Steroids, such as prednisone, can be a good thing, repairing and strengthening damaged muscles. But too much of a good thing can be a bad thing, and researchers at Northwestern University are convinced that steroids taken too frequently for long periods of time can weaken muscles. A Northwestern news release reports that the researchers working with mice, not humans, found that prednisone directs the production of annexins, proteins that stimulate muscle healing. The research showed that weekly doses of prednisone stimulated a molecule called KLF15, which is associated with improved muscle performance, while daily doses of prednisone reduced KLF15, leading to muscle wasting. They gave normal mice with a muscle injury steroids just before injury and for two weeks after the injury, and found that mice receiving two weekly doses of steroids after the injury performed better on treadmill testing and had stronger muscle than mice receiving a placebo. Mice that received daily steroids for two weeks after the muscle injury, on the other hand, performed poorly on the treadmill and in muscle strength studies, compared to placebo-treated mice.