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Alanine: improve sporting performance by reducing fatigue
Why you might expect to work out harder for longer with the help of the amino acid alanine
Many exercise scientists and sports nutritionists are extremely taken with the idea that dietary supplementation with amino acids – the building blocks of proteins – might enhance athletic performance, even in athletes whose diets are considered to be adequate in protein. One particular focus of attention has been an amino acid called alanine, because during exercise the muscles release alanine into the bloodstream in direct proportion to the intensity of the exertion(1). The alanine is then picked up by the liver, where it is converted into glucose and released into the blood plasma. Thus, alanine seems to help keep blood sugar levels stable during exercise; and since low levels of blood sugar have been linked with fatigue during exertion, some experts believe alanine supplements might enable athletes to exercise for longer periods of time at competitive intensities.
There has also been considerable interest in the branched-chain amino acids – valine, leucine and isoleucine. Some research has shown that muscles break down branched-chain amino acids during exercise, suggesting that supplementation might provide extra muscular fuel. However, a recent study found that supplementation with these amino acids did not change blood lactate concentrations or improve performance during high-speed swimming or cycling at an intensity above the lactate threshold(3).
How branched-chain amino acid supplements might keep fatigue at bay
By contrast, there is evidence that branched-chain supplementation may be quite helpful during extended exercise at intensities below the lactate threshold. The explanation goes like this: as blood concentrations of the branched-chain amino acids decline during exercise (a result, presumably, of their increased breakdown by muscles), levels of another amino acid – tryptophan – can increase by as much as 100%(4). Since tryptophan ‘competes’ with the branched-chain amino acids to squeeze through capillaries in the brain and gain access to neural tissue, this may well mean that athletes’ brains become relatively full of tryptophan and relatively devoid of branched-chain amino acids during extended exercise. That is not a lethal scenario, but it is worthwhile noting that tryptophan is easily converted inside the brain to a chemical called serotonin, which has sometimes been called the brain’s ‘sandman’, since it can induce feelings of extreme fatigue and sleepiness.
As a result, some scientists have suggested that supplementation with branched-chain amino acids might limit perceptions of fatigue during prolonged physical efforts, and thus enhance performance. Indeed, in one US study triathletes who took in about 14g per day of branched-chain amino acids were able to run considerably faster during the run portion of a triathlon than non-supplemented ‘controls’(5).
There is also increasing evidence that branched-chain amino acid supplementation is very important immediately after exercise. In a study carried out in Copenhagen by the noted Scandinavian exercise physiologists Eva Blomstrand and Bengt Saltin, athletes ingested branched-chain amino acids or a placebo during one hour of cycle-ergometer exercise and a two-hour post-workout recovery period(6). The supplements had little effect on protein metabolism during the training session, but seemed to produce a smaller release of amino acids from the leg muscles during the post-workout recovery. Blomstrand and Saltin concluded that ingested branched-chain amino acids may have a protein-sparing effect during recovery from exercise, which could have the knock-on effects of enhancing the quality of recovery, reducing the risk of injury to muscle tissue and making it easier for athletes to conduct high-quality workouts on subsequent days. Considerable more work needs to be carried out in this area, but research seems to indicate that leucine may be the key branched-chain amino acid associated with amplified protein synthesis following training(7).
There is also a general feeling (and a fair amount of evidence) that amino acids are used as fuel during exercise to a greater extent than was previously believed – and thus that protein requirements for athletes are higher than the intakes commonly recommended(8).
Adequacy of protein intake in athletes is usually assessed by means of nitrogen balance studies. These investigations are based on the principles that protein is about 16% nitrogen by weight, and that an athlete is considered to be in nitrogen balance when the amount of nitrogen ingested (determined by weighing food) is equal to the amount excreted. Elimination of more nitrogen than is consumed means an athlete is in negative balance, with potentially serious consequences for health and performance, including a decline in lean body mass.
So far, most of these studies have indicated that athletes in general do a good job of achieving nitrogen balance, but there is a catch: nitrogen found in urine is used as the indicator of how much nitrogen is leaving the body; this has always seemed reasonable, since it was assumed that about 85% of the nitrogen which leaves the body is excreted via the urinary system(9), but some studies have suggested that this technique may dramatically underestimate the amount of nitrogen which is lost. For example, one study found that the amount of nitrogen lost in sweat could increase as much as 150-fold during exercise, indicating that the sweat glands could be significant contributors to nitrogen losses(10). This study also indicated that the breakdown of amino acids contributed about 10% of the energy needed for exercise – far more than is usually attributed to amino-acid metabolism.
Recently, there has been considerable interest in the effects of two unique amino acids – aspartate and asparagine – on athletic performance. These two are closely related chemically and are very common in the plant world; (asparagines occurs in high concentrations in asparagus, as you might expect). Early research with aspartate and asparagine has suggested that the duo may in some way slow down glycogendepletion in the muscles and liver, thus prolonging an athlete’s ability to exercise(11). It is also believed that aspartate and asparagine may somehow help keep blood levels of tryptophan under control during prolonged exercise, possibly reducing the risk of mental fatigue during lengthy exertion(12).
- Rest/amino acids;
- Exhaustion/amino acids;
All the rats trained by swimming for 20 minutes per day on five occasions over a seven-day period. During this time, rats in the two amino acid groups ingested 35 millimoles (mM) per day of supplemental aspartate and 400 mM of supplemental asparagine daily; (all rats consumed standard lab food ad lib to satisfy their overall nutritional needs). Rats in the placebo group imbibed distilled water instead of the aspartate and asparagine. On the seventh day, animals in the exhaustion groups swam to exhaustion at an intensity slightly above lactate threshold.
A knockout win for the supplements
Supplementation with aspartate and asparagine produced some striking results. For example, after the week of supplementation, glycogen concentrations in the soleus muscles of the rest/amino acid rats were 59% higher than in those of the resting controls. Time to exhaustion while swimming at above lactate threshold intensity was also dramatically higher in the exhaustion/amino acid rats (68 minutes) than in the corresponding controls (41 minutes).
Very interestingly, blood lactate levels at the end of the exhaustive exercise were significantly lower in the supplemented group, averaging just 8.6 mM per litre, compared with 11.3 in the non-supplemented rats (a 24% difference). In addition, the rate of glycogen degradation for the supplemented rats was 77% lower in the gastrocnemius (calf) muscles, 30% lower in the extensor digitorum longus muscles (running from the fibula to the toes) and a whopping 85% lower in the liver than for the controls.
Overall, it was a knockout victory for aspartate and asparagine supplementation, with the amino acids producing longer endurance times, inducing more temperate blood lactate levels and promoting better conservation of precious glycogen. How did the two little amino acids actually produce such varied and impressively positive effects?
Apparently, there exists within muscle cells a mechanism known as ‘the malate-aspartate shuttle’, whose purpose is to transport hydrogen ions from the cytoplasm of muscle cells into their mitochondria, where the hydrogens become involved in the aerobic production of a high-energy compound called ATP. Increased concentrations of aspartate and asparagine seem to enhance the activity of this shuttle. This could account for the improved performance associated with aspartate-asparagine supplementation, since the hydrogen ions – if left in the cytoplasm – could lower intracellular pH, interfere with the muscle-contraction process and heighten fatigue.
As already mentioned, protein may play an important role as an energy substrate during sustained exercise. However, to provide energy the key amino acids which furnish energy during exercise (the branched-chain amino acids, aspartate, asparagines and glutamine) must first be converted into a compound that can readily enter the biochemical pathways associated with energy release. This process involves removing the nitrogen from the amino acids and passing it to other compounds via a process called transamination; once an amino acid has been transaminated, it exists as a ‘carbon skeleton’, which can be used for energy production. The importance of this process is demonstrated by the fact that muscles involved in heavy training adapt by increasing their concentrations of the enzymes which allow transamination to occur.
As it turns out, aspartate and asparagines are transaminated readily inside muscle cells. This leads to the formation of oxaloacetic acid, which happens to be a key component of the ‘Krebs cycle’, a complex series of chemical reactions that ultimately generate huge quantities of usable energy (ATP) for muscle cells. Carbohydrate is also utilised to form Krebs cycle components, and the ability of the aspartate and asparagine derivative, oxaloacetic acid, to substitute for carbs in the Krebs cycle may well explain the lower glycogen degradation rates (and corresponding increased resistance to fatigue) in the amino acid-supplemented rats. To put it another way, less carbohydrate may have been needed to furnish the energy required for exercise in the supplemented rats, since aspartate and asparagine were being so helpful. This would also explain the higher lactate levels observed in the placebo rats: high rates of carbohydrate breakdown tend to produce high lactate concentrations, but the metabolism of aspartate and asparagine does not produce any lactate at all.
The results of the Brazilian study are supported by a separate study which also examined the effects of aspartate and asparagine supplementation on muscle metabolism and exercise endurance(12). In this investigation, aspartate and asparagines increased the ability of muscles to spare glycogen – and heightened the capacity of muscles to break down fats for energy. In addition, time to exhaustion was about 40% longer with supplementation. Other research has indicated that even a single dose of aspartate can enhance fat oxidation during prolonged exercise(14).
So should you give aspartate-asparagine supplementation a try? There has been limited human research in this field, but the results of the Brazilian study are certainly impressive. No side effects are associated with aspartate-asparagine supplementation, providing the supplements are obtained from a reputable supplier. Athletes who are interested in giving this potential ergogenic aid a go might like to start off with a short-term course of supplements, perhaps for two weeks, just to gain a feeling for how the amino acids influence their ability to perform prolonged workouts.
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