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Review
. 2014 May;44 Suppl 1(Suppl 1):S71-7.
doi: 10.1007/s40279-014-0152-3.

A brief review of critical processes in exercise-induced muscular hypertrophy

Stuart M Phillips  1
Affiliations
Review

A brief review of critical processes in exercise-induced muscular hypertrophy

Stuart M Phillips. Sports Med. 2014 May.

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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Figures

Fig. 1
Fig. 1
Resistance exercise stimulates a prolonged elevation of MPS that can remain elevated for at least 48 h (dotted line) [1]. Protein ingestion at any point during this enhanced period of ‘anabolic potential’ will have an additive effect to these already elevated exercise mediated rates (solid lines) [26, 27]. Reproduced from Churchward-Venné et al. [29], with permission. MPS muscle protein synthesis
Fig. 2
Fig. 2
a The ‘leucine trigger’ concept, with data adapted from Tang et al. [6], as shown for isolated whey protein, soy protein, and casein proteins as a difference between rested and exercise values for MPS. b The speed of digestion of these proteins would be digested in the following order: whey ≥ soy ≫ casein; and the following leucine content: whey > casein > soy resulting in leucinemia and hypothetical intracellular leucine concentrations. Therefore, a greater and more rapid rise in blood and, probably, intramuscular leucine concentration triggers a greater rise in MPS. Values are mean ± SE. MPS muscle protein synthesis, FSR fractional synthetic rate, IC intracellular, [Leucine] concentration of leucine, * significantly different (p < 0.05) vs. casein (one-way analysis of variance), † significantly different (p < 0.05) than soy (one-way analysis of variance)
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