Which hormone is primarily associated with promoting protein synthesis and muscle growth?

• A. Cortisol
• B. Testosterone
• C. Adrenaline
• D. Melatonin

Answer: (B)

Testosterone is the primary anabolic hormone that drives muscle protein synthesis and growth. It works by binding to androgen receptors in muscle fibers, which increases transcription of genes coding for muscle proteins and stimulates the activity of satellite cells that fuse with existing fibers to enlarge them. It also boosts IGF-1 production and enhances signaling through pathways like mTOR, all of which work together to raise the rate of protein synthesis and result in muscle hypertrophy.

Cortisol, in contrast, tends to promote protein breakdown and can counteract muscle growth, especially under stress. Adrenaline mainly provides immediate energy for activity and does not directly promote long-term muscle protein synthesis. Melatonin governs sleep-wake cycles and has limited direct role in promoting muscle protein synthesis compared with testosterone.