Drugs to bulk up muscles may make injuries m...( ANN ARBOR Mich. Block the action of...),Health

ANN ARBOR, Mich. Block the action of a protein that normally regulates muscle mass, and watch your muscles grow.

That may sound like a good idea to people with muscle-wasting diseases such as muscular dystrophy, and to older people, whose muscles naturally get smaller and weaker with age. Drugs that restrict the protein myostatin, which normally prevents muscles from being overly bulky, are currently under study, but not on the market, for some medical conditions.

Such drugs, called myostatin inhibitors, also are stirring interest among body builders and athletes. There are already signs of a nascent black market for what might become another illegal performance-enhancing drug in organized sports.

Now, a new University of Michigan study in mice suggests that while myostatin inhibitors may indeed bulk up muscles, they may also bring a troubling side effect small, brittle tendons that could make muscle injuries more likely.

Those interested in myostatin inhibitors need to be aware of the fact that by doing these things to muscles, they may be having negative effects on tendons, says John A. Faulkner, Ph.D., the studys senior author and professor in the Department of Molecular and Integrative Physiology at the U-M Medical School. He is also a research professor at the U-M Institute of Gerontology and professor of biomedical engineering at the U-M College of Engineering. The study results appear in the Jan. 8 print issue of the Proceedings of the National Academy of Sciences.

When you lift weights at the gym, muscle tissue gets damaged. That sets off the release of myostatin, starting a process that clears away damaged proteins and sets the stage for muscle rebuilding, says the studys first author, Christopher L. Mendias, Ph.D. The study suggests we need normal myostatin action for other reasons, too.

It also appears to make tendons bigger and more flexible, says Mendias, a U-M post-doctoral research f
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