improved to a greater extent compared with moderate or low protein intakes.73


entirely surprising because MPS and breakdown have been shown to be tightly coordinated.9


These preliminary findings are not Lastly, studies of highly


trained cyclists who engaged in an exercise protocol similar to the Tour de France (ie, long, exhausting cycling) demon- strated that daily protein requirements of 1.5 to 1.8 g/kg are needed to maintain nitrogen balance under such vigorous exercise conditions.120,121 It seems that diet manipulation can influence the anabolic


response to endurance exercise, but moderate endurance exercise does not increase dietary protein requirements above those of the general population. Athletes engaged in vigorous training may need slightly more dietary protein; however, pro- vided that the athletes are consuming adequate daily energy and that 10% to 15% is coming from dietary protein, these individuals will be meeting their daily protein requirements. Overall, dietary protein requirements for an endurance


athlete have not been clearly defined. In particular, there are no data that describe the ingested protein dose-response curves on the postprandial MPS response during recov- ery from endurance exercise. Additional work is required to assess the effects of intensity or duration of the endurance exercise bout on dietary protein requirements for a spe- cific athlete, which may vary based on their specific phase of training. In particular, higher-intensity or longer-duration endurance exercise training increases oxidation of amino acids to be used for hepatic gluconeogenesis (or deamination) or as a fuel source for skeletal muscle mitochondria. As such, exercise intensity or duration may modulate dietary protein requirements for an endurance athlete. Moreover, Rowlands and Wadsworth demonstrated that the daily protein requirements of female endurance athletes may be slightly higher than those of male athletes.122


However, it seems likely that approximately 0.25 g


protein per kilogram per meal provides a reasonable recommendation to optimize repair, remodeling, or muscle protein accretion during recovery from endurance exercise until additional work that is specific to an endurance athlete is completed in this area.


INDIVIDUAL AMINO ACID SUPPLEMENTATION: FACT OR FICTION?


Glutamine and arginine are amino acids purported to have ergogenic effects if consumed in supplemen- tal form, especially during recovery from injury. Glutamine, a highly abundant amino acid in the body, is largely synthesized in skeletal muscle and released in plasma during exercise.123,124


Muscle glutamine


concentrations have been related to rates of MPS in skeletal muscle of rats, some of which were protein deficient, endotoxemic, or starved, which begs the question of whether the findings can be extended to humans.125


Glutamine supplementation combined with 6 weeks of resistance training in young adults had no added effect on muscle strength and fat-free mass accretion compared with a placebo group.126


Further-


more, data demonstrated that glutamine ingestion in healthy adult men and women was associated with an approximately fourfold increase (compared with control participants) in plasma growth hormone.127


It was


suggested that an increase in plasma growth hormone concentrations following glutamine supplementation may be significant for strength athletes to maximize training adaptations.87


However, it is not entirely clear


whether elevated concentrations of growth hormone within normal physiological concentrations would benefit strength-training athletes. Specifically, West and colleagues have established that exercise-induced


CHAPTER 3: PROTEIN AND EXERCISE 51


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