From Live Science:
Scientists have found and manipulated body chemistry linked to the aging of muscles and were able to turn back the clock on old human muscle, restoring its ability to repair and rebuild itself, they said today.
The study involved a small number of participants, however. And the news is not all rosy.
Importantly, the research also found evidence that aging muscles need to be kept in shape, because long periods of atrophy are more challenging to overcome. Older muscles do not respond as well to sudden bouts of exercise, the scientists discovered, and rather than building muscle a person can generate scar tissue upon, say, lifting weights after long periods of inactivity.
Read more ....