Resistance training is a potent stimulus to increase skeletal muscle mass. The muscle protein accretion process depends on a robust synergistic action between protein intake and overload. The intake of protein after resistance training increases plasma amino acids, which results in the activation of signaling molecules leading to increased muscle protein synthesis (MPS) and muscle hypertrophy. Although both essential and non-essential amino acids are necessary for hypertrophy, the intake of free L-leucine or high-leucine whole proteins has been specifically shown to increase the initiation of translation that is essential for elevated MPS. The literature supports the use of protein intake following resistance-training sessions to enhance MPS; however, less understood are the effects of different protein sources and timing protocols on MPS. The sum of the adaptions from each individual training session is essential to muscle hypertrophy, and thus highlights the importance of an optimal supplementation protocol. The aim of this review is to present recent findings reported in the literature and to discuss the practical application of these results. In that light, new speculations and questions will arise that may direct future investigations. The information and recommendations generated in this review should be of benefit to clinical dietitians as well as those engaged in sports.
Alex's notes: This brief review recommends that young adults consume a moderate-protein diet on a daily basis (1.4 g/kg) with 20 to 25 g of high-quality protein, providing 2.5 to 3 g of leucine, after exercise, and that older adults also consume a moderate-protein diet but with 35 to 40 g of high-quality, fast-digesting protein following resistance training. These recommendations are based on evidence to maximize MPS, skeletal muscle recovery, and adaptation. While the post-workout recommendations are sound, I do not completely agree with the daily protein intake recommendation and I believe it is too low for most resistance training individuals, regardless of age. Interestingly, the author's recommendation comes from one study examining protein oxidation at different protein intakes (0.86, 1.4, and 2.4 g/kg) in isocaloric diets. They assume that because 2.4g/kg did not provide additional protein synthesis but did increase oxidation, that it is too high. There is something anabolic about protein oxidation and this conclusion may be premature. The authors even go on to acknowledge and reference studies that show greater lean-body mass and muscle retention with higher protein diets during caloric restriction. Regardless, I would personally recommend that 2.2g/kg or 1 g/lb lean-body mass of protein is more than sufficient for most everyone.