The Role of Protein and Amino Acids in Sustaining and Enhancing Performance (1999) / Chapter Skim
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11 Physical Exertion, Amino Acid and Protein Metabolism, and Protein Requirements
11 Physical Exertion, Amino Acid and Protein Metabolism, and Protein Requirements
Pages 243-254
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From page 243... ...
National Academy Press 11 Physical Exertion, Amino Acid anct Protein Metabolism, and Protein Requirements Michael J Reties INTRODUCTION A whiff of vitalism, the 19th century philosophical doctrine that there is some spiritual essence associated with biological processes, is still discernible in relation to the question of how contractile activity affects protein and amino acid metabolism.
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From page 244... ...
EXERCISE AND AMINO ACID CATABOLISM Although this kind of exercise probably only contributes a small fraction to the total daily energy expenditure of soldiers in the field, it may be that repeated bouts of exercise have cumulative effects on protein and amino acid metabolism; we may get some clues as to what these are by investigating exercise under laboratory conditions. There is now a substantial body of work which allows us to make some reasonably firm statements about the relative importance of amino acid metabolism in skeletal muscle during increased contractile activity.
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From page 245... ...
The puzzling thing is that branched chain amino acids are transaminated at the expense of a-ketoglutarate to produce glutamate, which ought to protect muscle glutamate concentrations and to deplete a-ketoglutarate. The depletion of a-ketoglutarate would be catapleurotic if it extended to the mitochondria.
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From page 246... ...
. The question arises, would repeated muscular exercise lead to a diminution of amino acids from the intramuscular compartment thus possibly limiting any anaplerotic role?
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From page 247... ...
The arlabolic phase occurs in He post-exercise period and cart be maximised by the provision of exogenous amino acids. It has been difficult to make measurements of protein synthesis during exercise in human beings because of the difficulty of detecting sufficient change over a short period of time but it seems likely that muscle protein synthesis is depressed (Rennie, 1996; Dohm et al., 1980~; thus, the rebound observed postexercise (Chesley et al., 1992; Biolo et al., 1995)
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From page 248... ...
This is seen clearly in the results of Figure 11-1. INTERACTIONS BETWEEN ENERGY SUPPLY AND PROTEIN AND AMINO ACID METABOLISM IN THE CONTEXT OF INCREASED PHYSICAL ACTIVITY At rest provision of carbohydrate inhibits net protein catabolism, probably mainly by increasing insulin which has inhibitory effects on protein breakdown and stimulatory effects on protein synthesis; in addition the simple provision of carbohydrate inhibits gluconeogenesis from amino acids, diminishing the "pull" from the liver upon the peripheral lean body mass protein.
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From page 249... ...
POSSIBLE BENEFICIAL EFFECTS OF BRANCHED CHAIN AMINO ACID SUPPLEMENTATION Theoretically, branched chain amino acid supplementation could provide benefits in one of four ways there are to supply anaplerotic intermediates, to decrease the use of other fuels including glycogen, inhibit muscle protein breakdown, and inhibit the transport of tryptophan into the brain, thus limiting the increase in serotonin synthesis which is implicated in the central fatigue hypothesis (Hassmen et al., 19941. There is, in fact, some evidence that branched chain amino acid supplementation does, to some extent, spare muscle glycogen (MacLean et al., 1996; Blomstrand and Newsholme, 1996)
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From page 250... ...
We do know that increasing the protein content of the diet simply increases the activity of amino acid catabolizing enzymes and the capacity for branched chain amino acid oxidation during exercise is substantially increased by increasing total dietary protein (Figure 11-1~. In studies we carried out on subjects habituated to a high protein diet, amino acid oxidation was higher than normal during exercise suggesting no net benefit would accrue.
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From page 251... ...
Most food contains sufficient protein such that so long as energy balance is maintained sufficient protein is delivered to meet the requirements for amino acid oxidation and also probably for preservation and even growth of the lean body mass. There is no evidence that supplementation with individual amino acids is of benefit to physical performance or to maintenance or grown of lean body mass, especially muscle.
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From page 252... ...
1994. Branched-chain amino acids augment ammonia metabolism while attenuating protein breakdown during exercise.
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From page 253... ...
1995a. Ingestion of branched chain amino acids and tryptophan during sustained exercise in man: failure to affect performance.
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