Exercise- and nutrient-controlled mechanisms involved in maintenance of the musculoskeletal mass.
Level 5 - mechanism / opinion, no new human data
Narrative review synthesizing mechanistic and physiological studies without systematic search methods
PubMed 17956336 · doi:10.1042/BST0351302
What was done
This narrative review summarizes physiological mechanisms regulating protein mass across muscle, tendon, and bone, drawing on stable isotope protein turnover measurements, gene expression data, and signaling pathway analyses (such as mTOR phosphorylation).
What was found
The abstract reports no numerical data. Qualitatively, it highlights: - Amino acids, especially leucine and branched-chain amino acids, stimulate muscle protein synthesis in a dose-response manner through mTOR signaling independently of insulin, IGF-1, or growth hormone, with minimal effect on breakdown. - Insulin inhibits muscle protein breakdown with little impact on protein synthesis in human muscle. - Exercise increases protein synthesis in both skeletal muscle and tendon, whereas disuse atrophy reduces collagen synthesis in both. - Bone collagen synthesis is nutritionally responsive to amino acids, but not to glucose or lipids.
Why it matters
It outlines the distinct physiological mechanisms of nutrients and exercise on musculoskeletal tissues, separating the anabolic actions of amino acids from the anti-catabolic effects of insulin.
Limits
The abstract contains no primary quantitative data, sample sizes, or study selection methodology. Differences across age groups, clinical conditions, and long-term functional outcomes are not detailed.
Cited by
- contradicts A single dose of insulin activates mTOR for up to 24 hours, whereas leucine only activates mTOR for approximately one to two hours.