The quantity of protein intake for athletic populations has been a matter of controversy for several years. Interest in protein intake can even be traced to ancient Greece, where records from the Olympics indicated that athletes consumed huge amounts of meat to try to maximize strength performance.1 By the 18th century, muscle contraction was believed to be fueled by the oxidation of muscle protein.2 As the importance of lipid and carbohydrate (CHO) oxidation in muscle metabolism became clear, a central role for protein oxidation in the supply of energy during muscle contraction waned.3 In contrast, the quality of protein intake for athletic populations has received much less scientific attention. Only recently have researchers attempted to distinguish the potential benefits of varying compositions of amino acids and protein type (e.g., whey vs. casein). The question as to whether physical activity of any type alters the dietary requirement for protein remains open for debate.4-6
In this chapter, the pathways of protein metabolism in skeletal muscle with emphasis on the effects of exercise on metabolic and anabolic regulation will be reviewed, including the factors that modify these responses. We will then review studies that have attempted to determine whether athletes require dietary protein intakes higher than those for sedentary individuals and whether protein quality influences metabolic and anabolic regulation. Throughout the chapter, exercise will be broadly classified as either endurance or resistance to highlight the two major classifications of exercise at opposite ends of the metabolic demand spectrum. Endurance activities can be broadly defined as those that utilize predominantly oxidative phosphorylation as the primary energy source; resistance activities lead to increases in strength, power, and muscle mass as outcomes.
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