Could a blood hormone known as growth differentiation factor 11 (GDF11) be the next big thing for anti-aging and bodybuilding purposes? I found this pretty interesting.

Summary:Scientists have shown that a protein they previously demonstrated can make the failing hearts in aging mice appear more like those of young health mice, similarly improves brain and skeletal muscle function in aging mice. In two separate articles scientists report that injections of a protein known as GDF11, which is found in humans as well as mice, improved the exercise capability of mice equivalent in age to that of about a 70-year-old human.

http://www.sciencedaily.com/releases/2014/05/140504133205.htm

There seems to be little question that, at least in animals, GDF11 has an amazing capacity to restore aging muscle and brain function. GDF11 is naturally found in much higher concentration in young mice than in older mice, and raising its levels in the older mice has improved the function of every organ system thus far studied.

Barring unexpected developments, they expect to have GDF11 in initial human clinical trials within three to five years.