Women on the pill may gain less muscle

April 17, 2009 Scientist's presented the study at the American Physiological Society meeting and said they were surprised at the magnitude of differences in muscle gains between the two groups.

The women who weren't on the pill gained more than 60 percent greater muscle.

Women on the pill had lower levels of muscle building hormones such as testosterone and far higher levels of muscle breaking hormones such as cortisol.

Researchers aren't sure why this happens and say future studies are needed.