Protein performs the same functions in sedentary and physically active individuals.
However, protein requirements of athletes are increased above those of sedentary people due in part to changes in amino acid metabolism induced by exercise. A small amount of protein is used as fuel during endurance exercise. Extra protein is needed by strength-trained athletes to repair injuries to muscle fibers and to remodel muscle tissue in response to strength training. In addition, muscle and whole-body protein synthesis is suppressed during exercise. Increases in exercise intensity and duration further depress protein synthesis.