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AMINO ACIDS
Some studies suggest that tr yptophan can attenuate excitable behaviour
athletics and other sports where amino acidrich drinks and powdered supplements are often used. Why use amino acid supplements? Human athletes incorporate protein and amino acid supplements into their diet for a variety of reasons including to increase muscle mass, to reduce muscle damage during exercise, to reduce the incidence of exercise-related anemia and to promote glycogen resynthesis when taken with readily available carbohydrate post-exercise. While the general consensus appears to be that protein supplementation per se is perhaps not warranted, supplementing with amino acids either individually or in combination may have ergogenic effects that go beyond the role of total protein within the diet. Amino acids that have been discussed in this respect in human sports nutrition include tryptophan, branch chain amino acids (leucine, isoleucine, valine), glutamine, aspartate, arginine, tyrosine and taurine. Overall there is very little evidence for the beneficial effect of most of these amino acids in horses although some, like glutamine for example, have been looked at, so again we are left to draw inadequate conclusions from work that has been carried out in other species.
Potentially beneficial amino acids to look out for Glutamine Glutamine is a non-essential amino acid and is also one of the most abundant amino acids in the tissues of the body. Glutamine plays a major role in supporting immunity, as it provides an important energy source for cells of the gastro-intestinal tract and the immune system, such as lymphocytes and macrophages. Glutamine is also required for the synthesis of glutathione, which is an important antioxidant throughout the body but particularly within muscles and the lungs. Glutamine has also been suggested to promote muscle glycogen synthesis and muscle strength. Glutamine supplementation in horses has recently attracted some attention, as it is believed that a reduced supply of glutamine to the immune system, such as may occur during overtraining, could compromise future immune response. In humans, when plasma glutamine concentration is reduced this can be associated with a reduced immune response in terms of the proliferation of lymphocytes. It has also been suggested in human athletes that reduced availability of glutamine can contribute to an increased incidence of viral infections, although results in this area are equivocal.
Essential amino acids
Non-essential amino acids
Valine Leucine Isoleucine Lysine Methionine Threonine Phenylalanine Tryptophan Histidine
Tyrosine Glycine Alanine Cysteine Serine Aspartamine Asparagine Glutamate Glutamine Arginine Proline
Viral challenge in horses is associated with a major depletion in plasma glutamine concentration (>30%), but glutamine status can be restored through supplementation with either L-glutamine or ingredients such as hydrolyzed wheat gluten, which are a naturally rich source of natural glutamine. In humans, therapeutic benefits from glutamine supplementation have been reported in situations of stress, e.g. from athletic activity, or clinical disease. A similar effect would clearly benefit horses in intense and sustained training, or those under clinical stress due to infection, however as yet the true effectiveness of dietary glutamine supplementation in horses in training has not been fully evaluated. Branched chain amino acids The so-called branch chain amino acids (BCAA) refer collectively to leucine, isoleucine, and valine. These have been researched extensively in human athletes for their hypothesized beneficial effects on exercise performance in terms of delaying the onset or perception of fatigue – otherwise known as central fatigue – improving concentration, and reducing protein and muscle breakdown during intense exercise. The rationale for their effect on central fatigue is that they help maintain a high ratio of BCAA/tryptophan in the circulation. Tryptophan is a precursor for serotonin which depresses the central nervous system and contributes to the perception of fatigue. Exercise normally increases the exposure of the brain to increased levels of serotonin through an increase in the free tryptophan concentration in the blood. The role of branch chain amino acids is to compete with tryptophan for movement across the blood brain barrier hence reducing the exposure of the brain to serotonin, thus delaying fatigue. Results in human studies have been mixed and many of the trials have investigated endurance rather than short term highintensity exercise. In the horse, endurance exercise studies have confirmed a decrease in the BCAA/tryptophan ratio. Of the two BCAA ISSUE 11 TRAINERMAGAZINE.com 53