You might recall manipulation of myostatin touted as a potential therapy for age-related muscle decline and wasting diseases. EurekAlert! notes that the basic science has already been improved: "mice that lack the gene that makes myostatin have roughly twice the amount of body muscle as normal, mice without myostatin that also overproduce follistatin have about four times as much muscle as normal mice. ... follistatin was capable of blocking myostatin activity in muscle cells grown under lab conditions. When he gave it to normal mice, the rodents bulked up, just as would happen if the myostatin gene in these animals was turned off. He then genetically engineered a mouse that both lacked myostatin and made extra follistatin.... To my surprise and delight, there was an additive effect ... these muscular mice averaged a 117 percent increase in muscle fiber size and a 73 percent increase in total muscle fibers compared to normal mice. These findings show that the capacity for increasing muscle growth by targeting these pathways is much more extensive than we have appreciated."