Mice and men who lacked the protein myostatin were found to have twice as much muscle mass as their counterparts with the protein in an earlier study conducted by Se-Jin Lee, MD, PhD, a professor of molecular biology and genetics at Johns Hopkins.

In the latest research, also conducted by Lee and published in PloS One, the overproduction of the protein follistatin in mice who had none of the protein myostatin resulted in muscle mass four times that of normal mice.

The discovery could lead to treatments for patients with muscular dystrophy or other muscle-wasting diseases, said Lee. Another application might be to bulk up livestock.

Lee discovered that follistatin would block myostatin production in muscles cells grown in the laboratory. He then gave the protein to normal mice and found that their muscle mass increased, just as though their myostatin gene had been silenced.

Next, he genetically engineered a mouse that lacked myostatin and overproduced follistatin.

"To my surprise and delight, there was an additive effect," Lee reported. The mice had a 73 percent increase in muscle fibers, compared to normal mice.