Protein and Amino Acid Metabolism During Exercise

Abstract

Athletes associate performance with diet. Meat became a staple of ancient Greek and Roman athletes as they attempted to achieve the strength and endurance of carnivorous members of the animal kingdom. As knowledge of nutrition and muscle physiology increased, athletes became convinced that to increase muscle mass and strength required increased dietary protein. However, nutrition textbooks (1,2) and the Recommended Dietary Allowances (RDA's) established by the National Academy of Sciences (3) state that there is little or no need for extra protein for exercise.Review of the nutrition and exercise literature indicates that physical activity produces changes in protein metabolism. A few of these changes are increased urinary nitrogen, increased nitrogen in sweat, and increased protein mass of muscles. These physiological changes, which suggest an increased need for dietary protein, together with the renewed popular interest in exercise have led to a reevaluation of protein utilization during exercise. Aspects of this topic have been addressed in other recent reviews (4,5,6).To examine the influence of exercise on protein metabolism, it is important to consider the differences between types of exercise.The previous chapters by Terjung and Goodman have examined the effects of exercise intensity and duration on different muscles and the primary fuels required for specific activities.For the purpose of this chapter, exercise will be classified as anaerobic or aerobic. These terms indicate metabolic differences and imply differences in intensity and duration. Anaerobic activities are of brief duration and at, or approaching, maximum exertion.Anaerobic training emphasizes strength and frequently results in muscle hypertrophy.Aerobic exercise features prolonged activities at less than maximum exertion.Training emphasizes endurance work and results in increased oxidative capacity of the muscles with little or no change in muscle mass. Thus, the type of exercise can influence muscle mass and the amount of muscle proteins and presumably the needs for dietary protein.To conceptualize amino acid metabolism, it is useful to consider a model which describes the flux of amino acids through

Do Athletes Need More Dietary Protein and Amino Acids?

“…Henderson et al (33) confirmed this training effect on leucine oxidation using in vivo measures (Figure 13). Probably these adaptations are due to an increased amount of the branched-chain ketoacid dehydrogenase in the active form, because traininginduced increases of the enzyme have been measured in both muscle and liver ( Figure 14) (44). Unless a compensatory decrease (below baseline) in oxidation occurs between training sessions, these data indicate that chronic endurance exercise is likely to elevate daily requirements for leucine.…”

Beyond the Zone: Protein Needs of Active Individuals

“…19, NO. 5 changes in branched-chain oxoacid dehydrogenase activity [38]; however, more study is required, as at least one study doesn't support these data [39] and there is no apparent explanation for these contradictory observations. With strength training there is also some confusion.…”

Is Increased Dietary Protein Necessary or Beneficial for Individuals with a Physically Active Lifestyle?

“…Although considerable debate has gone on for years (Cathcart 1925, Lemon 1987, Butterfield 1991, Hickson and Wolinsky 1994, Layman et al 1994, Poortmans 1994, Rennie et al 1994a, recent scientific data indicate that dietary protein intake in excess of the current RDA is likdy needed for optimal muscle growth. However, the benefit appears to plateau at intakes well below the intakes typically consumed by many athletes.…”