The Role of Protein and Amino Acids in Sustaining and Enhancing Performance (1999) / Chapter Skim
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15 Supplementation with Branched-Chain Amino Acids, Glutamine, and Protein Hydrolysates: Rationale for Effects on Metabolism and Performance
15 Supplementation with Branched-Chain Amino Acids, Glutamine, and Protein Hydrolysates: Rationale for Effects on Metabolism and Performance
Pages 309-330
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M Wagenmakers~ INTRODUCTION Endurance athletes in periods of intense training with a high daily workload tend to believe that they need more protein and amino acids in the diet than sedentary subjects.
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PROTEIN AND AMINO ACID METABOLISM IN ENDURANCE EXERCISE Recent stable isotope tracer studies have reopened the discussion on whether net protein breakdown (protein synthesis < protein degradation) and increased amino acid oxidation occur during prolonged endurance exercise at the whole body level.
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Other tracers, [2Hs~phenylalanine and ['5N2jurea, did not show an increase of amino acid oxidation and net protein breakdown during exercise. Therefore, it is unclear whether proteins are broken down in highly demanding endurance and ultra-endurance exercise under laboratory conditions and in the field.
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Demanding endurance exercise may also lead to net protein breakdown in gut and liver, but direct evidence in humans has not been reported. BRANCHED-CHAIN AMINO ACIDS Central Fatigue Hypothesis Prolonged exercise that leads to glycogen depletion inevitably causes fatigue.
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Effects of Ingestion of Branched-Chain Amino Acids and Tryptophan on Endurance Performance The effect of BCAA ingestion on physical performance was investigated for the first time in a field test by BIomstrand et al., 1991. Male subjects (n = 193)
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. These treatments greatly increased the plasma concentration of the respective amino acids to values well outside the normal physiological range.
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Thus, performance studies have not provided experimental support for the central fatigue hypothesis as playing a dominant role in fatigue mechanisms during prolonged exercise. Interaction of the BCAA-Aminotransferase Reaction with the Tricarboxylic Acid (TCA)
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This could imply that the indicated carbon drain on the TCA cycle is greater after BCAA ingestion and that by this mechanism, BCAA ingestion leads to premature fatigue during prolonged exercise, leading to glycogen depletion. Wagenmakers et al., (1990)
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and military activities where performance depends on motor coordination. GLUTAMINE Glutamine is the main end product of muscle amino acid metabolism both in the overnight fasted state and during feeding (Marliss et al., 1971; Chang and Goldberg 1978a; Wagenmakers et al., 1985; Ella et al., 1989; Wagenmakers and Soeters, l99S; Nurjhan et al., 1995~.
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Plasma Glutamine Concentrations Following Prolonged Exercise During exercise, plasma glutamine concentrations may increase, decrease, or remain unchanged depending on the type, duration, and intensity of exercise. However, lowered plasma glutamine concentrations were observed for a period of several hours following demanding endurance exercise leading to glycogen depletion (e.g., Van Hall, 1996~.
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However, the link between glutamine metabolism and the immune system is not as strong as in critically ill or burn patients who tend to have much lower plasma glutamine concentrations and also low muscle glutamine stores. These patients have a reduced muscle mass and, therefore, may have a lower endogenous capacity to synthesize glutamine.
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If anything, a high protein intake strengthens the immune system. GLYCOGEN RESYNTHESIS FOLLOWING EXERCISE During prolonged exercise at intensities between 50 and 85 percent VO2m~`, muscle glycogen from a quantitative point of view is by far the most important energy source (Romijn et al., 1993~.
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reported that intravenous infusion of glutamine increased glycogen resynthesis rates (Table 15-2~. However, glycogen resynthesis was measured at submaximal rates in the absence of ingested glucose.
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AUTHOR'S CONCLUSIONS AND RECOMMENDATIONS No conclusive evidence supports net protein breakdown and increased amino acid oxidation during demanding endurance exercise in the laboratory and under field conditions. When energy balance is maintained, 100 g of protein should be more than enough to cover the protein requirements of subjects regularly involved in high workload exercise.
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1995. Effect of branched-chain amino acid and carbohydrate supplementation on the exercise induced change in plasma and muscle concentration of amino acids in human subjects.
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1996. Effects of glucose, glucose plus branched-chain amino acids or placebo on bike performance over 100 km.
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1995b. Deamination of amino acids as a source for ammonia production in human skeletal muscle during prolonged exercise.
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: Is it possible that the mechanism for increased glycogen storage after the addition of amino acid to the glucose may be repartitioning, in the sense that you now supply the nonessential amino acids that might have had to be synthesized from carbohydrate if you didn't supply them for muscle repair, so that in fact there is more glucose available for glycogen? ANTON WAGENMAKERS: I think that it is a major assumption that muscle repair is needed.
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But at the high points, the insulin was twice as high. MICHAEL RENNIE: So you could just give insulinogenic amino acids and see whether there is a beneficial effect.
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AMINO ACID SUPPLEMENTS TO ENHANCE PERFORMANCE 329 HARRIS LIEBERMAN: Several years ago, there was a report by a Spanish grou~Segura, I believe, was the principal investigator which suggested that if you gave pharmacologic doses of tryptophan, you actually would improve endurance performance. Would you care to comment on that?
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