Dietary protein, exercise, ageing and physical inactivity: interactive influences on skeletal muscle proteostasis.
Level 5 - mechanism / opinion, no new human data
Narrative review of mechanisms governing skeletal muscle proteostasis
PubMed 33023679 · doi:10.1017/S0029665120007879
What was done
This narrative review summarizes the mechanistic interactions between dietary protein intake, physical exercise, aging, and physical inactivity in regulating skeletal muscle proteostasis, muscle protein synthesis (MPS), and muscle protein breakdown.
What was found
The abstract reports physiological characteristics rather than empirical numerical trial data. At rest, essential amino acids (notably leucine) stimulate MPS for approximately 2–3 hours, after which MPS becomes refractory ('muscle full' phenomenon) despite continued amino acid availability and sustained mTORC1 signaling. This muscle full state is independent of protein dose or feeding pattern (bolus versus intermittent) and cannot be overcome by proximal nutrient feeding or pharmacological/nutraceutical increases in muscle blood flow. Resistance exercise delays the muscle full set-point to allow further EAA utilization, whereas aging causes anabolic resistance (blunted MPS) and physical inactivity (such as immobilization) triggers a premature muscle full response, accelerating muscle atrophy.
Why it matters
It outlines how mechanical stimulus from exercise interacts with dietary amino acids to sustain muscle protein synthesis, explaining why protein supplementation alone cannot overcome the anabolic resistance and accelerated refractory states induced by inactivity or aging.
Limits
The abstract provides no study counts, search criteria, or pooled quantitative data. As a narrative review, it does not evaluate the risk of bias or quality across the underlying primary human trials.
Cited by
- context Muscle protein synthesis requires resistance exercise loading in addition to dietary protein intake to be stimulated effectively.