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Antonio and Street42 propose that the ergogenic benefits of glutamine observed in certain groups of athletes and not in others may be due to its protective role against protein degradation, potentially enhancing recovery following resistance training sessions; however, this is yet to be determined among athletes participating in such sports. Since strength and resistance training result in glycogen depletion and increased protein turnover, Antonio and Street42 have suggested that glutamine supplementation may be beneficial for these athletes. However, the data on nonendurance activities and glutamine supplementation are scarce. Antonio et al.43 observed that pre-exercise glutamine supplementation (0.3 g/kg body weight) in men performing weight-lifting exercise did not result in any changes in maximal repetitions performed in the leg press or bench press, suggesting that short-term ingestion of glutamine does not enhance weight-lifting performance in resistance-trained men. The supposition that glutamine may act as a buffering agent for repeated bouts of high-intensity activities originates from the potential ability to maintain the acid-base balance in the body. However, Haub et al.44 in a study of the effects of glutamine or placebo supplementation (0.03 kg/kg) did not observe any beneficial effects of the supplementation on five repeated bouts of cycling at 100% VO2max peak (four bouts lasting 60 sec and the fifth bout continued to fatigue). The results indicated that acute ingestion of L-glutamine did not enhance buffering potential or performance or delay the onset of fatigue during high-intensity exercise in these athletes.

In another study, Candow et al.45 examined the effect of oral glutamine supplementation combined with a weight resistance program on 1 rep maximum leg press and bench press, peak knee extension torque, on lean tissue and muscle protein degradation. Subjects were supplemented with glutamine (0.9 g/kg lean body mass/day) or placebo for 6 weeks of training. Although increases in strength (31% for squat and 14% for bench press), torque (6%), lean tissue mass (6%) and 3-methylhistidine (41%) were observed in the glutamine-supplemented group, similar increases were observed in the placebo group. The researchers concluded that glutamine supplementation resulted in no significant effect on muscle performance, body composition, or muscle protein degradation during resistance training. Similarly, van Hall et al.31 also did not observe any beneficial effects of oral glutamine supplementation on glycogen resynthesis following intense interval exercise. Antonio et al.46 also investigated glutamine supplementation and its effects on weight-lifting performance. Resistance-trained individuals (n = 6) performed weight-lifting exercises in a double-blind, placebo-controlled, crossover design supplemented with glutamine or glycine (0.3 g/kg; average intake, 23 g) mixed with calorie-free fruit juice or placebo. One-hour postingestion of the supplement, subjects performed exercises to muscular failure. Acute ingestion of glutamine did not enhance weight-lifting performance, and no differences were observed in the average number of maximal repetitions performed in the leg or bench press exercises, suggesting that short-term ingestion of glutamine (1 h before the event) may not have any ergogenic benefits for individuals participating in resistance type activities. The effects of long-term ingestion of glutamine are yet to be determined.

This lack of an effect of glutamine supplementation during resistance training may be due to the utilization of glutamine by other tissues before it reaches the peripheral circulation and skeletal muscle. Glutamine serves as a gluconeogenic precursor when muscle glycogen is depleted by approximately 90%; however, resistance training typically produces approximately 40% depletion in muscle glycogen, which may not be severe enough to benefit from glutamine supplementation.46 Serving as an energy source of the immune cells is another proposed ergogenic effect of glutamine.19,40 Exhaustive endurance exercise has been shown to suppress the immune system in some athletes; however, heavy resistance exercise has not been observed to have any significant impact on the immune system,47,48 suggesting that some of the ergogenic benefits of glutamine may be dependent on the type of exercise performed. In a recent review by Ohtani et al.,49 chronic supplementation with a mixture of amino acids, including branched-chain amino acids, arginine, and glutamine, was observed to result in a quicker recovery from muscle fatigue, following eccentric exercise training. At the highest doses of the amino acid supplementation (6.6 g/day) for 1 month, blood oxygen-carrying capacity was increased, while muscle damage was observed to decrease, thus resulting in improved training efficiency.

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