A factor produced in working muscle fibers apparently tells surrounding muscle stem cell "higher ups" that it's time to multiply and join in, according to a study in the January Cell Metabolism, a Cell Press journal.In other words, that so-called serum response factor (Srf) translates the mechanical signal of work into a chemical one.[...]Mice with muscle fibers lacking Srf are no longer able to grow when they are experimentally overloaded, the new research shows. That's because satellite cells don't get the message to proliferate and fuse with those pre-existing myofibers.Srf works through a network of genes, including one known as Cox2. That raises the intriguing possibility that commonly used Cox2 inhibitors—think ibuprofen—might work against muscle growth or recovery, Sotiropoulos notes.