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A Brief Review of Critical Processes in Exercise-Induced Muscular Hypertrophy

Abstract

With regular practice, resistance exercise can lead to gains in skeletal muscle mass by means of hypertrophy. The process of skeletal muscle fiber hypertrophy comes about as a result of the confluence of positive muscle protein balance and satellite cell addition to muscle fibers. Positive muscle protein balance is achieved when the rate of new muscle protein synthesis (MPS) exceeds that of muscle protein breakdown (MPB). While resistance exercise and postprandial hyperaminoacidemia both stimulate MPS, it is through the synergistic effects of these two stimuli that a net gain in muscle proteins occurs and muscle fiber hypertrophy takes place. Current evidence favors the post-exercise period as a time when rapid hyperaminoacidemia promotes a marked rise in the rate of MPS. Dietary proteins with a full complement of essential amino acids and high leucine contents that are rapidly digested are more likely to be efficacious in this regard. Various other compounds have been added to complete proteins, including carbohydrate, arginine and glutamine, in an attempt to augment the effectiveness of the protein in stimulating MPS (or suppressing MPB), but none has proved particularly effective. Evidence points to a higher protein intake in combination with resistance exercise as being efficacious in allowing preservation, and on occasion increases, in skeletal muscle mass with dietary energy restriction aimed at the promotion of weight loss. The goal of this review is to examine practices of protein ingestion in combination with resistance exercise that have some evidence for efficacy and to highlight future areas for investigation.

 

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Alex’s Notes: If there are two things I love, it is heavy lifting and eating. Fortunately, this free review from Sports Medicine examines just that – the practices of protein ingestion in combination with resistance exercise. To start, however, you must know that muscle growth is the result of positive net protein turnover, or the total muscle synthesis (MPS) minus the breakdown (MPB).

 

Resistance exercise provides a loading stimulus to skeletal muscle that result in increases in skeletal MPS and MPB, with the MPS lasting for at least 48 hours. Promoting hyperaminoacidemia (having an excess of amino acids in the bloodstream) is another method for increasing MPS while blunting the rise in MPB, and therefore, when protein is ingested after resistance exercise it is the amino acids themselves that are driving the rise in post-exercise MPS. Furthermore, MPS in young adults is maximized at protein ingestion doses of approximately 20–25 g (~8.5–10 g of EAA) regardless of whether the subjects exercised or not, while older adults require closer to 40 g following resistance exercise and 20 g at rest. Beyond these levels, protein oxidation increases significantly (especially for leucine), but contrary to bro-science this oxidation may be an anabolic signal itself and thus isn’t “wasteful” where optimal stimulation of MPS is concerned.

 

Current evidence would also lead to a guideline stating that to achieve peak rates of MPS, a high leucine-containing protein that is rapidly digested, leading to rapid leucinemia and hyperaminoacidemia, should be consumed post-exercise. The dose of protein that appears most effective following resistance exercise, is approximately 0.25–0.30 g protein/kg BM/meal, at least when consuming isolated proteins.

 

Comments   

0 # cogrick2 2014-05-13 06:02
Ineresting point, Alex, about protein oxidation possibly being an anabolic signal.
Reply

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