Amino acids, proteins, and exercise performance

AMINO ACIDS, PROTEINS, AND EXERCISE PERFORMANCE
Sports Science Exchange Roundtable 42 VOLUME 11 (2000) - NUMBER 4
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Martin J. Gibala, Ph.D.
Department of Kinesiology
McMaster University
Hamilton, Ontario
Canada Kevin Tipton, Ph.D.
Division of Metabolism
Shriners Burn Institute
University of Texas Medical Branch
Galveston, Texas
MarkHargreaves, Ph.D.
School of Health Sciences
Deakin University
Burwood, Victoria
Australia

KEY POINTS
• In all but a few exceptional cases, the maximal contribution of protein as an energy source during exercise ranges between 2% and 10% of the total energy expended.
• In theory, amino acids could contribute to carbohydrate metabolism during exercise, but there is no hard evidence thatthis occurs or has any bearing on sport performance.
• Supplementation of the athlete's diet with branched-chain amino acids apparently does not benefit exercise performance.
• The most important factors for optimizing muscle growth when one trains with resistance exercise are making certain that the resistance is adequate, that the intake of dietary energy (calories) is sufficient, that at leasta small amount of carbohydrate and/or protein is consumed immediately after each training session, and that the athlete obtains plenty of rest between training sessions.
• With rare exceptions, the maximal daily dietary protein requirements for athletes are in the range of 1.2-1.6 grams of protein per kilogram of body weight or about 3-4 ounces of protein per day for an athlete who weighs 160pounds. This amount of protein can almost always be obtained in the normal diet.
• There is no solid evidence that special mixtures of amino acids provide any advantage over normal dietary proteins in stimulating muscle growth.
INTRODUCTION

For many years, experts and non-experts alike have been debating the question of whether or not athletes, particularly those who wish to gain musclemass, should consume extraordinary amounts of protein in their diets. Protein powders and special amino acid mixtures have held their places among the top sellers in the dietary supplement field for as long as most of us can remember. Athletes presumably spend hundreds of millions of dollars annually on protein shakes and flakes, but it is impossible to know for certain if these products have madeany difference in their physiques or in the performance of their sports.
What contribution does protein make to the energy requirements for weight lifting compared to endurance running or cycling? Does the consumption of carbohydrate speed up the production of protein in muscles? How much protein do athletes in various sports need in their diets? Can this protein intake be achieved by consumingnormal foods, or should athletes be ingesting protein supplements? Are proteins good enough, or is it better to consume specific mixtures of amino acids that are purported to markedly improve protein buildup in the muscles? We asked these and other questions to a panel of experts in amino acid and protein metabolism. Each of these respondents has had extensive experience with cutting-edge researchin metabolism at rest and during exercise. (A few of their many scientific publications are cited at the end of this roundtable.) Moreover, each of the panelists has a background of athletic participation and thus appreciates the practical aspects of this topic.
1. How much of the energy expended during exercise of various types can be attributed to the use of proteins and amino acids as fuels?Gibala: The majority of energy for all types of exercise is derived from carbohydrates and lipids. For short-duration exercise (e.g., sprinting or weightlifting), the contribution of amino acids and proteins to energy production is negligible, regardless of intensity. During more prolonged forms of exercise (e.g., endurance cycling or distance running), recent studies suggest that the oxidation...