The anabolic response to protein feeding in skeletal muscle is limited by a refractory period of approximately 3–4 hours, during which additional protein intake fails to further stimulate muscle protein synthesis, regardless of dose or timing.

After eating protein, leucine triggers a burst of muscle building by turning on a key molecular switch called mTORC1, which tells the cell to start making new muscle proteins. This surge lasts about 3–4 hours. After that, the cell’s protein-making factory gets overloaded, causing misfolded proteins to pile up in a compartment called the endoplasmic reticulum. This overload activates a safety system that shuts down protein production entirely, even if more amino acids are still present. The cell stays in this shutdown state until the backlog of misfolded proteins is cleared, which takes about 3–4 hours.