From the Journal of Endocrinology, a good preprint review paper (with full PDF available) on what scientists know about the biochemistry of sarcopenia: "This review describes the major hormonal factors that determine the balance between human skeletal muscle anabolism and catabolism in health and disease, with specific reference to age-related muscle loss (sarcopenia). The molecular mechanisms associated with muscle hypertrophy are described, and the central role of the satellite [stem] cell highlighted. ... The increasingly recognised role of myostatin, a negative regulator of muscle function, is described, as well as its potential as a therapeutic target. Strategies to counter age-related sarcopenia thus represent an exciting field of future investigation."