects of creatine supplementation on exercise performance. Sports Med. 1999 Jul;28(1):49-60.
- Bemben MG, Lamont HS. Creatine supplementation and exercise performance: recent findings. Sports Med. 2005;35(2):107-25.
- Kreider RB. Effects of creatine supplementation on performance and training adaptations. Mol Cell Biochem. 2003 Feb;244(1-2):89-94.
- Izquierdo M et al. Effects of creatine supplementation on muscle power, endurance, and sprint performance. Med Sci Sports Exerc. 2002 Feb;34(2):332-43.
- Becque MD et al. Effects of oral creatine supplementation on muscular strength and body composition. Med Sci Sports Exerc. 2000 Mar;32(3):654-8.
- Rawson ES, Volek JS. Effects of creatine supplementation and resistance training on muscle strength and weightlifting performance. J Strength Cond Res. 2003 Nov;17(4):822-31.
- Olsen S et al. Creatine supplementation augments the increase in satellite cell and myonuclei number in human skeletal muscle induced by strength training. J Physiol. 2006 Jun 1;573(Pt 2):525-34.
- van Loon LJ et al. Creatine supplementation increases glycogen storage but not GLUT-4 expression in human skeletal muscle. Clin Sci (Lond). 2004 Jan;106(1):99-106.
- Gualano B et al. Effects of creatine supplementation on glucose tolerance and insulin sensitivity in sedentary healthy males undergoing aerobic training. Amino Acids. 2008 Feb;34(2):245-50.
- Owen L, Sunram-Lea SI. Metabolic agents that enhance ATP can improve cognitive functioning: a review of the evidence for glucose, oxygen, pyruvate, creatine, and L-carnitine. Nutrients. 2011 Aug;3(8):735-55.
- Salomons GS et al. X-linked creatine transporter defect: an overview. J Inherit Metab Dis. 2003;26(2-3):309-18.
- Stöckler S et al. Creatine replacement therapy in guanidinoacetate methyltransferase deficiency, a novel inborn error of metabolism. Lancet. 1996 Sep 21;348(9030):789-90.
- McMorris T et al. Effect of creatine supplementation and sleep deprivation, with mild exercise, on cognitive and psychomotor performance, mood state, and plasma concentrations of catecholamines and cortisol. Psychopharmacology (Berl). 2006 Mar;185(1):93-103.
- Harris RC et al. The absorption of orally supplied beta-alanine and its effect on muscle carnosine synthesis in human vastus lateralis. Amino Acids. 2006 May;30(3):279-89.
- Budzeń S, Rymaszewska J. The Biological Role of Carnosine and Its Possible Applications in Medicine. Adv Clin Exp Med 2013, 22, 5, 739–744
- Derave W et al. beta-Alanine supplementation augments muscle carnosine content and attenuates fatigue during repeated isokinetic contraction bouts in trained sprinters. J Appl Physiol. 2007 Nov;103(5):1736-43.
- Stout JR et al. Effects of beta-alanine supplementation on the onset of neuromuscular fatigue and ventilatory threshold in women. Amino Acids. 2007;32(3):381-6.
- Gross M et al. Beta-alanine supplementation improves jumping power and affects severe-intensity performance in professional alpine skiers. Int J Sport Nutr Exerc Metab. 2014 Dec;24(6):665-73.
- Zaloga GP et al. Carnosine is a novel peptide modulator of intracellular calcium and contractility in cardiac cells. Am J Physiol. 1997 Jan;272(1 Pt 2):H462-8.
- Mizuno D et al. Protective activity of carnosine and anserine against zinc-induced neurotoxicity: a possible treatment for vascular dementia. Metallomics. 2015 Aug;7(8):1233-9.
- Babizhayev MA, Yegorov YE. An “enigmatic” L-carnosine (β-alanyl-L-histidine)? Cell proliferative activity as a fundamental property of a natural dipeptide inherent to traditional antioxidant, anti-aging biological activities: balancing and a hormonally correct agent, novel patented oral therapy dosage formulation for mobility, skeletal muscle power and functional performance, hypothalamic-pituitary- brain relationship in health, aging and stress studies. Recent Pat Drug Deliv Formul. 2015;9(1):1-64.
- Boldyrev AA et al. Physiology and pathophysiology of carnosine. Physiol Rev. 2013 Oct;93(4):1803-45.
- Hipkiss AR. Carnosine and its possible roles in nutrition and health. Adv Food Nutr Res. 2009;57:87-154.
- Nissen S et al. Effect of leucine metabolite beta-hydroxy-beta-methylbutyrate on muscle metabolism during resistance-exercise training. J Appl Physiol. 1996 Nov;81(5):2095-104.
- Panton LB et al. Nutritional supplementation of the leucine metabolite beta-hydroxy-beta-methylbutyrate (hmb) during resistance training. Nutrition. 2000 Sep;16(9):734-9.
- Jówko E et al. Creatine and beta-hydroxy-beta-methylbutyrate (HMB) additively increase lean body mass and muscle strength during a weight-training program. Nutrition. 2001 Jul-Aug;17(7-8):558-66.
- Tumilty L et al. Oral tyrosine supplementation improves exercise capacity in the heat. Eur J Appl Physiol. 2011 Dec;111(12):2941-50.
- Lobie PE et al. Requirement of tyrosine residues 333 and 338 of the growth hormone (GH) receptor for selected GH-stimulated function. J Biol Chem. 1995 Sep 15;270(37):21745-50.
- Gülçin I. Comparison of in vitro antioxidant and antiradical activities of L-tyrosine and L-Dopa. Amino Acids. 2007;32(3):431-8.
- Belviranli M, Okudan N. Well-Known Antioxidants and Newcomers in Sport Nutrition: Coenzyme Q10, Quercetin, Resveratrol, Pterostilbene, Pycnogenol and Astaxanthin. In: Lamprecht M, editor. SourceAntioxidants in Sport Nutrition. Boca Raton (FL): CRC Press; 2015. Chapter 5.
- Ripps H, Shen W. Review: taurine: a “very essential” amino acid. Mol Vis. 2012;18:2673-86.
- Taurine – monograph. Altern Med Rev. 2001 Feb;6(1):78-82.
- Lourenço R, Camilo ME. Taurine: a conditionally essential amino acid in humans? An overview in health and disease. Nutr Hosp. 2002 Nov-Dec;17(6):262-70.
- Spriet LL, Whitfield J. Taurine and skeletal muscle function. Curr Opin Clin Nutr Metab Care. 2015 Jan;18(1):96-101.
- Balshaw TG et al. The effect of acute taurine ingestion on 3-km running performance in trained middle-distance runners. Amino Acids. 2013 Feb;44(2):555-61.
- Zhang M et al. Role of taurine supplementation to prevent exercise-induced oxidative stress in healthy young men. Amino Acids. 2004 Mar;26(2):203-7.
- Miyazaki T et al. Optimal and effective oral dose of taurine to prolong exercise performance in rat. Amino Acids. 2004 Dec;27(3-4):291-8.
- Carneiro EM et al. Taurine supplementation modulates glucose homeostasis and islet function. J Nutr Biochem. 2009 Jul;20(7):503-11.
- De la Puerta C et al. Taurine and glucose metabolism. Nutr Hosp. 2010;25:910–9
- Estrada DE et al. Stimulation of glucose uptake by the natural coenzyme alpha-lipoic acid/thioctic acid: participation of elements of the insulin signaling pathway. Diabetes. 1996 Dec;45(12):1798-804.
- Ansar H et al. Effect of alpha-lipoic acid on blood glucose, insulin resistance and glutathione peroxidase of type 2 diabetic patients. Saudi Med J. 2011 Jun;32(6):584-8.
- Zhang Y et al. Amelioration of lipid abnormalities by α-lipoic acid through antioxidative and anti-inflammatory effects. Obesity (Silver Spring). 2011 Aug;19(8):1647-53.
- Alpha-lipoic acid. Monograph. Altern Med Rev. 2006 Sep;11(3):232-7.
- Packer L et al. alpha-Lipoic acid as a biological antioxidant. Free Radic Biol Med. 1995 Aug;19(2):227-50.
- Morawin B et al. The combination of α-lipoic acid intake with eccentric exercise modulates erythropoietin release. Biol Sport. 2014 Aug;31(3):179-85.
- Colodny L, Hoffman RL. Inositol–clinical applications for exogenous use. Altern Med Rev. 1998 Dec;3(6):432-47.
- Nestler JE et al. Ovulatory and metabolic effects of D-chiro-inositol in the polycystic ovary syndrome. N Engl J Med. 1999 Apr 29;340(17):1314-20.
- Ijuin T, Takenawa T. Regulation of insulin signaling and glucose transporter 4 (GLUT4) exocytosis by phosphatidylinositol 3,4,5-trisphosphate (PIP3) phosphatase, skeletal muscle, and kidney enriched inositol polyphosphate phosphatase (SKIP). J Biol Chem. 2012 Mar 2;287(10):6991-9.
- Bañuls C et al. Chronic consumption of an inositol-enriched carob extract improves postprandial glycaemia and insulin sensitivity in healthy subjects: A randomized controlled trial. Clin Nutr. 2015 May 23. pii: S0261-5614(15)00137-5.
- Genazzani AD et al. Myo-inositol modulates insulin and luteinizing hormone secretion in normal weight patients with polycystic ovary syndrome. J Obstet Gynaecol Res. 2014 May;40(5):1353-60.
- Solomon TP, Blannin AK. Effects of short-term cinnamon ingestion on in vivo glucose tolerance. Diabetes Obes Metab. 2007 Nov;9(6):895-901.
- Solomon TP, Blannin AK. Changes in glucose tolerance and insulin sensitivity following 2 weeks of daily cinnamon ingestion in healthy humans. Eur J Appl Physiol. 2009 Apr;105(6):969-76.
- Davis PA, Yokoyama W. Cinnamon intake lowers fasting blood glucose: meta-analysis. J Med Food. 2011 Sep;14(9):884-9.
- Miura T et al. Management of Diabetes and Its Complications with Banaba (Lagerstroemia speciosa L.) and Corosolic Acid. Evid Based Complement Alternat Med. 2012;2012:871495.
- Judy WV et al. Antidiabetic activity of a standardized extract (Glucosol) from Lagerstroemia speciosa leaves in Type II diabetics. A dose-dependence study. J Ethnopharmacol. 2003 Jul;87(1):115-7.
- Tsuchibe S et al. An inhibitory effect on the increase in the postprandial glucose by banaba extract capsule enriched corosolic acid. Journal for the Integrated Study of Dietary Habits. 2006;17:255–259.
- Miura T et al. Antidiabetic effects of corosolic acid in KK-Ay diabetic mice. Biol Pharm Bull. 2006 Mar;29(3):585-7.
- Ham DJ et al. Glycine administration attenuates skeletal muscle wasting in a mouse model of cancer cachexia. Clin Nutr. 2014 Jun;33(3):448-58.
- Nguyen D et al. Effect of increasing glutathione with cysteine and glycine supplementation on mitochondrial fuel oxidation, insulin sensitivity, and body composition in older HIV-infected patients. J Clin Endocrinol Metab. 2014 Jan;99(1):169-77.
- Ergo-log.com, (2016). Lysine supplementation boosts muscle strength. [online] Available at: http://www.ergo-log.com/lysine-supplementation-boosts-muscle-strength.html [Accessed 8 Feb. 2016].
- Unni U et al. The effect of a controlled 8-week metabolic ward based lysine supplementation on muscle function, insulin sensitivity and leucine kinetics in young men. Clinical Nutrition. 2012, 31(6), pp.903-910.
- Smriga M et al. Oral treatment with L-lysine and L-arginine reduces anxiety and basal cortisol levels in healthy humans. Biomed Res. 2007 Apr;28(2):85-90.
- Ergo-log.com, (2014). Combination of L-lysine and L-arginine reduces stress and lowers cortisol levels. [online] Available at: http://www.ergo-log.com/combination-l-lysine-and-l-arginine-reduces-stress-lowers-cortisol-levels.html [Accessed 8 Feb. 2016].
- Craig SA. Betaine in human nutrition. Am J Clin Nutr. 2004 Sep;80(3):539-49.
- Kathirvel E et al. Betaine improves nonalcoholic fatty liver and associated hepatic insulin resistance: a potential mechanism for hepatoprotection by betaine. Am J Physiol Gastrointest Liver Physiol. 2010 Nov; 299(5): G1068–G1077.
- Cholewa JM et al. Effects of betaine on body composition, performance, and homocysteine thiolactone. J Int Soc Sports Nutr. 2013 Aug 22;10(1):39.
- Chen YM et al. Higher serum concentrations of betaine rather than choline is associated with better profiles of DXA-derived body fat and fat distribution in Chinese adults. Int J Obes (Lond). 2015 Mar;39(3):465-71.
- Senesi P et al. Betaine supplement enhances skeletal muscle differentiation in murine myoblasts via IGF-1 signaling activation. J Transl Med. 2013 Jul 19;11:174.
- Apicella JM et al. Betaine supplementation enhances anabolic endocrine and Akt signaling in response to acute bouts of exercise. Eur J Appl Physiol. 2013 Mar;113(3):793-802.
- Ergo-log.com, (2015). Over seventies who do strength training will build more muscle by taking a collagen supplement. [online] Available at: http://www.ergo-log.com/strength-training-collagen-supplement.html [Accessed 8 Feb. 2016].
- Aoi W et al. Glutathione supplementation suppresses muscle fatigue induced by prolonged exercise via improved aerobic metabolism. J Int Soc Sports Nutr. 2015; 12: 7.
- Medved I et al. N-acetylcysteine enhances muscle cysteine and glutathione availability and attenuates fatigue during prolonged exercise in endurance-trained individuals. J Appl Physiol (1985). 2004 Oct;97(4):1477-85.
- Álvares TS et al. L-Arginine as a potential ergogenic aid in healthy subjects. Sports Med. 2011 Mar 1;41(3):233-48.
- Bailey SJ et al. Acute L-arginine supplementation reduces the O2 cost of moderate-intensity exercise and enhances high-intensity exercise tolerance. J Appl Physiol. 2010 Nov;109(5):1394-403.
- Yavuz HU et al. Pre-exercise arginine supplementation increases time to exhaustion in elite male wrestlers. Biol Sport. 2014 Aug;31(3):187-91.
- Angeli G et al. Investigation of the effects of oral supplementation of arginine in the increase of muscular strength and mass. Rev Bras Med Esporte _ Vol. 13, Nº 2 – Mar/Abr, 2007.
- Pérez-Guisado J, Jakeman PM. Citrulline malate enhances athletic anaerobic performance and relieves muscle soreness. J Strength Cond Res. 2010 May;24(5):1215-22.
- Wax B et al. Effects of Supplemental Citrulline-Malate Ingestion on Blood Lactate, Cardiovascular Dynamics, and Resistance Exercise Performance in Trained Males. J Diet Suppl. 2016 May 3;13(3):269-82. doi: 10.3109/19390211.2015.1008615. Epub 2015 Feb 12.
- Glenn JM et al. Acute citrulline malate supplementation improves upper- and lower-body submaximal weightlifting exercise performance in resistance-trained females. Eur J Nutr. 2015 Dec 11.
- Examine.com. Arginine – Scientific Review on Usage, Dosage, Side Effects | Examine.com. [online] Available at: http://examine.com/supplements/Arginine/ [Accessed 9 Feb. 2016].
- Morita M et al. Oral supplementation with a combination of L-citrulline and L-arginine rapidly increases plasma L-arginine concentration and enhances NO bioavailability. Biochem Biophys Res Commun. 2014 Nov 7;454(1):53-7.
- Alba-Roth J et al. Arginine stimulates growth hormone secretion by suppressing endogenous somatostatin secretion. J Clin Endocrinol Metab. 1988 Dec;67(6):1186-9.
- Kanaley JA. Growth hormone, arginine and exercise. Curr Opin Clin Nutr Metab Care. 2008 Jan;11(1):50-4.
- Orer GE, Guzel NA. The effects of acute L-carnitine supplementation on endurance performance of athletes. J Strength Cond Res. 2014 Feb;28(2):514-9.
- Karahan M et al. The effect of L-carnitine supplementation on 1500 m running performance. Ovidius University Annals, Physical Education and Sport/Science, Movement and Health Series 2010;10(Suppl 2):504-507.
- Parandak K et al. The effect of two-week L-carnitine supplementation on exercise -induced oxidative stress and muscle damage. Asian J Sports Med. 2014 Jun;5(2):123-8.
- Wall BT et al. Chronic oral ingestion of L-carnitine and carbohydrate increases muscle carnitine content and alters muscle fuel metabolism during exercise in humans. J Physiol. 2011 Feb 15;589(Pt 4):963-73.
- Ho JY et al. l-Carnitine l-tartrate supplementation favorably affects biochemical markers of recovery from physical exertion in middle-aged men and women. Metabolism. 2010 Aug;59(8):1190-9.
- Stephens FB et al. Skeletal muscle carnitine loading increases energy expenditure, modulates fuel metabolism gene networks and prevents body fat accumulation in humans. J Physiol. 2013 Sep 15;591(Pt 18):4655-66.
- Lee BJ et al. Effects of L-carnitine supplementation on oxidative stress and antioxidant enzymes activities in patients with coronary artery disease: a randomized, placebo-controlled trial. Nutr J. 2014 Aug 4;13:79.
- Cao Y et al. Single dose administration of L-carnitine improves antioxidant activities in healthy subjects. Tohoku J Exp Med. 2011;224(3):209-13.
- Blomstrand E et al. Branched-chain amino acids activate key enzymes in protein synthesis after physical exercise. J Nutr. 2006 Jan;136(1 Suppl):269S-73S.
- Howatson G et al. Exercise-induced muscle damage is reduced in resistance-trained males by branched chain amino acids: a randomized, double-blind, placebo controlled study. J Int Soc Sports Nutr. 2012 Jul 12;9:20.
- Rennie MJ et al. Branched-chain amino acids as fuels and anabolic signals in human muscle. J Nutr. 2006 Jan;136(1 Suppl):264S-8S.
- Shimomura Y et al. Nutraceutical effects of branched-chain amino acids on skeletal muscle. J Nutr. 2006 Feb;136(2):529S-532S.
- Matsumoto K et al. Branched-chain amino acid supplementation attenuates muscle soreness, muscle damage and inflammation during an intensive training program. J Sports Med Phys Fitness. 2009 Dec;49(4):424-31.
- Blomstrand E. A role for branched-chain amino acids in reducing central fatigue. J Nutr. 2006 Feb;136(2):544S-547S.
- Blomstrand E et al. Influence of ingesting a solution of branched-chain amino acids on perceived exertion during exercise. Acta Physiol Scand. 1997 Jan;159(1):41-9.
- Gualano AB et al. Branched-chain amino acids supplementation enhances exercise capacity and lipid oxidation during endurance exercise after muscle glycogen depletion. J Sports Med Phys Fitness. 2011 Mar;51(1):82-8.