King Grub
2018-02-07, 11:49
Skeletal muscle supports locomotion and serves as the largest site of postprandial glucose disposal; thus it is a critical organ for physical and metabolic health. Skeletal muscle mass is regulated by the processes of muscle protein synthesis (MPS) and muscle protein breakdown (MPB), both of which are sensitive to external loading and aminoacidemia. Hyperaminoacidemia results in a robust but transient increase in rates of MPS and a mild suppression of MPB. Resistance exercise potentiates the aminoacidemia-induced rise in MPS that, when repeated over time, results in gradual radial growth of skeletal muscle (i.e., hypertrophy). Factors that affect MPS include both quantity and composition of the amino acid source. Specifically, MPS is stimulated in a dose-responsive manner and the primary amino acid agonist of this process is leucine. MPB also appears to be regulated in part by protein intake, which can exert a suppressive effect on MPB. At high protein doses the suppression of MPB may interfere with skeletal muscle adaptation following resistance exercise. In this review, we examine recent advancements in our understanding of how protein ingestion impacts skeletal muscle growth following resistance exercise in young adults during energy balance and energy restriction. We also provide practical recommendations for exercisers who wish to maximize the hypertrophic response of skeletal muscle during resistance exercise training.
The human body is capable of digesting large quantities of dietary protein. However, not all the constituent amino acids are utilized by the translational machinery to synthesize new proteins. With consumption of an isolated protein source, beyond a protein intake of ~0.3 g/kg body mass (i.e., 0.24 plus the upper-end of the 95% CI), MPS is saturated and the rate of amino acid catabolism through oxidation and urea production increases and so less amino acids are available for protein synthesis. Individuals performing whole-body resistance exercise may require larger protein doses to maximize the anabolic effects of protein, yet these effects are only marginally greater than what is observed at 20 g protein. Given that the muscle becomes refractory to the presence of amino acids, such that MPS returns to basal levels after ~3 h despite sustained hyperaminoacidemia, protein meals should be separated by ~3–5 h to maximize MPS over the waking period. While these strategies have proven to be most effective in acute settings (i.e., over a 12 h capture period), the most salient variable determining the effectiveness of protein supplementation on gains in muscle size during resistance training is still total daily protein intake. In a large meta-analysis, protein intake was shown to promote additional gains in lean body mass beyond those observed with resistance exercise alone; however, beyond a daily intake of 1.6 g/kg body mass per day (up to as high as 2.2 g/kg/day), the additional effects of protein are greatly diminished. Rather than further stimulating MPS, large intakes of protein beyond what we are recommending may modulate anabolism by suppressing proteolysis; however, we lack experimental evidence for this in muscle. We caution against strategies that focus on suppressing MPB as we contend that efficient removal of damaged proteins would require a robust and fully functional proteolytic response. We are unaware of any potential improvements with respect to skeletal muscle hypertrophy by strategies that suppress MPB. Thus, athletes in energy-balance seeking to optimize the adaptive potential of their resistance-training programs are advised to first ensure that they are consuming ~1.6 g/kg body mass per day of protein, and tailor their dosing strategies to meet this overarching goal.
Recent Perspectives Regarding the Role of Dietary Protein for the Promotion of Muscle Hypertrophy with Resistance Exercise Training. Nutrients, 7 Februray 2018, 10(2), 180.
http://www.mdpi.com/2072-6643/10/2/180/htm
The human body is capable of digesting large quantities of dietary protein. However, not all the constituent amino acids are utilized by the translational machinery to synthesize new proteins. With consumption of an isolated protein source, beyond a protein intake of ~0.3 g/kg body mass (i.e., 0.24 plus the upper-end of the 95% CI), MPS is saturated and the rate of amino acid catabolism through oxidation and urea production increases and so less amino acids are available for protein synthesis. Individuals performing whole-body resistance exercise may require larger protein doses to maximize the anabolic effects of protein, yet these effects are only marginally greater than what is observed at 20 g protein. Given that the muscle becomes refractory to the presence of amino acids, such that MPS returns to basal levels after ~3 h despite sustained hyperaminoacidemia, protein meals should be separated by ~3–5 h to maximize MPS over the waking period. While these strategies have proven to be most effective in acute settings (i.e., over a 12 h capture period), the most salient variable determining the effectiveness of protein supplementation on gains in muscle size during resistance training is still total daily protein intake. In a large meta-analysis, protein intake was shown to promote additional gains in lean body mass beyond those observed with resistance exercise alone; however, beyond a daily intake of 1.6 g/kg body mass per day (up to as high as 2.2 g/kg/day), the additional effects of protein are greatly diminished. Rather than further stimulating MPS, large intakes of protein beyond what we are recommending may modulate anabolism by suppressing proteolysis; however, we lack experimental evidence for this in muscle. We caution against strategies that focus on suppressing MPB as we contend that efficient removal of damaged proteins would require a robust and fully functional proteolytic response. We are unaware of any potential improvements with respect to skeletal muscle hypertrophy by strategies that suppress MPB. Thus, athletes in energy-balance seeking to optimize the adaptive potential of their resistance-training programs are advised to first ensure that they are consuming ~1.6 g/kg body mass per day of protein, and tailor their dosing strategies to meet this overarching goal.
Recent Perspectives Regarding the Role of Dietary Protein for the Promotion of Muscle Hypertrophy with Resistance Exercise Training. Nutrients, 7 Februray 2018, 10(2), 180.
http://www.mdpi.com/2072-6643/10/2/180/htm