Several amino acids have been theorized to help decrease the incidence of over-training. Branched-chain amino acids (BCAA) supplementation before and\/or during exercise has been suggested to be an effective nutritional strategy to delay the onset of central fatigue. Although there is strong theoretical rationale to support the potential use of BCAAs as an ergogenic aid, research investigating the effects of BCAA supplementation on physiological and psychological responses to exercise and exercise performance is mixed. Several studies indicate that BCAA supplementation before or during exercise increases BCAA levels, minimizes increases in the free tryptophan to BCAA ratio, and may affect physiological and psychological responses to exercise. However, other studies have found limited effects and few studies have found that BCAA supplementation actually improves exercise performance capacity. Studies that have reported improved physiological and\/or psychological responses to exercise typically involve ingesting 4 to 21 g\/day BCAA during training and or 2 to 4 g\/hr of BCAA with a 6-8% GES drink before and during prolonged exercise. Additionally, there are several studies that indicate that ingesting carbohydrate with BCAA and\\or protein before and or following exercise during training helps promote greater training adaptations. In our view, the greatest potential application of BCAA supplementation is to help athletes tolerate training to a greater degree rather than a performance enhancement supplement. However, more research is needed to determine the role of BCAA on exercise capacity and markers of over-training before definitive conclusions can be drawn.The second amino acid that may help lessen the incidence of over-training is glutamine. As stated earlier, glutamine serves as the primary fuel for the lymphocyte, Some have suggested that glutamine supplementation may help athletes maintain immune function because exercise has been reported to decrease glutamine availability and immune function. Additionally, glutamine has been reported to regulate cellular hydration status, which has been shown to be an important regulator of protein synthesis. Consequently, glutamine supplementation (e.g., 6 to 12 g\/day) has become popular among athletes attempting to increase muscle mass and\/ or maintain a healthy immune system during training. Although there is a strong scientific basis to support a theoretical use of glutamine in athletes, studies on athletes are mixed or lacking. Several studies indicate that BCAA and glutamine supplementation can preserve and\/ or increase glutamine levels during exercise. Theoretically, a maintenance and or increase in glutamine levels should help lessen the negative impact of intense exercise on immune function. Studies investigating this hypothesis, however, have not consistently observed improved immune status. We are also not aware of any study that has evaluated the effects of glutamine alone on strength and muscle mass alterations during training. Consequently, additional research is necessary to determine whether glutamine supplementation may affect immune function and training adaptations before conclusions can be drawn. Another compound that may playa role in lessening the incidence of over-training is creatine. Classified as a methylglycocynamine, creatine supplementation has been shown to increase intramuscular creatine and phospho\u00adcreatine stores and improve performance capacity during intermittent high-intensity exercise. Additionally, creatine supplementation has been reported to allow athletes to maintain greater training volume and promote greater gains in strength and muscle mass. These findings suggest that creatine supplementation may allow an athlete to tolerate a greater training volume while maintaining positive training adaptations. Although it is unclear whether creatine supplementation may have a direct role in preventing over-training, creatine supplementation during intensified periods of training may help an athlete tolerate training to a greater degree and thereby lessen the susceptibility to over-training. More research is needed to investigate this hypothesis. Can amino acid supplementation help prevent over-training Although more research is needed to determine the potential ergogenic value of BCAA, creatine, and glutamine supplementation, it is our view that athletes involved in intense training should ingest a diet high in BCAAs, creatine, and glutamine. This can be accomplished either by selecting high-quality protein sources in the diet (e.g., caseine, whey protein, etc.) andlor by ingesting carbohydrate\/protein supplements that contain quality protein, BCAAs, and glutamine. It is also our view that given the evidence regarding the ergogenic value and medical safety, creatine supplementation can serve as an effective ergogenic aid for athletes involved in high \u00adintensity training. Whether creatine has a role in lessening the impact of over-training remains to be determined.