A true statement about the regulation of muscle size and protein synthesis?

• A. It exclusively regulates lipid metabolism.
• B. It is the major regulator of protein synthesis and muscle size.
• C. It is a transcription factor that controls gene expression.
• D. It has no role in skeletal muscle.

Answer: (B)

Muscle size and protein synthesis are governed primarily by the mTOR signaling pathway, which acts as the central regulator of translation and hypertrophy. When muscles are challenged by resistance exercise, fed with adequate nutrients, and exposed to growth signals like IGF-1, mTOR complex 1 (mTORC1) becomes activated. This leads to phosphorylation of downstream targets such as S6K1 and 4E-BP1, which lifts the brakes on protein translation and increases ribosome biogenesis. The outcome is enhanced protein synthesis that, over time, drives muscle fiber growth. Because of this pivotal role in coordinating inputs from nutrients, hormones, and mechanical load to boost protein production and muscle size, the statement that it is the major regulator of protein synthesis and muscle size is the best description. The idea that it exclusively regulates lipid metabolism isn’t accurate, since its primary and direct function centers on promoting protein synthesis and growth. It’s not a transcription factor; it’s a kinase that controls translational processes. And it certainly has a key role in skeletal muscle, especially in response to training and nutrition.