Hypertrophy

 In general, protein supplementation pre-workout and post-workout increases physical performance, training session recovery, lean body mass, muscle hypertrophy, and strength. Specific gains, differ however based on protein type and amounts. Studies on timing of consumption of milk have indicated that fat-free milk post-workout was effective in promoting increases in lean body mass, strength, muscle hypertrophy and decreases in body fat.

The leucine content of a protein source has an impact on protein synthesis, and affects muscle hypertrophy. Consumption of 3–4 g of leucine is needed to promote maximum protein synthesis. An ideal supplement following resistance exercise should contain whey protein that provides at least 3 g of leucine per serving.

A combination of a fast-acting carbohydrate source such as maltodextrin or glucose should be consumed with the protein source, as leucine cannot modulate protein synthesis as effectively without the presence of insulin. Such a supplement post-workout would be most effective in increasing muscle protein synthesis, resulting in greater muscle hypertrophy and strength. In contrast, the consumption of essential amino acids and dextrose appears to be most effective at evoking protein synthesis prior to rather than following resistance exercise.

Mechanisms of Muscle Hypertrophy

Many factors mediate the hypertrophic process and that mechanical tension, muscle damage, and metabolic stress all can play a role in exercise-induced muscle growth. 

• Bodybuilders generally train with moderate loads and fairly short rest intervals that induce high amounts of metabolic stress.

• Powerlifters, on the other hand, routinely train with high-intensity loads and lengthy rest periods between sets.

Fueling Growth

Low-Load RT routine (LL) where 25-35 repetitions were performed per set per exercise

High-Load RT routine (HL) where 8-12 repetitions were performed per set per exercise

• HL training is superior for maximizing strength:

To further enhance muscle hypertrophy and strength, a resistance weight-training program of at least 10–12 weeks 3–5 day intervals with compound movements for both upper and lower body exercises should be followed [31,33,35,36,38,40,41].

Types of Protein

There are numerous protein sources available to the consumer. This section describes each of these protein sources and compares their quality on the two scales most relevant to this review: Biological Value (BV) and Protein Digestibility Corrected Amino Acid Score (PDCAAS) [44].

The BV and PDCAAS are both important in understanding bioavailability and quality of different protein sources.

Three sources of dairy protein typically used in studies of muscle hypertrophy and strength are bovine milk, casein and whey.

Bovine milk

Bovine milk is a highly bioavailable source of protein, comprising 80% casein and 20% whey. Overall, bovine milk has a BV of 91 and a PDCAAS of 1.00 indicating that it is readily absorbed by the body, promoting protein synthesis and tissue repair, and provides all essential amino acids (EAAs).

Casein

Casein, with a BV of 77 and a PDCAAS of 1.00, is the predominate protein in bovine milk and gives milk its white color. It exists in micelle form, and within the stomach will gel or clot, thus resulting in a sustained release of amino acids. Compared with milk, it is less bioavailable, but like milk, it provides all EAAs.

Whey

Whey the other protein found in milk, is the liquid part of milk that remains after the process of cheese manufacturing [44]. With a BV of 104 and a PDCAAS of 1.00, whey is superior to both milk and casein. It contains all EAAs, and its excellent bioavailability leads to rapid protein synthesis [44,45].

Soy

Soy is a vegetable-based protein source that is useful for vegetarians and individuals who are lactose- or casein-intolerant. Soy has a BV of 74 and PDCAAS of 1.00, indicating that it is not as bioavailable as milk based protein, but does contain all EAAs [44].

Nutrition

Two essential, nutrition-related, tenets need to be followed by weightlifters to maximize muscle hypertrophy: the consumption of 1.2-2.0 g protein.kg -1 of body weight, and ≥44-50 kcal.kg-1 of body weight.

Protein Synthesis

Protein synthesis occurs when methionyl-transfer ribonucleic acid (methionyl-tRNA) binds to a eukaryotic small ribosomal subunit (40S ribosomal unit) resulting in the formation of a pre-initiation complex (43S pre-initiation complex) [16]. This initial step is mediated by eukaryotic initiation factor 2 (eIF2) [16]. The 43S complex subsequently binds to messenger ribonucleic acid (mRNA) near the cap structure. After successful engagement of the 43S pre-initiation complex to RNA, the molecule eukaryotic initiation factor 5 (eIF5) removes eIF2 while a molecule of guanosine triphospahte (GTP) is hydrolyzed so that eIF2 is recycled to its active form of eIF2-GTP [16]. This allows eIF2-GTP to continue with the initial step of protein synthesis. Once eIF2-GTP is released, the second step can occur. A ribosomal binding site/translation start site forms once eukaryotic initiation factor 4F (eIF4F) recognizes the molecule [16]. The eIF4F complex binds the eukaryotic initiation factor 4E (eIF4E) subunit of eIF4F to the m7GTP cap structure present in all eukaryotic mRNAs [16]. Replication of the mRNA strand occurs, thus indicating protein synthesis. The processes of protein synthesis appear to be highly regulated by the amino acid leucine [10-14].