Muscles constantly break down and rebuild. Resistance exercise is the main signal to build; protein supplies the bricks.
How it works, step by step
Resistance exercise creates mechanical tension.
Signaling pathways (like mTOR) switch on building.
Amino acids — especially leucine — fuel new proteins.
Over weeks, fibers grow thicker and stronger.
Aging
Muscle mass and strength decline with age (sarcopenia); strength training helps at every age.
Evidence & sources
Protein supplementation augments resistance-training gains in strength and muscle size, with benefits plateauing around 1.6 g/kg/day of total protein. Evidence: moderate. Known: Meta-analysis of 49 RCTs. Unknown: Effects are modest. Source: Morton et al., British Journal of Sports Medicine, A systematic review, meta-analysis and meta-regression of the effect of protein supplementation (2018).