Although resistance exercise (RE) alone is inherently anabolic (increases Muscle Protein Synthesis, MPS), we require protein and its constituent amino acids (AAs) to adequately facilitate the repair and remodeling of skeletal muscle cells in response to exercise.
Ultimately we’re interested specifically in muscle hypertrophy, but acute measures offer a useful indicator of long-term phenotypic potential . Acutely, the skeletal muscle adaptive response is often characterized by the balance between anabolic (Muscle Protein Synthesis, MPS) and catabolic (Muscle Protein Breakdown, MPB) reactions in muscle. When the aggregated effect of MPS exceeds MPB we’re in a Positive Net Protein Balance (NPB); creating a requisite environment for protein accretion. In order to augment this positive balance, conceptually increasing muscle growth, one can leverage the effects of amino acid ingestion and resistance exercise to drive the cascade of physiologic adaptations (as depicted in image below).
Skeletal muscle hypertrophy (growth) occurs when these aggregated acute anabolic and catabolic reactions result in a positive net protein balance over time. Although RE alone will augment MPS, breakdown is correspondingly increased, thus requiring nutrients (Amino Acids, AAs) to realize a positive protein balance . Post-exercise, the muscle cell is primed for nutrient intake – providing specific AAs (particularly Leucine) in sufficient quantity during this post exercise period comprises an essential role in the adaptive process. Notably, leucine has a unique capability to provide the impetus or instruction to build new proteins (signaling) and the substrate to carry it out (Muscle Protein Synthesis) .
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